Gas is often produced in injection mold, which may be related to the following points:
Air in the gating system and mold cavity.
Some raw materials contain water that is not removed by drying, which will be vaporized into steam at high temperature.
Due to the high temperature during injection molding, some unstable plastics will decompose and produce gas.
The gas produced by volatilization or chemical reaction of some additives in plastic raw materials.
At the same time, the causes of poor exhaust also need to be found out as soon as possible. Poor exhaust of injection mold also brings trouble to plastic parts. The main manifestations are 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, the melt filling will be difficult and the injection volume will not be enough to fill the cavity.
If the gas is not smooth, 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 tissue and craze.
Due to the high compression of the gas, the temperature in the mold cavity rises sharply, which causes the decomposition and burning of the surrounding melt, resulting in local carbonization and scorching of the plastic parts. It mainly appears at the confluence of two melts and the gate flange.
Due to the poor gas removal, the melt velocity entering each cavity is different, so flow marks and fusion marks are easy to form, and the mechanical properties of plastic parts are reduced.
Due to the obstruction of gas in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the tax collection efficiency will be reduced.
The distribution of bubbles in plastic parts is as follows
The bubbles produced by the accumulated air in the mold cavity are usually distributed in the position opposite to the gate.
The bubbles produced by decomposition or chemical reaction in plastic 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.
