Brown Fused Alumina Manufacturing Process and Raw Materials Introduction
The development history of China tabular alumina can be roughly divided into four stages: initial contact stage, understanding and development stage, trial production stage, and development and growth stage.
In the 1970s, Wuhan Iron and Steel Project 07 adopted high-alumina bricks produced with American tabular corundum as raw materials, so that the Chinese refractory industry came into contact with tabular corundum.
It was not until the 1990s that a thorough understanding of tabular corundum was achieved after in-depth analysis. However, due to the control of American technology, it is difficult for Chinese companies to obtain the production technology of tabular corundum. In order to promote the development of national industry, the China Refractory Industry Association attaches great importance to the development of sintered corundum, and the "Eighth Five-Year Plan" and "Ninth Five-Year Plan" development plans are both important research topics. Chinese research institutes and production units have also carried out continuous exploration. During this period, although the electric melting method was tried to produce tabular corundum and passed the technical appraisal, it failed to achieve the expected purpose due to the limitation of the use of technology, and the product performance and physical and chemical indicators did not meet the use requirements, so it did not form a market supply.
At the same time, Shandong experimented with the production of sintered tabular corundum, and Jinan vertical kilns produced sintered tabular corundum. It was not until 1999 that a certain enterprise in Hanzhong, based on extensive research and investigation, joined hands with the technical staff of the new material factory to build a sintered tabular corundum production line with an annual output of 4,000 tons in 2001. In September 2002, it produced products that met the user's requirements, opening the prelude to the large-scale production of sintered China tabular alumina.
Up to now, more and more enterprises have started to build production lines for sintering China tabular alumina. Through nearly 10 years of research and development, China has also successfully achieved the industrialization, scale and localization of sintered tabular corundum.
After years of development, the production process of China tabular alumina is similar, and its basic production process is:
Ball milling
Using Bayer method lightly calcined alumina powder as raw material, continuous ball milling is carried out, and the fineness and specific surface area must meet certain requirements, which is conducive to the sintering and densification of alumina powder.
Balling
The ground powder is balled using a balling disc or a balling cylinder. The formed blank ball must have a certain strength to avoid cracking during transportation to the dryer. The corresponding process optimization design is carried out to properly solve the problems of high moisture content, easy stratification, and difficult drying of the semi-finished balls during the balling process.
Drying
The formed blank ball enters the dryer and uses the countercurrent hot air in the vertical kiln to remove about 15% (w) of moisture. However, the temperature in the vertical kiln must be strictly controlled to avoid cracks and stratification inside the blank ball, or even agglomeration and furnace blockage, which will eventually cause the ball flow to be interrupted and the drying quality to decrease.
Sintering
After drying, the blank ball enters the vertical kiln. The sintering temperature is 1900~1950℃. By controlling the hot air temperature and flow rate in the vertical kiln, a plate-shaped corundum structure with fully developed crystals and complete sintering is obtained.
Refractory ≥ 1800℃, its melting point is as high as 2050℃.
It has a coarse crystal and well-developed a-Al2O3 crystal structure, which greatly improves the creep resistance.
Plate-like crystal structure, small open pores, low apparent porosity, low water absorption; more internal closed pores, good thermal shock resistance and peeling resistance.
No additives are added in the production process. Therefore, the purity is high; the volume stability is good; and the reburning shrinkage is extremely small.
As a high-quality refractory raw material, China tabular alumina is used in various metallurgical equipment and high-temperature kilns due to its unique performance advantages. Sintered corundum is added as the main raw material in most refractory products to improve the performance. With the accumulation and development of China's sintered corundum technology, the production technology and variety system of sintered corundum are becoming more and more mature.
