Refractory materials are the main components of glass melting furnaces, which have a decisive influence on glass quality, energy consumption and product costs. The future of glass melting technology depends to a certain extent on the advancement of refractory manufacturing technology and the improvement of product quality.
The structure of the glass melting furnace
For large float lines, the glass furnace is usually composed of an L-shaped suspended wall (usually using silica bricks), a melting part (the area directly in contact with the molten glass should use electric fused bricks, and the top part using silica bricks or electric Melting bricks), necks (usually silica bricks), cooling parts including ear pools (corundum materials are usually used where they are in direct contact with molten glass, and silica bricks or corundum are used where they are not in direct contact with molten glass), annealing kilns, Regenerator (consisting of high-alumina bricks, clay bricks, directly combined with magnesia-chrome bricks) and other parts.
A.Top of arch
The ceiling of the melting part and cooling part of the glass melting furnace (including the arch angle). These parts are at a working temperature of 1600 degrees Celsius. The refractory materials used in these parts must be able to withstand high temperature and load, but also withstand alkali steam and batch materials. Therefore, the refractory used as the top must have extremely high refractoriness, high load softening temperature and good creep resistance, and the thermal conductivity is small. The refractory at high temperature cannot pollute the molten glass. The bulk density should also be small, and the high temperature strength is good. High-performance, high-quality and high-purity silica bricks have just the above characteristics:
1. High load temperature is close to its refractoriness;
2. Good stability at high temperature and high compressive strength;
3. Due to the main component of SiO2, the content is more than 96%, and The main elements of the glass composition are the same, so the corrosive substances under high temperature conditions will not pollute the glass liquid;
4. The price is cheap. Therefore, high-purity and high-quality silica bricks have become the best choice in the production process of various glass domes.
The chemical attack caused by the high-temperature chemical reaction of the fly material and alkali steam with the refractory, as well as the phase migration and temperature-induced crystal transformation and structural compactness change are the main reasons for the damage of the roof brick. The research results show that the alteration process of high-quality glass kiln silica bricks used for the roof of the kiln is basically caused by impurity migration and miscellaneous phase transformation under the action of high temperature in the kiln, and the effects of chemical attack and melting are basically negligible. The effects of phase change and self-purification make the kiln operation zone gradually change its performance, and its high-temperature performance is improved.
B.The pool wall
1.The part in contact with glass liquid
The part where the melting part and the cooling part are in direct contact with the molten glass is subjected to high temperature, chemical erosion caused by the molten glass and mechanical physical erosion caused by the flow. The main condition for this part is that it has good resistance to the corrosion of the molten glass. At the same time, it cannot contaminate the glass liquid. Domestic glass furnaces generally use fused zirconia corundum bricks, α-β corundum bricks, and β corundum bricks for masonry. Fused zirconium corundum bricks are excellent in high temperature and resistance to glass liquid. This is because it has obtained the eutectic of oblique zircon and α-Al2O3, which is impossible to obtain by sintered refractory materials, so it is used as a glass kiln. The pool wall tiles in the melting part of the furnace are very suitable. The main crystal phase of α-β corundum brick and β corundum brick is corundum, and the glass phase content is only 1%-2%. It has good corrosion resistance. Compared with the performance of fused zirconia corundum brick, it does not contain ZrO2 crystals. The reaction layer has a low viscosity and is not stable at high temperatures. Therefore, the diffusion rate between the surface of the brick and the molten glass is relatively large, and the kiln lining is damaged quickly. But when the working temperature of the kiln is lower than 1350℃, the corrosion resistance of α-β corundum brick and β corundum brick is better than that of fused zirconia corundum brick. Therefore, α-β corundum bricks and β corundum bricks are ideal refractory materials for cooling parts and other parts when the temperature is lower than 1350 degrees Celsius.
2.The part not in direct contact with glass liquid
The part of the pool wall of the melting part and the cooling part that is not in direct contact with the molten glass (also called the breast wall). This area is mainly affected by the erosion of alkali steam and batch materials. Depending on the design, some use corundum material, and some use silicon Brick, these two materials can meet the requirements. Therefore, hook-turn and straight bricks are often used in this part.
1.Regenerator and side wall
The inner surface of the regenerator wall and side walls are corroded by high temperature, dust, and alkali vapor. From top to bottom, the degree of erosion gradually weakens. The temperature and the degree of erosion are different to determine. The top and side walls are generally recommended to use silica bricks and high-quality silica bricks. The middle side walls are generally recommended to use low-porosity clay bricks and high-alumina bricks; the lower part of the kiln generally uses general clay bricks and low-porosity clay bricks. According to different designs, in recent years, ordinary magnesia chrome bricks and alkaline bricks such as direct combined magnesia chrome bricks and magnesia alumina bricks have also obtained good results in the side walls.
2.Checker brick body
The grid body is subject to high temperature load, dust and alkali vapor, and the degree of erosion will be more severe than that of the sills and side walls, so the use conditions are more severe. The blockage and collapse of the grid are often one of the important reasons for the shutdown of the glass furnace for cold repair. Therefore, the lattice refractory is required to have high physical strength, low creep rate, strong defense against alkali corrosion due to changes in furnace temperature and atmosphere, no adhesion of dust, and slow damage.
At the top of the grid: the temperature is higher, which can reach 1400-1540°C, and it is more severely corroded by alkali vapor and dust. Generally, fused and combined magnesia bricks are used. Since there are less silicates in the fused magnesia bricks, the periclase crystals have grown, and the periclase crystals have formed a direct bond, delaying and preventing the periclase crystals from increasing gradually under the action of alkali vapor Speed, it is not easy to crack and chalk the bricks.
The upper part of the checker brick body : The temperature here can reach 1100-1430℃, and it is generally sufficient to use 95# combined with magnesia bricks.
The middle part of the checker brick body : the temperature is 800-1100°C, and the alkali metal sulfate is condensed in the range of 800-1100°C. The magnesium and calcareous checker brick body is severely corroded by SO3 and Na2O and chemical reactions occur, which will cause larger bricks. The body swells and the damage is serious, so this part is not suitable for magnesia bricks. Instead, magnesia-aluminum spinel bricks should be used or directly combined with magnesia-chrome bricks or magnesia-zirconium bricks and forsterite bricks.
The bottom of the checker brick body : This section has low operating temperature, heavy load, and is less corroded by alkali, but it is relatively close to the flue and is directly affected by cold air. The material required should be able to withstand rapid cold and heat, and the price is low. Therefore, low-porosity clay bricks with relatively low prices are generally used.