The raw materials and production process of silica bricks for glass kiln are as follows:
(1) Determination of raw material ratio and particle composition
The raw materials for the production of silica bricks mainly include quartz stone, waste bricks, lime, mineralizers and organic binders.
Adding waste silica bricks can reduce the sintering expansion of the bricks, 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 weight of the product, the more complex the shape, and the more added amount. Generally, it should be controlled within 20%. Lime is added to the billet in the form of milk of lime to act as a binding agent, increase strength after drying, and act as a mineralizer during firing. The mineralizer used in production is mainly rolled steel oxide scale. The commonly used organic binder is sulfite pulp waste liquid.
The general principles for determining the composition of silica brick particles 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 high-temperature firing volume.
② It is hoped that the critical particles in the blank are small and there are many fine particles.
③ When mixing different quartz stones, add coarse particles for those with high violent expansion temperature, and add fine particles for those with low expansion temperature; materials with dense texture can be coarser, and vice versa.
(2) Determination of the firing system of silica bricks
Silica brick undergoes phase change during the firing process, which makes firing more difficult. Therefore, comprehensive consideration should be given to the physical-chemical changes of the bricks during the firing process, the shape and size of the bricks, and the characteristics of the kiln.
① In the temperature range below 600°C, the temperature should be raised quickly and evenly.
② In the 700~1100°C temperature section, the heating rate can be evenly accelerated compared to the previous section.
③ In 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 make the temperature distribution uniformly throughout the kiln, and avoid flame impact on the bricks. After reaching the maximum sintering temperature, there must be sufficient holding time, which generally fluctuates in the range of 20~48h.
⑤ It can be cooled quickly above 600~800°C, and it should be cooled slowly at low temperature.
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