Glossary of technical terms for the use of metallurgical engineers Terms starting with alphabet ‘H’
Glossary of technical terms for the use of metallurgical engineers
Terms starting with alphabet ‘H’
Habit plane – It is the plane or system of planes of a crystalline phase along which some phenomenon, such as twinning or transformation, occurs.
Hackle (glassy materials, ceramics) – It is a line on a crack surface, running parallel to the local direction of cracking, separating parallel but non-coplanar portions of the crack surface.
Hackle marks (ceramics, glassy materials) – These are fine ridges on the fracture surface of a glass, parallel to the direction of propagation of the fracture.
Hadfield manganese steel – It is a high alloy steel which contains 12 % to 14 % manganese and 1 % carbon. It is austenitic at all temperatures and hence non-magnetic. Hadfield had done a series of test with the addition of ferro-manganese containing 80 % manganese and 7 % carbon to de-carbonized iron. Increasing manganese and carbon contents led to increasing brittleness up to 7.5 % manganese. At manganese contents above 10 %, however, the steel became remarkably tough. The toughness increased by heating the steel to 1,000 deg C followed by water quenching, a treatment which would render carbon steel very brittle. This alloy steel which was introduced commercially contained 1.2 % carbon and 12 % manganese in a 1 to 10 ratio. Hadfield manganese steel is unique in that it shows resistance to impact, high toughness, high ductility, high work hardening ability, excellent wear resistance, and slow crack propagation rates, in comparison to other potentially competitive materials. The steel has a unique property in that when the surface is abraded or deformed, it greatly increases surface hardness while retaining a tough core. The steel has the ability to harden in-depth in service as well as by induced means. It is also non-magnetic and can be work-hardened during service or can be surface-hardened to as high as 500 HB (Brinell hardness) by mechanical or explosive means prior to service. Because of these properties, Hadfield manganese steel gained rapid acceptance as a useful engineering material.
Hair, slitter – It is the minute hairlike sliver along edge(s) because of the shearing or slitting operation.
Hair grease – It is a grease which contains horse hair or wool fibre.
Hairline cracks – These are short, discontinuous internal cracks in ferrous metals attributed to stresses produced by localized transformation and hydrogen-solubility effects during cooling after hot working. In fracture surfaces, hairline cracks appear as bright, silvery areas with a coarse texture. In deep acid-etched transverse sections, they appear as discontinuities which are normally in the midway to centre location of the section.
Hairline craze – It consists of multiple fine surface separation cracks in composites which exceed 6 millimeters in length and do not penetrate in depth the equivalent of a full ply of reinforcement.
Half-cell – It is an electrode immersed in a suitable electrolyte, designed for measurements of electrode potential.
Half hard – It is a temper of non-ferrous alloys and some ferrous alloys characterized by tensile strength around mid-way between those of dead soft and full hard tempers.
Half journal bearing – It is a journal bearing extending 180-degee around a journal.
Half-life – It is the time needed for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear metallurgy to describe how quickly unstable atoms undergo radio–active decay or how long stable atoms survive, i.e., It is the time which it takes for half of the atoms in a radio-active element to decay. The term is also used more generally to characterize any type of exponential (or, rarely, non-exponential) decay.
Halite – It is the rock salt.
Hall effect – It is the development of a transverse electric field in a current-carrying conductor placed in a magnetic field.
Hall-Petch relationship – It is a general relationship for metals which shows that the yield strength is linearly related to the reciprocal of the square root of the grain diameter.
Hall process – It is a commercial process for winning aluminum from alumina by electrolytic reduction of a fused bath of alumina dissolved in cryolite.
Halogen – It consists of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine.
Hammer – It is a machine which applies a sharp blow to the work area through the fall of a ram onto an anvil. The ram can be driven by gravity or power.
Hammer crusher – It consists of a high-speed, normally horizontally shaft rotor turning inside a cylindrical casing. The crusher contains a certain number of hammers which are pinned to the rotor disk and the hammers are swinging to the edges because of centrifugal force. Feed is dropped to the crusher from the top of the casing and it is crushed between the casing and the hammers. After crushing the material falls through from the opening in the bottom.
Hammer forging – It is a type of forging in which the work is deformed by repeated blows.
Hammering – It is the working of metal sheet into a desired shape over a form or on a high-speed hammer and a similar anvil to produce the needed dishing or thinning.
Hammer welding – It means forge welding by hammering.
Hand – It is the softness of a piece of fabric, as determined by the touch (individual judgment).
Hand brake – It is a small manual folding machine designed to bend sheet metal, similar in design and purpose to a press brake.
Hand forge (smith forge) – It is a forging operation in which forming is accomplished on dies which are normally flat. The piece is shaped roughly to the needed contour with little or no lateral confinement, and operations involving mandrels are included. The term hand forge refers to the operation performed, while hand forging applies to the part produced.
Handhole – It is an access opening in a pressure part normally not exceeding 150 mm in its longest dimension.
Handhole cover – It is for the closure of a handhole.
Hand lay-up – It is the process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mould by hand.
Handling – It is the process by which materials are carried throughout the facility, by chain, wire, hook, or racked in a fixture.
Handling breaks – These are irregular breaks caused by improper handling of metal sheets during processing. These breaks result from bending or sagging of the sheets during handling.
Handling life– It is the out-of-refrigeration time over which a material retains its handleability.
Handling mark – For rolled products, it is an area of broken surface which is introduced after processing. The mark normally has no relationship to the rolling direction. For extrusions, it is the damage which can be imparted to the surface during handling operations.
Hand straightening – It is a straightening operation performed on a surface plate to bring a forging within straightness tolerance. A bottom die from a set of finish dies is frequently used instead of a surface plate. Hand tools used include mallets, sledges, blocks, jacks, and oil gear presses in addition to regular inspection tools.
Hand-wheel operated valve – It is a valve on which the handwheel drives the stem directly to operate the valve.
Hanging – Hanging is the phenomenon in the blast furnace which takes place, when the burden materials charged at the top of the blast do not move continuously towards the hearth of the furnace. Hanging originates when the burden, on its way down, meets a very high resistance resulting into the stoppage of the movement of the burden. Hanging takes place due to the bridging of the burden materials in the stack of the furnace. When it occurs, the material below the hang continues to move downward, forming a space which is void of solid material but filled with hot gas at very high pressure. This space continues to grow until the hang finally collapses.
Hanging burr – It is the loose or flexible portions of a burr which are not firmly attached to the work-piece (i.e., hanging from the work-piece). It is sdmetimes called a flag
Hanging-wall – It is the rock which is on the upper side of a vein or ore deposit.
Hard chromium – It is the chromium which is electro-deposited for engineering purposes (such as to increase the wear resistance of sliding metal surfaces) rather than as a decorative coating. It is normally applied directly to substrate and is customarily thicker (higher than 1.2 micrometers) than a decorative deposit, but not necessarily harder.
Hard coating – In anodizing of aluminum, it is an anodic oxide coating on aluminum with a higher apparent density and thickness and a higher resistance to wear than the conventional coatings.
Hard constraint – It is a design requirement which cannot be relaxed, i.e., a must requirement.
Hard drawn – It is an imprecise term which is applied to drawn products, such as wire and tubing. It indicates substantial cold reduction without subsequent annealing.
Hardenability – It is the relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is normally measured as the distance below a quenched surface at which the metal shows a specific hardness, for example 50 HRC (Rockwell hardness, C-scale) or a specific percentage of martensite in the micro-structure.
Hardener – It is an alloy rich in one or more alloying elements which is added to a melt to permit closer control of composition than is possible by the addition of pure metals, or to introduce refractory elements not readily alloyed with the base metal. Sometimes it is called master alloy or rich alloy.
Hardening – It means increasing hardness of metals by suitable treatment, normally involving heating and cooling. Steels can be hardened by the simple means of heating the steel to a temperature higher than the A3 transformation temperature, holding long enough to ensure the achievement of uniform temperature and solution of carbon in the austenite, and then cooling the steel rapidly (quenching). Complete hardening depends on cooling so rapidly that the austenite, which does not decompose on cooling through the A1 temperature and is maintained at relatively low temperatures. When this is accomplished, the austenite starts transforming to martensite on cooling below the ‘Ms’ temperature (around 220 deg C) and is completely transformed to martensite below ‘Mf’ temperature. When applicable, more specific terms are used, e.g., age hardening, case hardening, flame hardening, induction hardening, precipitation hardening, and quench hardening.
Hard face – It is a seal facing of high hardness which is applied to a softer material, such as by flame spraying, plasma spraying, electroplating, nitriding, carburizing, or welding.
Hard-facing – It consists of the application of a hard, wear-resistant material to the surface of a component by welding, spraying, or allied welding processes to reduce wear or loss of material by abrasion, impact, erosion, galling, and cavitation.
Hard-facing alloys – These are wear-resistant materials which are available as bare welding rod, flux-coated rod, long-length solid wires, long-length tubular wires, or powders which are deposited by hard-facing. Hard-facing materials include a wide variety of alloys, ceramics, and combinations of these materials. Conventional hard-facing alloys are normally classified as steels or low-alloy ferrous materials, chromium white irons, high-alloy ferrous materials, carbides, nickel-base alloys, or cobalt-base alloys.
Hard metal – It is a collective term which designates a sintered material with high hardness, strength, and wear resistance and is characterized by a tough metallic binder phase and particles of carbides, borides, or nitrides of the refractory metals. The term is in general use, while for the carbides the term cemented carbide is preferred, and the boride and nitride materials are normally categorized as cermets.
Hardness – It is a measure of the resistance of a material to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by pressing or abrasion. In general, different materials differ in their hardness. It can be thought of as a function of the stress needed to produce some specified type of surface deformation. There is no absolute scale for hardness, hence, to express hardness quantitatively, each type of test has its own scale of arbitrarily defined hardness. Indentation hardness can be measured by Brinell, Rockwell, Vickers, Knoop, and Scleroscope hardness tests. Macroscopic hardness is normally characterized by strong intermolecular bonds, but the behaviour of solid materials under force is complex, hence, hardness can be measured in different ways, such as scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elastic, stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.
Hardness, mineralogy – It is normally described as the resistance of a material to being scratched by another material. The ability of materials to resist scratching by another material can be ranked by referring to the Mohs scale which assesses relative hardness of the materials.
Hardness, metallurgy – It is defined as the ability of a material to resist plastic deformation. It is sometimes known as indentation hardness which is the resistance of a material to indentation. The usual type of hardness test is where a pointed or rounded indenter is pressed into a surface of the material under a substantially static load. Hardness measurement can be carried out at macro scale, micro scale or nano scale according to the forces applied and displacements obtained.
Hardness profile – It is the hardness as a function of distance from a fixed reference point (normally from the surface).
Hardness testing – Hardness testing is one of the simplest and most widely used inspection methods. It is a non-destructive method which can be used to predict the strength of the metals. Hardness testing consists of pressing an indenter of known geometry and mechanical properties into the test material. The hardness of the material is quantified using one of a variety of scales which directly or indirectly indicate the contact pressure involved in deforming the test surface. Since the indenter is pressed into the material during testing, hardness is also viewed as the ability of a material to resist compressive loads. The indenter can be spherical (Brinell test), pyramidal (Vickers and Knoop tests), or conical (Rockwell test). In the Brinell, Vickers, and Knoop tests, hardness value is the load supported by unit area of the indentation, expressed in kilograms per square millimeter. In the Rockwell tests, the depth of indentation at a prescribed load is determined and converted to a hardness number (without measurement units), which is inversely related to the depth. There exists a correlation between tensile strength and hardness for steels, brass, and nodular cast iron. All the heat-treated steels are subjected to hardness testing to verify that the heat treatment produced the correct hardness and hence strength.
Hardness, water – It is a measure of the quantity of calcium and magnesium salts in water. It is normally expressed as parts per million as calcium carbonate (CaCO3).
Hard solder – It is a term erroneously used to denote silver-base brazing filler metals.
Hard surfacing – It is the deposition of filler metal (material) on a base metal (substrate) to get desired properties or dimensions, as opposed to making a joint.
Hard temper – It is a temper of non-ferrous alloys and some ferrous alloys corresponding approximately to a cold-worked state beyond which the material can no longer be formed by bending. In specifications, a full hard temper is normally defined in terms of minimum hardness or minimum tensile strength (or, alternatively, a range of hardness or strength) corresponding to a specific percentage of cold reduction following a full anneal. For aluminum, a full hard temper is equivalent to a reduction of 75 % from dead soft, for austenitic stainless steels, a reduction of around 50 % to 55 %.
Hard water – It is the water which contains calcium or magnesium in a quantity which need an excessive quantity of soap to form a lather.
Haring cell – It is a four-electrode cell for measurement of electrolyte resistance and electrode polarization during electrolysis.
Harmonic – It is a wave-form which has a frequency which is an integer multiple of another frequency.
Harmonic distortion – It is an effect of a non-linear signal path which introduces frequencies which are integer multiples of an input frequency.
Harmonic mean – It is a kind of average, one of the Pythagorean means. It is the most appropriate average for ratios and rates such as speeds, and is normally only used for positive arguments. The harmonic mean is the reciprocal of the arithmetic mean of the reciprocals of the numbers.
Harmonic oscillator – It is an oscillator which produces sinusoidal output, such as a simple RLC (resistor, inductor, and capacitor) oscillator.
Harness satin – It is the weaving pattern producing a satin appearance. ‘Eight-harness’ means the warp tow crosses over seven fill tows and under the eighth (repeatedly).
Harrison number – It is a dimensionless group used in gas bearing calculations. For thrust bearings, the Harrison number relates viscosity, velocity, pressure, and clearance, and for journal bearings, the Harrison number relates to viscosity, rotational speed, pressure, radius, and clearance.
Harmonics – It is the distortion of the power line voltage because of non-linear loads such as rectifiers.
Hartmann lines – These are elongated surface markings or depressions, frequently visible with the unaided eye, that form along the length of sheet metal or a tension sample at an angle of 45-degree to the loading axis. It is caused by localized plastic deformation. They result from discontinuous (in-homogeneous) yielding. These are also known as Luders bands, or Luder lines.
Hastelloy alloy – It is a corrosion-resistant nickel alloy which contains other chemical elements such as chromium and molybdenum. This material has high temperature resistance and outstanding corrosion resistance. It has good sulphfidation resistance and high metallurgical stability, which makes it preferable material for high-temperature applications of thermal energy storing and electricity generating devices such as gas turbines. In addition, it has low cycle fatigue resistance superior to that of the majority of solid solution-strengthened alloys and it has a very good resistance to hot corrosion. The alloy is used to produce high-temperature gas path components such as turbine combustors, flame holders, liners, pressure vessels of some nuclear reactors, chemical reactors, and pipes / valves in the chemical industry.
Haze – It is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky.
HAZAN – It is ‘hazard analysis’ and covers a range of techniques which are used to analyze hazards. HAZAN includes analyzing the consequences of hazards and the safeguards for hazard prevention / or mitigation.
Hazard – It is any aspect of technology or human activity which produces risk, i.e., the potential for harm or damage to people, property, or the environment. It is a source of danger (i.e., material, energy source, or operation) with the potential to cause illness, injury, or death to a person or damage to a facility or to the environment (without regard to the likelihood or credibility of accident scenarios or consequence mitigation).
Hazard analysis – It is the determination of material, system, process, and plant characteristics which can produce undesirable consequences, followed by the assessment of hazardous situations associated with a process or activity. Largely qualitative techniques are used to pinpoint weaknesses in design or operation of the facility which can lead to accidents. The hazards analysis examines the complete spectrum of potential accidents which can expose members of the public, onsite workers, facility workers, and the environment to hazardous materials.
Hazards controls – These are the measures to eliminate, limit, or mitigate hazards to workers, the public, or the environment, including (i) physical, design, structural, and engineering features, (ii) safety structures, systems, and components, (iii) safety management programmes, (iv) technical safety requirements, and (iv) other controls necessary to provide adequate protection from hazards.
