A brief introduction to refractory materials for glass kilns
Glass melting furnace is a thermal equipment made of refractory materials for melting glass. When selecting refractory materials for glass kilns, you should consider the kiln type, use location, damage mechanism, type of melted glass, and type of pigment. The refractory materials used in glass kilns should first be able to resist the erosion of glass melt and gaseous reactants, and should have a sufficiently high load softening temperature and thermal stability.
It is usually hoped that the refractory materials in various parts of the kiln will not suffer from local premature corrosion to ensure that the entire kiln has a long enough service life. However, due to the different mechanical, physical and chemical conditions of various parts of the glass kiln, it is required that the performance of the refractory materials used must be suitable for them, and it must not have an adverse effect on other adjacent types of bricks.
The following analyzes the considerations for selecting refractory bricks for glass kilns from multiple aspects.
1. Clay bricks
Clay products are acidic refractory products, and their acidity increases as the SiO2 content increases. It has certain corrosion resistance to acidity, but poor resistance to alkaline corrosion. Clay bricks are available in different varieties, such as low porosity clay bricks, ultra-low porosity clay bricks, low creep, low porosity, low iron clay bricks, etc. Therefore, clay products should be used as refractory materials for acid kilns. Large clay bricks for glass kilns are clay refractory bricks with a unit weight of not less than 50kg for building glass kilns.
The usage conditions of clay bricks are different due to different molding methods and the aggregates and binders of clay bricks. According to these characteristics, different clay bricks can be used in different parts of the pool furnace due to different erosion conditions. The lower grate and checker bricks in the lower part of the regenerator are less eroded by batch dust and volatile matter, and have a lower temperature. However, due to their heavy load, these bricks require high mechanical strength. Therefore, the binder in the brick can contain an appropriate amount of SiO2 and Fe2O3. However, clay bricks used in high-temperature locations mainly require high refractoriness and few impurities in the binder.
2.Silica brick
Silicon refractory materials are acidic materials. They have strong resistance to acidic slag or solution erosion and have good high-temperature properties: for example, the refractory degree is 1690-1730°C, and the load softening starting temperature is 1640-1680°C. The volume expansion rate is large, and when the temperature is 1450°C, the total volume expansion is approximately 1,000, which is beneficial to ensuring the structural strength and air tightness of the masonry. Therefore, silica bricks are the main material of glass kilns and are widely used in large bricks, parapets, regenerator roofs and other parts.
Precautions when baking silica bricks in the kiln: When silica bricks are heated at 200-300°C and 573°C, the volume suddenly expands due to crystalline transformation. Therefore, when baking, do not heat up too quickly below 600°C. When cooling to below 600°C, Drastic temperature changes should be avoided and contact with alkaline substances should be avoided as much as possible.
3. Fused zirconium corundum brick
ZA series oxidation method fused zirconium corundum products are made from high-quality purified raw materials, using a special electric arc furnace, and through a long arc melting and oxidation treatment casting process. This electrofusion casting process has virtually no carbon contamination from the electrodes.
Due to the adoption of this melting and casting process and the use of high-purity raw materials, the ZA series oxidation method fused zirconium corundum products have special and high resistance to erosion by glass liquid, and have minimal pollution to the glass.
AZS-33 products are particularly superior in preventing contamination of glass liquid. It has a very small tendency to cause stones, bubbles and the precipitation of basic glass phases in the glass. It is suitable for the upper structure of the melting pool, the wall bricks and pavement bricks of the working pool, the material channel, etc.
AZS-36 is a standard oxidation method fused zirconium corundum brick. It has special characteristics of high resistance to glass liquid erosion and low contamination, and its performance in these two aspects is balanced. It is suitable for parts in the glass melting furnace that are in direct contact with the glass liquid, such as melting pool wall tiles, pavement tiles, feeding ports, etc.
AZS-41 is the highest-grade oxidation method fused zirconium corundum brick, which has the highest resistance to glass liquid corrosion and outstanding low pollution to glass liquid. It is suitable for parts in glass furnaces that require particularly high corrosion resistance, such as all-electric melting furnaces, liquid tunnels, kiln sills, bubbles, bricks at the corners of the feeding port, etc.
The properties and performance indicators of fused zirconium corundum bricks—the baddeleyite phase can resist the erosion of glass liquid. The glass phase can buffer the stress caused by volume changes, allowing the product to maintain an airtight structure. However, if the quantity is too large, the leakage temperature will increase with time. The lower it is, the worse the quality of the bricks will be. The exudation of the glass phase will destroy the structure of the brick and affect its lifespan. Bubbles will be released while exuding, and may produce stones that are insoluble in glass, seriously affecting the quality of the glass. The foaming index is usually used to express the exudation temperature.
4. Fused corundum brick
The main crystal phase of corundum bricks is corundum, which has excellent properties, such as high melting point, high hardness, and is a neutral mineral. Therefore, the product has high hardness, is resistant to erosion, wear, and erosion. Melting-cast α-Al2O3 bricks are mainly composed of α-type corundum with a tight and strong fine-grained structure. Mainly used in glass kilns. Suitable for melting borosilicate glass and opal glass. However, its high-temperature corrosion resistance is poor. At a high temperature of 1600°C, its resistance to glass liquid corrosion will rapidly decrease, so some borosilicate glass kilns tend to use fused quartz bricks. The bulk density of fused-cast α-Al2O3 brick products is 3.15-3.30g/cm3, containing a small amount of glass phase (about 2%), filling the gaps between crystals, and has high purity. Since it does not pollute the glass liquid and has good resistance to glass liquid erosion and excellent high temperature wear resistance below 1350°C, it is an ideal refractory material for the clarification section, cooling section, working pool and other parts of the glass melting furnace. Material.
β-Al2O3 is a white product composed of thick and bright crystals, containing 92%-95% Al2O3, with only less than 1% glass phase, and the structural strength of the product is low due to the loose crystal lattice. The Na2O contained in β-Al2O3 reacts with SiO2, resulting in a large volume shrinkage, which may cause cracks in the bricks and cause damage. Therefore, it is only applicable to superstructures that contain SiO2 fly ash, for example, the superstructure of the working pool, the breast wall near the combustion port, the small furnace nozzle and the hanging wall, etc. Because this brick does not interact with volatile alkali metal oxides, there is no need to worry about molten matter dripping from the brick surface contaminating the glass.
5. Magnesium refractory materials
(1) Magnesium materials for glass kiln regenerator
Generally, the uppermost layer of the regenerator grid uses high-grade magnesia bricks (w(MgO) > 97%); the upper layer uses mid-grade magnesia bricks (w(MgO) about 95% ~ 96%
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