Testing in the screening process: Spot check every mesh number of the ceramic Sand, to make sure that the single sieve mesh number concentration meets the requirement. Also test the running situation of the equipment.Testing of the mixed sand: Apply scientific sampling method to test whether the residual in each mesh number meets the requirements.Currently, we mainly provide the following size of the ceramic Sand: AFS20, AFS25, AFS30, AFS40, AFS65, AFS75, AFS90, AFS100, AFS125, AFS180, or other customized sand based on customers’ request.
Because of the grain shape of the spherical sand, the combination of the ceramic Sand follows normal distribution. Based on the requirements of AFS, different size of the ceramic Sand is mixed and stirred.
The traditional screening method for foundry sand is called three-screening method, which means that the concentration of three consecutive sieves is more than 75%. But this could not satisfy the need of the ceramic Sand, which is concentration of single sieve is more than 85%, and residual of two consecutive sieves is less than 15%. Because of the negative effect from the aluminum carbonate fiber and iron, the result of the screening is as follows:14Mesh: 0.141mm，70Mesh: 0.212mm，20Mesh: 0.85mm，100Mesh: 0.153mm，30Mesh: 0.6mm，140Mesh: 0.105mm，36Mesh: 0.425mm，200Mesh: 0.073mm，50Mesh: 0.3mm，Over 200Mesh.
The bauxite, as a kind of refractory, could stand for over 2000oC, so we must use electric arc melting to fuse it, by applying low voltage and strong current. The fusing voltage should range from 85V to 130V and the temperature should be over 2200oC. Then the melt mineral liquid forms spherical particles, through the blow of high-pressure air. The pressure of air should be 0.4MPa – 0.5MPa. In the cooling process of forming spherical particles, to avoid cooling pressure, we use slowing cooling and change the structure of the nozzle, so we could get expected size distribution.
The size of the bauxite varies a lot. For easy fusion and easy transportation, the bauxite needs to be atomized into pieces ranging from 30mm to 100mm and process another round of homogenization.
The percentage of Al2O3 in wrought aluminum is different from time to time. To keep the stability of Al2O3 and other minor elements and to insure the mineral phase to be Mullite phase, we need to homogenize bauxite.
Raw aluminum cores contains lots of free water, crystal water, and low melting point components. Using raw aluminum cores to produce consumes large amount of electric energy and it is difficult to eliminate low melting point components, causing the instability of the product and affecting product quality. So it is important and essential to calcine the raw aluminum cores and use wrought aluminum cores (so called bauxite) as main material.
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