JPH0138073B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a silica brick, and particularly to a silica brick that has extremely excellent thermal shock resistance and is suitable for use in hot repairs of kilns. [Prior Art] As is well known, conventional silica bricks have extremely poor resistance to rapid heating and cooling and are extremely susceptible to cracking. The reason for this is that when the main mineral phases, tridymite and cristobalite, suddenly change their crystal structure at a temperature in the range of 150 to 250°C, they undergo a large volume change, resulting in abnormal expansion or contraction. Therefore, it has been impossible to bring conventional silica bricks from cold to a furnace for repair without preheating. In order to prevent cracking at this time, a method used in the past was to preheat the silica bricks to over 400 degrees Celsius and then bring them into the furnace for repair. However, there are major problems in terms of safety and workability, and this method is rarely practiced at present.
Therefore, we recommend using other types of bricks, such as clay bricks, which are difficult to break even if the bricks are brought into a hot furnace at room temperature.
High alumina bricks, silicon carbide bricks, etc. have also been used to repair coke oven carbonization chambers. However, when used in a part of a completely different type of silica brick wall, gas leaks may occur from the joints between the bricks and the strength of the inserted bricks may deteriorate due to the difference in hot properties, especially the coefficient of hot linear expansion. Because of this, the desired effect has not been achieved. On the other hand, fused silica brick has an extremely small coefficient of hot linear expansion and contraction, as is well known, and therefore is extremely resistant to cracking even when heated rapidly. Even if these bricks are brought into a hot kiln at room temperature, they will not crack and can be used for repairs. However, when used continuously, particularly at temperatures above 1100°C, cristobalite transition occurs, the molten volume expands, the brick structure becomes brittle, and its strength deteriorates. Therefore, it is recognized that it cannot withstand long-term use in furnaces such as coke ovens. Semi-silica brick, which has intermediate properties between silica brick and clay brick, has a low coefficient of hot linear expansion and is relatively resistant to cracking. However, since the creep resistance in the high temperature range is significantly lower than that of silica brick, it has not been put to practical use in repairing coke oven carbonization chamber walls due to insufficient strength of the structure. [Object of the Invention] The object of the present invention is to solve the above-mentioned problems of the prior art, to provide a material with extremely excellent thermal shock resistance, and to be able to be brought into a hot kiln at room temperature for reloading or repairing brick walls. To provide a silica brick that does not crack under any conditions and can be used continuously as it is. [Structure of the Invention] The silica brick of the present invention contains 30 to 70% by weight of coarse particles of fused quartz having a particle size of 0.7 mm or more and 70 to 30% by weight of silica stone. (All percentages in the following content percentages are by weight.) Conventional fused silica bricks use a considerable amount of quartz glass in the form of fine powder, so at temperatures above 1100°C, this quickly converts to cristobalite. This was the main cause of the deterioration of the brick structure. The present inventors focused on improving this point, examined the degree of transition depending on the particle size of the fused silica raw material, and found that if coarse fused silica particles and silica stone were used together, extremely stable quality could be achieved under hot conditions. I found it. The silica brick of the present invention was created based on this knowledge. The present invention will be explained in detail below. The particle size of the coarse particles of fused silica used in the present invention is 0.7 mm or more. This is because when the grain size of fused silica is smaller than 0.7 mm, the rate of transition to cristobalite increases. Table 2 below
Table 1 shows the relationship between the particle size and transition rate of fused silica (quartz glass) having the composition shown in Table 1. Table 1. Example of chemical composition of fused silica raw material Component % SiO ₂ 99.50 MgO 0.07 TiO ₂ 0.04 Na ₂ O 0.03 Al ₂ O ₃ 0.05 K ₂ O 001 Fe ₂ O ₃ 0.08 Ig・loss 0.20 CaO 0.04

〔Example〕

It has the chemical composition shown in Table 1 above, and has a density of 2.203.
Three parts by weight of slaked lime and pulp waste liquid were added as a binder to 40 parts by weight of coarse particles of fused quartz having a particle size of 3 to 0.7 mm, 60 parts by weight of the calcined silica stone raw material, and 1 part by weight of boric acid, and the mixture was thoroughly kneaded to obtain brick clay. This was molded into a predetermined size, dried, and then fired at 1170°C to obtain a silica brick. Table 3 shows the composition of the fired silica stone raw material used and the composition of the manufactured silica brick.

〔Effect of the invention〕

As detailed above, the silica brick of the present invention has the following excellent effects and is suitable for use in hot repair of kilns such as coke ovens. Compared to conventional coke oven hot repair bricks, it has significantly better thermal shock resistance and has long-term durability even after repair, making it very useful for furnace maintenance. Preheating is not required at all during hot repair, and it is excellent in terms of safety and workability. Since the silica brick in the damaged area can be replaced with a homogeneous brick, gas leaks from the brick joints can be prevented.

Claims (1)

[Scope of Claims] 1. A silica brick characterized by containing 30 to 70% by weight of coarse particles of fused quartz having a particle size of 0.7 mm or more and 70 to 30% by weight of silica stone. 2. The silica brick according to claim 1, which has a hot linear expansion coefficient of 0.8% or less at 1000°C. 3. The chemical composition is: SiO ₂ 93-98% by weight, Al ₂ O ₃ 0.5-3.0% by weight, Fe ₂ O ₃ 0.5-3.0% by weight, CaO 1.5-3.0% by weight, B ₂ O ₃ 0.5% by weight or less. A silica brick according to claim 1 or 2.