The commonly used refractory materials in rotary kilns in China are magnesium chromium bricks and magnesium spinel bricks. Magnesium chromium bricks are environmentally friendly products that should be phased out due to the presence of hexavalent chromium pollution. Magnesium spinel bricks have a high thermal conductivity, which is not conducive to the insulation and insulation of the furnace lining, and have a high cost. The researchers developed phosphate bonded composite prefabricated components based on the furnace conditions and actual conditions of raw materials and fuels in the active lime rotary kiln of Wuhan Iron and Steel Group. The working layer of the developed refractory prefabricated components uses homogenized bauxite as the main aggregate, which can meet the requirements of material wear resistance. After forming, it does not need to be fired, and the cost is reduced by 30% compared to traditional magnesium chromium bricks and magnesium spinel bricks, and chromium pollution is eliminated. The working layer and insulation layer adopt basically the same matrix and binder system, which improves the chemical bonding strength of the two. The working layer and insulation layer form an interlocking structure in a serrated or gear shape, which can effectively improve the shear resistance of the interface between the two, and make the furnace lining have higher overall structural strength under dynamic conditions.

Research on Volume Expansion Performance of Refractory Prefabricated Parts

During the rolling operation of the rotary kiln body, it is necessary to maintain a close fit between the furnace lining and the kiln shell to prevent relative sliding between the gaps between the furnace lining and the shell, which may cause internal stress damage to the furnace lining. Therefore, the overall volume of the lining should have an appropriate expansion amount during operation, which requires the addition of an expansion agent in the formula. The researchers selected high-quality andalusite as the expansion agent, utilizing the volume expansion generated by the crystal transformation of andalusite into mullite structure during heating. It has good thermal shock resistance, high mechanical strength, high load softening point, and high chemical stability and corrosion resistance, which can enhance the high-temperature performance of the furnace lining.

During the experiment, the researchers added expansion agents at a constant amount of 1a% to 5a% (a is a constant) to the preform formula. According to GB/T 5072.2-2008 and GB/T 5988-2007, the compressive strength and rate of change in the reburning line of the preform working layer samples were tested. The results were analyzed as follows:

With the increase of the amount of expansion agent added in the formula, the compressive strength of the sample increases, but after adding more than 2a%, the strength tends to decrease; The rate of change of the sample's reburning line significantly increases with the increase of the amount of expansion agent added. The amount of expansion agent added needs to be comprehensively considered based on the working environment of the furnace lining. If the addition amount is too small, there will be residual shrinkage in the furnace lining, which affects the overall strength and service life; Excessive addition will cause excessive expansion of the furnace lining during use, which is more likely to cause structural damage. From the experimental results, it can be seen that when the amount of expansion agent added in the formula is about 2a%, the performance of the composite furnace lining is better.

Research on the Thermal Insulation Performance of Refractory Prefabricated Insulation Layer

In order to achieve better insulation and insulation effects, researchers used lightweight aggregates with lower density and added a certain amount of porous materials in the formulation of prefabricated insulation layers. They also compared the use effects of expanded perlite, vermiculite, and alumina hollow spheres. The experimental results show that adding alumina hollow spheres results in higher strength and smaller volume change rate of the material; Choosing perlite and vermiculite has a better effect on improving the insulation performance of the material.