Induction Furnace Refractory Lining with Silica Ramming Mass...

Induction Furnace Refractory Lining with Silica Ramming Mass Induction furnaces are used for melting cast iron, mild steel and various alloy steels in foundries and making of steel in mini steel plants using sponge iron. Lining is the important part of induction furnace. Furnace performance is directly related to the performance of its lining. Well laid and stabilized lining results in smooth working of furnace, optimum output, and good control of the metallurgical reactions. The lining practice best suited to a particular furnace depends upon the capacity and design of the furnace, operation practice adopted during making of a heat, and furnace output. For successful and consistent performance of the lining, the important aspects are (i) use of proper grade and quality of the lining material, (ii) careful and systematic lining practice, and (iii) consistency in working conditions.  Fig 1 shows the installed refractory lining of a coreless induction furnace, Fig 1 Installed refractory lining of a coreless induction furnace The characteristics of the lining material needed for consistent lining life include (i) thermal characteristics which means that it has to withstand the stresses developed by thermal cycles during the furnace operation, (ii) chemically inert to metal being melted, (iii) structural strength under operating conditions, (iv) high erosion resistance, (v) ease of installation, (vi) reparability of the lining, (vii) ease of dismantling, and (viii) economics. As such, it is very difficult to judge the suitability of a particular lining under various conditions like operating temperature, metal being melted, the type of formed slag, and furnace capacity. Chemical inertness to the liquid metal can be achieved by using acid and neutral lining for the acidic slag and neutral or basic lining for the basic slags. Normally, the selection of refractory for the furnace lining is...

Alumina and its Role in Iron and Steelmaking...

Alumina and its Role in Iron and Steelmaking Alumina is a chemical compound of aluminum (Al) and oxygen (O2) with the chemical formula aluminum oxide (Al2O3). It is the most commonly occurring of several aluminum oxides. It is significant in its use to produce aluminum metal. It is being used as an abrasive material because of its hardness. It is also being used as a refractory material owing to its high melting point. Aluminum oxide is an amphoteric substance. It can react with both acids and bases, acting as an acid with a base and a base with an acid, neutralizing the other and producing a salt.  It is insoluble in water. Aluminum oxide has a white solid appearance and is odorless. The molar mass of aluminum oxide is 101.96 grams per mole. Specific gravity of alumina is 3.986. It is insoluble in water. Melting point of aluminum oxide is 2072 deg C while the boiling point is 2977 deg C. Alumina affects the processes of producing iron and steel during the production of iron and steel. Besides alumina is a very important refractory material for the lining of furnaces and vessels in iron and steel plants. Role of alumina in ironmaking Alumina during ironmaking enters the process through impurities in the input materials mainly iron ore. Alumina affects the sintering of iron ore. The most harmful effect of alumina is to worsen the RDI (reduction degradation index) value of sinter. RDI value increases as the alumina content rises. It is seen that within a 10 % to 10.5 % CaO content range, an increase of 0.1 % in the alumina content raises the RDI by 2 points. The strength and quality of sinter deteriorate as the alumina content rises. Alumina promotes the formation of SFCA (silico ferrite of calcium and aluminum), which is beneficial for sinter strength, but the strength of the ore components is lower, since a...

Refractories and Classification of Refractories...

Refractories and Classification of Refractories Refractories are inorganic, nonmetallic, porous and heterogeneous materials composed of thermally stable mineral aggregates, a binder phase and additives. The principal raw materials used in the production of refractories are normally the oxides of silicon, aluminum, magnesium, calcium and zirconium. There are some non-oxide refractories like carbides, nitrides, borides, silicates and graphite. Refractories are chosen according to the conditions they face during their use. Some applications require special refractory materials. Zirconia is used when the material is required to withstand extremely high temperatures. Silicon carbide and carbon are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, since they oxidize and burn in atmospheres containing oxygen. Refractories are the materials which are resistant to heat and exposure to different degrees of mechanical stress and strain, thermal stress and strain, corrosion/erosion from solids, liquids and gases, gas diffusion, and mechanical abrasion at various temperatures. In simplified language, they are considered to be materials of construction which are able to withstand high temperatures. Refractories are usually inorganic non-metallic materials with refractoriness greater than 1500 deg C. They belong to coarse-grained ceramics having microstructure which is composed of large grains. The basis of body is coarse-grained grog joined by fine materials. Refractory products are a specific sort of ceramics that differs from any ‘normal’ ceramics mainly with their coarse-grained structure being formed by larger grog particles joined by finer intermediate materials (bonding). ASTM C71 defines refractories as ‘non-metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems that are exposed to environments above 538 deg C’. Refractories are to be chemically and physically stable at high temperatures. Depending on the operating environment, they...

