The pressure in the plastic injection process includes plasticizing pressure and injection pressure, and directly affects the plasticization of plastics and product quality.
(Back pressure) When using a screw injection machine, the pressure on the top of the screw when the screw is rotated and retreated is called the plasticizing pressure, also known as the back pressure. The size of this pressure can be adjusted by the overflow valve in the hydraulic system.
In injection, the size of the plasticizing pressure needs to be changed with the design of the screw, the requirements of the product quality, and the type of plastic. If these conditions and the speed of the screw are the same, increasing the plasticizing pressure will strengthen the shear Function, that is, it will increase the temperature of the melt, but it will reduce the efficiency of plasticization, increase the reverse flow and leakage, and increase the driving power.
In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the mixing of the pigments uniform, and the gas in the melt can be discharged. In general operation, the decision of plasticizing pressure should be as low as possible under the premise of ensuring good product quality. The specific value varies with the types of plastics used, but usually rarely exceeds 20 kg/cm².
In the current production, the injection pressure of almost all injection machines is based on the plunger or the top of the screw to the plastic
The applied pressure (converted from the oil pressure) shall prevail. The role of injection pressure in injection molding is to overcome the flow resistance of the plastic from the barrel to the cavity, to give the molten material the rate of filling the mold and to compact the molten material.