When the plastic melt filled cavity, must be discharged from the cavity and pouring the system of air and plastic heat or solidification of low molecular weight volatile gas. If the cavity for a variety of reasons due to the gas can not be ruled out, on the one hand will be formed in the plastic parts of the bubble, joints, surface contours and fillings and other defects, on the other hand gas pressure, the volume reduced and high temperature Will lead to plastic parts of the local carbonation or char, while the accumulation of gas will produce reverse pressure and reduce the filling speed. So the design must consider the exhaust problem.
Injection molding is usually carried out in the following ways:
(1) open exhaust slot exhaust groove is generally set in the front mold part of the melt flow of the end, the width of 5 ~ 8mm, length of 8 ~ 10mm or so. The depth of the exhaust groove varies from resin to resin, mainly to consider the viscosity of the resin and whether it is easy to break down. As a matter of principle, the viscosity of the resin, the depth of the exhaust groove should be shallow. Easy to break down the resin, the exhaust groove area to be large;
(2) the use of parting surface exhaust for a certain roughness of the parting surface, from the parting surface of the gas discharge;
(3) the use of plunger exhaust plastic parts of the middle position of the storm, you can add thimble, the use of thimble and the core between the fit gap, or intentionally increase the gap between the thimble to exhaust;
(4) the use of mosaic gap for the combination of cavity, the core, the use of their mosaic gap to exhaust. Use exhaust vent;
(5) forced exhaust. According to the structural characteristics of the plastic parts and the core cavity and the structure of the mold, the secondary mold because the cavity is mosaic structure, solid with the use of clearance with the exhaust, at the same time, fitter in the processing, Very small exhaust slot (PP exhaust groove depth of 0.02 mm).