Why should the injection mold set the exhaust system
Release time:
2021-11-12
The exhaust of injection mold is an important problem in mold design, especially in rapid injection molding, the exhaust of injection mold is more stringent.
The exhaust of injection mold is an important problem in mold design, especially in rapid injection molding, the exhaust of injection mold is more stringent.
1. The source of gas in the injection mold.
1) The air in the gating system and the mold cavity.
2) Some raw materials contain moisture that is not excluded from drying, and they are vaporized into water vapor at high temperatures.
3) Due to the high temperature during injection molding, the gas produced by the decomposition of some unstable plastics.
4) Some additives in plastic raw materials volatilize or react with each other to generate gas.
2. Hazards of poor exhaust
The poor exhaust of injection mold will bring a series of hazards to the quality of plastic parts and many other aspects. 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, it will cause difficulty in filling the melt and cause insufficient injection volume to fill the cavity.
2) the exclusion of poor gas will form high pressure in the cavity, and penetrate into the plastic under a certain degree of compression, resulting in pores, voids, loose organization, silver lines and other quality defects.
3) Because the gas is highly compressed, the temperature in the cavity rises sharply, which causes the surrounding melt to decompose and burn, and makes the plastic parts appear local carbonization and scorching phenomenon. It mainly occurs at the confluences of the two melts, the angle and the gate flange.
4) the removal of gas is not smooth, so that the melt velocity into each cavity is different, so it is easy to form flow marks and fusion marks, and the mechanical properties of plastic parts are reduced.
5) Due to the obstruction of the gas in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the production efficiency will be reduced.
3. Distribution of bubbles in plastic parts
The source of the gas in the cavity is mainly divided into three categories: the air accumulated in the cavity; the gas generated by the decomposition of the raw material; the water vapor of the residual water evaporation in the raw material, and the position of the bubbles generated by the different sources are also different.
1) The air bubbles generated by the accumulation of air in the mold cavity are often distributed on the opposite part of the gate.
2) The bubbles generated by the decomposition or chemical reaction in the plastic raw materials are distributed along the thickness of the plastic parts.
3) The bubbles generated by the gasification of residual water in the plastic raw materials are irregularly distributed throughout the plastic parts.
From the distribution of bubbles in the above-mentioned plastic parts, not only the nature of the bubbles can be judged, but also the exhaust parts of the mold can be judged correctly and reliably.
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