Why should the injection mold be equipped with an exhaust system
Update:30-04-2020
Summary:
The exhaust of the injection mold is an important issue […]
The exhaust of the injection mold is an important issue in the design of the mold. Especially in the rapid injection molding, the exhaust requirements of the injection mold are more stringent.
(1) The source of gas in the injection mold.
1) Air in the pouring system and mold cavity.
2) Some raw materials contain moisture that has not been excluded by drying, and they vaporize into water vapor at high temperature.
3) Due to the excessively high temperature during injection molding, the gas generated by the decomposition of certain unstable plastics.
4) Why the gas injection mold generated by the volatilization or chemical reaction of some additives in the plastic raw materials should be equipped with an exhaust system?
(2) Harm of poor exhaust
Poor exhaust of the injection mold will bring a series of harm 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 exhausted in time, it will cause difficulty in filling the melt and cause insufficient injection volume to fill the cavity.
2) Exhausted gas will form high pressure in the cavity and penetrate into the plastic under a certain degree of compression, causing quality defects such as pores, voids, loose tissue, and silver streaks.
3) 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 confluence of two melts, at the * corner and at the gate flange.
4) The removal of gas is not smooth, so that the melt velocity entering each cavity is different, so it is easy to form flow marks and fusion marks, and reduce the mechanical properties of plastic parts.
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 sources of gas in the cavity are mainly divided into three types: the air accumulated in the cavity; the gas generated by decomposition in the raw material; the vapor of the residual water evaporated in the raw material, the location of the bubbles generated due to the different sources, and the location of the injection mold. Exhaust system mold design.
1) The air bubbles generated by the accumulation of air in the mold cavity are often distributed on the part opposite to the gate.
2) The 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 materials are irregularly distributed on the entire plastic part.
Judging from the distribution of bubbles in the above plastic parts, it is possible to judge not only the nature of the bubbles, but also whether the exhaust part of the mold is correct and reliable.
