The production of lightweight corundum bricks by foam method is to mix foaming agent, stabilizer and water in a certain proportion, first make foam liquid, and then mix with alumina slurry, pour molding, curing, drying, baking and firing. , Made of light corundum bricks with high porosity.
The pores in the light corundum brick are formed by the foam specially added to the mud.
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Foam has a decisive influence on the properties of lightweight corundum bricks, and there is no foam in the dry green body. To make a stable foam, some substances must be added to the water to form an adsorption layer on the gas-liquid interface, so that the surface energy of the water is reduced and the foam is stable. Pure liquid will not form a stable foam. To make the foam stable, the surface layer of the foam film must have agglomeration viscosity, and stabilizers are used to increase the viscosity of the formed adsorption agglomeration layer. Substances that are incorporated into water to promote foam formation are called foam formers. Rosin soap or natural "soap root" is commonly used in the production of lightweight refractories. The gas is the dispersed phase, the liquid is the dispersion medium that separates the bubbles from each other, and the presence of the foam is to reduce the surface of the phase-separated bubbles to a minimum. The stronger the surface activity of the bubbles, the stronger the performance of adsorbing solid fine particles, and the stronger the adsorption layer formed. The stability of the adsorption layer is affected by the concentration of the foaming agent. In addition, the pH value of the colloidal solution produced by gas and liquid also affects the stability, and the closer the pH value is to 7, the better.
Rosin soap is prepared with pure rosin, caustic soda and water, and the proportions of the three are 43%, 7%, and 50% in turn. The rosin is melted in a metal container, stirred continuously during heating, and treated with 10% caustic soda solution. , until the rosin is completely saponified and loses its viscosity and has a certain consistency. After cooling to room temperature, wash 3 to 4 times with saturated salt solution by pouring method, and then wash once with pure cold water, the rosin soap is ready for use. When making foam liquids, gelatin is used as a foam stabilizer. Use 40% rosin soap, 10% calcium carbonate, 50% gelatin and enough water, heat and mix to form a homogeneous emulsion (ie, foam forming agent), and then prepare the aqueous solution of the emulsion in a cylindrical foamer. into bubbles.
Add an appropriate amount of clay, alum and water to the alumina powder to prepare a slurry, and then add the prepared foam to the slurry and stir evenly. The total water content of the mixture is about 80%. Then the mud mixed with a lot of foam is poured into the model.
The alumina dispersion component completely covers the surface of the air bubbles, the stability of the air bubbles is quickly improved, the suspension of the fine powder has a viscosity that prevents the disappearance of the air bubbles, and there is foam in the mud.
The raw material of the foamed alumina brick is industrial alumina, which is calcined, pulverized, purified, and made into fine powder with a particle size of less than 30 μm.
The particles should not be too coarse, otherwise the foam will be seriously damaged and the mud will be easily delaminated. The greater the true density of the material, the finer the particles and the greater the dispersion. The optimum pH of the alumina suspension is 2.5-5.
Increasing the foam content can reduce the density of the green body. If the structure of the mud material added to the foam is not uniform, although the content of the foam is increased, the effect is not necessarily good.
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The role of the liquid phase (water) is very important. When the liquid phase is insufficient, the density of the foam mud is high. This is because the viscosity of the suspension is too large, causing the mud to not stretch and the bubbles to be destroyed. The stable foam in the mud is the result of the optimum moisture of the suspension. If the moisture is too large, the shrinkage of the green body increases, and the bubbles are easily combined together.
At present, the foam method is used to produce lightweight refractory corundum bricks, which are basically still formed by pouring. The formed blanks and molds are dried in a drying room at 60-70 °C for about 4 days and demoulded, and then properly dried. Finally, it is fired at 1300～1550℃, and the total firing time is 50～60 h. The fired light corundum bricks usually do not have accurate shape and size, so the light corundum bricks after leaving the kiln should be cut by machine or by hand. Lightweight corundum heat-insulating bricks with a temperature of 1500-1700 ℃, and a thermal conductivity of 0.17 W/(m·K).
In the industry, we have fully mastered the process technology of foam production of light corundum refractory materials, and can produce various types of light corundum refractory materials according to user conditions. Some literatures introduce: unburned or pre-burned industrial alumina can be used, and finely ground TiO22% can be added. Use colloidal rosin, saponin, hydrolyzed resin, etc. to make foam. The so-called colloidal rosin is prepared from rosin soap (alkali salt of rosin acid) and water glue (1% to 2%). The foam mud is poured into the model, the green body is dried, and TiO is added. The green body should be fired at 1550 ℃. The green body without TiO2 was fired at 1740°C.
The foam mud can be dispensed into the model made of stainless steel sheet, the green body is dried in the model at 30-40 ℃ for day and night, then the model is removed, the semi-finished product is ribbed, and dried for 2 days and night. After 48 hours of firing in a batch kiln, the final temperature was 1600 °C and the temperature was kept for 6 hours. In the cooling process, it should be noted that the cooling rate above 800 °C does not exceed 100 °C/h, and the rest is 40 ~ °C/h. And the shape and size of lightweight corundum bricks are machined.
In order to improve the stability of the mud after foaming, 0.3% bone glue can be added during beating. The bone glue must be added after dissolving, otherwise there will still be lumps remaining in the mud. Models are generally made of cork or aluminum. The working surface in the mold should be smooth and not cracked, and should be brushed with oil.
According to the pouring place during molding, it is divided into two types: kang pouring and tunnel drying pouring. In some factories, the frequency is 2500 times/min, and the vibration is 30-60 S for pouring, and good results are obtained.
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After drying, the residual moisture of the bricks can be kiln fired when the residual moisture is below 3%. When the foam bricks are installed in the kiln, they should be erected or placed on the upper part of the dense and lightweight corundum bricks. The bricks with high density should be installed in the lower part, and the bricks with low density should be installed in the upper part of the kiln. extrusion. Cover protection should be provided for some bricks that are in direct contact with the flame. The fired light corundum bricks must be cut and ground.
When corundum bricks are produced by the foam method, the volume shrinks during firing, and the pores in the film are eliminated due to sintering, but it has no effect on larger air pores.
The foam method can produce high-quality light corundum light corundum bricks, but the process procedures are more and more complicated.
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