Hazardous event – It is the occurrence of a hazard, normally used in the context of the failure of a safety related system.
Hazardous material – It is that substance which can produce adverse health and / or safety effects to people or the environment.
HAZID – It is ‘Hazard Identification’.
HAZOP– HAZOP is ‘Hazard and Operability’ study. It is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems which can represent risks to personnel or equipment, or prevent efficient operation. A systematic method of identifying hazards using a team-based approach and applying a set of standard guide phrases to the elements of a design is to determine how these can deviate from the intent of the designers and what the results can be. The method originated in the chemical process industry where it was applied to plant and instrumentation diagrams, but has been adopted more widely and applied to a number of different design descriptions.
H-band steel -It is a carbon, carbon-boron, or alloy steel produced to specified limits of hardenability, the chemical composition range can be slightly different from that of the corresponding grade of ordinary carbon or alloy steel.
H-beam – It is a type of structural member with a H-shaped cross-section. It has equal or near-equal width and depth and is more suited to being oriented vertically to carry axial load such as columns in multi-storey construction. This beam is cost-effective, flexible and is superior in terms of strength, efficiency, higher axial and bending load-bearing capacities. It is a high-performance steel section due to its advantage of optimized cross sectional area distribution and reasonable ratio of strength to weight ratio. With the features of wide flange and thin web, H-beam has a large section modulus, high bending resistance. and excellent mechanical properties. This beam is normally heavier than I-beam and is useful as supports for retaining walls and the like. It can also be used as beam sections where head room is of concern. Because of its outstanding properties, H-beam is a popular section for the designers of steel structures. H-beam is typically made of structural steel and serves a wide variety of construction uses. The horizontal elements of the ‘H’ are called flanges, and the vertical element is known as the web. The web resists shear forces, while the flanges resist most of the bending moment experienced by the beam. The Euler–Bernoulli beam equation shows that the H-shaped section is a very efficient form for carrying both bending and shear loads in the plane of the web. On the other hand, the cross-section has a reduced capacity in the transverse direction, and is also inefficient in carrying torsion, for which hollow structural sections are frequently preferred.
H-bridge – It is an array of four controlled switches which coverts direct current to alternating current, with peak value equal to the supply voltage.
Header – A header is a larger pipe which supplies to or collects from a series of smaller pipes or tubes. It is also called a manifold. In forging, header is a type of forging equipment, related to the mechanical press, in which the principal forming energy is applied horizontally to the work-piece, which is gripped and held by prior action of the dies.
Head, fasteners – It is the enlarged shape that is formed on one end of the fastener to provide a bearing surface and a method of turning (or holding) the fastener.
Head grade – It is the average grade of ore which is fed into a mill.
Heading – It is the upsetting of wire, rod, or bar stock in dies to form parts which normally contain portions which are higher in cross-sectional area than the original wir =e, rod, or bar.
Head pulley – It is located at the discharge point of the conveyor. It normally drives the conveyor and frequently has a larger diameter than other pulleys. For better traction, the head pulley is normally lagged (with either rubber or ceramic lagging material).
Heads – Heads are the steel plates which close off the ends of the boiler drum. They are also referred to as end plates. If the shell contains tubes which are held in position by the heads, then they are normally called tube sheets.
Head-space – It is the space between the level of the contents of a container and the closure. Head-space is needed to allow for expansion of a product because of heat or pressure, and to allow the container to be grasped without spilling the contents.
Healed-over scratch – It is a scratch in a metallic object which has occurred in an earlier mill operation and has been partially masked in subsequent rolling. It can open up during forming.
Health and safety programme – It is a systematic combination of activities, procedures, and facilities designed to ensure and maintain a safe and healthy work-place.
Health impact assessment (HIA) – It is an assessment, normally carried out in advance of a particular project or course of action being approved, which seeks to analyze the likely impact on human health. The health impact assessment is to be used as a tool by decision-makers for the determination of the alternatives which have lesser impacts on health.
Heap leaching – It is a process whereby valuable metals, normally gold and silver, are leached from a heap, or pad, of crushed ore by leaching solutions percolating down through the heap and collected from a sloping, impermeable liner below the pad.
Hearth – It is the bottom portions of certain furnaces, such as air furnaces, and other reverberatory furnaces, which support the charge and sometimes collect and hold molten metal. In blast furnace, it is crucible shaped bottom of the blast furnace where produced hot metal accumulates before it is tapped. It is normally lined with carbon blocks. In industrial furnaces, hearth supports or carries the load for heating. It consists of refractory materials supported by a steel structure, part of which can be water-cooled.
Hearth diameter – it is the diameter of the inside face of the refractory lining of the blast furnace hearth, excluding any increases in wall thickness at the tap holes.
Hearth line – It is the horizontal line at the intersection of a vertical line through the nose of the tuyere cooler and sloping line of the bosh. With ceramic lined boshes, the line through the noses of the bosh plates determines the slope of the bosh.
Hearth zone, blast furnace – In this zone, the collection and separation and storing of hot metal and liquid slag takes place. The only activities which take place in this zone are desulphurization and carburization of hot metal. The liquid permeability is also important in this zone. The desirable measurements in this zone are (i) level of hot metal and slag and their behaviour, (ii) coke supply and its removal because of its combustion, (iii) desulphurization and carburization of hot metal, and metalloid reaction. Typical measurements in this zone which are needed are monitoring of the behaviour of hot metal and liquid slag as well as monitoring of hearth coke replacement and for this an estimation model using various mathematic models is presently being used.
Heat – It is a stated tonnage of metal obtained from a period of continuous melting in a furnace such as basic oxygen furnace, cupola, or the melting period required to handle this tonnage. In thermo-dynamics, heat is energy in transfer between a thermo-dynamic system and its surroundings by modes other than thermo-dynamic work and transfer of matter. Such modes are microscopic, mainly thermal conduction, radiation, and friction, as distinct from the macroscopic modes, thermo-dynamic work and transfer of matter. For a closed system (transfer of matter excluded), the heat involved in a process is the difference in internal energy between the final and initial states of a system, and subtracting the work done in the process.
Heat-activated adhesive – It is a dry adhesive which is rendered tacky or fluid by application of heat, or heat and pressure, to the assembly.
Heat-affected zone (HAZ) – It is that portion of the base metal which has not been melted during brazing, cutting, or welding, but whose micro-structure and mechanical properties have been altered by the heat.
Heat available – It is the thermal energy above a fixed datum which is capable of being absorbed for useful work.
Heat balance – It is an accounting of the distribution of the heat input, output, and losses.
Heat build-up – It is the rise in temperature in a part resulting from the dissipation of applied strain energy as heat or from applied mould cure heat.
Heat check – It is a pattern of parallel surface cracks which are formed by alternate rapid heating and cooling of the extreme surface metal. These are sometimes found on forging dies and piercing punches. There can be two sets of parallel cracks, one set perpendicular to the other.
Heat checking – It is a process in which fine cracks are formed on the surface of a body in sliding contact because of the build-up of excessive frictional heat.
Heat cleaned – It is a condition in which glass or other fibres are exposed to high temperatures to remove preliminary sizings or binders not compatible with the resin system to be applied.
Heat distortion temperature – The temperature at which a standard test bar deflects a specified quantity under a stated load.
Heat conduction – It is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature.
Heat convection – It occurs when the bulk flow of a fluid (gas or liquid) carries its heat through the fluid. All convective processes also move heat partly by diffusion, as well. The flow of fluid can be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), hence influencing its own transfer. The latter process is frequently called ‘natural convection’. The former process is frequently called ‘forced convection’. In this case, the fluid is forced to flow by use of a pump, fan, or other mechanical means.
Heat deflection temperature – It is the temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in several aspects of product design, engineering and manufacture of products using thermo-plastic components
Heat-disposable pattern – It is a pattern formed from a wax-base or plastic-base material which is melted from the mould cavity by the application of heat.
Heat distortion temperature (HDT) – It is the temperature at which a simple cantilever beam deflects a given quantity under load.
Heat engine – It is a system which converts heat or thermal energy, and chemical energy, to mechanical energy, which can then be used to do mechanical work.
Heat exchanger – It is a device which transfers heat from one system to another without physical transfer of any matter. It transfers heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids can be separated by a solid wall to prevent mixing or they can be in direct contact. The heat exchangers are widely used in space heating, refrigeration, air conditioning, power stations, iron and steel plants, chemical plants, petro-chemical plants, petroleum refineries, natural-gas processing, and sewage treatment.
Heat flow – It is the heat energy which flow in and between materials (solid / liquid / gas) as a result of a temperature difference. It is a process function (or path function).
Heat-flow and thermal-conductivity sensors – The accurate measurements of heat flow through thermal insulators and of the thermal conductivity of construction materials are both important. Such measurements are of interest for the purpose of safety and energy conservation. A common heat flow meter design involves the placing of a thin plate of known thermal conductivity on a heat radiating surface. It has been found that the heat flow through these elements is directly related to the temperature difference through them. This temperature difference is frequently detected by thermopiles, a large and even number of thermo-couples connected in series in such a manner that their high-temperature junctions are on the inside and their low-temperature junctions are on the outside surface of the sensing element. The heat flows which are encountered in different processes range from around 10 kilocalories per square metre hour through freezer walls to around 100,000 kilocalories per square metre hour through the shells of water-cooled electric furnaces. The thickness of the sensor plates is a few millimeters, and the plates are made of rubber, organic materials, or other heat-resistant materials, sometimes contained in a thin, stainless steel disk case.
Heating surface – It is that surfaces which is exposed to products of combustion on one side and water on the other. This surface is measured on the side receiving the heat.
Heating value – Heating value of a fuel is the quantity of heat released through complete combustion of a specified quantity of it. It is normally expressed in kilocalories per cubic metre The high heat values are conventionally measured with a bomb calorimeter. Low heat values are calculated from high heat value test data.
Heat mark – It is the extremely shallow depression or groove in the surface of a plastic visible because of a sharply defined rim or a roughened surface.
Heat recovery – It consists of utilizing the waste heat exiting through the flues. Some forms of heat recovery are air preheating, fuel preheating, load preheating, recuperative, regenerative, and waste heat boilers.
Heat recovery steam generator (HRSG) – It is an energy recovery heat exchanger which recovers heat from a hot gas stream, such as a combustion turbine or other waste gas stream. It produces steam which can be used in a process or used to drive a steam turbine. It is a high-efficiency steam boiler which uses hot gases from a gas turbine to generate steam in a thermodynamic Rankine cycle. This system is able to generate steam at different pressure levels as per the process requirements.
Heat release rate – It is the rate which describes the heat available per square metre of heat-absorbing surface in the furnace or per cubic metre of volume.
Heat resistance – It is the property or ability of plastics and elastomers to resist the deteriorating effects of high temperatures.
Heat-resistant alloy – It is an alloy which has been developed for very-high-temperature service where relatively high stresses (tensile, thermal, vibratory, or shock) are encountered and where oxidation resistance is frequently needed.
Heat resistant cast irons – These cast irons combine resistance to high temperature oxidation and scaling with resistance to softening or micro-structural degradation. Resistance to scaling depends mainly on high alloy content, and resistance to softening depends on the initial micro-structure along with the stability of the carbon containing phase. Heat resistant cast irons are normally ferritic or austenitic as cast. Carbon exists predominantly as graphite, either in flake or nodular form, which subdivides heat resistant cast irons into either gray or ductile cast irons. There are also ferritic and austenitic white cast iron grades, although they are less frequently used.
Heat resistant conveyor belt – It is a thermo-stable conveyor belt which is used for transporting materials with temperatures of 60 deg C and higher. Damage to cover rubber varies depending on the temperature or shape of transported materials and it is critical to choose suitable belt materials depending on the use conditions. The relationship between the temperatures of the material and the belt surface is especially noteworthy. This is since cooling is mainly achieved on the return trip as the temperature of the belt surface is different from that of the material, although it varies depending on the material shape, belt length, speed, operation environment, and operating hours
Heat resistant steels – These steels are extensively used for high temperature components, and they cover a broad range of applications. The properties of steel and its yield strength considerably decrease as the steel absorbs heat when exposed to high temperatures. Heat resistance means that the steel is resistant to scaling at temperatures higher than 500 deg C. Heat resistant steels are meant for use at temperatures higher than 500 deg C since they have got good strength at this temperature and are particularly resistant to short-term and long-term exposures to hot gases and combustion products at temperature higher than 500 deg C. These steels are solid solution strengthened alloy steels. The heat-resistant steels are normally classified into ferritic / martensitic steels and austenitic steels. The ferritic / martensitic steels have the same body centered cubic (bcc) crystal structure as iron. They are simply iron containing with relatively small addition of alloying elements, such as the main element chromium added from 2 % to around 13 %. These ferritic / martensitic grades also have a small percentage of manganese, molybdenum, silicon, carbon and nitrogen, mostly included for their benefits in the precipitation strengthening and encouraging high temperature behaviour. Ferritic grades are normally used since they are economical because of their low content of alloying elements. They also have some resistance to oxidation at red heat, and which is in direct proportion to the chromium content.
Heat sealing – It is a method of joining plastic films by simultaneous application of heat and pressure to areas in contact.
Heat-sealing adhesive – It is a thermo-plastic film adhesive which is melted between the adherend surfaces by heat application to one or both of the adjacent adherend surfaces.
Heat shield – It is a shield which is designed to protect an object from overheating by dissipating, reflecting, absorbing heat, or simply gradually burn and fall away from the part, pulling the excess heat with it. The term is very frequently used in reference to exhaust heat management and to systems for dissipation of heat due to friction.
Heat sink – It is a material which absorbs or transfers heat away from a critical element or part. It is also a structure intended to dissipate heat from an active device into the ambient environment.
Heat streak – It is a coloured band(s) parallel to the rolling direction which varies in both width and exact location along the length.
Heat tinting – It means colouration of a metal surface through oxidation by heating to reveal details of the micro-structure.
Heat transfer – It is a discipline of thermal engineering which hat concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into different mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they frequently occur simultaneously in the same system.
Heat treatable alloy – It is an alloy which can be hardened by heat treatment.
Heat treating – It is a term which is used to cover annealing, hardening, tempering, and so on.
Heat treating film – It is a thin coating or film, normally an oxide, formed on the surface of a metal during heat treatment.
Heat-treating furnaces – These furnaces are normally classified in two broad categories, batch furnaces and continuous furnaces. In batch furnaces, work-pieces normally are manually loaded and unloaded into and out of the furnace chamber. On the other hand, a continuous furnace has an automatic conveying system which provides a constant work load through the unit.
Heat treating processes – All the heat-treating processes consist of subjecting the steel to a definite time-temperature cycle. This time-temperature cycle has three components namely (i) heating, (ii) holding at particular temperature range (soaking), and (iii) cooling. Individual cases can differ, but certain fundamental objectives are there.
Heat treat lot – It is the material of the same mill form, alloy, temper, section, and size traceable to one heat treat furnace load (or extrusion charge or billet in the case of press heat treated extrusions) or, if heat treated in a continuous furnace, charged consecutively during an 8-hour period.
Heat treatment – It consists of heating and cooling a solid metal or alloy in such a way as to get desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.
Heat treatment solution – It is a treatment in which an alloy is heated to a suitable temperature and held at this temperature for a sufficient length of time to allow a desired constituent to enter into solid solution, followed by rapid cooling to hold the constituent in solution. The material is then in a super-saturated unstable state which may subsequently exhibit age hardening.
Heat treat stain – It is a discolouration because of the non-uniform oxidation of the metal surface during solution heat treatment.
Heavy-duty oil – It is an oil which is stable against oxidation, protects bearings from corrosion, and has detergent and dispersant properties. Heavy-duty oils are suitable for use in gasoline and diesel engines.
Heavy fuel oil – It is a category of fuel oils of a tar-like consistency. It is also known as bunker fuel, or residual fuel oil. This oil is the result or remnant from the distillation and cracking process of petroleum.
