Lightweight Corundum Mullite Castable

Lightweight corundum mullite castable is made of mullite lightweight aggregate and powder, with corundum powder with high wear resistance added. Lightweight corundum mullite castable has a small volume density and thermal conductivity, excellent high temperature performance, and relatively good thermal insulation effect. Since lightweight corundum mullite castable uses synthetic raw materials and is combined in the form of low cement or micro powder, it can be directly applied to high temperature parts in contact with flames.

 

As the main component of castables, lightweight mullite aggregate has a crucial influence on the performance indicators of castables, and its selection should be carefully carried out. Properly increasing the critical particle size of aggregate is conducive to enhancing the compressive strength of castables, but if the critical particle size is too large, it will have an adverse effect on the construction performance of the material. Through experiments, we determined that the critical particle size is 12mm. The ratio of particles to fine powder should be controlled at 65%~70%, and 32%~40% is more appropriate.

Because lightweight corundum mullite castable is used in the high temperature part of the heating furnace, the use temperature is about 1350℃, so pure calcium aluminate cement with excellent performance should be selected, and its AL2O3 content should generally be greater than 70%. If the cement impurity content is high, it is easy to react with the castable at high temperature to produce low melting products, which will affect the high temperature performance of the castable. Its addition amount is generally controlled at 5%~10%. Excessive addition will reduce the medium temperature strength of the castable, and will have an adverse effect on the high temperature strength and spalling resistance of the castable at high temperature.

Compared with dense castables, lightweight corundum mullite castables have lower fluidity. Especially for castables used in high-temperature areas, due to the constraints of use conditions, some subdivided addition amounts and addition varieties are subject to certain restrictions. In order to enhance the fluidity of this castable, composite micro powder is added. After comparative tests, it is believed that it is difficult to achieve good fluidity and performance of this castable by adding only a single alumina powder or silicon micro powder. For this reason, two kinds of micro powder are selected for composite addition. In order to improve the construction performance and high-temperature strength index of lightweight corundum mullite castables, we increased the amount of ultrafine powder added. Considering comprehensively, it is more appropriate to control the total amount of ultrafine powder at 10%~18%.

Since the lightweight corundum mullite castable aggregate has poor density performance, if the proportion is not properly controlled, it is easy to cause the high-temperature linear shrinkage of the castable to increase, which makes the castable prone to cracks and peeling when used at high temperatures, seriously affecting the high-temperature performance of the castable. For this reason, we add an appropriate amount of kyanite to control the linear change of the castable, and the addition amount is preferably 4%~6%.

1. Mixing: First add the lightweight corundum mullite castable into the mixer and dry mix for 2 minutes, then add water glass and modifier, wet mix for 3 minutes and then discharge. To prevent machine crash, the mixing amount should not exceed 40% of the mixer capacity. Discharge should be quick and timely. If the mixer fails, remove the material in the machine and rinse it with water. After work every day, clean the modified concrete in the machine and on the mixing plate. If the project volume is very small, manual mixing can be used.

2. Pouring: Brush a layer of thin glue on the construction surface, wait for it to solidify before pouring, and try to avoid leaving construction joints. If construction joints must be left, they should be left in an oblique shape and kept rough. When the lightweight corundum mullite castable is used for the next joint, apply thin glue first and then pour, and the joints should be smoothed and smeared. When the temperature is high in summer and autumn, the modified water glass concrete can be initially set in a few minutes, so the on-site tamping and smoothing speed should be fast. It is advisable to smooth the surface before the initial setting and form it in one time to avoid wrinkles after the initial setting, which will affect the appearance and reduce the anti-seepage and anti-corrosion performance.

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