What is the cause of shrinkage marks on the surface of injection molded products? Teach you a few measures to solve

During the production of injection molded products, some products may have uneven surface shrinkage due to uneven wall thickness, thus producing shrinkage marks. So what is shrinkage marks? Shrinkage marks refer to the phenomenon of pits, sinkholes or shrinkage marks on the surface of injection molded products. The depth of shrinkage marks is generally small. Here, we will analyze the causes of this problem and how to eliminate it.

Failure analysis and elimination methods

1、Improper control of molding conditions. Properly increase the injection pressure and injection speed, increase the compression density of the dissolved material, extend the injection and holding time, compensate for the shrinkage of the melt, and increase the injection buffer. However, the holding pressure should not be too high, otherwise it will cause convex marks.

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

2, mold defects. Combine with the specific situation, expand the gate and runner section appropriately, set the gate position at the symmetry as much as possible, and set the feed port at the thick wall part of the plastic part. If the dent and shrinkage occurs far from the gate, it is generally due to the poor flow of molten material in one part of the mold structure, which hinders the pressure transfer.

In this regard, the structural dimensions of the mold casting system should be enlarged appropriately, preferably so that the runner extends to the area where the dent is generated. For wall thickness plastic parts, wing type gate should be preferred.

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

4、The structure of the plastic part is not designed properly. When designing the structure of plastic parts, the wall thickness should be as consistent as possible. If the wall thickness of the plastic part differs greatly, it can be solved by adjusting the structural parameters of the pouring system or changing the wall thickness distribution.