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Analysis of the reasons why gas is often discharged from plastic molds

2025-07-24

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Analysis of the reasons why gas is often discharged from plastic molds:

Gas is often generated in injection molds, which may be related to the following points:

Some additives in the plastic raw materials volatilize or react with each other to generate gases.

Air in the pouring system and the mold cavity.

Due to the high temperature during injection molding, some unstable plastics will decompose and produce gas.

Some raw materials contain moisture that has not been dried and removed, and they will vaporize into water vapor at high temperatures.

Poor exhaust of injection molds also brings troubles to plastic parts. The main manifestations are as follows:

During the injection molding process, the melt will replace the gas in the cavity. If the gas is not discharged in time, it will cause difficulties in melt filling, resulting in insufficient injection volume and failure to fill the cavity.

Poorly discharged gas will form high pressure in the cavity, and penetrate into the interior of the plastic under a certain degree of compression, causing quality defects such as voids, pores, loose tissue and silver streaks.

Due to the high compression of gas, the temperature in the cavity rises sharply, which in turn causes the surrounding melt to decompose and burn, resulting in local carbonization and scorching of the plastic part. It mainly occurs at the confluence of two melts, at the gate flange, and at the end of filling.

Poor gas removal makes the melt entering each cavity at different speeds, so it is easy to form flow marks and fusion marks, and reduce the mechanical properties of the plastic part.

Due to the obstruction of gas in the cavity, the filling speed will be reduced, affecting the molding cycle.

Distribution of bubbles in plastic parts:

Bubbles generated by air accumulation in the mold cavity are often distributed in the area opposite to the gate.

Bubbles generated by the vaporization of residual water in the plastic raw material are irregularly distributed throughout the plastic part.

Bubbles generated by decomposition or chemical reaction in the plastic raw material are distributed along the thickness of the plastic part.

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