Selection of Components in Lightweight Mullite Castables

The selection of each component in the light mullite castable is as follows:

1. Selection of lightweight mullite aggregate

As the main component of castable, light mullite aggregate has a crucial influence on the performance index of castable, and its selection should be carried out carefully. First choose a regular manufacturer with quality assurance. Secondly, due to the differences in the detection methods of the bulk density and compressive strength of lightweight aggregates, the raw materials should not only detect the indicators of the lightweight aggregates, but also further detect the indicators of the castables produced with this aggregate, so as to judge the indicators of the aggregates. The quality of raw materials is very necessary. Properly increasing the critical particle size of the aggregate is beneficial to enhance the compressive strength of the castable, but if the critical particle size is too large, it will adversely affect the construction performance of the material. The ratio of particles to fine powder should be controlled at 65% to 70%: 32% to 40%.

2, the choice of cement

Because this castable is used in the high temperature part of the heating furnace, the operating temperature is about 1350 ° C, so pure calcium aluminate cement with excellent performance should be selected, and its Al2O3 content should generally be greater than 70%. If the impurity content of the cement is high, it is easy to react with the castable to produce low melt at high temperature, which will affect the high-temperature performance of the castable. The addition amount is generally controlled at 5% to 10%. If the addition amount is too large, the medium temperature strength of the castable will be reduced, and the high temperature strength and spalling resistance of the castable will be adversely affected at high temperature.

3. Selection of micropowder

Compared with dense castables, lightweight castables have lower flow properties, especially for castables used in high temperature parts. Due to the restriction of use conditions, the amount and variety of fine powder added are subject to certain restrictions. degree of restriction. In order to enhance the flow properties of this castable, the form of adding composite micropowder is adopted. After the comparison test, it is believed that it is difficult to make this castable achieve good fluidity and performance by adding only a single alumina powder or silicon powder. In order to improve the construction performance and high temperature strength index of the castable, we increased the amount of ultrafine powder added, and it is more appropriate to control the total amount of ultrafine powder at 10% to 18%.

4. Determination of the amount of kyanite added

Due to the poor compactness of the lightweight castable aggregate, if the ratio is not properly controlled, it is easy to cause the high temperature linear shrinkage of the castable to increase, so that the castable is prone to cracks and spalling when it is used at high temperature, which seriously affects the high temperature performance of the castable. For this reason, we add an appropriate amount of kyanite to control the line change of the castable, and the appropriate amount is 4% to 6%.