Heavy media separation – Heavy media separation devices has been developed as a more effective alternative to jigging for the upgrading of the iron ores. Heavy media separation processes operate on the sink and float principle. A suspension of fine (minus 200 mesh) ferro-silicon in water is used to create a fluid media with a specific gravity of around 3. Silica rich particles with a specific gravity of about 2.6 float on the surface of such a medium while the denser and heavier iron ore particles with a specific gravity over 4 settles to the bottom. The conventional medium for concentrating coarse ore is ferro-silicon containing 15 % silicon and 85 % iron. Water suspensions containing 64 % to 85 % of finely ground ferro-silicon have specific gravities ranging from 2.2 to 3.6. The separation vessels for coarse ore (plus 9 millimeters) are normally spiral classifiers, rake classifiers or rotating drums. Ore finer than 9 millimeters and coarser than 3 millimeters can be separated in heavy media cyclones where the high gravitational forces accelerate the settling of the heavy iron ore particles. Finely ground magnetite is used to make up the heavy media for the cyclone separators rather than ferro-silicon. The dynamics of the cyclone create the density and media fluidity needed despite the lower specific gravity of the magnetite. Further the cost of magnetite is much less than ground ferro-silicon. The medium, ferro-silicon and magnetite, is washed from the sink and float products on fine screens equipped with wash troughs and water sprays and is recovered from the wash water with magnetic separators and recycled.
Heavy metal, Heavy alloy – It is a sintered tungsten alloy with nickel, copper, and / or iron, the tungsten content being at least 90 % and the density being at least 16.8 grams per cubic centimeter.
Heavy water – It is the water which is enriched to contain significantly more than the natural proportions (one in 6,500) of heavy hydrogen (deuterium, D) atoms to ordinary hydrogen atoms. Heavy water, effective in slowing neutrons down and having a low probability of absorbing neutrons, is used as a moderator in some reactor designs.
Hedging – It is taking a buy or sell position in a futures market opposite to a position held in the cash market to minimize the risk of financial loss from an adverse price change.
Heel – It is the surface on which a single-point tool rests when held in a tool post. In steelmaking, it means molten steel from a previous heat which has been retained for the nest heat to assist melting.
Heel block – It is a block or plate normally mounted on or attached to a lower die in a forming or forging press which serves to prevent or minimize the deflection of punches or cams.
Height above ground level – It is a height which is measured with respect to the underlying ground surface.
Height above mean sea level – It is a measure of a location’s vertical distance (height, elevation, or altitude) in reference to a vertical datum based on a historic mean sea level.
Height between bottom of large bell and top of hopper – It is the vertical distance between bottom of the large bell closed and the intersection of the hopper or the hopper extension with the gas seal.
Height of bosh – It is the vertical distance between the hearth and bosh line.
Height of hearth – It is the vertical distance between the hearth line and the centre-line of the tap hole. The latter is determined by the centre of the tap hole opening in the hearth jacket.
Height of in-wall – It is the vertical distance between the bottom in-wall line and the bend line.
Height of large bell hopper – It is the vertical distance between the inner large bell seat and the inter-section of the hopper or hopper extension with the gas seal.
Helical gears – These gears differ from spur gears in that helical teeth are cut across the gear face at an angle rather than straight. Hence, the contact line of the meshing teeth progresses across the face from the tip at one end to the root of the other, reducing the noise and vibration characteristic of spur gears. Also, several teeth are in contact at any one time, producing a more gradual loading of the teeth which reduces wear substantially. The increased quantity of sliding action between helical gear teeth, however, places higher demands on the lubricant to prevent metal-to-metal contact and resulting premature gear failure. Also, since the teeth mesh at an angle, a side thrust load is produced along each gear shaft. Hence, thrust bearings are to be used to absorb this load so that the gears are held in proper alignment.
Helical winding – In filament-wound items, a winding in which a filament band advances along a helical path, not necessarily at a constant angle, except in the case of a cylinder.
Helium (He) – It is a colourless, odourless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressures. It is the second-lightest after hydrogen. Liquid helium is used in cryogenics (its largest single use), and in the cooling of super-conducting magnets, with its main commercial application in magnetic resonance imaging (MRI) scanners. Helium’s other industrial uses are as a pressurizing and purge gas, as a protective atmosphere for arc welding, and in processes such as growing crystals to make silicon wafers
Helmholtz coil – It is an arrangement of coils which is useful for producing a uniform magnetic field within a certain volume.
Helmholtz free energy, Helmholtz energy) – It is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature (isothermal). The change in the Helmholtz energy during a process is equal to the maximum quantity of work which the system can perform in a thermodynamic process in which temperature is held constant. At constant temperature, the Helmholtz free energy is minimized at equilibrium.
Hematite ore – It is an oxide of iron, and one of that metal’s most common ore minerals. Hematite refers to a ferric oxide containing no crystal water, and its chemical formula is Fe2O3 (ferric oxide). The pure hematite theoretical iron content is 69.94 %. Its appearance is from red to light gray, sometimes black, and the stripes are dark red. It is normally known as ‘red mine’. The hematite crystal structure is different, from very dense to very loose and very soft powder, so the hardness is not the same. The former is generally between 5.5 and 6.5 on Mohs scale, while the latter is very low. The specific gravity is between 4.8 and 5.3. It melts at 1,565 deg C. it has metallic to splendent luster. Hematite is abundant in nature, but pure hematite is less, frequently co-existing with magnetite and limonite. Hematite ore is a direct-shipping ore with naturally high iron content.
Hemming – It is a bend of 180-degree made in two steps. First, a sharp-angle bend is made; next the bend is closed using a flat punch and a die.
Henry’s law – It is a gas law which states that the quantity of dissolved gas in a liquid is directly proportional to its partial pressure above the liquid. The proportionality factor is called Henry’s law constant. In simple words, it can be said that the partial pressure of a gas in vapour phase is directly proportional to the mole fraction of a gas in solution.
HERF – It is an abbreviation for high-energy-rate forging. It is a closed-die hot-forging or cold-forging process in which the stored energy of high-pressure gas is used to accelerate a ram to unusually high velocities in order to effect deformation of the work-piece. Ideally, the final configuration of the forging is developed in one blow or, at most, a few blows. In high-energy-rate forging, the velocity of the ram, rather than its mass, generates the major forging force.
Herringbone – It is a pattern made up of rows of parallel lines which in any two adjacent rows slope in opposite directions
Herringbone bearing – It is a plain, sleeve, or thrust bearing with herringbone-shaped oil grooves.
Herringbone gears – Teeth in these gears resemble the geometry of a herring spine, with ribs extending from opposite sides in rows of parallel, slanting lines. Herringbone gears have opposed teeth to eliminate side thrust loads the same as double helicals, but the opposed teeth are joined in the middle of the gear circumference. This arrangement makes herringbone gears more compact than double helicals. However, the gear centres are to be precisely aligned to avoid interference between the mating helixes.
Herringbone pattern – It is fractographic pattern of radial marks (shear ledges) that look like nested letters ‘V’. Herringbone pattern is typically found on brittle fracture surfaces in parts whose widths are considerably higher than their thicknesses. The points of the herringbones can be traced back to the fracture origin.
Hershey number – It is a dimensionless number which is used to evaluate the performance of bearings. It relates the load per unit width (P), surface velocity (U), and dynamic viscosity (V) and given by the expression ‘P / U x V’. This number is normally written as ‘Z x N / p’, where ‘Z’ denotes the dynamic viscosity, ‘N’ the frequency of rotation, and ‘p’ the pressure.
Hertz (Hz) – It is the unit of frequency in the International System of Units (SI), frequently described as being equivalent to one event (or cycle) per second. For high frequencies, the unit is normally expressed in multiples namely kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).
Hertzian contact area – It is the contact area (also, diameter or radius of contact) between two bodies calculated as per the Hertz’s equations of elastic deformation. It is also the apparent area of contact between two non-conforming solid bodies pressed against each other, as calculated from Hertz’s equations of elastic deformation.
Hertzian contact pressure – It is the pressure at a contact between two solid bodies calculated as per the Hertz’s equations of elastic deformation. It is also the magnitude of the pressure at any specified location in a Hertzian contact area, as calculated from Hertz’s equations of elastic deformation.
Hertzian stress – It is the pressure at a contact between two solid bodies calculated according to Hertz’s equations for elastic deformation. The theoretical area of contact between two non-conforming surfaces is frequently quite small. The interaction between these surfaces is frequently described as either point or line contact. Common examples of point contact are mating helical gears, cams and crowned followers, ball bearings and their races, and train wheels and rails. If the mating parts can be considered semi-infinite and if material behaviour is linearly elastic, then the local stress state can be described by Hertzian theory, as long as the contacting surfaces can be modeled as quadratic functions of those spatial coordinates defining the surfaces. Even in the absence of friction, the resulting three-dimensional stress state is quite complex, and although the local stress state is compressive, i.e., the principal stresses beneath the load are negative, large subsurface shear stresses, which can serve as crack initiation sites, exist beneath the load.
Heterogeneity – This term is used in statistics to describe samples or individuals from different populations, which differ with respect to the phenomenon of interest. If the populations are not identical then they are said to be heterogeneous, and by extension, the sample data is also said to be heterogeneous.
Heterogeneous – It is the descriptive term for a material consisting of dissimilar constituents separately identifiable. It is a medium consisting of regions of unlike properties separated by internal boundaries. It is to be noted that not all the non-homogeneous materials are necessarily heterogeneous.
Heterogeneous equilibrium – In a chemical system, a state of dynamic balance among two or more homogeneous phases capable of stable coexistence in mutual or sequential contact.
Heterojunction bipolar transistor – It is a type of bipolar junction transistor which uses different semi-conductor materials for the emitter and base regions, creating a heterojunction. The heterojunction bipolar transistor improves on the bipolar junction transistor in that it can handle signals of very high frequencies, up to several hundred giga hertz.
Heterojunction with intrinsic thin film layer (HIT) – It is a type of solar cell which is composed of a mono-thin-crystalline silicon wafer surrounded by ultra-thin amorphous silicon layers. These solar cell modules are more efficient than typical crystalline modules, but they are more expensive.
Heteroscedasticity – In regression analysis, the property that the conditional distributions of the response variable ‘Y’ for fixed values of the independent variables do not all have constant variance. Non-constant variance in a regression model results in inflated estimates of model mean square error. Standard remedies include transformations of the response, and / or employing a generalized linear model.
Hetero-structure – It is a semiconductor device which is built of two or more dissimilar materials.
Hexa – It is the short form of hexa-methylene-tetramine, a source of reactive methylene for curing novolacs.
Hexagonal (lattices for crystals) – It consists of having two equal coplanar axes, ‘a1’ and ‘a2’, at 120-degree to each other and a third axis, ‘c’, at right angles to the other two. ‘c’ may or may not equal ‘a1’ and ‘a2’.
Hexagonal close-packing – It is a structure containing two atoms per unit cell located (0, 0, 0) and (1/3, 2/3, 1/2) or (2/3. 1/3, 1/2). It is one of the two ways in which spherical objects can be most closely packed together so that the closed-packed planes are alternately staggered in the order A-B-A-B-A-B. Each atom has twelve nearest neighbours in hexagonal close packing. In the ideal structure, the distance between the planes is 1.633a, where a is the distance between the atoms. Some metals with hexagonal close-packed crystal structures include cobalt, cadmium, zinc, and the alpha phase of titanium.
HEX tails – It is the types of uranic material arising from the uranium enrichment process (part of the nuclear fuel production cycle).
Hiding power – It is the ability of a paint to mask the colour or pattern of a surface. It is normally expressed as square metre per litre.
High-alloy graphitic cast iron – It is used mainly for applications needing corrosion resistance or a combination of strength and oxidation resistance. This type of cast iron is produced in both flake graphite (gray cast iron), or spheroidal graphite (ductile cast iron).
High alloy cast steels – These steels are extensively used for their corrosion resistance in aqueous media at or near room temperature and for service in hot gases and liquids at elevated temperatures (more than 650 deg C). High alloy cast steels are very frequently specified on the basis of composition. Some of the high alloy cast steels show several of the properties of cast carbon and low alloy steels. Some of the mechanical properties of these grades (e.g. hardness and tensile strength) can be altered by suitable heat treatment. The high alloy cast steel grades which contain more than 20 % to 30 % chromium + nickel, however, do not show the phase changes observed in plain carbon and low alloy steels during heating or cooling between room temperature and the melting point. These materials are hence non hardenable, and their properties depend on composition rather than heat treatment. Hence special consideration is to be given to each grade of high alloy cast steel with regard to casting design, foundry practice, and subsequent thermal processing (if any).
High alloy steel – These steels include steels with a high degree of fracture toughness. High alloy steels are ultra-high strength steels and consist of corrosion resistant steels, heat resistant steels, and wear resistant steels. High alloy steels also include maraging steels, austenitic manganese steels, tool steels, and stainless steels.
High aluminum defect – It is an alpha-stabilized region in titanium containing an abnormally large quantity of aluminum which can span a large number of beta-grains. It contains an inordinate fraction of primary alpha, but has a micro-hardness only slightly higher than the adjacent matrix.
High-conductivity copper – It is the copper which, in the annealed condition, has a minimum electrical conductivity of 100 % IACS (International Annealed Copper Standard). High conductivity copper is a term to describe copper which is exceptionally effective at conducting electricity. It is a versatile material, which means it has a wide variety of functions and applications. High conductivity copper, e.g., is most frequently used to make electrical items, such as cords or outlets. Depending on the need of the product it is being used to create, the material is either very low in oxygen content or completely free from oxygen. Additionally, materials made from high conductivity copper are resistant to corrosion, making it ideal for products which need require durability.
High-cycle fatigue – It is the fatigue which occurs at relatively large numbers of cycles. The arbitrary, but normally accepted, dividing line between high-cycle fatigue and low-cycle fatigue is considered to be around 10 to the power 4 cycles to 10 to the power 5 cycles. In practice, this distinction is made by determining whether the dominant component of the strain imposed during cyclic loading is elastic (high cycle) or plastic (low cycle), which in turn depends on the properties of the metal and on the magnitude of the nominal stress. High-cycle fatigue is controlled mainly by crack initiation behaviour of the material, as opposed to crack growth behaviour.
High-density inclusions (HDI) – These are mainly resulted by high density refractory metal elements. The known high-density inclusions can be classified into two categories: refractory metal elements (tungsten, molybdenum, tantalum, and niobium etc.) and their compounds (tungsten carbide, and titanium-tungsten etc.).
High density poly-ethylene (HDPE) – it is the resin of choice in blow moulding since it is stiff, chemical resistant, has good processing behaviour and good environmental stress crack resistance.
High-efficiency particulate air (HEPA) filter – It is also known as a high-efficiency particulate arresting filter. It is an efficiency standard of air filters. Filters meeting the high efficiency particulate air standard are to satisfy certain levels of efficiency. Common standards need that a high efficiency particulate air filter is required to remove, from the air which passes through, at least 99.95 % of particles whose diameter is equal to 0.3 micrometers, with the filtration efficiency increasing for particle diameters both less than and higher than 0.3 micrometers. High efficiency particulate air filters capture pollen, dirt, dust, moisture, bacteria (0.2 micrometers to 2 micrometers viruses (0.02 micrometers to 0.3 micrometers), and sub-micron liquid aerosol (0.02 micrometers to 0.4 micrometers).
High-electron-mobility transistor – It is also known as heterostructure field effect transistor (FET) or modulation-doped field effect transistor, is a field-effect transistor incorporating a junction between two materials with different band gaps as the channel instead of a doped region.
High-energy-rate compacting – It consists of compacting a powder at a very rapid rate by the use of explosives in a closed die.
High-energy-rate forging (HERF) – It is a closed-die hot-forging or cold-forging process in which the stored energy of high-pressure gas is used to accelerate a ram to unusually high velocities in order to effect deformation of the work-piece. Ideally, the final configuration of the forging is developed in one blow or, at most, a few blows. In high-energy-rate forging, the velocity of the ram, rather than its mass, generates the major forging force.
High-energy-rate forming – It is a group of forming processes which applies a high rate of strain to the material being formed through the application of high rates of energy transfer.
