With the continuous development of new refractory materials, the quality of refractory materials has been continuously improved, which has enabled the glass industry to achieve excellent results in high-temperature enhanced melting technology.
Refractory materials for glass melting furnaces are subject to physical and chemical erosion by high temperature, flame, alkaline fly material, glass liquid, etc. Therefore, refractory materials for glass furnaces must meet the special requirements of glass melting process except for general industrial furnace refractory materials' require. For example, it must have high temperature mechanical strength, and high temperature volume stability.
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Refractory materials can be divided into ordinary refractory products according to their refractoriness, general refractoriness is 1580 ~ 1770 ℃, and high refractory products with refractoriness 1770 ~ 2000 ℃, in addition, there are extra high refractory products with refractoriness higher than 2000 . The refractory materials commonly used in glass melting furnaces can be simply divided into the following categories:
1. SiO 2 based siliceous refractory
a. White foam stone.
It is a natural refractory material of quartz sandstone bonded by kaolinite. Appearance selection should be blue-gray, dense and hard, free of impurities and streaks. Its main crystalline phases are mainly quartz and kaolinite. There is obvious layered structure and anisotropy. The refractoriness of white piolite fluctuates between 1650 and 1730 °C.
The expansion of white piolite is different from that of silica brick. The thermal expansion coefficient is the largest at 700 ~ 800 ℃, and it is most likely to burst at this time. After calcination, the softening temperature and compressive strength of the calcined white piolite are significantly improved, the residual expansion is small, the volume is stable, and the thermal shock resistance is also greatly improved. It has been widely used as pool bricks in small and medium-sized pool kilns.
b. Silica brick.
Silica brick is a refractory material mainly composed of SiO 2 . It is made of high-purity, fine-crystalline quartz rock mixed with a small amount of lime milk and then calcined. The clinker is waste silica brick powder. Its composition range is: SiO 94%～98%; CaO 1.5%; 3.5%; Al2O3 0.2%～2%; Fe2O3 0.3%～3.0%; R2 O 0～0.5%, national The standard stipulates that there are three grades.
The main refractory mineral phases of silica bricks are tridymite and cristobalite, a small amount of untransformed residual quartz, and a very small amount of glassy phase. The crystal transformation of various variants in silica bricks is accompanied by volume changes. The maximum thermal expansion occurs below 300°C, therefore, special attention must be paid to the baking kiln; generally, the silica brick masonry will not be damaged when the temperature is above 700°C. The thermal stability of silica brick is poor, and the number of times that the silica brick at 850°C is quenched in water without breaking is only 1 to 2 times. Silica brick is an acid refractory material, which has good resistance to acid slag, but has poor corrosion resistance to alkaline components and poor glass erosion resistance.
Due to the high softening temperature under load and the poor resistance to R2O in the glass liquid, silica brick is suitable for masonry of various stiles, gables, cooling part parapets, etc. It is not suitable for masonry walls that are in contact with the glass liquid phase, etc.
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2. Aluminosilicate refractories (Al 2 O 3 -SiO 2 series)
(1) Clay bricks.
Clay bricks are refractory bricks made of refractory clay as the main raw material. The content of Al 2 O 3 is 30% to 46%, the main crystal phase is mullite and part of SiO 2 crystal (mainly cristobalite), and there is a considerable amount of glass phase. The refractoriness can reach 1580 ~ 1750℃, but the softening temperature under load is only 1300 ~ 1450℃. Therefore, the allowable operating temperature is also reduced accordingly, generally below 1300°C. It is mainly used in the lower temperature parts of the furnace, such as the bottom bricks of the pool, the lowermost pool wall bricks of the melting part and the cooling part, the girder bricks, the walls of the lower part of the regenerator, the grate slats, the lower part of the lattice bricks, and the flue slats. Wait.
It is made of high alumina bauxite and fired at 1500°C. With the increase of Al 2 O 3 , it can be divided into sillimanite products, mullite products, mullite-corundum products, corundum-mullite products and corundum products. The main crystalline phase varies with the content of Al 2 0 3 . When the content of Al 2 O 3 is low, it is dominated by mullite crystal phase, and when the content of Al 2 O 3 is high, it is dominated by corundum crystal phase, both of which contain a small amount of glass phase.
High alumina bricks have higher refractoriness, softening temperature under load and corrosion resistance to glass liquid than clay bricks. Therefore, it is mainly used for load-bearing parts with high temperature, such as the partition wall and side wall of the regenerator, and the semi-circular doll of the regenerator.
3. A1 2 O 3 -SiO 2 -ZrO 2 series fused refractory material
The raw materials of the refractory are melted in an electric arc furnace, then cast and formed, and finally slowly cooled. It is characterized by compact structure, low porosity, high bulk density, high softening temperature under load, and excellent corrosion resistance.
(1) The earliest fused refractory material: fused zirconium mullite brick (also known as black iron brick)
(2) Fused zirconium corundum brick
Fused zirconium corundum brick, also known as white iron brick, the main crystal phase is baddeleyite zircon (Zr0 2 ) and corundum (α-Al 2 0 . ) which coexist closely, and the content of glass phase is relatively small. This kind of stable and dense zirconium corundum brick has strong resistance to glass erosion and is currently the best anti-glass erosion material.
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The composition range of fused zirconium corundum brick is: A1 2 0 3 47% ~ 51%; ZrO 2 30% ~ 43%; Si0 2 10% ~ 18%. Generally, fused zirconium corundum bricks are divided into 36 #, 33 #, 41 # and other grades according to the ZrO 2 content. For example, the parts that are in contact with the glass liquid phase, such as the feeding pool of the melting furnace, the pool wall, the liquid hole, the nozzle brick, and the lower intermittent brick, are the main materials of fused zirconium mullite brick and fused zirconium corundum brick.
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