1. Uneven wall thickness of the product causes uneven surface shrinkage, resulting in shrinkage marks.
2. Causes and solutions
1. Improper control of molding conditions. Appropriately increase the injection pressure and injection speed, increase the compression density of the solution, extend the injection and pressure holding time, compensate for the shrinkage of the melt, and increase the injection buffer. But the pressure can not be too high, otherwise it will cause convex marks.

If the depression and shrinkage occur near the gate, it can be solved by extending the pressure holding time; When the plastic parts are depressed at the wall thickness, the cooling time of the plastic parts in the mold should be appropriately extended; If the local shrinkage of the melt around the insert causes depression and shrinkage marks, which is mainly caused by the temperature of the insert is too low, the temperature of the insert should be increased; If the surface of the plastic parts is depressed due to insufficient supply, the supply amount should be increased. In addition, the cooling of the plastic part in the mold must be sufficient.

2. Mold defects. According to the specific situation, the section of the gate and the runner should be appropriately expanded, the position of the gate should be set in a symmetrical place as far as possible, and the feed port should be set in the part of the thick wall of the plastic part. If the depression and shrinkage occur away from the gate, it is generally due to the poor flow of molten material in a certain part of the mold structure, which prevents pressure transfer.

In this regard, the structural size of the mold pouring system should be appropriately expanded, and it is best to extend the flow channel to the part where the depression occurs. For wall thickness plastic parts, the wing gate should be preferred.

3, the raw material does not meet the molding requirements. For plastic parts with relatively high surface requirements, low shrinkage resin should be used as far as possible, and an appropriate amount of lubricant can also be added to the raw material.

4, plastic body structure design is unreasonable. When designing the plastic body structure, the wall thickness should be as consistent as possible. If the difference in wall thickness of plastic parts is large, it can be solved by adjusting the structural parameters of the pouring system or changing the wall thickness distribution.

We have made more than ten years of mold making experience, such problems are generally caused by design reasons, so we must consider the problem of shrinkage when designing.