Glossary of technical terms for the use of metallurgical engineers Terms starting with alphabet ‘J’
Glossary of technical terms for the use of metallurgical engineers
Terms starting with alphabet ‘J’
Jack – It is a mechanical lifting device which is used to apply large forces or lift heavy loads. A mechanical jack uses a screw thread for lifting heavy equipment. A hydraulic jack uses hydraulic power.
Jack arch – It is a sprung arch in which the outer surface is horizontal and the inner surface is either horizontal or arched with a large radius.
Jack chain – It is a type of chain made of thin wire, with figure-eight-shaped links and loops at right angles to each other. Jack chains are frequently used to suspend fixtures such as lights or signs, for decorative purposes, or as part of a cable lock. Jack chain can be manufactured as either single-jack chain or as double-jack chain. If double-jack, the lower loop is formed of two strands of wire rather than just one as in a single-jack.
Jack dam drills – Jack dam drills are for drilling a hole in the skimmer plate / wall of the main trough of the blast furnace. This ensures that cast products are fully drained from the furnace. The drills are made specific to the blast furnace to meet the specific requirements such as the main trough location, foundations, columns and fixed equipment for each specific cast house. Equipment drives are either hydraulic or pneumatic and are powered by either the general pump unit of the equipment system or independently. The drills are made either portable or stationary. Jack dam drill is a useful tool for the blast furnace cast house.
Jacket, shell or casing – The metal casing of the furnace enclosing the refractory brickwork.
Jacking gear – It is also known as a turning gear. It is a device placed on the main shaft of an engine or the rotor of a turbine. The jacking gear rotates the shaft or rotor and associated machinery (such as reduction gears and main steam or gas turbines), to ensure uniform cool-down. Without turning, hogging or sagging can occur. Additionally, the jacking gear’s assistance in rotation can be used when inspecting the shaft, reduction gears, bearings, and turbines. As an auxiliary function, the jacking gear also helps to maintain a protective oil membrane at all shaft journal bearings.
Jackhammer – It is a pneumatic or electro-mechanical tool which combines a hammer directly with a chisel. Hand-held jackhammers are generally powered by compressed air, but some are also powered by electric motors. Larger jackhammers, such as rig-mounted hammers used on construction machinery, are normally hydraulically powered. These tools are typically used to break up rock, pavement, and concrete. A jackhammer operates by driving an internal hammer up and down. The hammer is first driven down to strike the chisel and then back up to return the hammer to the original position to repeat the cycle. The effectiveness of the jackhammer is dependent on how much force is applied to the tool. It is normally used like a hammer to break the hard surface or rock in construction works and it is not considered under earth-moving equipment, along with its accessories (i.e., pusher leg, lubricator).
Jackscrew – It is a type of jack that is operated by turning a leadscrew. It is normally used to lift moderate and heavy weights and as adjustable supports for heavy loads.
Jamb – It is the vertical refractory brickwork of a furnace door or any other opening. It is also a vertical structural member forming the side of an opening in a furnace wall. Jamb is also a type of refractory brick shapes, intended for use in sides of wall opening.
Jamb brick – It is a brick., normally square-shaped, with one side forming part of the oven wall and the side at right angles to it forming part of the outside wall of the battery. It is also a brick, in which one end face is completely rounded off to join one side face.
Jars – These are glassware which are used in chemical laboratories. These are cylindrical containers with wide openings which can be sealed. Bell jars are used to contain vacuums.
Jasper – It is a type of quartz which can be brown, yellow, or green, but is very frequently a mottled, brick red colour.
Jaw crusher – Jaw crusher is used as primary crusher. It uses compressive force for breaking the material. This mechanical pressure is achieved by the two jaws of the crusher. Reduction ratio is usually 6:1. The jaw crusher is consisting of two vertical jaws installed to a ‘V’ form, where the top of the jaws is further away from each other than the bottom. One jaw is kept stationary and is called a fixed jaw while the other jaw, called a swing jaw, moves back and forth relative to it, by a cam or pitman mechanism. The volume or cavity between the two jaws is called the crushing chamber. The movement of the swing jaw can be quite small, since complete crushing is not performed in one stroke. The inertia required to crush the material is provided by a weighted flywheel that moves a shaft creating an eccentric motion that causes the closing of the gap. Jaw crusher is used for the primary disintegration of metal pieces, ores, or agglomerates into coarse powder. In jaw crusher rock is broken by the action of steel plates.
Jeffries’ method – It is a method for determining grain size based on counting grains in a prescribed area.
