The selection of refractory materials for kilns may seem simple but is actually very complex. Suitable materials must have specific properties, such as high fire resistance, resistance to temperature changes, resistance to mechanical and chemical reactions, and insulation ability. Although refractory bricks and refractory castables were still used as basic materials for building kilns and lining several years ago, the development of insulation refractory materials and fiber materials has opened up a new path for selecting kiln body materials, making the structure lighter. A few years ago, based on the operating temperature of the kiln, the thickness of the kiln wall could reach 1m.
However, using new materials now only requires about one-third of the thickness to achieve the same efficiency as before.
Insulation materials have the characteristics of low thermal conductivity and low heat capacity, which is common knowledge. At present, it is these insulation products that form the foundation of various lightweight industrial kiln structures. Along with other materials, lightweight heat-insulating clay refractory bricks, mullite insulation bricks, lightweight corundum bricks, and refractory fibers are all included in this group of products. Refractory fibers are produced by using thermochemical processes to centrifuge or atomize liquids of pure kaolin, alumina, or aluminum salt solutions.
The main advantages of these refractory fiber products are their low volume density and relatively low heat capacity, low thermal conductivity, and high resistance to temperature changes. The temperature range used is 1200~1600 ℃. The disadvantage of refractory fiber products is poor stability, that is, they are only suitable for kiln linings with low mechanical stress and corrosion. Due to the effect of thermal force, fibers undergo hysteresis shrinkage and compression effects, resulting in changes in the fiber structure of various high-temperature fibers. In order to eliminate this lagging shrinkage effect, many methods have been adopted during production. Therefore, the contraction and compression effects can generally be reduced from about 3% to 1%.
1. Advantages and disadvantages of using fibers as kiln lining
1.1 Advantages of intermittent kilns
① The heating and cooling time is short, so the entire firing cycle is also short;
② Low energy consumption;
③ High yield.
1.2 There are the following advantages for tunnel kilns:
① Due to the effective use of small section tunnel kilns, the optimal temperature balance can be achieved;
② Equipped with exhaust gas treatment system, which can reduce environmental pollution;
③ The quality of the finished product is more uniform;
④ There is a possibility of low-temperature operation or kiln shutdown in a short period of time;
⑤ If corresponding storage capacity is provided, it can be produced for 7 days