Gas is often produced in injection mold, which may be related to the following points:
Air in the pouring system and mold cavity.
Some raw materials contain water that has not been dried out. They will be vaporized into water vapor at high temperature.
Because of the high temperature in injection molding, some unstable plastics will decompose and produce gas.
Gases produced by volatilization or chemical reaction of some additives in plastic raw materials.
At the same time, the cause of poor exhaust should be found out as soon as possible. Poor exhaust of injection mold also brings troubles to plastic parts. The main performance is as follows:
In the process of injection molding, the melt will replace the gas in the cavity. If the gas is not discharged in time, it will lead to the difficulty of filling the melt, resulting in insufficient injection volume and unable to fill the cavity.
If the gas is not removed smoothly, it will form high pressure in the mold cavity and penetrate into the interior of the plastic under a certain degree of compression, resulting in quality defects such as cavities, pores, sparse tissues and crazes.
Because the gas is highly compressed, the temperature in the mold cavity rises sharply, which causes the surrounding melt to decompose and burn, resulting in local carbonization and burning of plastic parts. It mainly occurs at the confluence of two melts and the gate flange
.
Because of the poor discharge of gas, the melt velocity into each cavity is different, so flow mark and fusion mark are easy to form, and the mechanical properties of plastic parts are reduced.
Because of 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:
The bubbles produced by the air accumulated in the mold cavity are often distributed on the position opposite to the gate.
The bubbles produced by decomposition or chemical reaction in plastic raw materials are distributed along the thickness of plastic parts.
The bubbles produced by the residual water gasification in the plastic raw materials are irregularly distributed on the whole plastic part.
