Chemical composition:
Silica bricks are made by mixing high-purity quartz stone with a small amount of lime milk after sintering and selection. A part of the aggregate can be used after crushing waste silica bricks. High-grade silica brick raw materials are subject to special chemical treatment. to remove impurities.
Raw material and production process:
1. Determination of raw material ratio and particle composition
The raw materials for producing silica bricks mainly include quartz stone, waste silica bricks, lime, mineralizers and organic binders. Adding waste silica bricks can reduce the firing expansion of bricks, but it will also reduce the refractoriness and strength of products. Therefore, it should be determined according to different situations. The principle is that the larger the unit weight of the product, the more complex the shape, and the more the amount added, generally it should be controlled within 20%. Lime is added to the raw material in the form of lime milk, which acts as a binder, increases strength after drying, and acts as a mineralizer during firing. The mineralizer used in production is mainly rolled steel oxide scale. The commonly used organic binder is sulfurous acid pulp waste liquor.
The general principles for determining particle composition are as follows:
① When selecting the critical particle size, it is necessary to ensure that the brick can obtain the maximum density and the stability of the high-temperature firing volume.
② It is hoped that the critical particles in the billet are small and there are many fine particles.
③ When mixing different quartz stones, add coarse particles with high initial expansion temperature, and add fine particles with low initial expansion temperature; denser raw materials can be thicker, and vice versa.
2. Determination of firing system
Silica bricks undergo a phase change during firing, making firing more difficult. Therefore, comprehensive consideration should be given to the physical and chemical changes of the brick during firing, the shape and size of the green body, and the characteristics of the kiln.
① In the temperature range below 600°C, the temperature should be raised quickly and evenly.
②In the temperature range of 700-1100 ℃, the heating rate can be evenly accelerated compared with the previous one.
③In the temperature range of 1100-1430°C, the heating rate should be gradually reduced.
④ In the high-temperature stage, use a weak reducing flame to fire, and at the same time make the temperature distribution in the kiln uniform, and avoid the impact of the flame on the adobe. After reaching the highest firing temperature. There must be enough heat preservation time, which generally fluctuates within the range of 20-48h.
⑤ It can be cooled rapidly above 600°C, and it should be cooled slowly at low temperatures. Table 10-4 lists the heating rate in different temperature ranges.