have a high expansion coefficient and there are seven crystal forms, which need to be fully transformed to ensure that the silicon bricks will not crack during use. Because the shapes of these seven crystal forms are different, a certain proportion of cementing agents, such as lime and iron scale, are usually added during the production process to accelerate the transformation of the crystal form. Only when the crystal form is completely transformed will the silica refractory bricks not have problems such as cracks.
After firing, spots of varying depths may appear on the surface of silica fire bricks. These spots are the manifestation of residues on the surface of the brick after the crystal form is fully transformed. The color of silica firebricks is usually yellow or slightly reddish yellow, and sometimes it may be white and yellowish. Although there are spots on the surface, this does not affect any performance indicators or quality issues.
Silica bricks are fired in a reducing atmosphere. During the firing process, the temperature rise below 600℃ should be carried out slowly; in the stage from 700℃ to 1100℃, the temperature can be raised quickly and evenly; and between 1100℃ and the firing temperature of 1430℃, the heating rate should be reduced and kept uniform to avoid cracks in the bricks. In the high temperature stage, the temperature distribution in the kiln must be uniform to prevent the high temperature flame from directly impacting the bricks.
During the cooling process, especially when cooling below 600℃, the temperature should be lowered slowly to prevent cracks. At the same time, there needs to be enough insulation time, generally between 20 and 48 hours. This is why the length of the tunnel kiln for firing silica firebricks usually needs to be more than 150 meters, and shorter tunnel kilns cannot meet the firing requirements of bricks.
In addition, the particle ratio of silica refractory bricks is also crucial. The particle size should generally not exceed 3mm, and many manufacturers control it below 2.5mm. Different particle ratios have a significant effect on the performance of silicon bricks. If the particles are too large, the expansion coefficient of the silica firebrick raw materials will be difficult to control, which is easy to cause size expansion. The process ratio and firing process of this bricks are extremely important. Only by strictly controlling the production process can qualified products be produced. Although spots may appear on the surface of silicon bricks, these spots are the result of complete transformation of the crystal form and have no effect on the quality of the product.
Although the light-colored spots on the surface of silica bricks may affect their appearance, these spots have no effect on the quality of silica refractory bricks. The color of silicon firebricks is usually yellow or slightly reddish yellow, and sometimes it may be white and yellowish. These color changes are mainly due to the transformation of different crystal forms and the distribution of residues during the firing process.In general, the light-colored spots on the surface of silica firebricks are the natural result of the transformation of the crystal form during the firing process, and have no negative impact on the performance and quality of silica alumina refractory bricks.
