1. Gas is often produced in
injection molds and may be related to the following points.
(1) The air stored in the casting system and the mold cavity.
(2) Some raw materials contain moisture that is not removed by drying, and they are vaporized into water vapor at high temperatures.
(3) Due to the high temperature during injection molding, some unstable plastics may decompose to generate gas.
(4) Gases formed by volatilization or chemical reaction of certain additives in plastic raw materials.
2, the reason for poor exhaustion at the same time, also need to find out as soon as possible. Poor exhaust of the injection mold also causes problems for 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 discharged in time, the melt filling will be difficult, resulting in insufficient injection volume to fill the cavity.
(2) Excessive gas removal will form a high pressure in the cavity, and will penetrate into the interior of the plastic under a certain degree of compression, resulting in quality defects such as voids, pores, fine structure and silver streaks.
(3) Due to the high compression of the gas, the temperature in the cavity rises sharply, which causes decomposition and burning of the surrounding melt, causing local carbonization and charring of the plastic part. It mainly occurs at the junction of the two melts at the gate flange.
(4) The gas is not well removed, 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 lowered.
(5) Due to the obstruction of gas in the cavity, the filling speed is reduced, the molding cycle is affected, and the taxation efficiency is lowered.
3. Distribution of bubbles in plastic parts
(1) The bubble generated by the accumulation of air in the cavity is often distributed on the portion opposite to the gate.
(2) Bubbles generated by decomposition or chemical reaction in the plastic raw material are distributed along the thickness of the plastic part.
(3) The bubbles generated by the vaporization of residual water in the plastic raw material are irregularly distributed on the entire plastic part.
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