[China Glass Net] Stone is a crystalline inclusion in a glass bottle and is a serious defect in glass products. It can destroy the appearance and optical uniformity of glass products. In addition, since the coefficient of thermal expansion of the stone and the main body glass is different, interface stress is easily caused during heating or cooling of the product. It is also the main cause of cracks and cracks in glass products. According to the genesis of stones, it can be divided into the following categories:
1. Mixing stones
The compound stone is the unmelted particles in the batch material. In most cases, it is quartz grain, the color is white, the edge is rounded due to gradual dissolution, and the surface is often grooved. There is a layer of SiO2 around the quartz grain. A high colorless ring, which has a high viscosity and is not easily diffused, often resulting in the formation of thick ribs. Crystals of cristobalite and tridymite tend to appear at the edges of quartz particles. The production of batch stones is not only related to the quality of the preparation of the batch, but also related to the feeding mode of the melting, the level of the melting temperature and the fluctuation. Common stones are cristobalite and tridymite.
2. Refractory stones
When the refractory material is subjected to erosion and spalling, or after the molten glass interacts with the refractory material at a high temperature, some debris may be trapped in the glass article to form a refractory stone. The kiln and the chest wall are usually made of silicon brick. Under the influence of high temperature or under the influence of alkaline flying material, it will be altered. Sometimes it will form a melting material under the armpit, or it will drip into the glass liquid. This is a refractory stone. Another source.
Therefore, in order to reduce refractory stones, high-quality refractory materials must be used. In general, the porosity, structural density, uniformity of microstructure, masonry quality, melting temperature, alkalinity of the glass itself, melting stratification, and the type of raw materials used are closely related to the refractory material.
Common refractory stones are aluminum siliceous stones such as mullite, nepheline, leucite and the like.
3, crystallization stones
The crystal precipitated from a homogeneous glass at a certain temperature is a crystallization stone. The crystallization stones in the glass tend to cause the glass to create a faint white spot or to present a product with a distinct crystalline state. The crystallization stones are particularly prone to occur at the two-phase interface. For example, on the surface of the molten glass, on the bubble, at the interface with the refractory material. The glass composition has a significant effect on the generation of crystallization stones, because the nucleation rate and crystal growth rate are also different. In the composition, the oxide with a small tendency to devitrify should be selected to reduce the content of the easily crystallized oxide; in addition, the temperature system of the kiln and the structure of the kiln have a great influence on the crystallization, and the former should make the glass as much as possible Less stay in the crystallization temperature range, while the latter should try to reduce the dead angle of the glass liquid.
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