Sometimes the processed injection-molded products will show shrinkage and depression, what's the matter? What causes these conditions?

01 Machine aspect

If the nozzle hole is too large, the molten material will flow back and shrink, and if the resistance is too small, the material will be insufficient and the shrinkage will occur.

The Insufficient clamping force will cause the flash to shrink. Check the clamping system for problems.

If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be selected to check whether the screw and barrel are worn.

02 Mold aspect

The design of the parts should make the wall thickness uniform and ensure consistent shrinkage.

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

The pouring system must be smooth, and the resistance should not be too large. For example, the size of the main channel, the diverter channel, and the gate should be appropriate, the smoothness should be sufficient, and the transition area should be rounded.

The temperature should be increased for thin parts to ensure smooth flow, and the mold temperature should be lowered for thick-walled parts.

The gate should be opened symmetrically, try to open in the thick-walled part of the part, and the volume of the cold material well should be increased.

03 Plastic 

Crystalline plastics shrink more strongly than non-crystalline plastics, and the number of materials should be appropriately increased during processing, or nucleating agents should be added to the plastics to accelerate crystallization and reduce shrinkage depressions.

04 Processing

The temperature of the barrel is too high, and the volume changes greatly, especially the temperature of the front furnace. The temperature of the plastic with poor fluidity should be appropriately increased to ensure smoothness.

The injection pressure, speed, back pressure is too low, and the injection time is too short, so that the amount of material or density is insufficient and the contraction pressure, speed, back pressure is too large, and the time is too long, causing the flash to shrink.

The feeding amount is that the injection pressure is consumed when the cushion is too large, and if it is too small, the feeding amount is insufficient.

For parts that do not require precision, after the injection pressure is maintained, the outer layer is basically condensed and hardened, and the sandwich is still soft and can be ejected. Exit the mold early and let it cool slowly in the air or hot water. The shrinkage depression is gentle and not so conspicuous and does not affect the use.