Jet – It is a stream of fluid which is projected into a surrounding medium, normally from some kind of a nozzle, aperture or orifice. Jets can travel long distances without dissipating. Jet fluid has higher speed compared to the surrounding fluid medium. In the case that the surrounding medium is assumed to be made up of the same fluid as the jet, and this fluid has viscosity, some of the surrounding fluid is carried along with the jet in a process called entrainment.
Jet cooling – It uses a high-pressure jet of steam to cool water or other fluid media. Typical uses include industrial sites, where a suitable steam supply already exists for other purposes.
Jet impingement cooling – It works by spraying a working fluid onto a surface being cooled.
Jet engine – It is a type of reaction engine, discharging a fast-moving jet of heated gas (normally air) which generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
Jet Kote surfacing system – It is a high-pressure combustion thermal spray process in which a spray gun burns a fuel e.g., methyl acetylene propadiene mixture (MAPP) gas, or propane, with a high volume of oxygen within a combustion chamber. Using a nitrogen carrier gas, the powder is injected into the combustion products and is rapidly heated and accelerated to impact at high speed against the work surface to be coated. Unlike the detonation gun process, the Jet Kote system is based on continuous combustion within the gun.
Jet producing apparatus – It is a device which produces a jet of air or inert gas which impinges on the stream of molten metal and disintegrates it into small particles. These irregularly shaped (nodular) particles, together with a substantial volume of cooling air, are drawn through a chiller chamber and into a cyclone and / or bag filter collecting system. The atomized powers are then graded by screening.
Jet pulverizer – It is an equipment which comminutes metal pieces or agglomerates by means of pressurized air or steam injected into a chamber.
Jet vapour deposition – It is a vacuum deposition method in which evaporated atoms or molecules are ‘seeded’ into a supersonic jet flow of inert gas into a rapidly pumped vacuum chamber. The jet flow transports the atoms and molecules to the substrate surface, where they are deposited.
Jewel bearing – It is a bearing which is made of diamond, sapphire, or a hard substitute metal.
Jewelry application, powder metallurgy – Powder metallurgy allows for higher precision and consistency in the production of metal components. Metal powders are used in the production of a wide range of jewelry items, including rings, necklaces, earrings, bracelets and brooches.
JFET – It is a field effect transistor with a reverse-biased PN junction between gate and channel.
J-groove weld – It is a type of groove weld.
Jib crane – It is a type of crane where a horizontal member (jib or boom), supporting a moveable hoist, is fixed to a wall or to a floor mounted pillar. Jib cranes are used in industrial premises and on vehicles. The jib can swing through an arc, to give additional lateral movement, or be fixed.
JIC fittings – These are a type of flare fitting machined with a 37-degree flare seating surface. JIC (Joint Industry Council) fittings are widely used in fuel delivery and fluid power applications, especially where high pressure (up to 69 MPa) is involved.
Jig – It is a mechanism for holding a part and guiding the tool during machining or assembly operation. It is also a piece of milling equipment which is used to concentrate an ore on a screen submerged in water, either by the reciprocating motion of the screen or by the pulsation of water through it.
Jig borer – It resembles a specialized kind of milling machine which provides tool and die makers with a higher degree of positioning precision (repeatability) and accuracy than those provided by general machines. Although capable of light milling, a jig borer is more suited to highly accurate drilling, boring, and reaming, where the quill or headstock does not see the significant side loading that it would with mill work. The result is that it is a machine which is designed more for location accuracy than heavy material removal.
Jig boring – It is the boring with a single-point tool where the work is positioned upon a table which can be located so as to bring any desired part of the work under the tool. Hence, holes can be accurately spaced. This type of boring can be done on milling machines or jig borers.
Jiggering – It is a plastic forming process used with clay-based ceramics in which a plastic mass is pressed under relatively low pressure into a plaster die, and the final shape is achieved by rotating the die and shaping the plastic mass with a fixed tool. Jiggering is a mechanical version of the potter’s wheel and produces shapes with circular cross sections.
