In July 23 tons refractory high alumina bricks are packed for delivering to customer in Korea . High quality and best price refractory material and products in Topower Refractory.
We produce high-quality high-alumina bricks. Some customers may face the situation of black-hearted high-alumina bricks. Zhuolipu's professional sales staff will answer for everyone.
What are the three main reasons for the "black heart" of high-alumina bricks?
1. Raw materials
The main raw material for producing high alumina bricks is bauxite. The higher the Al2O3 content of high-alumina bricks, the higher the grade of the selected bauxite, that is, first-grade or special-grade bauxite. However, the iron oxide content and titanium dioxide content in high-grade bauxite are often high. Iron and titanium ions are coloring ions. The presence of iron and titanium compound impurities makes it possible for high-alumina brick products to produce "black hearts". The higher the impurity content, the greater the possibility of high-alumina brick products to produce "black hearts".
The coexistence of iron and titanium impurities and oxides has different effects on the coloring of products. When titanium ions exist alone, the coloring is not significant and the product is slightly blue; when iron ions exist alone, the product is orange-brown. The coexistence of iron and titanium ions can increase the coloring and sintering of alumina and produce "black hearts" even in an oxidizing atmosphere. Under reducing atmosphere conditions, the presence of ferroxenic ions alone or together can color the product and cause "black heart" to varying degrees, but the coexistence of ferroxenic ions is more serious than the single presence of ferroxenic ions. In addition, the presence of low-melting materials (such as CaO, MgO, K2O+Na2O, etc.) in the raw materials reduces the firing temperature of the product, promotes the sintering of the product, and increases the amount of liquid phase during the firing process of the product. Therefore, at a lower temperature, under the impetus of unreasonable factors, the movement of ferroxenic ions is accelerated, the coloring reaction is promoted, and the "black heart" of the product is accelerated.
2. Brick stacking method
The loading position and loading method of high alumina bricks also affect the degree of "black heart". If the loading position of high-alumina bricks is near the combustion chamber designed in the tunnel kiln, that is, close to the flame position, the flame will heat the product rapidly, and the local temperature rise rate will be faster, which will aggravate the coloring reaction of iron ions; if the brick density is large or the loading is unreasonable, the fire channel between the brick columns is small, there is no rice bran or less rice bran between the two bricks, so that they form a "face-to-face" and the bricks are less exposed to fire, the heating is uneven, the oxidation atmosphere between the bricks is insufficient, and the heat is rapidly transferred between the bricks in the form of heat conduction. Then, the heated bricks heat up quickly, and the following reactions will occur at high temperatures. In this way, the coloring changes from light red to brown and black, which deepens and aggravates the coloring of the brick surface, resulting in the generation of "black heart".
3. Firing atmosphere and heating rate
Firing atmosphere and heating rate are very important conditions for the generation of "black heart" of high-alumina bricks. If the raw materials contain a lot of Fe2O3, FeO, and TiO2 impurities, and the temperature rises too fast during firing, that is, the temperature and oxidizing atmosphere in the rear area of the preheating zone and the front area of the firing zone are very strong, then the degree of "black heart" of high alumina bricks will be aggravated. The firing temperature of high-alumina bricks above the first grade is relatively high, and an oxidizing atmosphere is used. For example, the average firing temperature of high-alumina bricks with an Al2O3 content of more than 60% is 1450℃. A strong oxidizing atmosphere is used, and the air excess coefficient a is not less than 1.15. When firing high-alumina bricks in a high-temperature tunnel kiln, the temperature in the rear area of the preheating zone must meet the basic temperature requirements. For a shorter high-temperature tunnel kiln, if there is any improper operation during the heating operation, the temperature will rise too fast, causing the oil gun in the front area of the firing zone to spray a large amount of oil, and the flame will be thick. After the circulating stirring air curtain in the rear area of the preheating zone, the flame becomes clear and the temperature rises, so the basic temperature of the preheating zone will increase significantly. At this high temperature and under the reducing atmosphere formed by the local flame, the Fe2O3 (pink) in the brick will decompose into FeO (dark brown), and the TiO2 in the brick will partially transform into Ti2O3. Ti2O3 synthesizes black FeO·Ti2O3 spinel with Feo at high temperature. The common result of the reaction of Fe2O3 and TiO2 is to deepen the color of the brick body and increase the degree of "black heart" of the product. Therefore, if the firing is too fast, the temperature rise operation is improper, and the atmosphere is not reasonable, the "black heart" of high-alumina bricks will be aggravated.
