The production of high alumina bricks usually uses soft clay or semi-soft clay as a binder. The role of clay in the compounding is to improve the molding properties of the mud and to make the molded and dried body have a certain strength. However, during the firing process, the free si02 in the clay and the free Alz0 in the high alumina bauxite clinker occur a secondary mulliteization reaction, and this reaction intensifies as the amount of combined clay increases. The stronger the secondary mullite chemical effect, the higher the porosity of the burned product, and the greater the possibility that the strength and bulk density will decrease. For this reason, the amount of binding clay added to the ingredients should be minimized. The mixing amount of clay powder in the first-class high alumina brick is generally 5%, and the mixing amount of the second-class high alumina brick is generally not more than 10%; when the third-class high alumina brick is produced, because the third-class bauxite clinker does not contain free Al203, The amount of combined clay added can be determined according to the process conditions such as molding and firing and the requirements of the product, without considering the problem of secondary mullite petrochemical.
In order to obtain high alumina bricks with stable volume, high alumina bauxite powder can be used as a binding agent or high alumina rock powder and clay powder can be mixed in a predetermined ratio to prepare synthetic mullite as a binding agent. If full clinker or raw rock soil is used instead of bound clay, it is the most thorough way to eliminate the volume expansion effect produced by the secondary mullite reaction.
The particle composition has an important influence on the density of the green body, the density and the strength of the product. Therefore, the principle of determining the composition of the particles is: a good bulk density should be formed without adverse effects on the product performance and appearance quality. For Ⅱ class bricks, the volume expansion caused by the secondary mullite reaction should also be considered. High alumina bricks usually use coarse, medium and fine three-level ingredients, but two or four-level ingredients can also be used.
In general brick making process, the upper limit of coarse particles is 2-3mm, and the mixing amount is 40-50%; for special-shaped products, the upper limit of coarse particles can be reduced to 1-2mm, and the intermediate particles are limited to 10-20%; fine powder is generally At 40-50%.
What are the effects of different particle size particle production processes
(1) The critical particle size of the coarse particles should be appropriately increased. The critical particle size of the coarse particles and the amount added to the mud can be increased. When the fine powder is sufficient, the bulk density and molding performance of the mud can be improved. The small specific surface area can weaken the secondary mullite petrochemical effect and facilitate the sintering of the bricks, thereby reducing the porosity of the product, and improving the starting temperature of load softening, thermal stability and mechanical strength.
However, when the critical particle size increases to 4-5mm, the edges and corners of the product and the uniformity of the structure will be affected. Moreover, the larger the clinker particles, the greater the particle segregation during the production process. Therefore, the maximum critical particle size of the high-alumina mud is 3mm.
(2) The fine clinker powder is beneficial to the sintering of the green body and increase the density of the product. In particular, the appropriate amount of fine powder can not only adjust the secondary mulliteization effect of the brick during firing to the fine powder, but also the volume shrinkage produced by the strong sintering effect of the fine powder can weaken or offset the internal factors of the brick. The expansion and loosening of the green body caused by the submullite petrochemical reaction, but too much fine powder will cause difficulty in forming, and the green brick is prone to spalling and large firing shrinkage during firing. Therefore, the appropriate amount of fine powder added is about 50%.
(3) The intermediate particles in the intermediate particle ingredients have neither the skeleton function of coarse particles nor the sintering function of fine powder. Therefore, in the production process, according to the specific production
The amount of intermediate particles added is usually limited to the minimum amount. Generally speaking, reducing the amount of intermediate particles added can improve the bulk density of the mud and increase the body of the product.
Build density and improve its thermal stability. However, if all the intermediate particles are eliminated, under the condition of larger coarse particle size, the product will not only produce cracks and poor appearance quality after burning, but also bring certain difficulties to the handling of materials. Therefore, the appropriate amount of intermediate particles should be about 10%.
Preparation of mud for high alumina bricks
First, prepare the clay mud. The clay mud is prepared in a mud mixer, the density of the mud is 1.50~1.65g/cm3, and the temperature is 50~70℃.
The mud is prepared in a wet mill. The preparation procedure is as follows: first unload the cone material into the wet mill according to the ingredient ratio, add the clay slurry and the sulfite pulp waste liquid, mix for 2 to 3 minutes, then add the drum mill, and then mix for 10 to 20 minutes.
The moisture content of the mud should meet the following requirements:
Generally 5.5~6.5% of high alumina bricks; 5.3~5.8% of blast furnace high alumina bricks, 9.2~9.7% of hand-formed high alumina bricks with a unit weight of more than 60kg, and 9.7~10.2% of high alumina bricks with a weight less than 60kg. 61~66% of high-alumina bricks; 6.8-7.3% of high-alumina bricks with a height of less than 200mm.
The mud should be trapped after mixing. Material trapping conditions: temperature 15~30℃, relative humidity above 80%, time not less than 20h. The wet sack should be covered during the trapping period to reduce water evaporation.
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