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) The air contained 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 a high temperature.
3) Gas generated by decomposition of some unstable plastics due to excessive temperature during injection molding.
4) Gas injection molds generated by volatilization or mutual chemical reaction of certain additives in plastic raw materials Why should the exhaust system be installed in the exhaust system injection mold?
(2) The harm of poor exhaust
Poor exhaust of the injection mold will bring a series of hazards to the quality of 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) Excluding the unsatisfactory gas will form a high pressure in the cavity and penetrate into the plastic inside under a certain degree of compression, resulting in quality defects such as pores, voids, loose tissue, 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 scorching of the plastic part. It mainly occurs at the junction of the two melts, the * corner and 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 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 gas in the cavity is mainly divided into three types, the air accumulated in the cavity; the gas generated by the decomposition of the raw material; the water vapor evaporated from the residual water in the raw material, and the position of the bubble generated by the source is different. Exhaust system mold design.
1) Air bubbles generated by the accumulation of air in the cavity are often distributed on the opposite part of 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.