The bubbles caused by the contact between impurities or pores in the refractory material and glass liquid are called refractory bubbles.
Factors such as the porosity, iron content, and carbon content of refractory materials will cause the formation of bubbles through chemical interactions between glass and refractory materials. The pores of refractory materials often contain gas. When the refractory material contacts the molten glass, the molten glass is sucked in due to the capillary action of the pores, and the gas in the pores is expelled into the molten glass. Refractory materials fired in reducing flames contain carbides and low-valent oxides of multivalent elements. When silicon carbide abrasive materials are used to process refractory bricks, CO2 bubbles will be generated if the cleaning is not sufficient. The iron-containing compounds in refractory materials catalyze the decomposition of raw materials in the batch to produce bubbles. In addition, the refractory material rich in SiO2 and Al2O3 is infiltrated into the liquid material, and its viscosity is different from that of the entire glass liquid. The solubility of the gas is also different, which will lead to the generation of bubbles when re-fused. The main components of this bubble are CO2, O2 and air. The gas discharged from the pores of the refractory material in the cooling part and the forming part or the iron silicate is reduced on the surface of the refractory material will produce a large number of small bubbles. Bubbles caused by refractory materials are most dangerous when close to forming parts, such as bricks at the launder.
Refractory materials are the innate factor that determines bubbles. Therefore, when designing and selecting bricks in contact with glass liquid, attention should be paid to the use of high-quality low-porosity refractory materials to avoid congenital defects. Refractory materials that are not easy to react with the molten glass to form bubbles should be selected close to the forming part to help improve the quality of the molten glass. In terms of operation, the operating system of the furnace should also be stabilized as much as possible, that is, the temperature system should be stable, the temperature should not be too high, and the liquid level should be kept relatively stable to avoid aggravating the erosion of the refractory materials.
Are knot defects in glass products related to refractory materials?
In the process of glass production, in addition to the bubbles and stones we mentioned before, product defects also include nodules. The cause of nodules has a certain relationship with glass raw materials and kiln lining refractory materials in the glass production process.
Nodule is also a glassy inclusion with a composition different from that of the bulk glass. It is generally understood as a nearly spherical glass-like independent part. It appears as a transparent mass on the glass plate with a long tail. Most nodules are droplets or pellets formed at high temperatures and deform due to differences in viscosity and surface tension from the matrix glass.
Nodules come in various shapes and sizes, with two main forms: spherical and filamentous. Spheroid nodules come in many shapes, including oval and tailed. Sometimes there are opaque substances in the middle, such as zirconia, nepheline, etc.; some nodules contain bubbles near them; linear nodules are rarely accompanied by foreign matter (high degree of diffusion). According to the shape and composition of nodules, the cause of nodule formation can be determined. It may be caused by the melting of large particles of raw materials without time to diffuse; or it may be formed by refractory materials that have fallen off but are not completely vitrified, so sometimes they contain more or less eroded solid objects.
Erosion of side wall bricks near fluid holes and bridge walls may also cause linear nodules. Nodules are mixed in normal glass. Generally, the appearance color is not significantly different from that of glass, but the optical properties are different from those of the base glass, which will cause severe optical deformation and generate stress, reducing the strength of the glass.
In short, the glass melt is not evenly mixed; the stones in the glass melt are melted; the liquid droplets produced on the top of the kiln drip on the glass liquid; the batch materials are unevenly mixed and the melting is incomplete; the refractory material is contaminated by batch dust or Glass liquid erosion can lead to nodule defects.
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