High-frequency heating – It is the heating of materials by di-electric loss in a high-frequency electrostatic field. The material is exposed between electrodes and is heated quickly and uniformly by absorption of energy from the electrical field.
High frequency resistance welding – It is a group of resistance welding process variations which uses high frequency welding current to concentrate the welding heat at the desired location.
High frequency electric resistance welding process – The process is used for the production of welded pipes. The process involves application of high frequency alternating current in the range of 200 kilo hertz to 500 kilo hertz. The pipe forming and energy input operations are performed by separate units. The strip is shaped in a roll forming mill or in an adjustable roll stand (natural function forming) into an open seam pipe for a wide range of pipe products. These include line pipes and structural pipes in the size ranges of around 20 millimeters to 600 millimeters outer diameter and wall thickness range of 0.5 millimeters to 16 millimeters and pipe blanks for a downstream stretch-reducing mill. The starting material is hot rolled wide steel strip or skelp. Depending on the pipe dimension and application, and particularly in case of precision pipes, the steel strip can undergo an upstream pickling operation, or cold rolled strip is used.
High gas pressure control – It is a control to stop the burner if the gas pressure is very high.
High grade – It is the rich ore. As a verb, it refers to selective mining of the best ore in a deposit.
High gradient magnetic separators – Several types of high gradient magnetic separators have been developed based on the fact that high magnetic field gradients can produce large magnetic forces. These separators are also called ‘induced pole’ separators because the field gradients are produced by applying a relatively uniform background magnetic field to a ferro-magnetic structure (grids, screens, grooved plates or steel wool) and inducing magnetic poles along properly oriented edges. Since large magnetic field gradients can generally exist only in small volumes these separators are designed for the separation of small magnetic particles. Producing high gradients and large magnetic forces over a surface area large enough to trap practical numbers of particles is a major issue. Needles with their axes parallel to the applied field produce high gradients in relatively low fields but the available trapping surface is very limited. By contrast filaments magnetized perpendiculars to their long axis have a large demagnetizing factor, but much greater surface area.
High interstitial defect – It consists of interstitially stabilized alpha-phase region in titanium of substantially higher hardness than surrounding material. It arises from very high local nitrogen or oxygen concentrations which increase the beta-transus and produce the high-hardness, frequently brittle alpha-phase. Such a defect is frequently accompanied by a void resulting from thermo-mechanical working. These defects are also termed type ‘I’ or low density interstitial defects, although they are not necessarily of low density.
High-level waste – It is the radio-active wastes which are highly radio-active materials, normally produced as a by-product of reactions which occur inside nuclear reactors. High-level waste takes one of two forms namely (i) spent (used) reactor fuel when it is accepted for disposal, or (ii) waste materials remaining after spent fuel has been reprocessed. High-level waste is heat-generating and, as a result, the temperature of the high-level waste can rise considerably over time. This has to be taken into account when designing storage or disposal facilities.
High-lighting – It means buffing or polishing selected areas of a complex shape to increase the lustre or change the colour of those areas.
Highly active liquor (HAL) – It is an intermediary stage in the vitrification process. Strict limits are imposed on the quantities of highly active liquor which can be stored. Highly active liquor consists of components of spent fuel other than uranium (i.e., radio-active by-products) dissolved in concentrated nitric acid after separation by the PUREX process.
Highly active liquid effluent facility (HALEF) – It is made of seismically qualified reinforced concrete and comprises a series of storage tanks used to store radio-active waste arising from nuclear processing operations.
Highly deformed layer – In tribology, it is a layer of severely plastically deformed material which results from the shear stresses imposed on that region during sliding contact.
Highly enriched uranium (HEU) – It is the uranium which has been modified by increasing the concentration of the fissionable isotope Uranium-235, containing 20 % or more of the isotope Uranium-235. A quantity of highly enriched uranium can be described in terms of either the total mass of all the Uranium isotopes, or as the mass of the fissile isotope Uranium-235, e.g., 100 kilograms of 70 % enriched highly enriched uranium can also be described as 70 kilograms Uranium-235.
High-pass filter – It is an electrical network which tends to pass higher frequencies and block lower ones.
High oil temperature control – It is a control to stop the burner if the oil temperature is very high.
High performance grinding – It is the applications of high-speed grinding (HSG) which have expanded the field of grinding from traditional finishing operation to now more widely employed high-performance machining. In this way, process development has led to a new grinding paradigm, which refers to the configuration of improved process with high-performance capabilities. In this way, high-performance grinding corresponds to the dual attributes of high-efficiency and high-precision, which are needed for competitive grinding processes.
High-performance liquid chromatography – It is formerly referred to as high-pressure liquid chromatography. It is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures.
High pressure briquetting process – It is the process in which the pressure applied is above 100 MPa. This process uses a heating device and the process is normally carried out for materials having inherent binders (lignin) and hence no external binder is used. However, some of the materials need binders even under high pressure conditions.
High-pressure laminates – These are laminates moulded and cured at pressures not lower than 6.9 MPa, and normally in the range of 8.3 MPa to 13.8 MPa.
High-pressure moulding – It is a term which is applied to certain types of high-production sand moulding machines in which high-pressure air is instantly released from a large pressure vessel to produce extremely hard, high-density moulds from green sand.
High-pressure spot – Localized area of insufficient resin, usually identified by low gloss, dry spots, or fiber showing on the surface.
High-pressure steam boiler – A high-pressure steam boiler is a steam boiler which operates at pressures above 103 kPa. These are also called power boilers.
High-recovery valve – It is a valve design which dissipates relatively little flow stream-energy because of streamlined internal contours and minimal flow turbulence. Hence, pressure downstream of the valve vena contracta recovers to a high percentage of its inlet value. Straight-through flow valves, such as rotary ball valves, are typically high-recovery valves.
High residual phosphorus copper – It is the deoxidized copper with residual phosphorus present in quantities (normally 0.013 % to 0.04 %) normally sufficient to decrease appreciably the conductivity of the copper.
High-resolution transmission electron microscopy – It is an imaging mode of specialized transmission electron microscopes that allows for direct imaging of the atomic structure of samples. It is a powerful tool to study properties of materials on the atomic scale, such as semi-conductors, metals, nano-particles and sp2-bonded carbon (e.g., graphene, carbon nano-tubes). This term is also frequently used to refer to high resolution scanning transmission electron microscopy, mostly in high angle annular dark field mode.
High-solids paint – It is the paint containing 35 % to 80 % solids. These products have become popular because of the reduction in solvent emissions associated with their use.
High speed diesel (HSD) oil – It is a complex mixture of hydro carbons. It is a brown-coloured oily liquid with pungent smell. It has a pungent smell. Its vapour density is 3.0 to 5.0 (air=1). It is insoluble in water. Its specific gravity is in the range of 0.81 to 0.91 (water=1). It is a neutral liquid (neither acidic nor basic). HSD is flammable with a flash point ranging from 32 deg C to 96 deg C. Its auto ignition temperature is 256.6 deg C. It is used in diesel engines of mobile equipment, automobiles, diesel-generator sets, and locomotives. It is the prime mover in a wide range of power generation and pumping applications. The diesel engines are normally of high compression and self-ignition engines. Fuel is ignited by the heat of high compression. High speed diesel oil is normally used as a fuel in medium-speed and high-speed compression ignition engines (operating above 750 rpm).
High-speed machining – It consists of high-productivity machining processes which achieve cutting speeds in excess of 600 metres per minute and up to 18,000 metres per minute.
High speed tool steels – Steels which are alloyed in such a way that they can be used as a cutting tool material to machine other metals at high speeds, and still retain its cutting ability, even though the tool tip is at a low red heat. The different grades of these steels contain 0.6 % or more of carbon, a combined content of 7 % or more of the elements like tungsten, molybdenum, and vanadium, 3 % to 6 % of chromium and in those needed to operate at the highest temperatures additions of 4 % to 13 % of cobalt. These steels are widely used for the production of taps, dies, twist drills, reamers, saw blades and other cutting tools. These steels form a special class of highly alloyed tool steels, combining properties such as high hot hardness and high wear resistance. These are so named mainly because of their ability to machine materials at high cutting speeds.
High strength bolts – These bolts are made from high-strength carbon steel or from tempered alloy steel. The high-strength materials tend to increase the bolt strength roughly by 25 % to 50 %.
High strength cast steels – These steels cover the tensile strength range of 1,200 MPa to 2,060 MPa. Cast steels with these strength levels and with considerable toughness and weldability were originally developed for military applications. These cast steels can be produced from any of the above medium alloy compositions by heat treating with liquid quenching techniques and low tempering temperatures.
High-strength low-alloy (HSLA) steels – These steels are designed to provide better mechanical properties and / or higher resistance to atmospheric corrosion than conventional carbon steels. They are not considered to be alloy steels in the normal sense since they are designed to meet specific mechanical properties rather than a chemical composition (High strength low alloy steels have yield strengths higher than 275 MPa). The chemical composition of a specific high strength low alloy steel can vary for different product thicknesses to meet mechanical property requirements. The high strength low alloy steels have low carbon contents (0.05 % to 0.25 %) in order to produce adequate formability and weldability, and they have manganese contents up to 2 %. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium are used in different combinations.
High strength steels – These are carbon low alloy steels which have yield strength higher than 275 MPa and can be classified normally in four types namely (i) as-rolled carbon-manganese steels, (ii) as rolled high strength low alloy steels also known as micro-alloyed steels, (iii) heat treated (normalized or quenched and tempered) carbon steels, and (iv) heat treated low alloy steels. These four types of steels have higher yield strengths than mild carbon steel in the as hot rolled condition. The heat-treated low alloy steels and the as rolled high strength low alloy steels also provide lower ductile-to-brittle transition temperatures than do carbon steels.
High-stress abrasion – It is a form of abrasion in which relatively large cutting forces are imposed on the particles or protuberances causing the abrasion, and which produces considerable cutting and deformation of the wearing surface. In metals, high-stress abrasion can result in considerable surface strain hardening. This form of abrasion is common in mining and agricultural equipment, and in highly loaded bearings where hard particles are trapped between mating surfaces.
High-temperature combustion – It is an analytical technique for determining the concentrations of carbon and sulphur in samples. The sample is burned in a graphite crucible in the presence of oxygen, which causes carbon and sulphur to leave the sample as carbon di-oxide and sulphur di-oxide. These gases are then detected by infrared or thermal conductive means.
High temperature corrosion – It is the corrosion by gases or deposits or both gases and deposits occurring at high temperatures under conditions where aqueous electrolytes no longer exist. It is to be noted that the high temperature corrosion can become significant at temperatures above 170 deg C depending on material and environment.
High-temperature flow – High temperatures because of a manifestation of viscous dissipation cause non-equilibrium chemical flow properties such as vibrational excitation and dissociation and ionization of molecules resulting in convective and radiative heat-flux.
High-temperature hydrogenation – It consists of non-catalytic hydrogenation which takes place only at very high temperatures. Among different hydrogenation methods, high-temperature hydrogenation is a critical approach with specific applications. By subjecting materials to high temperatures in a hydrogen-rich environment, this treatment method can induce chemical reactions and micro-structure changes, tuning materials’ mechanical performance.
High-temperature hydrogen attack – It is a loss of strength and ductility of steel by high-temperature reaction of absorbed hydrogen with carbides in the steel resulting in decarburization and internal fissuring.
High-tensile steel – High-tensile steels are low-carbon, or steels at the lower end of the medium-carbon range, which have additional alloying elements in order to increase their strength, wear properties or specifically tensile strength. These alloying elements include, chromium, molybdenum, silicon, manganese, nickel, and vanadium. Impurities such as phosphorus and sulphur have their maximum allowable content restricted.
High-velocity forming – High-velocity forming methods include techniques such as explosive forming and electro-magnetic forming. These techniques are distinct from most other metal forming methods in that the explosive or electro-magnetic force first accelerates the work-piece to a high velocity, and the kinetic energy of the work-piece is considerable. The sheet metal work-piece then changes shape,
either as it strikes a die or as it is decelerated by plastic deformation. High-velocity forming is characterized by first imparting a high velocity to a work-piece, and this energy is turned to plastic deformation by constraint of the part or impact with a die. The velocity distribution for the part is determined by the pressure distribution or developed from the explosive, electro-magnetic pressure distribution (determined by coil shape) or shock wave profile. Changing the quantity of energy available changes the absolute values of the velocities. Once the velocity is imparted, the shape can be developed either by free forming or die forming.
High-velocity oxygen fuel (HVOF) – It is a high velocity thermal spraying process which produces coatings with excellent adhesion and wear resistance. It is a thermal spraying coating method in which a mixture of oxygen and fuel is injected into the combustion chamber and subsequently ignited. The gas released in the combustion chamber is expelled at high velocities through a nozzle at very high pressures and temperatures. This thermal spray coating process is used to improve or restore a component’s surface properties or dimensions, hence extending equipment life by significantly increasing erosion and wear resistance, and corrosion protection.
High voltage (HV) – It is the voltage at which safety concerns apply. In some contexts, anything over 100 volts can be a high voltage. In electric power transmission, voltages over 66,000 volts are considered high voltage.
High voltage alternating current (HVAC) – Depending on context, it can be hundreds or hundreds of thousands of volts.
High-voltage (HV) cable – It is a flexible insulated electrical conductor designed to withstand a considerable voltage. ‘High’ voltage can be hundreds or hundreds of thousands of volts, depending on the context.
High voltage direct current (HVDC) converter station – It is an element of a high-voltage direct current power transmission system. Each end of the transmission line has a converter station connected to the local alternating current grid.
High-voltage direct current (HVDC) – It is a system for power transmission which uses high direct current voltages for reasons of economy or stability.
High-voltage (HV) switchgear – It is the electrical apparatus which is designed for control of high-voltage circuits.
High volume low activity (HVLA) waste – It is a subset of low-level waste (LLW) which is arising from decommissioning activities. Chemical properties of high-volume low activity waste are such that it can potentially be disposed of to a lower level of containment than low-level waste.
Hill yield criterion – It is a criterion used to describe the onset of plastic deformation for anisotropic materials. In its most general form, it assumes the presence of three different axial yield stresses and three different shear yield stresses. The criterion is formulated mathematically so as to reduce to the von Mises yield criterion if the material is isotropic.
Hindered contraction – It is the contraction where the shape does not permit a metal casting to contract in certain regions in keeping with the coefficient of expansion.
Hinge – It is a mechanical bearing which connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other around a fixed axis of rotation, with all other translations or rotations prevented. Hence, a hinge has one degree of freedom. Hinges can be made of flexible material or moving components.
Hinge area – It is the juncture of a hanging burr with the more rigidly adhered portion of a burr.
HIsarna process – It is a smelting reduction process for producing liquid iron directly from iron ore fines and coal. It represents a new, potentially more efficient way of making iron and is being developed for substantial reduction of carbon emissions from the ironmaking process. It eliminates prior processing of raw materials as needed by the blast furnace process. The process consists of pre-reduction of iron ore fines in cyclone converter furnace (CCF) of Isarna technology and bath smelting of iron in smelting reduction vessel (SRV) of HIsmelt process. The process name derives by combining the names of the two technologies (‘HI’ from HIsmelt and ‘sarna’ from Isarna, a celtic word for iron). The process cuts both carbon and costs. HIsarna process takes place in a special reactor which has a narrow cyclone furnace on top of a wider convertor.
HIsmelt process – It is an air based direct smelting technology. The process is for the production of liquid iron (hot metal) using iron ore fines or any other appropriate ferrous feed material. The smelting is carried out in a molten iron bath using coal as the reductant and energy source material. The principal raw materials needed for the process are iron ore fines, coal, and fluxes (limestone and dolomite). HIsmelt is short for ‘high intensity smelting’. It is a direct smelting process for making liquid iron straight from the iron ore. The process has been developed to treat iron ore fines with minimum of pre-treatment, making the process more flexible in terms of the quality of iron ore it can treat. The process allows the use of non-coking coal and iron ore fines with significant impurities. The main product of the process is liquid iron or hot metal which can be used in steel melting shop or can be cast in pig casting machine to produce pig iron. The by-product of the process is slag and the off gas.