Jigging process – It is an ore concentration process which is carried out in any fluid whose effectiveness depends on differences in the density of the granular mineral particles. It consists of separation of the particles into layers of different specific gravities followed by the removal of the separated layers. It is the process of sorting different materials in the ore in a fluid by stratification, based upon the movement of a bed of particles, which are intermittently fluidized by the pulsation of the fluid in a vertical plane. The stratification causes particles to be arranged in layers with increasing density from the top to the bottom. This particle arrangement is developed by several continuously, varying forces acting on the particles, and is more related to particle density than most other gravity concentrating methods. In the jigging process, the particles are introduced to the jig bed (normally a screen) where they are thrust upward by a pulsating water column or body, resulting in the particles being suspended within the water. As the pulse dissipates, the water level returns to its lower starting position and the particles once again settle on the jig bed. As the particles are exposed to gravitational energy whilst in suspension within the water, those with a higher density settle faster than those with a lower density, resulting in a concentration of material with higher density at the bottom, on the jig bed. The particles are now concentrated according to density and can be extracted from the jig bed separately. In case of the beneficiation of the iron ore, the denser material is the desired enriched ore and the rest is needed to be discarded as floats (or tailings).
Jig grinder – It is a machine tool which is used for grinding complex shapes and holes where the highest degrees of accuracy and finish are needed. The jig grinder is very similar to a jig borer, in that the table positioning and spindles are very accurate.
J-integral – It is a mathematical expression. It is a line or surface integral which encloses the crack front from one crack surface to the other, used to characterize the fracture toughness of a material having appreciable plasticity before fracture. The J-integral eliminates the need to describe the behavior of the material near the crack tip by considering the local stress-strain field around the crack front. ‘JIc’ is the critical value of the J-integral needed to initiate growth of a preexisting crack.
Jitter – It is the deviation from true periodicity of a presumably periodic signal, frequently in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significant, and normally undesired, factor in the design of almost all communications links. Jitter can be quantified in the same terms as all time-varying signals, e.g., root mean square (RMS), or peak-to-peak displacement. Also, like other time-varying signals, jitter can be expressed in terms of spectral density.
Jittered dot-plot – In a simple dot plot, the dots can overlap. In some cases, they can coincide completely, so obscuring some of the points. A solution is to randomly move the dots perpendicularly from the axis, to separate them from one another. This is called jittering. It results in a jittered dot-plot.
Job production – It is a specific type of production system. It involves production of special type of products which vary in nature and size. In this type of production system, products are produced as per the order and specifications of the customers.
Johansen’s test – In statistics, the Johansen test is a procedure for testing cointegration of several time series. It is a way to determine if three or more time series are cointegrated. More specifically, it assesses the validity of a cointegrating relationship, using a maximum likelihood estimates (MLE) approach. It is also used to find the number of relationships and as a tool to estimating those relationships. There are two types of Johansen’s test namely one uses trace (from linear algebra), the other a maximum eigenvalue approach (an eigenvalue is a special scalar, when one multiplies a matrix by a vector and get the same vector as an answer, along with a new scalar, the scalar is called an eigenvalue).
Jog (inch) – It is a function which provides momentary operation of an actuator to achieve a small movement of the valve.
Joining processes – Joining processes, include (i) metallurgical joining, such as welding and diffusion bonding, and (ii) mechanical joining, such as riveting, shrink fitting, and mechanical assembly. Metallurgical joining processes, such as welding, brazing, and soldering, form a permanent and robust joint between components. Mechanical joining processes, such as riveting and mechanical assembly, bring two or more parts together to build a sub-assembly which can be disassembled conveniently. Joining processes are necessary for different various engineering activities and in the development of virtually every manufactured product. These processes frequently appear to consume higher fractions of the product cost and to create more of the production difficulties than normally expected. There are a number of reasons for this. First reason is that the joining is multifaceted, both in terms of process variations and in the disciplines needed for problem solving (such as mechanics, materials science, physics, chemistry, and electronics etc.). An engineer with unusually broad and deep training is needed to bring these disciplines together and to apply them effectively to a variety of processes. The second reason is that joining difficulties normally occur far into the manufacturing process, where the relative value of scrapped parts is high. The third reason is that a very large percentage of product failures occur at joints since they are normally located at the highest stress points of an assembly and are hence the weakest parts of the assembly. Careful attention to the joining processes can produce high incentives in manufacturing economy and product reliability.
Joint – It is the location where two or more members are to be or have been fastened together mechanically or by welding, brazing, soldering, or adhesive bonding. It is also junction of members or the edges of members which are to be joined or have been joined. In case of refractory lining, joint is a space between refractory bricks normally filled with refractory mortar / cement.
Joint, adhesive – The location at which two adherends or substrates are held together with a layer of adhesive. The general area of contact for a bonded structure.
Joint, butt – It is a type of edge joint in which the edge faces of the two adherends are at right angles to the other faces of the adherends.
