- (1) Air in the pouring system and mold cavity.
- (2) Some raw materials contain moisture that has not been removed by drying, and they will vaporize into water vapor at high temperature.
- (3) Because the temperature is too high during injection molding, some unstable plastics will decompose and generate gas.
- (4) Gases generated by the volatilization or chemical reaction of certain additives in plastic raw materials.
At the same time, the reason for poor exhaust is also to be found as soon as possible. Poor exhaust of the injection mold also caused 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, it will cause difficulty in filling the melt, resulting in insufficient injection volume to fill the cavity.
- (2) Exhausted gas will form high pressure in the cavity, and penetrate into the interior of the plastic under a certain degree of compression, causing quality defects such as voids, pores, loose tissue and silver streaks.
- (3) Because the gas is highly compressed, the temperature in the cavity rises sharply, which in turn causes the surrounding melt to decompose and burn, causing local carbonization and scorching of plastic parts. It mainly appears at the junction of 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 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 tax collection efficiency will be reduced.
Distribution of bubbles in plastic parts.
- (1) Vapor bubbles generated by the accumulation of air in the mold cavity are often distributed on the part opposite to the gate.
- (2) Bubbles generated by decomposition or chemical reaction in plastic materials are distributed along the thickness of plastic parts.
- (3) The bubbles generated by the vaporization of residual water in the plastic raw materials are irregularly distributed on the entire plastic part.