Cement Manufacturers Association (CMA)

34 Due to the extremely high melting point of common metals like iron, nickel and copper, metallurgists have to raise furnace temperatures to over 2800°F. Furnaces are lined with refractory materials such as magnesia, which has a melting point of 5070 degrees. Requirements of Right Refractory The general requirements of a refractory material can be summed up as: 1. It can endure high temperatures and efficiently retain heat within a confined space, similar to that of a furnace. 2. It can endure exposure to molten metal, high temperatures, and erosion by slag, among other factors. 3. It can withstand the load under normal operating conditions. 4. It can remain uncontaminated when in contact with other materials. 5. It can maintain stable dimensions even when subjected to high temperatures and repeated thermal fluctuations. 6. It can effectively retain and preserve heat. Properties of refractories Key properties of refractories include chemical composition, bulk density, apparent porosity, apparent specific gravity, and strength at ambient temperatures. These qualities are typically utilized as key benchmarks during the production and quality assurance phases. The chemical composition plays a vital role in the categorization of refractories, while density, porosity, and strength are affected by various variables such as raw material type and quality, particle size Melting point Chart Key Materials Melting Temperatures ( 0 F) Iron 2800 0 F Nickel 2650 0 F Copper 1980 0 F Aluminum 1220 0 F Zinc 780 0 F Lead 620 0 F Tin 450 0 F Melting point Chart of pure compounds Refractory Element Melting Temperatures ( 0 F) Graphite C Pure 6300 0 F Thoria, ThO 2 Pure Sintered 5430 0 F Magnesia, MgO, Pure Sintered 5070 0 F Zirconia, ZrO 2 , Pure Sintered 4890 0 F Lime, CaO 4660 0 F Beryllia, BeO, Pure Sintered 4620 0 F Silicon Carbide, SiC, Pure 4080 0 F Maganesia, 90-95% 3980 0 F Chromite, FeO-Cr 2 O 3 3960 0 F Chromium Oxide 3880 0 F Alimina, AI 2 O 3 , Pure Sintered 3720 0 F Chromite, 38%, Cr 2 O 3 3580 0 F Alimina Fuse Bauxite 3400 0 F Silicon Carbide, 80-90% 3400 0 F Fireclay 3400 0 F Titania, TiO 2 3360 0 F Kaolin, AI 2 O 3 , SiO 2 3300 0 F Silica, SiO 2 3120 0 F and distribution, moisture levels during molding, pressing pressure, temperature, firing duration, and cooling rate. Some of the important characteristics of refractories are Melting Point: The melting temperatures of materials indicate how well they can endure high temperatures without undergoing chemical alteration or physical damage. The melting points of some elements that form refractory substances in their pure form range from 3100°–6300°F, as illustrated in the following table: The melting point is an adequate factor to assess the heat resistance of refractory mixtures and is a key feature that denotes the highest temperature they can withstand. Size and Dimensional Stability: Factors like the dimensions and configuration of refractories play a crucial role in design due to their significant