How to Select High Quality Silica Brick for the Glass Furnace

Silica brick is mainly used in the doghouse crown, suspended wall of channel, top crown and inlet sealing in the glass furnace. There are mainly four factors to consider when select high quality silica brick for the glass furnace. 

1) High pure raw materials

The raw materials for the production of silica brick, according to the crystalline state, can be divided into crystalline silica and silica cement. High purity, hard and dense crystalline silica with a low impurity content and high SiO2 content ((SiO2>99%)) is preferably used as a raw material. Since the silica cement has a high impurity content and high refractoriness and is not hard and compact enough, it is seldom used. Silica cement is soft silica and is apt to be transformed into tridymite rather than Cristobalite, it is not ideal for the glass furnace. 

2) High content of Cristobalite

High quality silica brick is mainly composed of Cristobalite, tridymite and a small amount of residual quartz. Among them, Cristobalite is the main crystal phase. The softening beginning temperature under load of the silica brick with Cristobalite as its main crystal phase is the destruction temperature of cristobalite, while for the silica brick with tridymite as the mian crystal phase, the softening beginning temperature under load is the temperature when a large amount of Cristobalite is transformed into tridymite. The former is 20-30℃ higher than the latter. The softening beginning temperature under load of the silica brick with Cristobalite as its main crystal phase is 1690℃, close to its refractoriness. It has great advantage in the glass furnace. In addition, it has better corrosion resistance than other silica brick. Moreover, a low content of residual quartz makes it have good volume stability, so it has a lognser service life.

3) Low melt index

The melt index (Al2O3+2R2O) is an indicator that more and more users consider when select high quality silica brick for the glass furnace. In the firing process, Al2O3 and R2O act as the mineralizing agent. When the content of Al2O3 and R2O is less, liquid phase produced in the firing process is less and has a weak ability to promote the conversion of quartz, which will affect the sintering degree and the strength, porosity and true specific gravity of products. The products will be easy to crack. When the mineralizing agent is too much, it will greatly reduce the refractoriness and increase the content of tridymite. Under the condition of  CaO<2.0% and Fe2O3<0.5%, the melt index (Al2O3+2R2O) <0.5% and SiO2≥96%, the residual quartz can be controlled under 1.0% by enhancing the firing process to get high quality silica brick. 

4) Shape and dimension

The computer-controlled electronic batching system ensures the accuracy of the batching and the stability of the particle classification, which has laid a good foundation for the uniform appearance of the products. Rigorous examination of the apparent size of semi-finished products and dry and wet green bodies ensure the dimensional accuracy of the finished products.