Slag and its Role in Blast Furnace Ironmaking Aug07

Slag and its Role in Blast Furnace Ironmaking...

Slag and its Role in Blast Furnace Ironmaking Blast furnace (BF) is the oldest (more than 700 years old) of the various reactors which are being used in the steel plants. It is used for the production of liquid iron (hot metal). The blast furnace is a complex high temperature counter current reactor and is in the shape of a shaft in which iron bearing materials (ore, sinter/pellet) and coke are alternately charged at the top along with flux materials (limestone, dolomite etc.) to create a layered burden in the furnace. Preheated air is blown in from the lower part of the furnace through tuyeres. This hot air reacts with the coke to produce reducing gases. Descending ore burden (iron oxides) is reduced by the ascending reducing gases and is melted to produce hot metal. The gangue materials and coke ash melt to form slag with the fluxing materials. The liquid products (hot metal and slag) are drained out (tapped) from the furnace at certain intervals through the tap hole. The quality of hot metal obtained is dependent on the formation of the slag and its mineralogical transformations. A good quality slag is necessary for a quality hot metal. The slag is a mixture of low melting chemical compounds formed by the chemical reaction of the gangue of the iron bearing burden and coke ash with the flux materials in the charge. All unreduced compounds such as silicates, aluminosilicates, and calcium alumino silicate etc. also join the slag. It is well known that the components of slag namely silica (SiO2) and alumina (Al2O3) increase the viscosity whereas the presence of calcium oxide reduces the viscosity. The melting zone of slag determines the cohesive zone of blast furnace and hence the fluidity and melting characteristics...

Alumina and Alumina Refractories...

Alumina and Alumina Refractories Alumina (Al2O3) refractories are the part of alumina- silica (SiO2) group of refractories and belongs to the SiO2 -Al2O3 phase equilibrium system as shown in diagram at Fig 1. They differs from fire clay refractories in term of Al2O3 content and normally have Al2O3 content of more than 45 %. The raw material base for these refractories are different than the fire clay bricks. Fig 1 SiO2 – Al2O3 phase diagram As seen in the diagram, refractoriness increases with the increase in the Al2O3 content. The eutectic at 1595 deg C has a composition of 94.5 % SiO2 and 5.5 % Al2O3. As the Al2O3 content is increased, the melting point of the refractory increases to a maximum of 2054 deg C which is the melting point of pure corundum. The only stable compound in the system is mullite, which has a defective space lattice and decomposes into corundum and liquid phase at around 1840 deg C. The classification of Al2O3-SiO2 refractories as per the Al2O3–SiO2 phase equilibrium diagram is given in Tab 1. Tab 1 Classification of Al2O3-SiO2 refractories as per the Al2O3–SiO2 phase equilibrium diagram Range of Al2O3  Phases as per common terminology General performance of refractories in conditions of the absence of slag corrosion or alkali attack Al2O3 less than 50 % Fireclay (Chamotte); Phases on phase diagram are mullite and glass; can contain free SiO2 Normally made from 100 % fireclay, Highest quality grades (super duty bricks) usable to about 1600 deg C,  Usually contain 38 % to 42 % Al2O3 and are based on fireclay minerals Al2O3 50 % or 60 % Sillimanite, andalusite, or kyanite; Phases on phase diagram are mullite as major phase and glass as minor phase; can contain free SiO2 These...