How to solve the sunken parts of injection molding parts?

How to solve the sunken parts of injection molding parts?

Sometimes the processed plastic injection products will shrink and sink. What's the matter? What are the causes of these situations?

1. Machine side

The nozzle hole is too large to cause the melt to flow back and shrink. Too much resistance, too much material is insufficient to shrink.

Insufficient clamping force causes the flash to shrink, so check if the clamping system has a problem.

Inadequate plasticizing should use a large amount of plasticizing machine, check the screw and barrel wear.

2. Mold aspects

The design of parts should be uniform in wall thickness to ensure consistent shrinkage.

The cooling and heating system of the mold must ensure that the temperature of each part is the same.

The gating system should be smooth and the resistance should not be too large. For example, the dimensions of the main roads, runners and gates should be adequate, the smoothness should be sufficient, and the transition zone should be arced.

Thin parts should be raised in temperature to ensure smooth material flow, and mold temperature should be reduced for thick-walled parts.

Gates should be symmetrically opened, as far as possible in the thick parts of parts, should increase the volume of cold wells.

3. Plastics

Crystalline plastics shrink more severely than non-crystalline plastics. During processing, the amount of material must be appropriately increased, or nucleating agents should be added to plastics to accelerate crystallization and reduce shrinkage dents.

4. Processing

The barrel temperature is too high, the volume change is large, especially the temperature of the forehearth, the plastic with poor fluidity should be properly increased in temperature, ensure smooth.

Injection pressure, speed, back pressure is too low, injection time is too short, so that the amount of material or density is not enough and the contraction pressure, speed, back pressure is too large, too long time caused by flash and shrink.

The amount of charge is the consumption of injection pressure when the cushion is too large. If the load is too small, the amount of material is insufficient.

For parts that do not require precision, after the injection pressure is maintained, the outer layer is basically condense-hardened and the sandwich part is still soft and can be ejected. The mold can be ejected early, allowing it to slowly cool in air or hot water, which can make Shrinking depressions are flat and not noticeable without affecting use.