What is the reason for the shrinkage depression of injection molding products?

1. Mold:

(1) the design of parts shall make the wall thickness uniform and ensure the same shrinkage.

(2) the cooling and heating system of the mold shall ensure that the temperature of each part is the same.

(3) the pouring system shall be smooth, and the resistance shall not be too large. For example, the size of main flow channel, shunt channel and gate shall be appropriate, the finish shall be sufficient, and the transition area shall be arc transition. Professional plastic knowledge exchange wechat group plus small editor wechat: nb58250988

(4) for thin parts, the temperature shall be increased to ensure smooth materials, and for thick wall parts, the mold temperature shall be reduced.

(5) the gate shall be set symmetrically, and try to be set at the thick wall part of the workpiece, and the volume of the cold well shall be increased.

2. Machine:

(1) if the nozzle hole is too large, the melt will flow back and shrink. If it is too small, the resistance will be too large and the material quantity will be insufficient.

(2) if the clamping force is not enough, the flash will also shrink. Check whether there is any problem with the clamping system.

(3) the plasticizing quantity should not be enough. The plasticizing machine should be used to check whether the screw and the barrel are worn.

3. Plastic:

The shrinkage time of crystalline plastics is longer than that of non crystalline plastics. The amount of material should be increased or the change agent should be added to the plastics to accelerate the crystallization and reduce the shrinkage depression.

4. Processing:

(1) if the barrel temperature is too high and the volume changes greatly, especially the front furnace temperature, the temperature of the plastic with poor fluidity shall be properly increased to ensure smoothness.

(2) the injection pressure, speed and back pressure are too low, and the injection time is too short, so that the material volume or density is insufficient, and the shrinkage pressure, speed and back pressure are too large, and the time is too long, resulting in the flash and shrinkage.

(3) when the buffer pad is too large, the injection pressure will be consumed. If the buffer pad is too small, the injection pressure will be insufficient.

(4) for the parts that do not require precision, after injection and pressure maintaining, the outer layer is basically condensed and hardened, while the sandwich part is soft and can be ejected, the mold shall be ejected as early as possible, and the parts shall be cooled slowly in air or hot water, so that the shrinkage depression is gentle, not so obvious and does not affect the use.