Cracking, including thread-like cracks, micro-cracking, top white, cracking on the surface of the part, or trauma crisis caused by sticking of the part and sticking of the flow channel, demolding cracking, and application cracking according to cracking time.

There are mainly the following reasons:

Processing

(1) If the processing pressure is too high, the speed is too fast, the more filling, the injection and the pressure holding time are too long, it will cause excessive internal stress and cracking;

(2) Adjust the mold opening speed and pressure to prevent the demolding cracking caused by rapid and strong drawing of the parts;

(3) Properly adjust the temperature of the mold to make the parts easy to de-mold, and appropriately lower the temperature of the material to prevent decomposition

(4) Prevent cracks from occurring due to the deterioration of plastic due to fusion marks and plastic degradation;

(5) Appropriate use of release agent, pay attention to often eliminate the aerosol and other substances attached to the mold surface;

(6) The residual stress of the workpiece can be eliminated by annealing and heat treatment immediately after forming to reduce the generation of cracks.

Mold aspect

(1) Ejection should be balanced. For example, the number of ejector rods and the cross-sectional area should be sufficient, the draft angle should be sufficient, and the cavity surface should be smooth enough to prevent cracking due to the concentration of ejection residual stress due to external force

(2) The structure of the parts should not be too thin, and the transition part should use arc transition as far as possible to avoid stress concentration caused by sharp corners and chamfers;

(3) Minimize the use of metal inserts to prevent the increase in internal stress caused by the difference in shrinkage between the inserts and the parts;

(4) Appropriate demolding air inlet holes should be provided for deep bottom parts to prevent the formation of vacuum negative pressure;

(5) The mainstream channel is enough to allow the gate material to be de-molded in the future, so it is easy to de-mold;

(6) The joint of the main liner bushing and the nozzle should prevent the drag of the cold material and make the workpiece stick to the fixed mold.

Material

(1) The content of recycled materials is too high, resulting in too low strength of parts.

(2) Excessive humidity causes some plastics to react chemically with water vapor, reducing the strength and causing ejection cracking.

(3) The material itself is not suitable for the processing environment or the quality is not good, and pollution will cause cracking.

Machine aspect

The plasticizing capacity of the injection molding machine should be appropriate. If the plasticizing capacity is too small, it will not be fully mixed and become brittle. If it is too large, it will degrade.