Refractory products made of hollow spheres have good high temperature resistance, good insulation properties, good thermal shock resistance and high strength. Since those materials have low bulk density and low thermal capacity, they can improve the thermal efficiency of high temperature furnaces, shorten the production cycle and significantly reduce the weight of the furnace. It can be directly used in the linings of high temperature furnaces. 

 

Alumina bubble bricks can be used at 1800℃ for a long time. At high temperature, they have good chemical stability and corrosion resistance. But they can keep stable in a hydrogen atmosphere. 

 

Alumina raw materials are melted in an electric arc furnace at 2200℃. When pouring the melt out, blow the melt with high pressure air to make the melt dispersed into small droplets. During the cooling process, the droplets form alumina hollow balls due to surface tension effects. 

 

The hollow balls are screened to remove fine powder and big fragments and particles. Iron is removed with the magnetic iron. Broken balls are removed with a ball selecting machine. Then the alumina hollow spheres are packed as the finished products. 

 

Alumina bubble bricks are made of 70% alumina hollow spheres and 30% sintered alumina powder, bonded with aluminum sulfate, molded by vibration molding in a wooden mold by applying pressure. After drying, the green body is sintered at high temperature or light burned into bricks. 

 Refractory products made of hollow spheres have good high temperature resistance, good insulation properties, good thermal shock resistance and high strength. Since those materials have low bulk density and low thermal capacity, they can improve the thermal efficiency of high temperature furnaces, shorten the production cycle and significantly reduce the weight of the furnace. It can be directly used in the linings of high temperature furnaces. 

 

Alumina bubble bricks can be used at 1800℃ for a long time. At high temperature, they have good chemical stability and corrosion resistance. But they can keep stable in a hydrogen atmosphere. 

 

Alumina raw materials are melted in an electric arc furnace at 2200℃. When pouring the melt out, blow the melt with high pressure air to make the melt dispersed into small droplets. During the cooling process, the droplets form alumina hollow balls due to surface tension effects. 

 

The hollow balls are screened to remove fine powder and big fragments and particles. Iron is removed with the magnetic iron. Broken balls are removed with a ball selecting machine. Then the alumina hollow spheres are packed as the finished products. 

 

When using fused brown corundum or white corundum as raw materials, the frits should be smashed and then processed by removing the ferro-silicon alloy and other impurities. White corundum should be processed by removing the flaky sodium aluminate crystals and other low-melting substances. The impurities are easy to be identified since they have low density and float in the surface of corundum frits. 

 

There are a few harmful ingredients in the corundum which will cause poor sintering or cracking, so corundum should be pre-calcined before use. The residual ferro-silicon alloy is oxidized and decomposed into Fe2O3 and SiO2 at 500-1000℃ and Ti in the minerals can be oxidized into TiO2 (rutile), which can cause large volume expansion. After pre-calcining, the stress caused by those decomposition reactions and oxidation reactions can be eliminated during the pre-calcining process and cracks caused by the volume expansion of those impurities can be avoided during the sintering process. 

 

Fused corundum block has large volume, so it should be smashed with drop hammers and other ways and then pulverized. The pulverized fused corundum is stored by size after screened. Fused corundum is hard and difficult to grind. Therefore it is wet ground by ball mills or vibration ball mills. The grain size can be less than 40μm or even 10μm. The iron in the granular material can be removed with electromagnets and the iron in the fine powder can be washed with acids. 

 

The batching of granular materials should be according to the principles of tightly packing, multilevel ratio, less intermediate particles and more fine powder. This can improve the density and sintering of the products. The additives include aluminum phosphate, phosphoric acid, aluminum chromium phosphate, cellulose and pulp waste solution. Among them, he most promising is active phosphate. Recently, ammonium phosphate is on the trial and achieves good results. The mud should be mixed evenly with a moisture content of 3-4%. After high pressure molding, high dense bricks are obtained. 

 

The fused cast alumina block has high purity. It is difficult to sintere and should be sintered at 1800℃. The type of the kilns used depends on the production scale. For small batch production, high-temperature batch kiln is better. For batch stable production, the small high-temperature tunnel kiln is used. 

 

Zhengzhou Sunrise Refractory is a refractory supplier from China. We provide various refractory materials such as fused cast AZS, fused cast alumina block, silica brick, zircon brick, etc..