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Injection Molds Are Often Gas Discharge, How Is It
Jun 05, 2018

Gases are often generated in injection molds and may be related to the following points.

 

    (1) Air in the pouring system and mold cavity.

 

    (2) Some raw materials contain moisture that has not been removed by drying and they vaporize into water vapor at high temperatures.

 

    (3) Because the temperature is too high at the time of injection molding, some unstable plastics will decompose and generate gas.

 

    (4) Gases generated by certain additives in plastic raw materials that volatilize or react with each other.

 

    At the same time, the reason for poor exhaust is also needed to find out as soon as possible. The poor exhaust of the injection mold has also brought troubles to the plastic parts. The main performance is as follows:

 

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

 

    (2) Excluding poor gas will form high pressure in the cavity, and infiltrate into the interior of the plastic under a certain degree of compression, resulting in defects such as voids, pores, sparse tissue, and silver lines.

 

    (3) As the gas is highly compressed, the temperature in the cavity rises sharply, causing the surrounding melt to decompose and burn, causing local carbonization and scorching of the plastic parts. It occurs mainly at the junction of the two melts, at the gate flange.

 

    (4) The removal of gas is not smooth, so that the melt velocity entering each cavity is different, so flow marks and fusion marks are easily formed, and the mechanical properties of the plastic parts are reduced.

 

    (5) Due to the obstruction of the gas in the cavity, the filling rate will be reduced, affecting the molding cycle and reducing the taxation efficiency.

 

    The distribution of air bubbles in plastic parts.

 

    (1) Bubbles generated by the accumulation of air in the cavity are often distributed on the opposite side of the gate.

 

    (2) Bubbles generated by decomposition or chemical reactions in plastic raw materials are distributed along the thickness of the plastic parts.

 

    (3) Bubbles generated by gasification of residual water in plastic materials are irregularly distributed on the entire plastic part.