How to minimize shrinkage depression in plastic molded part?

If there is shrinkage depression in plastic molded part, we can consider the solution from the following aspects.

1. If the nozzle hole is too large, the melt will flow back. On the contrary, if it is too small, the resistance will be large and the shot size will be insufficient. Both of these cases lead to shrinkage.
2. Insufficient clamping force will cause flash and shrinkage. It need to check whether there is a problem with the clamping system.
3. If the plasticizing amount is insufficient, it should use a machine with a large plasticizing amount. Besides, check whether the screw and barrel are worn.

1. The wall thickness should be uniform in the part design to ensure consistent shrinkage.
2. The cooling and heating system of the mold should ensure the consistent temperature of each part.
3. In order to ensure the smooth melt flow of the gating system and reduce its resistance, the main runner, sub-runner and gate, the size of them should be appropriate and the finish should be sufficient. Besides, the transition zone should be a circular transition.
4. For thin-walled Parts, the temperature should be increased to ensure smooth melt flow. However, for thick-walled parts, the mold temperature should be lowered.
5. The gates should be designed symmetrically and in the wall thickness as far as possibly. Besides, the volume of the cold slug well should be increased.

The shrinkage of crystalline plastics is larger than non-crystalline plastics. Therefore, during processing, it need to increase the shot size appropriately or add a nucleating agent in the plastic, which can accelerate crystallization and reduce shrinkage depression.

1. Too high barrel temperature will increase the plastic volume changes, especially the front furnace temperature. Therefore, for plastics with poor fluidity, the temperature should be appropriately increased to ensure smooth flow.
2. The injection pressure, speed, back pressure are too low, and the injection time is too short, which makes insufficient shot size or density. In this case, it will also lead to excessive shrinkage pressure, speed, back pressure and time and then flash and shrinkage occur.
3. When the shot size or padding is too large, the injection pressure will be consumed. However, if it is too small, the shot size is insufficient.
4. For parts without precision requirement, after the injection holding pressure, the part outside is basically frozen and hardened, and the inside is still soft but can be removed. In this case, it should demould early and cool slowly in air or hot water, resulting in the shrinkage depression without obviousness and affecting the use.