Analysis of the causes of swelling, bubbling and tremolo of injection products

- Jul 13, 2019-

Some plastic parts appear swelling or bubbling on the back of the metal insert or on the thick part after molding and demoulding.This is because the plastic, which has not been cooled and hardened completely, expands by releasing gas under internal pressure.

Injection molding


1. Effective cooling.Reduce mold temperature, extend mold opening time, reduce material drying and processing temperature.

2. Reduce mold filling speed, forming cycle and flow resistance.

3. Increase pressure and time.

4. Improve the condition that the wall surface is too thick or the thickness changes greatly.

Analysis of the cause of vibration pattern of injection products

PS and other rigid plastic products in its gate near the surface, to the gate as the center of the formation of a dense ripple, sometimes known as seismic lines.

The reason is that when the melt viscosity is too large and the mold is filled in the form of stagnation, the material at the front end will condense and contract quickly upon contact with the cavity surface, and then the molten material expands and expands the cold material which has shrunk and continues to advance. The continuous alternations of the process make the material flow form the surface shock pattern in the advance.


(1) increase the temperature of the cylinder, especially the temperature of the nozzle, and also increase the temperature of the mold.

(2) increase the injection pressure and speed, so that it can quickly fill the model cavity.

(3) improve the size of runner and gate to prevent excessive resistance.

(4) mold exhaust should be good, to set up a large enough cold material well.

(5) the parts should not be too thin.