Defects And Solutions For Injection Molding

- Jul 14, 2018-

10. Bubbles

According to the cause of the bubble, the solution to the problem is as follows:

(1) When the wall thickness of the product is large, the outer surface is cooled faster than the center portion. Therefore, as the cooling progresses, the resin at the center portion is expanded toward the surface while being shrunk, so that the center portion is insufficiently filled. This condition is called a vacuum bubble. The main solutions are:

1) Determine the reasonable gate and runner size according to the wall thickness. Generally, the height of the gate should be 50% to 60% of the wall thickness of the product.

2) Until the gate is sealed, a certain amount of supplementary injection material is left.

3) The injection time should be slightly longer than the gate sealing time.

4) Reduce the injection speed and increase the injection pressure.

5) Use a material with a high melt viscosity grade.

(2) The bubbles caused by the generation of volatile gases are mainly solved by:

1) Fully pre-drying.

2) Lower the resin temperature to avoid decomposition gas.

(3) Bubbles caused by poor fluidity can be solved by increasing the temperature of the resin and the mold and increasing the injection speed.

11. Whitening

The whitening phenomenon mainly occurs in the introduction part of ABS resin products. The poor release effect is the main reason. It can be used to reduce the injection pressure, increase the draft angle, increase the number or area of the push rod, and reduce the surface roughness value of the mold. Of course, the spray release agent is also a method, but care should be taken not for the subsequent process. Such as hot stamping, painting, etc. have adverse effects.