Cold crushing strength The cold crushing strength is the resistance of the

Cold crushing strength the cold crushing strength is

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Cold crushing strength: The cold crushing strength is the resistance of the refractory to crushing, which mostly happens during transport. It only has an indirect relevance to refractory performance, and is used as one of the indicators of abrasion resistance. Other indicators used are bulk density and porosity. Pyrometric cones and Pyrometric cones equivalent (PCE) : The ‘refractoriness’ of (refractory) bricks is the temperature at which the refractory bends because it can no longer support its own weight. Pyrometric cones are used in ceramic industries to test the refractoriness of the (refractory) bricks. They consist of a mixture of oxides that are known to melt at a specific narrow temperature range. Cones with different oxide composition are placed in sequence of their melting temperature alongside a row of refractory bricks in a furnace. The furnace is fired and the temperature rises. One cone will bends together with the refractory brick. This is the temperature range in oC above which the refractory cannot be used. This is known as Pyrometric Cone Equivalent temperatures. Refer Figure below.
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Figure 3: Pyrometric Cones (Bureau of Energy Efficiency, 2004) Creep at high temperature: Creep is a time dependent property, which determines the deformation in a given time and at a given temperature by a refractory material under stress. Volume stability, expansion, and shrinkage at high temperatures: The contraction or expansion of the refractories can take place during service life. Such permanent changes in dimensions may be due to: The changes in the allotropic forms, which cause a change in specific gravity A chemical reaction, which produces a new material of altered specific gravity The formation of liquid phase Sintering reactions Fusion dust and slag or by the action of alkalies on fireclay refractories, to form alkali- alumina silicates. This is generally observed in blast furnaces. Reversible thermal expansion: Any material expands when heated, and contracts when cooled. The reversible thermal expansion is a reflection on the phase transformations that occur during heating and cooling.
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Thermal conductivity: Thermal conductivity depends on the chemical and mineralogical composition and silica content of the refractory and on the application temperature. The conductivity usually changes with rising temperature. High thermal conductivity of a refractory is desirable when heat transfer though brickwork is required, for example in recuperators, regenerators, muffles, etc. Low thermal conductivity is desirable for conservation of heat, as the refractory acts as an insulator. Additional insulation conserves heat but at the same time increases the hot face temperature and hence a better quality refractory is required. Because of this, the outside roofs of open-hearth furnaces are normally not insulated, as this could cause the roof to collapse. Lightweight refractories of low thermal conductivity find wider applications in low temperature heat
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