Generally speaking, the refractoriness of refractory bricks indicates high temperature resistance. However, high refractoriness is not necessarily a refractory brick, and other properties must be considered comprehensively. When choosing refractory bricks for glass pool furnaces, this situation will be encountered. Refractory bricks with low refractoriness also have good results. For example, the large bricks of the pond wall use high alumina refractory bricks and electric fused cast zirconium corundum bricks. The former has a refractoriness of 1875℃, while the latter is only 1805℃. However, as a result of the use of soda-lime glass tank furnaces, the former has a service life of only 2 years, while the latter can reach more than 3 years.
High-alumina refractory bricks have high refractoriness, but low life. Zirconia corundum refractory bricks have low refractoriness, but long life. Another type of electro-fused cast corundum refractory brick has a refractoriness of 1875-1900℃. This type of refractory brick can only be used for three years when used in the same occasion. It can be seen that it is not comprehensive to judge the quality of refractory bricks by refractoriness. Refractory bricks with exactly the same refractoriness and chemical composition have different manufacturing methods and very different use effects. Like the chemical composition, clay bricks with a refractoriness of 1730℃, hand-formed and high-pressure formed products are also used as checker bricks in the regenerator. The former is severely damaged during cooling, while the latter becomes slightly damaged. Refractory bricks should not only be judged by refractoriness, but also selected according to properties such as strength and thermal shock resistance.
Therefore, it is impossible to imagine all the characteristics of refractory bricks based on their characteristics. This is like a blind man touching his feet, and when he touches his feet, he thinks that the elephant is a big pillar, which is indeed wrong. If the refractory bricks with known refractory properties are crushed into extremely small particles and reshaped by appropriate methods, the refractory properties will change. It can be seen that the structure of refractory bricks has a great influence on refractory properties. Therefore, judging its refractory properties by average chemical composition is also one-sided.
From the above analysis, it can be seen that the selection of refractory bricks must not be just one or two performances, but also a comprehensive analysis of all the properties of refractory bricks, through small-scale tests, and then evaluate its applicability.
The use conditions and types of refractory bricks in the main parts of the melting furnace
1. Peak.
The top of the melting part and cooling part of the glass melting furnace (including the arch), these parts are at a working temperature of 1600 degrees. The refractory materials used in these parts must withstand the scouring effect of high temperature, load, alkali vapor and matching materials. Therefore, the refractory materials used as the top must have extremely high refractory, high load softening temperature and good resistance to deformation, and the thermal conductivity is small. The refractory materials at high temperature cannot pollute the glass liquid, the material capacity is also small, and the high temperature strength is good. High-performance high-purity silica bricks have the above characteristics: 1. The load temperature is high and close to the refractory 2. Good high-temperature stability and high compressive strength 3. The main component SiO2, the content is >96%, which is the same as the main component of glass. The erosion under high temperature conditions will hardly pollute the glass liquid 4. The price is cheap. Therefore, at the top of various glasses, high-purity silica bricks have become a priority in various glass production processes.
The chemical erosion caused by the high-temperature chemical reaction of the flying material and the alkali vapor and the refractory material, the phase transfer and the crystal changes and structural density changes caused by the temperature are the main reasons for the damage of the tower bricks. The research results show that the etching process of the glass kiln silica bricks at the top under the high temperature of the kiln is basically caused by impurity transfer and impurity phase change, and chemical erosion and melting can be basically ignored. The phase change and self-purification effect gradually change the performance of the kiln operation belt and improve its high temperature performance.
2. Pool wall.
a) Part in contact with glass liquid.
The part of the pool wall of the melting part and the cooling part that directly contacts the glass liquid is subject to high temperature, chemical erosion caused by the glass liquid and mechanical and physical scouring caused by the flow. The main condition for the refractory material is to have good resistance to glass liquid erosion and not to pollute the glass liquid. Domestic glass kilns are generally built with fused zirconium corundum bricks, α-β corundum bricks, and β corundum bricks. Fused zirconium corundum bricks have excellent high temperature and glass liquid resistance. They are eutectics of badly zircon and α-Al2O3 with very good corrosion resistance that cannot be obtained by sintered refractory materials. They are very suitable as pool wall bricks for the melting part of the glass kiln. 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 zirconium corundum brick, it does not contain ZrO2 crystals, and its reaction layer viscosity is small. It is not very stable at high temperature. Therefore, the diffusion rate between the brick surface and the glass liquid is large, and the kiln lining is damaged quickly. However, when the kiln operating temperature is lower than 1350℃, the corrosion resistance of α-β corundum brick and β corundum brick is better than that of fused zirconium corundum brick. Therefore, α-β corundum brick and β corundum brick are ideal refractory materials for cooling parts and other parts when the temperature is lower than 1350 degrees Celsius.
b) The part that is not in direct contact with the glass liquid.
The part of the pool wall of the melting part and the cooling part that is not in direct contact with the glass liquid (also called the chest wall), this area is mainly affected by the scouring of alkali vapor and matching materials. According to different designs, some use corundum materials and some use silica bricks. Both materials can meet the requirements. Therefore, hook rotation and straight bricks are often used in this part.
3. Regenerator.
(1) Regenerator and side walls.
The inner surface of the regenerator and side walls is corroded by high temperature, dust and alkaline vapor. The degree of corrosion gradually decreases from top to bottom. The selection of refractory materials depends on the temperature and degree of corrosion of the upper, side walls, middle and lower parts of the glass kiln regenerator. Silica bricks and silica bricks are generally recommended for the upper part and side walls, low-porosity clay bricks and high-alumina bricks are generally recommended for the middle side walls, and general clay bricks and low-porosity clay bricks are generally selected for the lower part of the kiln. According to different designs, in recent years, in the side walls, ordinary magnesia-chrome bricks and direct magnesia-chrome bricks are generally used for the upper part, and alkaline bricks such as magnesia-alumina bricks have also achieved good results.
(2) Lattice.
Since all bricks of the lattice are under high temperature load, they are corroded more severely than the skin and side walls under the action of dust and alkaline vapor, and the use conditions are more stringent. The blockage and collapse of the lattice are often one of the important reasons for the shutdown of the glass kiln. Therefore, the lattice refractory material has high physical strength and low creep rate, and has strong defense against alkali erosion caused by changes in kiln temperature and atmosphere, does not adhere to dust, and has a slow damage rate.
Top of the lattice: The temperature is high, up to 1400-1540℃, and the alkali vapor and dust erosion are serious. Generally, fused magnesium bricks are used. Since there are fewer silicates in the fused magnesium bricks, the quartz crystals grow and the quartz crystals are directly combined, which slows down the speed at which the quartz crystals gradually increase under the action of alkali vapor, and it is not easy to cause the bricks to break or pulverize.
Upper part of the lattice: The temperature in this place reaches 1100-1430℃, and generally 95# fused magnesium bricks can be used.
Middle part of the lattice: The temperature is 800-1100℃. Alkali metal sulfate condenses in the range of 800-1100 degrees. The magnesium and calcium lattices are severely corroded by SO3 and Na2O, chemical reactions occur, large bricks expand, and are severely damaged. Therefore, magnesium bricks are not suitable for this part.
Lower part of the lattice: The working temperature is low, the load is heavy, and the alkali corrosion is small, but it is close to the flue and is directly affected by cold air. The required material should be resistant to rapid cold and heat and cheap. Therefore, low-porosity clay bricks with lower prices are generally used.
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