Joint clearance – It is the distance between the faying surfaces of a joint. In brazing, this distance is referred to as that which is present before brazing, at the brazing temperature, or after brazing is completed.
Joint, edge – It is a joint made by bonding the edge faces of two adherends.
Joint efficiency – It is the ratio of the strength of a welded joint to the strength of the base metal, expressed in percent.
Joint, expansion – It is an assembly to allow it to expand and contract as the environment conditions move from hot to cold and helps to ensure that the system remains functional.
Joint filler powder – It is a chemical compound which is used to fill the gap between two parts of a structure or two adjacent structures.
Joint health and safety committee – The joint health and safety committee is a committee in work-place. The responsibilities and powers of joint committee can include obtaining information on work-place hazards, identifying work-place hazards, and recommending how to make the work-place safer and healthier.
Jointing, cable – Cable joint is a device used to join two or more cables together for extension of lengths or to branch. These joints are made to perform at the same voltage class and ratings of the intended cables and are able to withstand the normal and emergency loading conditions. Selection of the proper cable accessories, proper jointing techniques, skill and workmanship is important. The quality of joint is to be such that it does not add any resistance to the circuit. All underground cable joints are to be mechanically and electrically sound and it is protected against moisture and mechanical damage. The joint is to be further resistant to corrosion and chemical effects. The basic types of cable joints are (i) straight through joint which is used to connect two cables lengths together (simple straight through joints which are for jointing same type of cables and transition straight through joints which are for jointing two different type cables), and (ii) tee joint / branch joint which is normally used for jointing a service cable to the main distribution cable in distribution network.
Jointing accessories, cable – Several types of jointing accessories are mainly used for jointing all types of low voltage and medium voltage power cables. Every jointing kit is provided with an instruction manual supplied by the manufacturer. Joints are to be made as per the guidelines given in the instruction manual. The cable jointing has (i) heat shrinkable jointing kit (preferred), (ii) cold shrinkable jointing kit, (iii tapex tape type jointing kit, (iv) push on type jointing kit, and (v) cast resin jointing kit.
Jointing material refractory – It is the refractory material which is intended for laying and jointing brick(s) or block(s) by troweling, grouting in the joints or dipping. These materials are mixtures of fine aggregate and bond, supplied in the dry state or mixed with suitable liquids ready for use.
Joint, lap – It is a joint made by placing one adherend partly over another and bonding the overlapped portions.
Joint penetration – It is the depth which a weld extends from its face into a joint, exclusive of reinforcement.
Joint probability – The joint probability is the joint density function of two random variables, or bivariate density.
Joint root – It is that portion of a joint which is to be welded where the members approach closest to each other. In cross section, the joint root can be either a point, a line, or an area.
Joint, scarf – It is a joint made by cutting away similar angular segments on two adherends and bonding the adherends with the cut areas fitted together.
Joint type – It is a weld joint classification based on the five basic arrangements of the component parts such as butt joint, corner joint, edge joint, lap joint, and T-joint
Joist – It is a horizontal structural member used in framing to span an open space, frequently between beams which subsequently transfer loads to vertical members. Steel joists can take on various shapes, resembling the Roman capital letters ‘C’, ‘I’, ‘L’ and ‘S’.
Jolt ramming – It consists of packing sand in a mould by raising and dropping the sand, pattern, and flask on a table. Jolt-type, jolt squeezers, jarring machines, and jolt rammers are machines using this principle. It is also called jar ramming.
Jolt-squeezer machine – It is a combination machine which uses a jolt action followed by a squeezing action to compact the sand around the pattern.
Jominy end quench test – It is used to measure the hardenability of a steel, which is a measure of the capacity of the steel to harden in depth under a given set of conditions. It is a standardized method according to ISO 642. The test sequence can be broken down into four steps namely (i) creation of the mold and preparation of the sample, (ii) heating of the sample to a specified temperature in the austenitic range for a defined duration, (iii) quenching of the sample on the front surface with a water jet under predefined conditions, and (iv) testing the hardness at defined points in the longitudinal direction of the ground specimen test surface.
Jominy equivalent cooling rate – It is the cooling rate at 704 deg C for each Jominy position for which there is a cooling time–temperature curve.
Jominy test – It is a laboratory procedure for determining the hardenability of a steel or other ferrous alloy. It is also referred to as the end-quench hardenability test. Hardenability is determined by heating a standard sample above the upper critical temperature, placing the hot sample in a fixture so that a stream of cold water impinges on one end, and, after cooling to room temperature is completed, measuring the hardness near the surface of the sample at regularly spaced intervals along its length. The data are normally plotted as hardness against distance from the quenched end.
