1, Causes of dents:
1. The thickness of each part of plastic products is different
2. Insufficient internal pressure of mould
3. Insufficient mold cooling
4. Deformation due to insufficient cooling time
In the process of producing products, dents are the most frequent of the undesirable phenomena. The plastic injected into the mold shrinks in volume when it cools. The early cooling part, that is, the surface first hardens, and bubbles will be generated inside. The so-called dents, that is, the slow cooling part produces prominent dents in the direction of bubble shrinkage.
The materials with large shrinkage are easy to produce dents. When the forming conditions are to be changed to eliminate dents, the direction with small shrinkage under the set conditions should be set. That is to say, die temperature and barrel temperature decrease and injection pressure increase, but it should be noted that residual internal stress may be caused.
Because the dent is better to be inconspicuous, if it does not affect the appearance, it is deliberately processed on the mold into a corrosive shape, such as grain, granular, etc. In addition, if the molding material is hips, it is also effective to reduce the finish by reducing the mold temperature. However, once these methods have dents, it is difficult to repair the polished products.
2, Solution:
1. Increase the injection pressure, extend the injection holding time, reduce the barrel temperature and mold temperature, and force cooling at the place where the dent occurs.
2. Short term: fill up the flow edge at the place where the dent occurs, and thicken this part of the edge when there is a narrow part of the material through the edge at the place where the dent occurs.
3. Long term: the thickness difference of the designed products shall be completely avoided, and the reinforcing ribs prone to dents shall be avoided, and the narrow and long shape shall be as short as possible.
