Air bubbles
According to the causes of bubbles, the solutions are as follows:
1) when the wall thickness of the product is large, its external surface cooling speed is faster than that of the central part. Therefore, with the cooling process, the resin edge of the central part shrinks and expands to the surface, resulting in insufficient filling at the central part.This is called a vacuum bubble.The solutions are:
A) determine the reasonable gate and runner size according to the wall thickness.Generally, the gate height should be 50% ~ 60% of the product wall thickness.
B) until the gate is sealed, a certain amount of supplementary injection material is reserved.
C) the injection time should be slightly longer than the sealing time of the gate.
D) reduce the injection speed and increase the injection pressure.
E) materials with high melt viscosity grade are adopted.
2) bubbles caused by the production of volatile gases are mainly solved by:
A) sufficient pre-drying.
B) lower the temperature of the resin to avoid the generation of decomposition gas.
3) bubbles caused by poor fluidity can be solved by increasing the temperature of resin and mold and increasing the injection speed.