Alumina Bubble Bricks are made of alumina hollow balls and alumina powder as the main raw materials, combined with other binders, and fired at a high temperature of 1750 degrees. It belongs to a kind of ultra-high temperature material energy-saving thermal insulation material.
Performance
The Al2O3 content of alumina hollow ball bricks is not less than 98%, the SiO2 content is not more than 0.5%, the Fe2O3 content is not more than 0.2%, the bulk density is 1.3~1.4g/cm3, and the apparent porosity is 60%~ 80%, the compressive strength is not less than 9.8MPa, the soft temperature under load (0.2MPa) is not less than 1700℃, and the thermal conductivity is 0.7~0.8W/(m?K).
Manufacture First prepare alumina hollow spheres, and then make Alumina Bubble Bricks.
Step 1. Preparation of alumina-aluminum hollow spheres
The preparation of alumina hollow spheres is made of industrial alumina as raw material, which is melted by electrofusion method and then sprayed. The electric melting equipment is an electric arc furnace. The molten pool is made of graphite products or other refractory materials, a flow port is built on the edge, and a compressed air nozzle is installed outside the flow port. The nozzle is connected with the compressed air device by a pipe; the furnace body can be tilted; the electrode is made of graphite.
After adding industrial alumina powder into the molten pool, it can be powered and melted. When the temperature of the molten metal reaches or exceeds 2200 °C, the molten molten metal rolls, that is, the furnace body is tilted to make the molten molten metal flow out; Due to the effect of melt viscosity and surface tension, the melt forms a hollow sphere wrapped with air during the blowing and condensation process. After collection and screening, they are stored separately as different particles.
The proportion of the number of alumina hollow spheres with different particle sizes varies with the injection pressure of compressed air. The greater the pressure, the more the number of small spheres.
The wall thickness of the hollow sphere varies with the particle size. When the particle size fluctuates in the range of 5-0.5mm, the wall thickness correspondingly fluctuates in the range of 0.3-0.1mm.
The larger the particle size of the hollow sphere, the smaller its natural bulk density; the smaller the particle size, the larger its natural bulk density. For example: when the particle size is 5.13-3.22mm, the natural bulk density is 470g/L; when 3.22-2.0mm, 670g/L; when 2.0-1.0mm, 810g/L; 1.0 ~0.5mm, 915g/L.
Step 2: Making Alumina Bubble Bricks
Manufacture of alumina hollow ball bricks The alumina hollow balls, sintered alumina fine powder and binder are batched, shaped, dried and fired in a certain proportion to obtain alumina hollow ball bricks.
Alumina fine powder is made from industrial alumina as raw material, calcined at 1500℃, ground, pickled and dried.
The binder used in brick making is usually aluminum sulfate aqueous solution or aluminum dihydrogen phosphate aqueous solution.
The particle size of alumina hollow spheres is generally 5-0.5mm, the rainfall is 65%-70%, the amount of alumina fine powder is 30%-35%, and the amount of binder is 5%.
The above materials are mixed evenly and formed by vibration molding method. After drying, the bricks are fired at 1500-1800 °C to obtain fired bricks; unfired products can also be produced without firing, or the furnace lining can be directly constructed with amorphous materials.
Application of Alumina Bubble Brick
Alumina hollow ball bricks are mainly used as linings for high-temperature industrial kilns below 1800°C, such as lining bricks for high-temperature kilns in refractory, electronics, and ceramic industries; thermal insulation layers for high-temperature thermal equipment, such as petrochemical industrial gas Insulation bricks for chemical furnaces, gas making furnaces, carbon black industrial reactors, and induction furnaces in metallurgical industry. Application in the above fields can save energy by 20% to 30%. This kind of brick is used as the lining of high temperature kiln, and the heating speed should not be too fast during baking, otherwise cracks will occur and the strength and service life will be reduced; because of its high apparent porosity, it cannot be used in the part that contacts the slag, otherwise it will Damaged by penetration of slag.
