Why is there gas in the injection mold

Update:21-05-2020
Summary:

There are often gas generation in injection molds that […]

There are often gas generation in injection molds that may be related to the following:

Air in the pouring system and mold cavity.

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

Injection molds for pipe fitting

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

Gases generated by the volatilization or chemical reaction of certain additives in plastic raw materials.

At the same time, the reason for poor exhaust is also to be found as soon as possible. Poor exhaust of the injection mold also caused problems for the plastic parts. The main performance is as follows:

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

Exclusion of poor 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.

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

The poor removal of gas makes the melt velocity entering each cavity different, so it is easy to form flow marks and fusion marks, and reduce the mechanical properties of plastic parts.