Histogram – It is a graphical representation (bar chart) of the distribution of data. It is an estimate of the probability distribution of a continuous variable. It is a representation of tabulated frequencies, shown as adjacent rectangles, erected over discrete intervals (bins), with an area equal to the frequency of the observations in the interval. The height of a rectangle is also equal to the frequency density of the interval, i.e., the frequency divided by the width of the interval. The total area of the histogram is equal to the quantity of data. A histogram can also be normalized displaying relative frequencies. It then shows the proportion of cases which fall into each of several categories, with the total area equaling one. The categories are normally specified as consecutive, non-overlapping intervals of a variable. The categories (intervals) are to be adjacent, and are frequently chosen to be of the same. The rectangles of a histogram are drawn so that they touch each other to indicate that the original variable is continuous. Histograms are used to plot the density of data, and frequently for density estimation which is the estimating the probability density function of the underlying variable. The total area of a histogram used for probability density is always normalized to one.
Historic estimates – Historic resource quantities frequently possess high uncertainty in respect to geological knowledge regarding quantities and qualities (G-axis), technical feasibility (F-axis), and the environmental-socio-economic axis categories (E-axis). The estimates can be based on an ‘Identified Project’ but until a commercial operator is engaged and has verified or updated the estimates of the quantities, it is probably to be mapped under the ‘Non-Viable Project’ class.
Hob – It is a rotary cutting tool with its teeth arranged along a helical thread, used for generating gear teeth or other evenly spaced forms on the periphery of a cylindrical workpiece. The hob and the Work-piece are rotated in timed relationship to each other while the hob is fed axially or tangentially across or radially into the work-piece. Hobs is not to be confused with multiple-thread milling cutters, rack cutters, and similar tools, where the teeth are not arranged along a helical thread.
Hoberman mechanism, Hoberman linkage – It is a deployable mechanism which turns linear motion into radial motion.
Hohman A-6 wear machine – It is a widely used type of wear and friction testing machine in which a rotating ring sample is squeezed between two diametrically opposed rub blocks. This design is said to eliminate shaft flexure such as that found in other machines whose load application from the rub block to the ring is from one side only. Block geometry can be changed from flat to conforming or V-block. This type of machine is designed for use with either lubricated or unlubricated samples.
Hogging – It means machining a part from bar stock, plate, or a simple forging in which much of the original stock is removed.
Hoist – It is a device which is used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It can be manually operated, electrically or pneumatically driven and can use chain, fibre or steel wire rope as its lifting medium. The most familiar form is an elevator, the car of which is raised and lowered by a hoist mechanism. Majority of the hoists couple to their loads using a lifting hook. In mines, it is the machine which is used for raising and lowering of the cage or other conveyance in a shaft.
Hold-down plate (pressure pad) – It is a pressurized plate designed to hold the work-piece down during a press operation. In practice, this plate frequently serves as a stripper and is also called a stripper plate.
Holding – In heat treating of metals, it is that portion of the thermal cycle during which the temperature of the object is maintained constant.
Holding devices – These are the fixtures used to connect fabrications / parts to the handling equipment in the facility.
Holding force (Fm), magnet – It is the force perpendicular to the attraction faces needed to hold the attracted piece. It is normally shown in the specification sheets of the magnets and it refers to the whole contact face. The holding force for a magnet is affected by the composition of the material being lifted. Alloys with higher iron content are typically more susceptible to magnetic fields than those with lower iron content.
Holding furnace – It is a furnace into which molten metal can be transferred to be held at the proper temperature until it can be used to make castings.
Holding temperature – In heat treating of metals, it is the constant temperature at which the object is maintained.
Holding time – It is the time for which the temperature of the heat-treated metal object is maintained constant.
Hole – It is a void in rolled product. Typical cause of it is a non-metallic inclusion during rolling.
Hole expansion test – It is a simulative test in which a flat metal sheet sample with a circular hole in its centre is clamped between annular die plates and deformed by a punch, which expands and ultimately cracks the edge of the hole.
Hole flanging – Holes can be flanged, or collared, to strengthen them and to provide an area for threading, if needed. Collaring is accomplished by hole punching and expansion or by piercing and expansion. Hole flanging is the forming of an integral collar around the periphery of a previously formed hole in a sheet metal part.
Hole punching – Hole making in sheet metal involves the use of a punch and die to separate a slug from the sheet by shearing. After a small amount of plastic indentation by the punch, severe shearing deformation occurs between the punch edge and the die corner. Cracks begin to form within this shear zone at the punch and die corners and then progress toward each other. Final separation of the slug from the sheet involves tearing, resulting in a burr around the exit perimeter of the hole.
Holidays – These are discontinuities in a coating (such as porosity, cracks, gaps, and similar flaws) which allow areas of substrate to be exposed to any corrosive environment which contacts the coated surface.
Hollow cathode – It is made of a single element or alloy of the element to be analyzed to ensure sharp analytical lines with an absolute minimum of interfering spectral components.
Hollow cathode lamp – It is a type of glow discharge tube which uses a hollow cathode to improve the emission intensity.
Hollow structural section (HSS) – It is a type of metal profile with a hollow cross section. Hollow structural section members can be circular, square, or rectangular sections, although other shapes such as elliptical are also available. These sections are normally made from structural steel.
Holographic non-destructive testing – It is an effective technique for use with metal welded or braze bonded components, frequently with complex geometries. A single large ultrasonic transducer which sends out ultrasonic waves towards the object under study and it scans the object. The scattered waves from the object from the object waves. A received transducer collects the scattered object wave and converts them into electrical signals. The reference electrical waves are given by the radio frequency (RF) oscillator and these object to reference waves are made to interference by the electronic adder. The interference pattern is formed on the fluorescent screen of the cathode photographic film is developed. The developed photographic film serves as a hologram. The hologram is illuminated by a low power laser which acts as the optical reference source. The television camera takes the video-graph of the 3 D image of the object and it displays on the television monitor.
Homogeneity – This term is used in statistics to describe samples or individuals from populations, which are similar with respect to the phenomenon of interest. If the populations are similar then they are said to be homogenous, and by extension, the sample data is also said to be homogenous.
Homogeneous – It is the descriptive term for a material of uniform composition throughout. It is a medium which has no internal physical boundaries. Homogeneous is a material whose properties are constant at every point, i.e., constant with respect to spatial coordinates (but not necessarily with respect to directional coordinates).
Homogeneous carburizing – It is the use of a carburizing process to convert a low-carbon ferrous alloy to one of uniform and higher carbon content throughout the section.
Homogenizing – It is a heat-treating practice whereby a metal object is held at high temperature to eliminate or decrease chemical segregation by diffusion.
Homologous pairs – These are spectral lines for different elements which respond in the same way to changes in excitation conditions. One line can be used as an interval standard line for the other.
Homopolar generator – It is a generator in which current and magnetic field direction are constant as the machine rotor revolves.
Homopolar motor – It is a motor which produces torque from a current and magnetic field which does not change direction.
Homoscedasticity – In regression analysis, it is the property that the conditional distributions of ‘Y’ for fixed values of the independent variable all have the same variance.
Honeycomb– It is the manufactured product of resin-impregnated sheet material (paper, glass fabric, and so on) or metal foil, formed into hexagonal-shaped cells. It is used as a core material in sandwich construction.
Honeycomb structures -These are structures which have the geometry of a honeycomb to allow the minimization of the quantity of used material to reach minimal weight and minimal material cost. The geometry of honeycomb structures can vary widely but the common feature of all such structures is an array of hollow cells formed between thin vertical walls. The cells are frequently columnar and hexagonal in shape. A honeycomb-shaped structure provides a material with minimal density and relatively high out-of-plane compression properties and out-of-plane shear properties.
Honing – It is a low-speed finishing process which is used mainly to produce uniform high dimensional accuracy and fine finish, most frequently on inside cylindrical surfaces. In honing, very thin layers of stock are removed by simultaneously rotating and reciprocating a bonded abrasive stone or stick which is pressed against the surface being honed with lighter force than is typical of grinding.
Hook – It is an abrupt deviation from straightness. Hook can be caused by non-uniform metal flow during break-through.
Hook block assembly – It is a vital component in a crane’s lifting mechanism. It consists of a hook, sheaves (pulleys), bearings, and a strong structural framework. This assembly is designed to manage the wire rope, distribute load weight evenly, and provide a secure point of attachment for lifting.
Hook, lifting – It is a device for grabbing and lifting loads by means of a device such as a hoist or crane. A lifting hook is normally equipped with a safety latch to prevent the disengagement of the lifting wire rope sling, chain or rope to which the load is attached.
Hooke’s law – It is a generalization applicable to all solid material, which states that stress is directly proportional to strain and is expressed as stress / strain = s/e = E, where ‘E’ is the modulus of elasticity or Young’s modulus. The constant relationship between stress and strain applies only below the proportional limit.
Hoop – It is the ply laid onto a mandrel at a 90-degree angle. It is mainly used in reference to filament winding of cylindrically shaped objects.
Hoopes process – It is an electrolytic refining process for aluminum, using three liquid layers in the reduction cell.
Hoop stress – It is the circumferential stress in a material of cylindrical form subjected to internal or external pressure.
Horizontal batch furnace – It is a versatile batch-type furnace which can give light or deep case depths, and because the parts are not exposed to air, horizontal batch furnaces can give surfaces almost entirely free of oxides.
Horizontal fixed position pipe welding – It is the position of a pipe joint in which the axis of the pipe is approximately horizontal, and the pipe is not rotated during welding.
Horizontal position fillet weld – It is the position in which welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface.
Horizontal position groove weld -It is the position of welding in which the weld axis lies in an approximately horizontal plane and the weld face lies in an approximately vertical plane.
Horizontal rolled position pipe welding – It is the position of a pipe joint in which the axis of the pipe is approximately horizontal, and welding is performed in the flat position by rotating the pipe.
Horizontal return tubular (HRT) boiler – A horizontal return tubular boiler is a fire-tube boiler normally supported in a brick combustion chamber. The hot gases from combustion sweep along the underside of the shell then return through the fire tubes to the chimney connection.
Horn – In a resistance welding machine, it is a cylindrical arm or beam which transmits the electrode pressure and normally conducts the welding current. It is also a cone-shaped member which transmits ultrasonic energy from a transducer to a welding or machining tool.
Hornfels – It is a fine-grained contact metamorphic rock.
Horn press – It is a mechanical metal forming press which is equipped with or arranged for a cantilever block or horn which acts as the die or support for the die. It is used in forming, piercing, setting down, or riveting hollow cylinders and odd-shaped work.
Horn spacing – It is the distance between adjacent surfaces of the horns of a resistance welding machine.
Horse – It is a mass of waste rock lying within a vein or ore-body.
Horsepower (hp) – It is a unit of measurement of power, or the rate at which work is done, normally in reference to the output of engines or motors. There are several different standards and types of horsepower. Two common definitions used today are the imperial horsepower as in ‘hp’ or ‘bhp’ (brake horse power) which is around 745.7 watts, and the metric horsepower as in ‘cv’ (cavallo vapore, or cavalo-vapor) or ‘PS’ (PferdStarke) which is around 735.5 watts.
Horseshoe thrust bearing – It is a tilting-pad thrust bearing in which the top pads are omitted, making an incomplete annulus.
Horst – It is an upfaulted block of rock.
Host rock – It is the rock surrounding an ore deposit.
Hot blast air – It is the air which is heated in the hot blast stoves and fed to the BF through the tuyeres for the combustion of the fuel.
Hot blast main – It is the refractory lined pipe which connects the hot blast stoves with the bustle pipe.
Hot blast stove – Hot blast stove is used to preheat blast air used in the blast furnace for the combustion of fuel. It works as a counter-current regenerative heat exchanger. It consists of tall, cylindrical steel structures lined with different kinds of refractories and almost completely filled with checker bricks where heat is stored and then transferred to the fresh air to heat it to a specified temperature.
Hot blast valve – It is a critical equipment for the operation of the blast furnace. This valve is intended for complete separation of a hot blast stove from a hot blast main under ‘on-gas’ operation of the stove. This valve is also effectively being used as a shut-off valve and back drafting valve. This valve when used for separation of a gas burner from the hot blast stove under ‘on-blast’ operation of the stove is known as burner valve or gas shut off valve. Hot blast valve is installed vertically in a pipeline. Hot blast valves are normally installed in the horizontal hot blast main near the stove. The pipeline is opened and closed by the movement of the valve disk with the use of electro-mechanical drive. In the event of power failure, it is possible to operate the drive manually. Hot blast valve normally consists of a water-cooled disc resting on a water-cooled seat, and moving vertically within a water-cooled valve body and bonnet, and other supporting members and mechanisms which maintains a smooth, exact seating and non-stick release of the disc.
Hot box process – In foundry practice, it is a resin-base (furan or phenolic) binder process for moulding sands which is similar to shell core-making. Cores produced with it are solid unless mandrelled out.
Hot briquetted iron (HBI) – It is a compacted form of direct reduced iron which is manufactured with well-defined, consistent chemical and physical characteristics. It is produced by reducing iron oxide lumps, pellets, or fines, and compressing the material at a temperature of at least 650 deg C to achieve an apparent density of at least 5,000 kilograms per cubic meter. It is 100 times more resistant to reoxidation than conventional direct reduced iron and picks up 75 % less water. It also generates lesser fines, which provides higher value to users and reduces safety concerns during handling and shipping.
Hot cathode gun – It is an electron gun which derives its electrons from a heated filament, which can also serve as the cathode.
Hot cathodes – These cathodes typically achieve much higher power density than cold cathodes, emitting considerably more electrons from the same surface area.
Hot chamber machine – It is a die casting machine in which the metal chamber under pressure is immersed in the molten metal in a furnace. The chamber is sometimes called a gooseneck, and the machine is sometimes called a gooseneck machine.
Hot-cold working – It is a high-temperature thermomechanical treatment consisting of deforming a metal above its transformation temperature and cooling fast enough to preserve some or all of the deformed structure. It is also a general term which is synonymous with warm working.
Hot corrosion – It is an accelerated corrosion of metal surfaces which results from the combined effect of oxidation and reactions with sulphur compounds and other contaminants, such as chlorides, to form a molten salt on a metal surface which fluxes, destroys, or disrupts the normal protective oxide.
Hot crack – It is a crack which forms, normally at high temperature, because of the shrinkage stresses accumulating during solidification of a metal casting.
Hot cracking – It is also called solidification cracking. Hot cracking of weldments is caused by the segregation at grain boundaries of low-melting constituents in the weld metal. This can result in grain-boundary tearing under thermal contraction stresses. Hot cracking can be minimized by the use of low impurity welding materials and proper joint design.
Hot cracks – These are the cracks which develop in a weldment or casting during solidification. These cracks include several types of cracks which occur at high temperatures in the weld metal or heat affected zone. In general, hot cracks are normally associated with steels having high sulphur content. The common types of hot cracks include solidification cracks and liquidation cracks.
Hot-die forging – It is a hot forging process in which both the dies and the forging stock are heated. Typical die temperatures are 110 deg C to 225 deg C which are lower than the temperature of the stock. .
Hot dip – It consists of covering a surface by dipping the surface to be coated into a molten bath of the coating material.
Hot dip coating – It is a metallic coating got by dipping the substrate into a molten metal.
Hot dip galvanizing – It is a process in which an adherent, protective coating of zinc and iron-zinc alloys is developed on the surfaces of iron and steel products by immersing them in a bath of molten zinc. Majority of zinc coated steel is processed by hot dip galvanizing. One method of hot dip galvanizing is the batch process, which is used for fabricated steel items such as structures or pipes. This method involves cleaning the steel articles, applying a flux to the surfaces, and immersing them in a molten bath of zinc for different time periods to develop a thick alloyed zinc coating. The most common form of hot dip galvanizing for steel sheet is done on a continuous galvanizing line. Coiled sheet is fed from pay-off reels through flatteners. It is then cleaned, bright annealed, and passed through the coating bath. After leaving the coating bath, the coating thickness is controlled by an air knife or steel rolls. The sheet is then cooled and recoiled or cut into lengths. The hot dip process normally coats both sides of the sheet.
