The production of refractory materials for glass melting furnaces is fundamentally different from the production of refractory materials for other types of furnace equipment. The difference lies in the fact that the former has two characteristics:
1) The size of its main type of product is very large, which greatly complicates the production technology;
2) It must meet the special requirements of the glass industry for the quality of refractory materials that are particularly strict.
The molten glass can corrode the refractory materials used to build the kiln pool. Small pieces of refractory materials leave the kiln pool wall, fall into the glass liquid and melt in it to form "lines" - uneven glass, or they do not have time to completely dissolve. At that time, there are not only lines in the finished product, but also stones, which are more serious defects. In many cases, while the refractory materials are corroded, bubbles are precipitated in the glass liquid near the kiln pool wall. Small pieces of refractory materials and bubbles can remain in the glass liquid. This is because:
1) The viscosity of the melt is very high: at the melting temperature, the viscosity of the glass liquid is about 10,000 times higher than that of water, and the viscosity of the molten metal is 5,000 times higher, and at the molding temperature, it is tens of thousands or even hundreds of thousands of times higher.
2) The density of the glass melt is very different from that of the refractory. This is also a condition for the slow dissolution of small pieces of refractory in the glass melt (the smaller the density difference between the glass melt and the refractory, the slower the relative movement of the small pieces of refractory and the melt). The refractory in the flame space of the glass melting furnace is greatly damaged by the high temperature, temperature fluctuations and flying materials, which also results in the dirty glass melt. The crucible for melting glass is subjected to strong wear during use, especially when melting special glasses.
Everyone knows that improving the durability of refractory materials for glass melting furnaces and reducing glass waste caused by refractory materials will provide great savings for glass factory production. This is true even when the cost of refractory materials is significantly increased.
From the above, it can be seen how important it is to ensure that the highest quality refractory materials are available in the possible range in glass production. The common basic requirements that various refractory materials, especially fused zirconium corundum bricks, used in glass melting furnaces should meet are as follows:
1. The refractory materials have sufficient mechanical strength
2. The refractory materials have excellent resistance to long-term mechanical loads at operating temperatures, or in the terms suggested by the author - have a high degree of burn resistance.
3. The refractory materials have high resistance to the erosion of the components of the molten batch and the glass. The glass defects caused by the refractory materials - stones, lines, bubbles and coloring - should be minimal. Under the conditions of the glass industry, the latter two requirements - minimizing bubbles and coloring defects - are the most important in most cases.
4. The refractory materials have the ability to withstand temperature increases, decreases and fluctuations at a considerable rate for a long time without being damaged. This property is called resistance to rapid cooling and heating.
5. The refractory materials have a fixed volume at operating temperature, that is, their residual shrinkage or residual expansion values are very small.
6. The style is correct, the size is accurate, and the shape meets the technical requirements.
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