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Why is the gas often discharged when the mold is injected, and what is the impact?

Update:12-10-2022
Summary:

The bubbles generated by the accumulated air in the Pla […]

The bubbles generated by the accumulated air in the Plastic Pail Moulds are often distributed on the part opposite to the gate. The air bubbles generated by the decomposition or chemical reaction in the plastic raw material are distributed along the thickness of the plastic part. The bubbles generated by the vaporization of residual water in the plastic raw material are distributed irregularly on the entire plastic part. Gas is often generated in injection molds, which may be related to the following points:
1. Air in the gating system and the mold cavity.
2. Some raw materials contain moisture that has not been removed by drying, and they will gasify into water vapor at high temperatures.
3. Due to the high temperature during injection molding, some unstable plastics will decompose and generate gas.
4. The gas generated by the volatilization or chemical reaction of some additives in the plastic raw material.
At the same time, the cause of the poor exhaust gas also needs to be found out as soon as possible. The poor exhaust of the injection mold also brings troubles to the plastic parts. The main performance is 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 difficulty in filling the melt, resulting in insufficient injection volume to fill the cavity. The poorly exhausted gas will form a 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, sparse tissue and silver streaks.
Because the gas is highly compressed, the temperature in the cavity rises sharply, which in turn causes the decomposition and burning of the surrounding melt, resulting in local carbonization and burning of the Plastic Pet Moulds parts. It mainly occurs at the confluence of two melts, at the gate flange. Poor removal of gas makes the melt velocity into each cavity different, so it is easy to form flow marks and fusion marks, and reduce the mechanical properties of plastic parts.

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