Zirconium ramming mass is widely used for sealing and heat preservation of glass kiln pool bottom, and is one of the important factors affecting the life of glass kiln. This article introduces the performance of two commonly used zirconium ramming mass, and puts forward reference opinions for reasonable selection through analysis and comparison.It is a kind of amorphous refractory material with low plasticity, which is mainly composed of zirconium aggregate, powder, binder and additive. It is rammed into shape after being mixed in a certain ratio, and is widely used for sealing and heat preservation of glass kiln pool bottom.
Although the amount of ramming mass accounts for a small proportion of the total amount of refractory materials used in glass kilns, the position where it is located is a very important and special pool bottom. On the one hand, the environment where it is located is complex and harsh, the temperature is high, and it is eroded by glass liquid and withstands the long-term static pressure penetration of glass liquid; on the other hand, it is difficult or impossible to repair it during the operation cycle of the kiln. Once the glass liquid leaks, the danger and loss are huge.
In recent years, in order to increase the melting rate of glass kilns and save energy, the temperature of the pool bottom has been continuously increased, resulting in a significantly accelerated loss rate of the pool bottom ramming material; in the broken glass recycled outside, metal debris will settle on the pool bottom, gradually penetrate into the back-beating layer, forming downward drilling erosion, which aggravates the erosion and damage of the ramming material. The premature loss of the pool bottom ramming layer has become one of the important factors affecting the age of glass kilns.
When different zirconium ramming materials are eroded by glass liquids of different components, the physical and chemical reactions that occur are not completely consistent. Therefore, according to the glass components melted by different kilns, suitable zirconium ramming materials are selected to obtain the best matching effect.
1. Two commonly used zirconium ramming materials and their performance advantages
The performance of refractory materials in resisting high-temperature glass liquid erosion is an important factor in determining the life of glass kilns and the quality of glass products. Zirconium ramming materials can be widely used in the bottom of glass kilns. In addition to having the characteristics of good integrity, good sealing, and strong adaptability, they also benefit from the superior corrosion resistance and ultra-high refractoriness of zirconium materials. Zirconium aggregate is the skeleton of zirconium ramming mass, and plays an important role in the high-temperature physical properties of zirconium ramming mass. At present, there are two main types of zirconium ramming mass used in glass kiln pool bottom in China: one is fused AZS ramming mass and the other is zircon ramming mass.
AZS ramming mass is made by crushing fused zirconium corundum bricks into particles of about 5mm as aggregate, and then mixing them with other auxiliary materials. It retains the advantages of fused zirconium corundum bricks, has strong resistance to glass liquid erosion, small porosity, extremely stable performance, and can well inhibit the invasion of glass liquid and metal. Zircon ramming mass is made by adding a certain proportion of crushed sintered zircon brick fragments as aggregate to zircon mud powder, and then adding other auxiliary materials. It has high refractoriness and good resistance to glass liquid erosion. When constructing the two types of zirconium ramming materials, you only need to add an appropriate amount of water in proportion to mix them. After mixing evenly, the ramming materials will be moist and loose, and then they will be rammed and sintered at high temperature to form a solid whole. The construction has abandoned the previous use of phosphoric acid as a binder, which is safer and more convenient.
2 Application and selection of two zirconium ramming materials
Although both zirconium ramming materials have good resistance to glass liquid erosion and only have extremely low pollution to glass liquid, they still need to be reasonably selected according to the properties of the produced glass when used.
Ramming materials are composed of gas phase, crystal phase and glass phase. Although the existence of glass phase is beneficial to sintering, compared with the crystal phase, its resistance to glass liquid erosion is poor. It is the weak link of erosion resistance of ramming materials and other refractory materials. Its properties and content have an important influence on the performance of ramming materials.
Pores are the passages for glass liquid to penetrate into the interior of ramming materials. With high porosity, ramming materials have poor resistance to chemical erosion. This is because most of the pores are concentrated in the binding phase. Once the glass liquid penetrates into the interior of the ramming material, the gas phase, glass phase and etchant multiphase intersect to form the weakest point of erosion resistance. Therefore, if the chemical composition is constant, the lower the total porosity, the stronger the erosion resistance
The type and composition of the etchant also play a big role in the erosion resistance of the ramming material. In a glass kiln, the etchant mainly refers to the high-temperature glass liquid and the dense metal or metal oxide deposited on the bottom of the pool. Different glass liquids have different effects on ramming materials. The characteristic rate and form of erosion are very different between soda-lime-silica glass, borosilicate glass, lead glass and other types of glass.
As shown in above table, the main difference between the fused AZS ramming material and the zircon ramming material is the content and porosity of Al2O3. Since there are masonry gaps in the paving bricks located on the upper layer of the zircon ramming material, the glass liquid will penetrate into the ramming layer through the brick joints. The anti-erosion performance of the ramming material will vary depending on the chemical composition, movement speed and temperature of the glass liquid. The corrosiveness of the soda-lime-silica glass melt is high because the melt contains ionized alkali. When they come into contact with the ramming material, the ionized alkali is the driving force of the corrosion mechanism. The viscosity of the melt also has a great influence on the erosion rate, regardless of the range of the glass system. The erosion effect increases sharply with the decrease of viscosity.
The following is a further explanation of the effects of zircon ramming mass and fused AZS ramming mass when they come into contact with alkaline glass liquid.
(1) Contact between fused AZS ramming mass and alkaline glass liquid
An aluminum (Al2O3) layer is formed at the contact interface. The ZrO2 in the ramming mass is dissolved in the glass liquid to a very low degree, the viscosity increases, the interface layer has a passivation characteristic, and the ramming mass has enhanced resistance to mechanical wear and chemical corrosion.
(2) When zircon ramming mass comes into contact with alkaline glass liquid, since there is no aluminum in the zircon ramming mass, zircon is easily decomposed. The decomposed SiO2 will reduce the viscosity, thereby accelerating the erosion and causing damage to the ramming layer.
3 Conclusion
Although the two commonly used zircon ramming materials have similar anti-glass erosion performance, the Al2O3 content in zircon ramming materials is extremely low, and the apparent porosity of the two ramming materials is different. Through analysis and comparison, the fused AZS ramming material is more suitable for the bottom ramming layer of soda-lime-silica glass, electric vacuum glass and other alkaline glass furnaces, while the zircon ramming material is more suitable for the bottom ramming layer of weakly alkaline glass furnaces such as borosilicate.
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