Cause analysis of swelling, blistering and vibration lines of injection molded parts

Cause analysis of swelling, blistering and vibration lines of injection molded parts

Some plastic parts appear swelling or bubbling on the back of the metal insert or in the extremely thick parts after the molding and demoulding. This is due to the expansion of the gas released by the plastic which is not completely cooled and hardened under the action of internal pressure penalty.

Solutions:
1. Effective cooling. Reduce the mold temperature, prolong the mold opening time, reduce the drying and processing temperature of the material.
2. Reduce the filling speed, forming cycle and flow resistance.
3. Increase the holding pressure and time.
4. Improve the condition that the wall of the part is too thick or the thickness changes greatly.
Analysis on the cause of vibration crack in injection molded parts
PS and other rigid plastic parts in the gate near the surface, to the gate as the center of the formation of dense ripples, sometimes known as jarring.
The reason is that when the melt viscosity is too high and the mold is filled in the form of stagnant flow, the material at the front end will condense and contract as soon as it contacts the surface of the cavity, and the later molten material will expand and shrink, and the cold material will continue to move forward. The continuous alternation of the process makes the material flow form surface chatter marks in the process of advancing.
resolvent:
(1) The mold temperature should also be increased to increase the barrel temperature, especially the nozzle temperature.
(2) The injection pressure and speed were increased to fill the cavity quickly.
(3) Improve the size of runner and gate to prevent excessive resistance.
(4) The exhaust of mould should be good, and enough cold material well should be set up.
(5) Do not design the parts too thin.