Forming is a very important process in the production process of sintered Corundum Fire Resistant Brick products. Most Corundum Fire Resistant Brick products are formed by semi-dry method on friction brick press or hydraulic press. Products with complex shapes and large sizes are rammed with air hammers, vibrated and cast by isostatic pressing.
The mold used for semi-dry pressing is made of metal, and the molding mold has a direct impact on the quality of the product.
If the hardness of the contact part between the mold and the mud is not uniform enough, soft spots will appear during use, resulting in potholes and corrugated grooves, and layered cracks will appear in the brick during the brick production process; if the mold hardness is too low, wear and tear Seriously, the corresponding adobe section is enlarged accordingly. When the enlarged adobe section passes through the smaller section above, the Corundum Fire Resistant Brick adobe is subjected to considerable extrusion force, resulting in dendritic cracks or mouths. Edge cracks; if the rigidity of the mold is not enough, the brick will be repeatedly subjected to the elastic action of the mold to cause longitudinal cracks; if the strength of the mold is not enough, it will not only be damaged quickly, but also the deformation of the bottom plate or the punch will cause the brick to be twisted; if If the finish of the mold is not enough, the resistance of the top brick will be increased, and the density difference of the brick brick will be increased due to the increase of the upper and lower pressure difference of the brick brick. Because the mold is a composite component, it can withstand the strong force of the press and the abrasive effect of the bricks. Therefore, the mold must have sufficient comprehensive strength, certain toughness, high hardness and wear resistance. Some data believe that the hardness of the mold is not less than 0.8 of the hardness of the refractory particles. As we all know, the hardness of corundum is very high (Mohs hardness is 9), and the mold is generally not easy to meet the requirements of corundum bricks. In recent years, my country’s refractory molds have achieved rapid development. Cemented carbide (YG series) insert molds, steel-bonded cemented carbide (GT series) insert molds, alloy tool steel molds, etc. have replaced the past carbon steel molds. Sintered corundum refractory plays a very good role.
The most important parameter that determines the density of Corundum Fire Resistant Bricks in semi-dry pressing is unit pressure.
When forming pure corundum products with sintered corundum clinker and fused corundum as the main raw materials, the pressure is increased from 20~30MPa to 70~80MPa, and the porosity of the green body and the product is correspondingly reduced by 15%~20% (from 23% to 19%~20%); the pressure is increased to 120MPa, but the effect on the density of the adobe is very small. Only by taking a large pressure, that is, above 200~500MPa, can the density of the bricks increase greatly. It is obvious that the high pressure destroys the corundum particles. Under the pressure of 150MPa, many particles are destroyed. The pressure increases to more than 500MPa, which can disperse and redistribute the fine powder raw materials. down to 2.5), the average size of pores is reduced from 55~60Mm to 10Mm, and the high temperature creep is also reduced a lot
When the molding pressure is high, the content of fine powder in the mud must be reduced, generally to 15%~25%, otherwise it is easy to cause overpressure of the green body. This deteriorates the sintering performance of the product when it is fired. However, according to the existing factory equipment level in my country, it cannot guarantee that a large number of corundum products are formed by high pressure, so the molding of sintered corundum products should generally be 60~100MPa or 80~100MPa according to the shape and size of the product. Formed under 130MPa pressure.
When making dense products with fine powder (less than 10Mm) activated sintered material, the unit pressure of molding should be no more than 25~30MPa (generally 10~15MPa), because excessive pressure will cause overpressure. The equation for the relationship between the porosity of the Corundum Fire Resistant Brick and the molding pressure is as follows:
The constant a of the corundum mud, which represents the capacity of the mud to fill the volume without external force, is between 32 and 64. The constant # represents the effect of molding pressure on mud filling and is in the range of 3 to 9. The porosity of sintered corundum clinker increases, and the two constants increase. There is also a relationship between these constants of corundum mud, b=0.2a-4.
