A Detailed insight about refractory products
Refractories include high-density refractories, refractory and insulating bricks, fiber-based refractories, and unshaped products. They are mainly load-bearing and insulating. Refractory products should be able to withstand high temperatures and corrosive environments, such as the inner lining of high-temperature furnaces. Depending upon the application, they are exposed to mechanical, thermal and chemical stresses. High heat resistance or refractoriness under load are other prerequisites for the required dimensional stability, that is, creep of refractory materials and subsequent sintering are not allowed. The planned temperature cycle in use also needs to have high resistance to temperature changes and thermal shocks. For applications where refractory materials are in direct or indirect contact with corrosive gases or molten materials, high wear resistance is also an important prerequisite. On the other hand, for insulating components, such as in permanent linings, thermal conductivity and low heat capacity are decisive to ensure that the design of the refractory lining is compact and energy efficient. The above characteristics cannot be fully realized in single refractory materials, and even some of them contradict each other. High strength usually requires high relative density, however, this leads to higher thermal conductivity and volumetric heat capacity. Reducing the relative density by generating additional porosity leads on the one hand to lower thermal conductivity, however, this generally leads to a reduction in mechanical properties and wear resistance. Dense materials with low thermal conductivity are generally susceptible to thermal shock. In order to optimize performance in this conflict of goals, systematic evaluation criteria are necessary.
Dense refractories are heavy and have low porosity, though the mechanical strength is high. The most common form of dense refractory is refractory brick. Made of hydrated aluminum silicate containing small amounts of other elements, it is versatile and relatively inexpensive. Flint with a high alumina content can be used at high temperatures. Refractories containing 99% aluminum oxide, known as gypsum, are used in processes above 1500°C, including casting steel, glass making, re-smelting, sintering and superalloy casting.
Insulating refractory has high porosity, which results in low density and low thermal conductivity. This leads to an increase in efficiency and reduced energy required for the process.
Zircon refractory's principal ingredient is zirconium silicate which is extremely strong up to temperatures over 1750°C. They are used in the construction of kilns, crucibles in the metallurgical industry because they do not react with liquid metals, and are used in glass furnaces because they are not wetted by molten glass.
Casting refractories are also called refractory concretes and contain a high amount of alumina cement. They are used in kiln cars, boilers, and covering floors, doors, walls, and other surfaces subject to high-temperature treatment in the steel industry. The insulating mold contains lightweight aggregates such as vermiculite. They are weaker than standard castables.
Plastic refractories are provided in the form of clay-like blocks, which can be cut to a certain size and fixed in place. They are designed for brick or integral siding repairs and are also used for buckets and gaskets.
Insulating refractory bricks are made of alumina-added refractory clay and organic fillers, which are burned during the firing process to leave lightweight porous bricks. Bricks are classified according to the temperature levels they can withstand and are used for lining furnaces, or as secondary insulation materials, flue gas linings, soaking pits, and reaction chambers.
Insulating wool Fibers spun from a mixture of molten alumina and silica are made into blankets, paper, rope, cardboard, and block modules. Ceramic fiber products are light in weight, low in thermal conductivity, and good in thermal shock resistance. They can be used for heat insulation around boilers and furnaces, furnace cars, glass melting furnace tops, and expansion joints, forming a seal around the oven door, as a lining renovation and the pyrolysis of the petrochemical industry.
Silica refractories are made of quartzite and silica deposits, with low aluminum and alkali content. They are chemically combined with 3% to 3.5% lime. Silica refractories have good high-temperature load resistance, wear resistance, and are especially suitable for acidic slag. In various grades-coke oven quality, regular and super service-super service with a particularly low impurity content is used in the upper structure of the glass melting furnace.
High alumina refractories are made from bauxite, which is a natural material containing aluminum hydroxide (Al [OH] 3) and kaolin. These raw materials are fired to produce a mixture of synthetic alumina and mullite (an aluminosilicate mineral with the chemical formula 3Al2O3·2SiO2). By definition, high alumina refractories contain 50% to 87.5% alumina. In high-temperature and basic environments, they are much stronger than fire clay refractories. In addition, they have better volume stability and abrasion resistance. High alumina bricks are used in blast furnaces, blast furnace stoves, and ladle.