Back Pressure Of Injection Molds

Back pressure refers to the pressure that needs to be overcome when the screw reverses and retreats the stock. The use of high back pressure is conducive to the dispersion of pigments and the melting of plastics, but at the same time prolongs the screw retraction time, reduces the length of plastic fibers, and increases the pressure of the injection molding machine, so the back pressure should be lower, generally not more than 20% of the injection pressure. When injecting foam, the back pressure should be higher than the pressure formed by the gas, otherwise the screw will be pushed out of the barrel. Some injection molding machines can program the back pressure to compensate for the reduction in screw length during melting, which reduces the input heat and lowers the temperature. However, since the result of this change is difficult to estimate, it is not easy to adjust the machine accordingly.