1、 Causes of deformation
1. The residual stress caused by the relationship between the shape of the product, especially the forming shrinkage and the thickness of the product.
2. Residual stress due to forming conditions
3. Residual stress during demoulding
4. Deformation due to insufficient cooling time
2、 Associated knowledge
1. The deformation (warping, bending, small wrinkles) of the product is the same as the cause of cracks. I.e. internal defects of products
Residual internal stress. The setting conditions of forming shall be set in the direction of eliminating the internal stress of products. That is, raise the temperature of the barrel
After the mold temperature, the injection pressure should not be too high when the material fluidity becomes better.
2. In order to reduce the residual internal stress, annealing treatment has been carried out, i.e. under the temperature of 10 ℃, 2
More than hours of heating has the effect of eliminating internal stress. But this way of annealing is not used because of its high cost
3. If the cooling water hole of the mold can not cool the product evenly, it will also produce residual stress, which is
It means that the cooling water hole should not be too shallow.
Three, the solution.
1. Instant: fully cool and solidify in the mold (extend the cooling time timer), improve the temperature of the barrel,
Reduce the injection pressure.
2. Short term: make mold cooling uniform.
3. Long term: avoid the difference of product thickness, set gate (1-1) at the place with large product thickness, because
The straight line is easy to cause warpage, which can be made into a large R-curve. The product can be bent reversibly, and the number of ejector rods can be increased,
Increase the draft angle.
4、 Differences in materials:
1. Crystalline materials (polyethylene, polypropylene, polyformaldehyde, nylon) have large molding shrinkage, and also contain
It is easy to cause bias, and non crystalline materials (polystyrene, ABS) are easy to cause residual stress.
1. After molding, it can be kept at room temperature with the appliance, which can slightly prevent deformation, but can not have too much expectation.
2. In thin box forming, the bending caused by the forming temperature is usually caused by thermal expansion alone
(6) Processing of plastic products -- methods to eliminate product cracks