Hot direct reduced iron (HDRI) – It is produced in the vertical shaft kiln. It can be transported to an adjacent electric arc furnace at a temperature up to 650 deg C to take advantage of the sensible heat, which allows increase productivity during the steelmaking and reduction in the production cost. There are four alternatives which are being commercially available for the transport of hot direct reduced iron. These are (i) transport in a hot transport vessel, (ii) gravity transport of hot direct reduced iron, (iii) pneumatic transport of hot direct reduced iron, and (iv) hot transport conveyor system. Each of these alternatives has its best application, depending on such factors as transport distance, component arrangement, and conveying capacities.
Hot etching – In metallography, it is the development and stabilization of the micro-structure at high temperature in etchants or gases.
Hot extrusion – It is a process whereby a heated billet is forced to flow through a shaped die opening. The temperature at which extrusion is performed depends on the material being extruded. Hot extrusion is used to produce long, straight metal products of constant cross section, such as bars, solid and hollow sections, tubes, wires, and strips, from materials which cannot be formed by cold extrusion.
Hot film anemometer – This method uses the flow rate dependent heat transfer from a heated body to the measuring medium. In the fields which are relevant for process engineering, this flow rate dependent cooling is not a function of the pressure and temperature, but of the type and number of particles which get into contact with the hot surface. This means the method determines the mass flow rate of the measuring medium directly. The sensor unit consists of two measurement resistors that are part of an electrical bridge circuit. One of these resistors assumes the temperature of the flowing gas, whereas the other resistor is electrically heated and, at the same time, cooled by the gas mass flow. A control circuit applies heat to the resistor so that a constant temperature difference exists between the resistors. The power is, hence, a measure of the gas mass flow rate. This provides the measured value directly in the units namely kilograms per hour or standard cubic metre per hour. The density correction of the measured value otherwise required is no longer necessary. The compact design of the sensor unit assures a minimum pressure drop of typically 0.1 kilopascal. For thin film sensors the response time is in the milliseconds range. Vibration insensitivity and an extremely wide span at accuracies up to 1 % of rate are the rule for all thermal mass flow meters.
Hot forging – Hot forging is the most widely used forging process. In hot forging process, forging is carried out at a temperature above the recrystallization temperature of the metal which means at the temperature at which the new grains are formed in the metal. This kind of extreme heat is necessary in avoiding strain hardening of the metal during deformation. Hot forging is a forging process in which the die and / or forging stock are heated. It is also the plastic deformation of a pressed and / or sintered powder compact in at least two directions at temperatures above the recrystallization temperature.
Hot forming – It is the plastic deformation of metal at such a temperature and strain rate that
Hot isostatic pressing (HIP) – It is a manufacturing process, which is used to reduce the porosity of metals and increase the density of several ceramic materials. This improves the mechanical properties and workability of the material. The process can be used to produce waste form classes. It is also a process for simultaneously heating and forming a compact in which the powder is contained in a sealed flexible sheet metal or glass enclosure and the so-contained powder is subjected to equal pressure from all directions at a temperature high enough to permit plastic deformation and sintering to take place. Hot isostatic pressing is also a process which subjects a component (casting, or powder forgings etc.) to
both high temperature and isostatic gas pressure in an autoclave. The most widely used pressurizing gas is argon. When castings are hot isostatically pressed, the simultaneous application of heat and pressure virtually eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion.
Hot line pickup – It consists of small particles of metal and metal oxide generated in the roll bite, which subsequently transfer to the rolled product. It can be distributed uniformly and / or in streaks.
Hot-melt adhesive – It is an adhesive which is applied in a molten state and forms a bond after cooling to a solid state. It is a bonding agent which achieves a solid state and resultant strength by cooling, as contrasted with other adhesives which achieve the solid state through evaporation of solvents or chemical cure. It is a thermoplastic resin which functions as an adhesive when melted between substrates and cooled.
Hot metal – Hot metal is the output of a blast furnace. It is liquid iron which is produced by the reduction of descending ore burden by the ascending reducing gases.
Hot metal detector – It is the sensor which is necessary to determine the head and the tail of the bar for the bar position tracking.
Hot metal ladle – It is a bucket shaped refractory lined vessel in which hot metal is tapped for its transportation. Hot metal ladle can be open top or torpedo shaped known as open top ladle or torpedo ladle respectively.
Hot metal trough – Hot metal trough is a deep trench through which the hot metal and slag flow down once the tap hole is drilled open.
Hot mill – It is a production line or facility for hot rolling of metals.
Hot press forging – It consists of plastically deforming metals between dies in presses at temperatures high enough to avoid strain hardening.
Hot-pressed silicon nitride (HPSN) ceramic – It a type of ceramic material made from silicon nitride (Si3N4) powder. It is the fully dense version manufactured in graphite dies typically at temperatures in excess of 1,650 deg C. A small quantity of a hot-pressing aid is typically added, such as 0.5 % to 2 % MgO (magnesium oxide) or 3 % to 8 % Y2O3 (yttrium oxide).
Hot pressing – It consists of simultaneous heating and forming of a powder compact.
Hot pressure welding – It is a solid-state welding process which produces coalescence of materials with heat and application of pressure sufficient to produce macro-deformation of the base material. Vacuum or other shielding media can be used.
Hot quenching – It is an imprecise term for different quenching procedures in which a quenching medium is maintained at a prescribed temperature above 70 deg C.
Hot rate – It is the temperature rise of the holding electromagnet over the determined ambient temperature due to the power absorption under voltage. The temperature for reference is normally 35 deg C, if nothing against is indicated.
Hot rolled coil – It is a type of flat steel product which is wound into a coil immediately after the final rolling pass. It is produced through a high-temperature rolling process by which a steel slab is rolled in multiple passes at temperature frequently exceeding 1,000 deg C.
Hot rolled heavy sectional products – These products are in the form of beams are either steel joists or parallel flange beams. These products have the characteristics namely (i) the web height is equal to or higher than 80 millimeters (ii) the surfaces of the webs are continued by fillets to the inside faces of the flange, (iii) the flanges are normally symmetrical and of equal widths, and (iv) the outside faces of the flanges are parallel. In case of steel joists, the flanges are of decreasing thickness from the web to the edge. Steel joists are also called sloping flanged beams or tapered flanged beams. In case of parallel flange beams the inner surface of the beams are also parallel and the flanges are of uniform thickness. These beams are also known as universal beams. Beam sections are sometimes slitted in order to obtain two tee sections.
Hot rolled light and medium sectional products – These products consist of several sections namely (i) small channels (‘U’ sections) which are with cross-section resembling the letter ‘U’ and have a height which is less than 80 mm, (ii) angles which are with cross-section resembling the letter ‘L’ with the classification of equal angle and unequal angle depending on the ratio of the flange width and have rounded corner of the flange, (iii) Tee sections which are with equal flanges and the product cross-section resembling the letter ‘T’ and has the rounded corners and equal and slightly tapered flanges and slightly tapered web, and (iv) bulb flats which have a cross-section which is normally rectangular and has a bulge along the full length of a longitudinal edge of one of the wider surface and a width normally less than 430 millimeters.
Hot rolled long sectional products -These are those products which has a cross section resembling a shape such as equal angle, unequal angle, channel, tee, beams (with ‘I’ and ‘H’ sections), and piling section etc. These products are rolled generally in box passes or in universal rolling mills. When the cross-section is rectangular, the dimensional limitations apply to differentiate them from wide flats. These products are mostly delivered in straight lengths, rarely in folded bundles, but never in coils. Depending on the cross-sectional size, the sectional products can be (i) heavy sections, and (ii) light and medium sections.
Hot rolled plate and sheet -These are hot rolled flat products with the edges being allowed to deform freely. These products are supplied flat and normally in a square or rectangular shape, with a width higher than 600 millimeters. The edges may be as-rolled or sheared or flame-cut or chamfered. Hot rolled plate and sheet, according to thickness, can be categorized as (i) sheet when thickness less than 5 millimeters or plate when thickness is 5 millimeters minimum.
Hot rolled steel – it is the steel rolled on a hot rolling mill. Normally, hot rolled steels are further processed into other finished products.
Hot rolled strip – These are flat product which, immediately after the final rolling pass in a hot rolling mill is wound into a coil. Hot rolled strip as rolled has very slightly convex edges, but it can also be supplied with trimmed edges or slit from wider strip. Hot rolled strip, according to its actual width, can be categorized as (i) hot rolled wide strip with a width of 600 millimeters minimum, and (ii) hot rolled narrow strip with a width of less than 600 millimeters. After decoiling and cutting to length, hot rolled narrow strip can be produced as cut lengths.
Hot rolling mill – It is that mill in which rolling is done above the recrystallization temperature of the metal. During rolling in this mill, the grains, which deform during the process of rolling, recrystallize, maintain an equiaxed micro-structure and prevent the metal from work hardening. In this type of rolling, hot rolled metal has very little directionality in the mechanical properties and deformation induced residual stresses.
Hot-setting adhesive – It is an adhesive which needs a temperature at or above 100 deg C to set.
Hot shortness – It is a tendency for some alloys to separate along grain boundaries when stressed or deformed at temperatures near the melting point. Hot shortness is caused by a low-melting constituent, which is frequently present only in minute quantities, that is segregated at grain boundaries.
Hot spot – It is dark gray or black surface patches appearing after anodizing. These areas are normally associated with lower hardness and coarse magnesium silicide precipitate caused by non-uniform cooling after extrusion.
Hot strip mill – It is a flat rolling mill which rolls hot steel strips from slabs. Hot strips are produced in the form of coils.
Hot tear – It is a fracture formed in a metal during solidification because of hindered contraction. It occurs when low melting point materials segregate during the solidification and hence when they try to shrink during solidification cracks then tears develop since the surrounding material has already solidified. Also, hot tears occur at the joining of thin sections with larger sections because of the difference of the cooling rate and thus solidification.
Hot tension and compression testing – The testing consists of short-term tests at high temperatures for the determination of high temperature mechanical properties of the metals. The basic methods and Samples are similar to room-temperature testing, although the sample heating, test set-up, and material behaviour at higher temperatures do introduce some additional complexities and special issues for the high temperature testing.
Hot top – It is a reservoir, thermally insulated or heated, which holds molten metal on top of a mould for feeding of the ingot or casting as it contracts on solidifying, hence preventing formation of pipe orvoids. It is also a refractory-lined steel or iron casting which is inserted into the tip of the mould and is supported at different heights to feed the ingot as it solidifies.
Hot trimming – It is the removal of flash or excess metal from a hot part (such as a forging) in a trimming press.
Hot upset forging – It is a bulk forming process for enlarging and reshaping some of the cross-sectional area of a bar, tube, or other product form of uniform (normally round) section. It is accomplished holding the heated forging stock between grooved dies and applying pressure to the end of the stock, in the
direction of its axis, by the use of a heading tool, which spreads (upsets) the end by metal displacement. It is also called hot heading or hot upsetting.
Hot-wire analyzer – It is an electrical atmosphere analysis device which is based on the fact that the electrical resistivity of steel is a linear function of carbon content over a range from 0.05 % carbon to saturation. The device measures the carbon potential of furnace atmospheres (typically). This term is not to be confused with the hot-wire test which measures heat extraction rates.
Hot wire barretter – It is a current dependent resistor formed of a fine wire in an envelope. It is useful for regulating current.
Hot-wire test – It is the method used to test heat extraction rates of various quenchants. Faster heat-extracting quenchants permit more electric current to pass through a standard wire because it is cooled more quickly.
Hot work die-steels – These steels are high quality steels made to close compositional and physical tolerances. These steels are alloyed tool steels for use in applications in which surface temperature is normally above 200 deg C. During the application the die comes into contact with hot material, the temperatures of which are well above 200 deg C. Besides long -erm thermal load, there is the additional stress due to the periodic change of temperature. Hot work die-steels for such applications have to be able to withstand not only up to the universal mechanical and abrasive stresses normally occurring in die steels, but also, these steels have to withstand thermal load as well. These steels are used to make dies for forming or shaping a material into a part or component adapted for a definite use.
Hot-worked structure – It is the structure of a material which has been worked at a temperature higher than the recrystallization temperature.
Hot working – It is the plastic deformation of metal at such a temperature and strain rate that recrystallization takes place simultaneously with the deformation, hence avoiding any strain hardening. It is also referred to as hot forging and hot forming. Hot working is also controlled mechanical operations for shaping a product at temperatures above the recrystallization temperature.
Housekeeping – It is a way of controlling hazards along the path between the source and the worker. Good housekeeping means having no unnecessary items in the work-place and keeping all necessary items in their proper places. Housekeeping at the work-place is closely linked to the industrial safety. The degree, to which this activity is effectively managed, is an indicator of the safety culture of the organization.
Housing, rolling mill – Housing creates a framework of the rolling mill stand and for absorbing the total metal pressure on rolls during the process of rolling. Hence, the housing is to be solid and its structure is to enable easy and fast roll changing. Also, there need to be easy access to all parts of the housing and other details of the roll stand. Each of the roll stands has two housings, in which rolls are placed with chocks (bearings). In the upper part of the housing, there are adjusting screws and the roll counter-balancing device along with their drives. From the structural viewpoint, the housings can be classified into three types. These are (i) enclosed housing where the whole housing is made of one piece and which is more beneficial from the strength point of view, (ii) open housing which has the separated cap, connected to the housing by screws for easier rolls changing, and (iii) housing-less roll stand which has rigid chocks connected by solid and pre-stressed joints. The housing-less roll stand has limited stress relaxation (spring-back) of rolls and has smaller and lighter structure.
House of quality – It is the quality function deployment (QFD) which is frequently called the house of quality because of the house shaped quality function deployment matrices. It is a product planning tool which uses a matrix to map the customer wants to the quantified specifications of the design (product). The house of quality approach is used at the first stage of product planning and can be deployed all the way down the stage of production planning on the shop floor.
H-sections with broad or very broad flanges – These are sections in which the flange width is higher than 0.66 × the nominal height, or 300 mm or over. Sections with flanges wider than 0.8 × the nominal height are sometimes called columns.
Hub – It is a boss which is in the centre of a forging and forms a part of the body of the forging.
Hubbing – It is the production of forging die cavities by pressing a male master plug, known as a hub, into a block of metal.
Hue – In colour theory, hue is one of the main properties of a colour, defined technically as ‘the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, orange, yellow, green, blue, violet’, within certain theories of colour vision.
Hull cell – It is a special electro-deposition cell which is giving a range of known current densities for test work. Hull cell is a trapezoidal box of non-conducting material with electrodes arranged to permit observation of cathodic or anodic effects over a wide range of current densities.
Human error – It is the term used today to include not just worker’s error, but also engineering deficiency and lack of adequate organizational control which together account for an accident.
Human error probability – It is the term which is used in safety engineering. It is the probability which is assigned to represent the likelihood that a human, normally the operator, fails to complete a particular action correctly.
Human factors – They are those biomedical, psycho-social, work-place environment, and engineering considerations pertaining to people in a human-machine system. Some of these considerations are allocation of functions, task analysis, human reliability, training requirements, job performance aiding, personnel qualification and selection, staffing requirements, procedures, organizational effectiveness, and workplace environmental conditions.
Human resource development (HRD) – it is a process for developing and unleashing human expertise through organization development and personnel training and development for the purpose of improving performance. It is concerned with an organized series of learning activities, within a specified time limit, designed to produce behavioural change in the learner.
Human resource management (HRM) – It is defined as composed of policies, practices and systems which influence employees’ behaviour, attitude and performance. Human resource management practices can play three major roles, namely (i) building of critical organizational capabilities, (ii) enhancing employees’ satisfaction, and (iii) improving customer and stakeholder satisfaction. Proper human resource management practices do make a difference in the working efficiency of the organization. They improve internal capabilities of the organization to deal with current challenges being faced or future challenges to be faced by the organization.
