Raw materials and production process of silica bricks

The raw materials and production process of silica bricks for glass kilns are as follows:

(1) Determination of raw material ratio and particle composition

The raw materials for producing silica bricks mainly include quartz stone, waste bricks, lime, mineralizer and organic binder.

Adding waste silica bricks can reduce the expansion of the bricks during firing, but it will also reduce the refractoriness and strength of the products. Therefore, it should be determined according to different situations. The principle is that the larger the unit weight of the product and the more complex the shape, the more the amount added, which should generally be controlled within 20%. Lime is added to the blank in the form of lime milk, acting as a binder to increase strength after drying and as a mineralizer during firing. The mineralizer used in production is mainly rolled iron oxide. The commonly used organic binder is sulfite pulp waste liquid.

The general principles for determining the particle composition of silica bricks are as follows.

① When selecting the critical particle size, it is necessary to ensure that the bricks obtain the maximum density and the stability of the volume after high-temperature firing.

② It is hoped that the critical particles in the blank are small and there are more fine particles.

③ When mixing different quartz stones, coarse particles are added to the ones with high initial expansion temperature, and fine particles are added to the ones with low initial expansion temperature; the raw materials with dense texture can be coarser, and vice versa.

(2) Determination of the firing system of silica bricks

Silica bricks undergo phase changes during the firing process, making them more difficult to fire. Therefore, the physical and chemical changes of the bricks during the firing process, the shape and size of the blanks, and the characteristics of the kiln should be considered comprehensively.

① The temperature should be raised quickly and evenly in the temperature range below 600°C.

② The heating rate in the temperature range of 700~1100°C can be evenly accelerated compared with the previous period.

③ In the temperature range of 1100-1430°C, the heating rate should be gradually reduced.

(3) Use a weak reducing flame to fire in the high temperature stage, and at the same time make the temperature distribution uniform throughout the kiln, and avoid flame impact on the bricks. After reaching the highest firing temperature, there should be enough insulation time, which generally fluctuates within the range of 20-48h.

⑤ Rapid cooling is possible above 600~800°C, but slow cooling is recommended at low temperatures.