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Why is gas often discharged during injection molding?
- Oct 31, 2018 -

The distribution of bubbles in plastic parts:

The bubbles generated by the accumulated air in the mold cavity are often distributed on the part opposite to the gate.

The bubbles produced in the decomposition or chemical reaction of plastic materials are distributed along the thickness of the plastic parts.

The bubbles generated by gasification of residual water in plastic raw materials are distributed on the whole plastic parts irregularly.

Gas injection often occurs in injection moulds, which may be related to the following points:


1. The air in the gating system and mold cavity.

2, some raw materials contain moisture which is not dried and removed. They will be vaporized into water vapor at high temperatures.

3, because the temperature is too high in injection molding, some unstable plastic will produce gas.

4, some additives in plastic raw materials volatilized or produced by chemical reactions.


injection molding machine

At the same time, the cause of bad exhaust is also need to find out as soon as possible. The poor exhaust of injection mold also brings troubles to the plastic parts. The main findings are as follows:

In the process of injection molding, the melt will replace the gas in the cavity. If the gas is not discharged in time, the melt filling will be difficult, resulting in insufficient injection volume and can not fill the cavity.

Removal of the blocked gas in the cavity will form a high pressure, and under a certain degree of compression infiltration into the internal plastics, resulting in holes, pores, loose tissue and other quality defects.

Because the gas is highly compressed, the temperature in the cavity rises sharply, and then causes the melt around to decompose and burn, resulting in local carbonization and scorching of the plastic parts. It occurs mainly at the junction of two melts, and at the gate flange.

Gas removal is not smooth, making the melt into the cavity speed is different, so it is easy to form flow marks and fusion marks, and make the mechanical properties of plastic parts reduce.

Because of the obstruction of gas in mold cavity, the filling speed will be reduced, the molding cycle will be affected, and the efficiency of Taxation will be reduced.