Humidistat – It is a switch which operates automatically on detecting a change in moisture content of the air.
Humidity – It is the concentration of water vapour present in the air. Water vapour, the gaseous state of water, is normally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depends on the temperature and pressure of the system of interest.
Humidity, absolute – It is expressed as either mass of water vapour per volume of moist air (in grams per cubic meter)https://en.wikipedia.org/wiki/Humidity#cite_note-3 or as mass of water vapour per mass of dry air (normally in grams per kilogram).
Humidity, relative – It is frequently expressed as a percentage, indicates a present state of absolute humidity relative to a maximum humidity given the same temperature.
Humidity, specific – It is the ratio of water vapour mass to total moist air parcel mass.
Humidity test and Kesternich-test (sulphur dioxide) – It is a test for corrosion. In the humidity test, samples are exposed to an atmosphere with 100 % relative humidity. This test can be combined with the addition of a certain amount of sulphur di-oxide gas. This causes a highly corrosive and acidic environment for simulating the effect of heavy pollution normally associated with industry.
HVAC drawing – HVAC (heating, ventilation, and air conditioning) drawing provides information about the heating and ventilation systems. It also includes the air conditioning patterns and layout which are to be constructed inside the building. The HVAC drawing provides an insight into these complex systems and helps in planning the construction process accordingly. The HVAC plan is a schematic diagram which visually represents the structure and components of mechanical systems installed for thermal comfort, air-conditioning, and better air quality. HVAC symbols are used to depict the layout of devices, ventilation network, and other components of a HVAC system. The purpose of using HVAC symbols is to design an accurate HVAC plan which satisfies the environmental requirements of comfort by adjusting the outdoor air conditions. There are two common types of HVAC plans. The central HVAC plan is used when the need is to locate the system away from the building. It uses delivery ductwork to deliver the conditioned air. The local HVAC systems are normally positioned near or inside the conditioned zone with ductwork requirements.
Hybrid – It is a composite laminate consisting of at least two distinct types of matrices or reinforcement. Each matrix or reinforcement type can be distinct because of its (i) physical and / or mechanical properties, (ii) material form, and (iii) chemical composition.
Hybrid belts – These belts combine merits of the flexibility of nylon belt and low elongation of polyester belt. Satisfactory improvement is confirmed on those lines where belts are lengthened since sufficient take-up stroke is not secured.
Hybrid coil – It is a kind of transformer which is used for bi-directional transmission of signals over one pair of wires.
HYBRIT process – It replaces coal with hydrogen for the direct reduction of iron, combined with an electric arc furnace. The process is almost completely fossil-free, and result into substantial reduction in its greenhouse gas emissions. The product from the hydrogen-direct reduction process is direct reduced iron or sponge iron, which is fed into an electrical arc furnace, blended with suitable shares of scrap, and further processed into steel. The main characteristics of the process are (i) non fossil fuels are used in iron ore pellet production, (ii) hydrogen is produced with electrolysis using fossil-free electricity, (iii) storage of hydrogen in a specially designed unit is used as a buffer to the grid, (iv) a shaft furnace is used for iron ore reduction, (v) tailor-made pellets are used as iron ore feed, (vi) the reduction gas / gas mixture is preheated before injection into the shaft, (vii) the product can either be direct reduced iron or hot briquetted iron free of carbon or carburized, and (viii) the direct reduced iron / hot briquetted iron is melted together with recycled scrap in an electric arc furnace.
Hydrant valve – It is also called landing valve. It provides the means to draw water for fire-fighting from the fire water piping network.
Hydraulic actuators – These actuators work using essentially the same principal as pneumatic actuators, but the design is usually altered. Instead of a flexible chamber, there is a sealed sliding piston. Also, instead of using a spring as the opposing force, hydraulic fluid is contained on both sides of the piston. The differential pressure across the area of the piston head determines the net force. Hydraulic actuators on the other hand use an incompressible fluid, so the response time is essentially instantaneous. Hydraulic actuators offer the advantages of being small and yet still providing immense force. Draw-backs of hydraulic actuators are mainly the high capital cost and difficulty in maintaining them.
Hydraulic cement – This cement has the ability to set in the presence of water. Hydraulic cements set and become adhesive through a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates which are not very water-soluble. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack.
Hydraulic-circuit diagrams – These diagrams are complete drawings of a hydraulic circuit. Included in the diagrams is a description, a sequence of operations, notes, and a components list. Accurate diagrams are essential to the designer, the people who build the machine, and the people who maintain the hydraulic system. There are four types of hydraulic-circuit diagrams. They are block, cutaway, pictorial, and graphical. These diagrams show (i) the components and how they will interact, (ii) how to connect the components and (iii) how the system works and what each component is doing.
Hydraulic conveying – Moving bulk materials along pipes or channels (troughs) in a stream of water is called ‘hydraulic conveying’. The mixture of materials and water is termed as pulp. Pump is used for conveying of pulp through pipe under pressure. In channels the conveying takes place down the inclination due to gravity. A hydraulic conveying system normally consists of a mixer where the material and water are mixed to form the requisite pulp. Depending on starting size of the bulk material, the materials can have to be crushed / ground in a crushing plant and screening facility. The prepared pulp is then pumped by a suitable pumping and piping system. In certain installation a suitable recovery system can be incorporated at the delivery end for dewatering the material. The most important consideration in a hydraulic conveying system is that the material is not to get settled and choke the pipeline. Hydraulic conveyors are used in several industries, mining operations and construction works. Some of the popular uses are to dispose ash and slag from boiler rooms, deliver materials from mines and sand and water to fill up used mines, to remove slag from concentration plants, to quench, granulate and convey furnace slag to disposal points, to move earth and sand in large construction projects and for land filling etc.
Hydraulic engineering – It is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the movement of the fluids. Hydraulic engineering is the application of the principles of fluid mechanics to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water.
Hydraulic fluid – Hydraulics is a technology for transferring of potential or kinetic energy (pressure and movements) using a fluid as the energy carrier. The fluids which are used for this purpose are known as hydraulic fluids. Hydraulic fluid is the medium by which power is transferred in hydraulic machinery. The hydraulic fluid frequently being referred as ‘hydraulic oil’, creates volume flow between pump and hydrostatic motor, and is in contact with all the components in a hydraulic system. Hydraulic fluid is a complex liquid which has to serve several different purposes and possess several different characteristics. Fully formulated hydraulic fluids consist of a blend of a base fluid and an additive package. Hydraulic fluid plays a very important role in the operation of machines. Common hydraulic fluids are based on mineral oil or water. Hydraulic systems work very efficiently if the hydraulic fluid used has zero compressibility.
Hydraulic gap control (HGC) – It is done by a controller which receives a gap reference and measures the gap coming from position encoders placed in the hydraulic cylinder and produces the servo-valve command which indeed controls the oil mass flow generating the movement of the cylinder. Obviously, the measured gap can be significantly different from the physical gap of the stand because of the stand elastic stretch.
Hydraulic hammer – It is a gravity-drop forging hammer which uses hydraulic pressure to lift the hammer between strokes.
Hydraulic-mechanical press brake – It is a mechanical press brake which uses hydraulic cylinders attached to mechanical linkages to power the ram through its working stroke.
Hydraulic press – It is a press in which fluid pressure is used to actuate and control the ram. Hydraulic presses are used for both open- and closed-die forging.
Hydraulic press brake – It is a press brake in which the ram is actuated directly by hydraulic cylinders.
Hydraulic reservoir – It is a container for holding the fluid required to supply the system, including a reserve to cover any losses from minor leakage and evaporation. The reservoir is normally designed to provide space for fluid expansion, permit air entrained in the fluid to escape, and to help cool the fluid. Hydraulic reservoirs are either vented to the atmosphere or closed to the atmosphere and pressurized. Fluid flows from the reservoir to the pump, where it is forced through the system and eventually returned to the reservoir. The reservoir not only supplies the operating needs of the system, but it also replenishes fluid lost through leakage. Furthermore, the reservoir serves as an overflow basin for excess fluid forced out of the system by thermal expansion (the increase of fluid volume caused by temperature changes), the accumulators, and by piston and rod displacement.
Hydraulic retention time – It is the average time in the aeration basin equivalent to the volume of the basin divided by the average flow and expressed as hours. The hydraulic retention time is required to be sufficiently long to remove the prerequisite biological oxygen demand (BOD) and is dependent on the type of the biological treatment system. It can range from 0.5 hours to 120 hours. The lower the hydraulic retention time the quicker the wastewater reaches the outlet.
Hydraulics – It is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids.
Hydraulic shear -It is a shear in which the cross-head is actuated by hydraulic cylinders.
Hydraulic system – It is one of the drive systems which are being used for the control of machinery and equipment. Typically, the fluid used in a hydraulic system is an incompressible liquid such as mineral based hydraulic oil. Pressure is applied by a piston to fluid in a cylinder, causing the fluid to press on another piston which delivers energy to a load. If the areas of the two pistons are different, then the force applied to the first piston is different from the force exerted by the second piston. This creates a mechanical advantage. The hydraulic system works on the principle of Pascal’s law which says that the pressure in an enclosed fluid is uniform in all the directions. The force given by fluid is given by the multiplication of pressure and area of cross section. As the pressure is same in all the direction, the smaller piston feels a smaller force and a large piston feels a large force. Hence, a large force can be generated with smaller force input by using hydraulic systems.
Hydride phase – It is the phase TiHx formed in titanium when then hydrogen content exceeds the solubility limit, normally locally because of some special circumstance.
Hydride powder – It is a powder produced by the removal of hydrogen from a metal hydride.
Hydride process – It consists of the hydrogenation of such reactive metals as titanium and zirconium, followed by comminution of the brittle compound and vacuum treatment to remove the hydrogen from the powder.
Hydro-blast process – It is a process for descaling of steel. In this process sand is mixed with water and propelled by the water pressure.
Hydro-carbon – It is a chemical compound of hydrogen and carbon.
Hydrochloric acid – It is an aqueous solution of hydrogen chloride (HCl). It is a colourless solution with a distinctive pungent smell. It is classified as a strong acid. It is the acid which is used for pickling of steel.
Hydrodynamic lubrication – It is also known as full film or fluid film lubrication. It is a system of lubrication in which the shape and relative motion of the sliding surfaces causes the formation of a fluid film which has sufficient pressure to separate the surfaces The high lubricant viscosity creates enough fluid pressure to build a supporting film and eliminates all solid-surface contact. The film thickness is quite high in this type of lubrication system compared to others.
Hydro-dynamic machining – It is the removal of material by the impingement of a high-velocity fluid against a work-piece.
Hydrodynamic seal – It is a seal which has special geometric features on one of the mating faces. These features are designed to produce interfacial lift, which arises solely from the relative motion between the stationary and rotating portions of the seal.
Hydro-electricity – It is the generation of electric power from the kinetic energy of falling water.
Hydrogen – It is the simplest of all elements. One can visualize a hydrogen atom as a dense central nucleus with a single orbiting electron. In most hydrogen atoms, the nucleus consists of a single proton, although a rare form (or ‘isotope’) of hydrogen contains both a proton and a neutron. This form of hydrogen is called deuterium or heavy hydrogen. Other isotopes of hydrogen also exist, such as tritium with two neutrons and one proton, but these isotopes are unstable and decay radioactively. Hydrogen is the first element in the periodic table with the atomic number 1. It is the lightest and most abundant element in the universe representing 75 % by mass or 90 % by volume of all matter. On earth, it is mostly found in compounds with almost every other element. It also exists as a free element in the atmosphere, but only to the extent of less than 1 parts per million by volume. Free ionic hydrogen is more reactive than molecular hydrogen, the non-polar covalent compound of two hydrogen atoms. Hydrogen can be considered an ideal gas over a wide temperature range and even at high pressures. At standard temperature and pressure conditions, it is a colourless, odourless, tasteless, non-toxic, non-corrosive, non-metallic di-atomic gas, which is in principle physiologically not dangerous. One of its most important characteristics is its low density, which makes it necessary for any practical applications to either compress the hydrogen or liquefy it. It is positively buoyant above a temperature of -251 deg C, i.e., over (almost) the whole temperature range of its gaseous state. The molecules of hydrogen gas are smaller than all other gases, and it can diffuse through many materials considered air-tight or impermeable to other gases. This property makes hydrogen more difficult to contain than other gases. Gaseous hydrogen, with a density of 0.08345 kilogram per cubic metre, has a specific gravity of 0.0696 and is hence around 7 % the density of air. Liquid hydrogen, with a density of 70.78 kilogram per cubic metre, has a specific gravity of 0.0708 and is hence around (and coincidentally) 7 % the density of water
Hydrogen-assisted cracking (HAC) – It is characterized by the brittle fracture of a normally ductile alloy under sustained load in the presence of hydrogen. It causes a reduction in the ductility of a metal because of the absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress needed for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen-assisted cracking occurs in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminum, and stainless steels are less susceptible to hydrogen embrittlement.[
Hydrogen-assisted stress-corrosion cracking (HSCC) – It is a series of small cracks which present themselves in material after exposure to a corrosive environment containing hydrogen, high temperatures, high tensile or shear stress, or a combination of these factors.
Hydrogen based steelmaking route – It has been studied in ULCOS (ultra-low CO2 steelmaking) project, Hydrogen is considered to be produced by water electrolysis using hydraulic or nuclear electricity. Iron ore is considered to be reduced to direct reduced iron by hydrogen in a shaft furnace, and carbon-free direct reduced iron is considered to be treated in an electric arc furnace to produce steel. This route shows promising performance regarding carbon di-oxide emissions which is less than 300 kilograms of carbon di-oxide per ton of steel, including the carbon di-oxide-cost of electricity with the emissions from the direct reduction furnace itself being almost zero. This represents 85 % cut in carbon di-oxide emissions as compared to the present around 1,850 kilograms of carbon di-oxide per ton of steel of the blasé furnace-basic oxygen furnace route. This new route hence is a more sustainable way for making steel. However, its future development is largely dependent on the emergence of a so-called hydrogen economy, when this gas becomes available in large quantities, at competitive cost, and with low carbon di-oxide emissions for its production.
Hydrogen blistering – It consists of the formation of blisters on or below a metal surface from excessive internal hydrogen pressure. Hydrogen may be formed during cleaning, plating, or corrosion.
Hydrogen brazing – It is a term which is sometimes used to denote brazing in a hydrogen-containing atmosphere, normally in a furnace. Use of the appropriate process name is preferred.
Hydrogen cracks – Hydrogen cracking results from the presence of hydrogen medium and normally occurs in conjunction with the presence of applied tensile stress or residual stress. Hydrogen can be already present in the metal due to previous processes such as electroplating, pickling, and welding in moist atmosphere or the melting process itself. Also, hydrogen can come from the presence of hydrogen sulphides, water, methane or ammonia in the work environment of a material. Hydrogen can diffuse in the metal and initiate very small cracks at subsurface cites (normally at the grain boundaries) subjected to high values of stress. The presence of such cracks at several locations causes ductile materials to show brittle fracture behaviour.
Hydrogen damage – It is a general term for the embrittlement, cracking, blistering, and hydride formation which can occur when hydrogen is present in some metals.
Hydrogen embrittlement – It is a process resulting in a decrease of the toughness or ductility of a metal because of the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first, known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes super-saturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during high-temperature thermal treatments and in service during electro-plating, contact with maintenance chemicals, corrosion reactions, cathodic protection, and operating in high-pressure hydrogen. In the absence of residual stress or external loading, environmental hydrogen embrittlement is manifested in various forms, such as blistering, internal cracking, hydride formation, and reduced ductility. With a tensile stress or stress-intensity factor exceeding a specific threshold, the atomic hydrogen interacts with the metal to induce sub-critical crack growth leading to fracture. In the absence of a corrosion reaction (polarized cathodically), the normal term used is hydrogen-assisted cracking (HAC) or hydrogen stress cracking (HSC). In the presence of active corrosion, normally as pits or crevices (polarized anodically), the cracking is normally called stress corrosion cracking (SCC), but it is more properly be called hydrogen assisted stress-corrosion cracking (HSCC). Hence, hydrogen stress cracking and electro-chemically anodic stress corrosion cracking can operate separately or in combination (hydrogen assisted stress-corrosion cracking). In some metals, such as high-strength steels, the mechanism is believed to be all, or nearly all, hydrogen stress cracking. The participating mechanism of hydrogen stress cracking is not always recognized and can be evaluated under the generic heading of stress corrosion cracking.
