During the injection molding process, air bubbles are a very common phenomenon that can seriously and directly affect the actual quality of the injection molded products. The reason of producing these gases may be the high temperature and the degradation of plastic under the long time heat; it may also be caused by the moisture and volatile substances contained in the raw materials. Usually, air bubbles appear mainly in the thick wall of the product or at the final seam. The causes of air bubbles are different, the phenomenon is different, and the treatment methods will also be different.
There are two causes of air bubbles in the plastic injection molding process.
1）Bubbles due to the presence of moisture
Cause: The degree of drying of plastic material is not enough to cause plastic material for hydrolysis.
Solution:
Adequate pre-drying and attention to the hopper insulation management.
2）Vacuum bubble
Causes of vacuum bubble: injection molding process, in the product wall thickness, is larger, the outer surface of the cooling rate than the center of the faster, therefore, with the cooling process, the center of the resin shrinkage while expanding to the surface, so that the center of the underfilling, this situation is known as vacuum bubble.
Solution.
1, according to the wall thickness, determine a reasonable gate, and sprue size. Generally, the gate height should be 50%~60% of the product wall thickness.
2, until the gate is closed, leave a certain amount of supplementary injection material.
3、Injection time should be slightly longer than the gate sealing time.
4、Lower the injection speed and increase the injection pressure.
5、Use the material with high melt viscosity grade.
6、The bubbles are caused by the generation of volatile gas, the solution mainly includes
7、Full pre-drying.
8、Lower resin temperature to avoid decomposition gas.
9、Bubbles caused by poor fluidity can be solved by increasing the temperature of resin and mold, and increasing the injection speed.