What effects will gas release during injection molding have?

2026-03-19

① Gas generation causes

Gas is often generated in Injection Molds, which may be related to the following points:

1.Air trapped in the gating system and mold cavity.

2.Some raw materials contain moisture that hasn't been removed by drying, which will vaporize into water vapor at high temperatures.

3.Because the temperature is too high during injection molding, some unstable plastics will decompose and produce gas.

4.Gases generated by volatilization of certain additives in plastic raw materials or chemical reactions with each other.

② Poor venting causes

At the same time, the cause of poor venting also needs to be found out as soon as possible. Poor venting of injection molds also causes problems for plastic parts. The main performances are as follows:

1During the injection molding process, the melt will replace the gas in the cavity. If the gas isn't discharged in time, it will be difficult to fill the melt, resulting in insufficient injection volume and failure to fill the cavity.

2The gas that isn't discharged smoothly will form high pressure in the mold cavity and penetrate into the interior of the plastic under a certain degree of compression, causing quality defects such as cavities, pores, sparse tissue and silver streaks.

3Because the gas is highly compressed, the temperature in the mold cavity rises sharply, which in turn causes the surrounding melt to decompose and burn, causing local carbonization and scorching of the plastic parts. It mainly appears at the confluence of two melts and at the gate flange.

4Poor gas removal results in different melt speeds entering each cavity, which easily forms flow marks and fusion marks, and reduces the mechanical properties of the plastic parts.

5Due to the obstruction of gas in the cavity, the mold filling speed will be reduced, the molding cycle will be affected, and the taxing efficiency will be reduced.

③ Distribution of bubbles in plastic parts

1Bubbles generated by air accumulated in the mold cavity are often distributed in the parts opposite to the gate.

2The bubbles produced by decomposition or chemical reaction in the plastic raw materials are distributed along the thickness of the plastic part.

3The bubbles generated by the vaporization of residual water in the plastic raw materials are irregularly distributed throughout the plastic injection part.