Hydrogen flakes – Hydrogen is available during the different process operations (from decomposition of water vapour, hydrocarbons, or atmosphere etc.) and it dissolves in material at temperatures above 200 deg C. Hydrogen flakes are thin subsurface discontinuities which develop during cooling of large size sections produced by rolling or forging because of the entrapment of hydrogen resulting from rapid cooling.
Hydrogen fuel – Hydrogen is able to react chemically with most other elements. In connection with oxygen, hydrogen is highly flammable over a wide range of concentrations. As a fuel, it represents a clean, environmentally friendly energy source. The mass-related energy density of hydrogen is very high. 1 kilogram of hydrogen contains 132.5 MJ (mega joule), which is around 2.5 times more energy than is contained in 1 kilogram of natural gas. The energy content of hydrogen is given either as lower heating value (LHV) of 242 kJ/mol or as higher heating value (HHV) of 286 kJ/mol. The difference is 15.4 %, which is large compared to other gases. It is because of the heat liberated upon condensation of the water vapour (which can be captured in a turbine, but not in a fuel cell). A stoichiometric hydrogen-air mixture, where all fuel is consumed upon reaction, i.e., where maximum combustion energy is released, contains 29.5 % by volume of hydrogen. The combustion product of hydrogen is water vapour. It burns in a non-luminous, almost invisible pale blue, hot flame to water vapour liberating the chemically bound energy as heat (gross heat of combustion). The flame temperature of a burning (pre-mixed stoichiometric) hydrogen-air mixture is 2,130 deg C maximum. There is a wide flammability range of hydrogen (at room temperature) between 4 % and 75 % by volume of concentration in air and up to 95 % by volume in oxygen. The lower flammability limit (LFL) as the minimum amount of fuel which supports combustion, is normally the ‘more important’ limit, since it is reached first in a continuous leakage. The flammability range widens with higher temperatures.
Hydrogen-induced cracking (HIC) – It is the cracking in low-to medium-strength steels in the absence of applied stress where the driving force for crack propagation is molecular hydrogen pressure build-up within the crack.
Hydrogen-induced delayed cracking – It is a term sometimes used to identify a form of hydrogen embrittlement in which a metal appears to fracture spontaneously under a steady stress less than the yield stress. There is normally a delay between the application of stress (or exposure of the stressed metal to hydrogen) and the onset of cracking.
Hydrogen loss – It is the loss in weight of metal powder or a compact caused by heating a representative sample as per a specified procedure in a purified hydrogen atmosphere. Broadly, it is a measure of the oxygen content of the sample when applied to materials containing only such oxides as are reducible with hydrogen and no hydride-forming element.
Hydrogen over-voltage – In electro-plating, it is the over-voltage associated with the liberation of hydrogen gas.
Hydrogen stress cracking (HSC) – It is characterized by the brittle fracture of a normally ductile alloy under sustained load in the presence of hydrogen. It is a form of cracking occurring when corrosion from certain acids causes atomic hydrogen to penetrate higher strength steels.
Hydrolysis – It consists of decomposition or alteration of a chemical substance by water. In aqueous solutions of electrolytes, it is the reactions of cations with water to produce a weak base or of anions to produce a weak acid.
Hydro-mechanical press – It is a press in which the moulding forces are created partly by a mechanical system and partly by a hydraulic system.
Hydro-metallurgy – It is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. It is the industrial winning or refining of metals using water or an aqueous solution. Hydro-metallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques which complement hydro-metallurgy are pyro-metallurgy, vapour metallurgy, and molten salt electro-metallurgy. Hydro-metallurgy is typically divided into three general areas namely leaching, solution concentration and purification, and metal or metal compound recovery.
Hydrophilic – It means tending to absorb water. It also means tending to concentrate in the aqueous phase.
Hydrophobic – It means tending to repel water. It also means lacking an affinity for water.
Hydrophobic cement – This cement is produced by mixing certain materials (stearic acid, oleic acid etc. by 0.1 % to 0.4 %) with ordinary Portland cement before grinding, to form water repellent layer around the cement particles. The water repellent film formed around each grain of the cement reduces the deterioration of the cement during the long storage, transportation and unfavourable environment. Water repellent film formed also improves the workability. The water repellent film is removed during the mixing process with water.
Hydro-power – It is the power (now nearly always electric power) generated from falling water.
Hydro-refining of crude benzol – Hydro-refining treatment method of crude benzol is based on the hydrogenation reactions of sulphur and unsaturated compounds admixtures. During the hydro-refining of crude benzol, treatment of crude benzol is carried out in the presence of hydrogen gas over a catalyst under pressure. Hydrogen gas is used as a hydrogenation agent. Hydrogen gas is separated from coke oven gas by pressure swing adsorption (PSA) method. The process parameters (temperature, pressure, hydrogen / raw materials molar ratio, contact time, catalyst type) are selected in such a way so to ensure almost hydrogenation of entire quantities sulphur, unsaturated, oxygen-containing and nitrogen-containing impurities but by avoiding the hydrogenation reactions of aromatic hydrocarbons. Hydrogen gas is mainly consumed for destructive hydrogenation of thiophene and carbon sulphide (CS2) and hydrogenation of cyclopentadiene and styrene. Initially, the crude benzol is purified from sulphur, non-aromatics and other compounds to produce BTXS (benzene, toluene, xylene, and solvent naphtha) raffinate for processing in the extractive distillation unit. This unit consists of three sections namely (i) de-fronting section, (ii) reaction section, and (iii) purification section.
Hydrostatic bearing – It is a bearing in which the solid bodies are separated and supported by a hydrostatic pressure, applied by an external source, to a compressible or incompressible fluid interposed between those bodies.
Hydrostatic compacting – It is a special case of isostatic pressing which uses a liquid such as water or oil as a pressure transducing medium and is hence limited to near room-temperature operation.
Hydrostatic extrusion – It is a method of extruding a billet through a die by pressurized fluid instead of the ram used in conventional extrusion. In the hydrostatic extrusion, the container is filled with a fluid. Extrusion pressure is transmitted through the fluid to the billet. Friction is eliminated in this process since there is no contact between billet and container wall. Brittle materials can be extruded by this process. Highly brittle materials can be extruded into a pressure chamber. Higher reductions are possible by this method. Pressure involved in the process can be as high as 1,700 MPa. Pressure is limited by the strength of the container, ram, and die materials. Vegetable oils such as castor oil are used. Normally hydrostatic extrusion process is carried out at room temperature.
Hydrostatic lubrication – It is a system of lubrication in which the lubricant is supplied under sufficient external pressure to separate the opposing surfaces by a fluid film.
Hydrostatic modulus – It is the measure of resistance to change in volume; the ratio of hydrostatic stress to the corresponding unit changes in volume.
Hydrostatic mould – It is a sealed flexible mould made of rubber, a polymer, or pliable sheet made from a low melting point metal such as aluminum.
Hydrostatic pressing – It is a special case of isostatic pressing which uses a liquid such as water or oil as a pressure transducing medium and is hence limited to near room-temperature operation.
Hydrostatic pressure measurement – The hydrostatic pressure is the force exerted by a column of water above a reference point. The measured pressure is proportional to the height. The measuring cell operates as a differential pressure meter in the sense that the minus side is open to the atmospheric pressure. This pre-pressure is applied to both sides of the diaphragm and is, thus, self-cancelling. As the transmitter is mounted to the side wall, the zero of the transmitters can be adjusted such that the lower range value is based on the channel floor. Naturally, communication between the device and modern process control systems is possible through an interface or a fieldbus coupler. The measuring ranges lie between 0.01 kilogram per square centimeter and 102 kilograms per square centimeter. The diaphragm flush-mounted to the inner wall of the flume is unaffected by deposits and contamination.
Hydrostatic seal – It is a seal incorporating features which maintain an interfacial film thickness by means of pressure. The pressure is provided either by an external source or by the pressure differential across the seal. The interfacial pressure profile of a seal face is normally speed-dependent, while the interfacial pressure profile of the hydrostatic seal is not speed-dependent.
Hydrostatic stress – It is the general three-dimensional state of stress acting on a body consists of three independent shear stresses and three independent normal stresses. The hydrostatic stress is defined as the mean value of the normal stresses. Constant volume materials cannot permanently deform when the loading conditions create a stress state that is purely hydrostatic. Hence, the presence of a hydrostatic stress is important for understanding of brittle fracture.
Hydrostatic tension – It consists of three equal and mutually perpendicular tensile stresses.
Hydrostatic test – It is a strength and tightness test of a closed pressure vessel by water pressure.
Hydrostatics – It is the branch of fluid mechanics which deals with fluids at hydrostatic equilibrium and the pressure in a fluid or exerted by a fluid on an immersed body. It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion.
Hydro-thermal – It is relating to hot fluids circulating in the Earth’s crust.
Hygroscopic – It is the possessing a marked ability to accelerate the condensation of water vapour. It is applied to condensation nuclei composed of salts which yield aqueous solutions of a very low equilibrium vapour pressure compared with that of pure water at the same temperature. It is also pertaining to a substance whose physical characteristics are appreciably altered by effects of water vapour. It is also pertaining to water absorbed by dry soil minerals from the atmosphere with the quantities depend on the physico-chemical character of the surfaces, and increase with rising relative humidity.
Hygrothermal behaviour – Hygrothermal behaviour of cured composite materials relates to the combined and commonly synergistic effects of moisture absorption and temperature on different physical, chemical and mechanical properties. While effects for polymer-matrix composites can be substantial, thermo-setting matrices are typically much more affected than thermo-plastic matrices. Although hygrothermal effects are irrelevant for meta-land ceramic-matrix composites, their responses as newer materials and as classes are still somewhat uncertain.
Hygrothermal effect – It is the change in properties and shape change of a material (particularly plastics and polymer matrix composites) because of the moisture absorption and temperature change.
HYL process – This process is designed for the conversion of iron ore (pellet / lump ore) into metallic iron, by the use of reducing gases in a solid-gas moving bed reactor. Oxygen is removed from the iron ore by chemical reactions based on hydrogen and carbon mono-oxide for the production of highly metallized direct reduced iron / hot briquetted iron. HYL process uses a shaft reduction furnace to produce direct reduced iron. The main characteristics of the HYL process consists of (i) utilization of hydrogen rich reducing gases with hydrogen to carbon mono-oxide ratio of more than 4, (ii) high reduction temperature normally more than 930 deg C, and (iii) high operating pressure normally in the range of 0.5 MPa to 0.8 MPa. The higher operating pressure has several characteristics which include (i) lower gas velocity, (ii) lower dragging force, (iii) lesser dust carry over, (iv) lower consumption of iron bearing materials, (v) higher ratio of plant capacity/size, and (vi) lower power consumption due to lower compression factor. High operating pressure in the shaft furnace also results into a high furnace productivity which is around 9 tons per hour per square meter area.
Hyper-eutectic alloy – In an alloy system showing a eutectic, it is an alloy whose composition has an excess of alloying element compared with the eutectic composition and whose equilibrium micro-structure contains some eutectic structure.
Hyper-eutectoid alloy – In an alloy system showing a eutectoid, it is an alloy whose composition has an excess of alloying element compared with the eutectoid composition, and whose equilibrium micro-structure contains some eutectoid structure.
Hypersonic speed – It is the speed which exceeds five times the speed of sound, frequently stated as starting at speeds of Mach 5 and above.
Hypertext mark-up language (HTML) – It is the standard mark-up language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is frequently assisted by technologies such as Cascading Style Sheets and scripting languages such as JavaScript.
Hypo-eutectic alloy – In an alloy system showing a eutectic, it is an alloy whose composition has an excess of base metal compared with the eutectic composition and whose equilibrium micro-structure contains some eutectic structure.
Hypo-eutectoid alloy – In an alloy system showing a eutectoid, it is an alloy whose composition has an excess of base metal compared with the eutectoid composition and whose equilibrium micro -structure contains some eutectoid structure.
Hypoid gear lubricant (hypoid oil) – It is a gear lubricant with extreme-pressure characteristics used in hypoid gears.
Hypoid gears – These gears resemble spiral bevels, but the shaft axes of the pinion and driven gear do not intersect. This configuration allows both shafts to be supported at both ends. In hypoid gears, the meshing point of the pinion with the driven gear is around midway between the central position of a pinion in a spiral-bevel and the extreme top or bottom position of a worm. This geometry allows the driving and driven shafts to continue past each other so that end-support bearings can be mounted. These bearings provide higher rigidity than the support provided by the cantilever mounting used in some bevel gearing. Also adding to the high strength and rigidity of the hypoid gear is the fact that the hypoid pinion has a larger diameter and longer base than a bevel or spiral-bevel gear pinion of equal ratio. Although hypoid gears are stronger and more rigid than the majority of other types, they are one of the most difficult to lubricate because of high tooth-contact pressures. Moreover, the high levels of sliding between tooth surfaces, reduces efficiency. In fact, the hypoid combines the sliding action of the worm gear with the rolling movement and high tooth pressure associated with the spiral bevel. In addition, both the driven and driving gears are made of steel, which further increases the demands on the lubricant. As a result, special extreme pressure lubricants with both oiliness and anti-weld properties are required to withstand the high contact pressures and rubbing speeds in hypoids.
Hypothesis – A statistical hypothesis is a hypothesis concerning the value of parameters or form of a probability distribution for a designated population or populations. More generally, a statistical hypothesis is a formal statement about the underlying mechanisms which generated some observed data.
Hypothesis test – Testing of hypotheses is a common part of statistical inference. To formulate a test, the question of interest is simplified into two competing hypotheses, between which one has a choice. The first is the null hypothesis, denoted by H0, against the alternative hypothesis, denoted by H1. For example, with 50 years of annual rainfall totals a hypothesis test can be whether the mean is different in El Nino and ordinary years. Then normally (i) the null hypothesis, H0, is that the two means are equal, i.e., there is no difference, and (ii) the alternative hypothesis, H1, is that the two means are unequal, i.e., there is a difference. If the 50 years are considered as being of three types, El Nino, ordinary, and La Nina then normally (i) the null hypothesis, H0, is that all three means are equal, and (ii) the alternative hypothesis, H1, is that there is a difference somewhere between the means. The hypotheses are frequently statements about population parameters.
Hypothetical resources – These are undiscovered Resources which are similar to known mineral bodies and which can be reasonably expected to exist in the same producing district or region under analogous geological conditions. If exploration confirms their existence and reveals enough information about their quality, grade, and quantity, they get reclassified as Identified resources.
Hysteresis – It is a characteristic of a system where its state is history-dependent. As an example, a magnet can have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of the moment frequently form a loop or hysteresis curve, where there are different values of one variable depending on the direction of change of another variable. Hysteresis occurs in ferro-magnetic and ferro-electric materials, as well as in the deformation of rubber bands and shape-memory alloys and several other natural phenomena. In natural systems, it is frequently associated with irreversible thermodynamic change such as phase transitions and with internal friction, and dissipation is a common side effect.
Hysteresis (magnetic) – It is the lag of the magnetization of a substance behind any cyclic variation of the applied magnetizing field.
Hysteresis (mechanical) – It is the phenomenon of permanently absorbed or lost energy which occurs during any cycle of loading or unloading when a material is subjected to repeated loading.
Hysteresis loop – It characterizes the magnetization / demagnetization characteristics as a function of the applied magnetic field for ferro-magnetic materials. Powder metallurgy products can differ from wrought products because of porosity or impurity traces.
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