The powder with high hardness has a large elastic after-effect when pressed, and the elastic after-effect value increases as the hardness of the powder increases. The elastic aftereffect value of WC-Co alloy mixture is generally lower than that of WC-TiC-Co alloy mixture. The elastic aftereffect value of the high-cobalt alloy mixture is lower than that of the low-cobalt mixture, and the high content of powder oxides and impurities will also increase the elastic aftereffect value. The parameters in the hard alloy pressing process are as follows:
Compression ratio: The ratio of the filling height of the powder in the cavity to the height of the compact is called the compression ratio. The main factor affecting the compression ratio is the packing density of the powder. The density of the powder packed in the cavity is slightly larger than the loose packing density of the powder, which is closer to the tap density. The finer the particle size of the powder or the mixed material, the smaller the bulk density, the larger the filling volume, and the larger the compression ratio when compacting the compact with the desired density. In general, the compression ratio of cemented carbide mixture is in the range of 2.5~4.0, the spray material is generally 3.5~4.0, and the mechanical granulation is 2.5~3.0.
Shrinkage factor: The ratio of the size of the compact to the size after sintering is called the linear shrinkage factor. It is related to the compaction density. The greater the compact density within a certain range, the smaller the shrinkage coefficient. The shrinkage coefficient is usually determined by the size of the green compact without delamination, cracks, uncompacted, cobalt pool and the actual measured size after sintering. Due to the non-uniformity of the density distribution of the green compact, the average linear shrinkage factor is actually used. The average linear contraction coefficient can be obtained from the body contraction coefficient.
There are many factors that affect the shrinkage coefficient, involving the quality of the mixture, the molding process, and the product requirements. Such as the composition of the mixture, the density of the powder, the type and amount of the forming agent, the forming method, the shape and size of the product, etc. The finer the powder, the larger the amount of forming agent, the more complex the shape of the product, and the larger the size, the greater the shrinkage coefficient.
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