Joule (J) – It is the derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second.
Joule heating – It is the process by which the passage of an electric current through a conductor produces heat.
Joule heating effect – It is the physical effect by which the pass of current through an electrical conductor produces thermal energy. This thermal energy is then evidenced through a rise in the conductor material temperature, hence the term ‘heating’.
Joule-Thomson effect – It is a change in temperature in a gas undergoing Joule-Thomson expansion.
Joule-Thomson expansion – It is the adiabatic, irreversible expansion of a gas flowing through a porous plug or partially open valve.
Journal – It is the part of a shaft or axle which is in contact with or enclosed by a bearing. The journal of the shaft (the part in contact with the bearing) slides over the bearing surface.
Journal bearing – in this, the bearing pressure is exerted at right angles to the axis of the axis of the shaft. The portion of the shaft lying within the bearing is known as journal. Shaft is normally made of mild steel.
Journal failure, rolls – The journal of the roll can suffer a cross-sectional failure. It normally starts at the bottom of the radius adjacent to the barrel. The fracture face follows the radius and then continues into the side of the barrel, and shears away a portion of the barrel end face. Under shock load conditions the peak load can exceed the ultimate bending strength of the core material and fracture occurs, normally at the most highly stressed cross-sectional area. The failure of the journal can take place because of the bending fracture. Fracture lines start from the outside and spread over the whole cross-section, particularly starting in the fillet area and very frequently after fatigue crack propagation. This failure arises from high bending loads which exceed either the ultimate bending strength or fatigue strength of the journal. This kind of breakage can be caused by (i) high rolling loads combined with a weak roll design, (ii) rolling abnormalities with extreme bending forces, (iii) inadequate roll quality as far as journal strength is concerned, and (iv) a notch effect as a consequence of too small a fillet radius, circumferential grooves, and fatigue cracks induced by corrosion etc.
Joystick – It is an input device consisting of a stick which pivots on a base and reports its angle or direction to the device it is controlling. Joysticks are also used for controlling machines such as cranes, mining trucks, and excavators. Joysticks has virtually replaced the traditional mechanical control lever in nearly all modern hydraulic control systems. Joysticks for industrial applications are also produced using Hall effect (contactless sensing) technology. Another technology used in joystick design is the use of strain gauges to build force transducers from which the output is proportional to the force applied rather than physical deflection. Miniature force transducers are used as additional controls on joysticks for menu selection functions.
J-R curve – It is a graph of crack-extension resistance as a function of stable crack extension, which is the difference between either the physical crack size or the effective crack size and the original crack size. J-R curves normally depend on sample thickness and, for some materials, on temperature and strain rate.
Judder – It is an intermittent motion arising from design features that allow an increase in tangential force or displacement to produce an increase in normal force.
Junction – It consists of the points or surfaces in structures where different elements or components come together. It is also a point (as in a thermocouple) at which dissimilar metals make contact. It is also an interface in a semiconductor device between regions with different electrical characteristics.
Junction, electrical – It is a point or area where (i) two or more conductors or (ii) different semi-conducting regions of differing electrical properties make physical contact. Electrical junction types include thermo-electricity junctions, metal–semiconductor junctions and p–n junctions. Junctions are either rectifying or non-rectifying. Non-rectifying junctions comprise ohmic contacts, which are characterized by a linear current–volage relation. Electronic components using rectifying junctions include p–n diodes, Schottky diodes and bipolar junction transistors.
Junctions, metal casting – Junctions are areas of natural localized thickness – like T-Junction or an X-Junction. Hence, it is necessary to take care when designing features which result in these ‘Junction’. Typical examples of junctions are internal features, ribs and webs or external protrusions such as fins or brackets. Less obvious junctions can appear when external and internal geometry, which are functionally unrelated are located on the same part of the casting wall. For example, a boss or lug on the outside of the casting occupying the same part of the casting wall as an internal rib.
Justified for development – In case of mineral deposits, justified for development needs that the project has been demonstrated to be technically feasible and viable, and there is a reasonable expectation that all necessary approvals / contracts for the Project to proceed to development is forthcoming.
Just-in-time (JIT) – It is an inventory management method in which goods are received from suppliers only as they are needed. The main objective of this method is to reduce inventory holding costs and increase inventory turnover.
Leave a Comment