Pressure control: The pressure in the injection molding process includes plasticizing pressure and injection pressure, and directly affects the plasticization of plastics and the quality of products.
1. Plasticizing pressure: (back pressure) When the screw injection machine is used, the pressure on the molten material at the top of the screw when the screw rotates backward is called plasticizing pressure, also called back pressure. The pressure can be adjusted through the relief valve in the hydraulic system. In injection, the plasticizing pressure is constant with the screw speed, so increasing the plasticizing pressure will increase the melt temperature, but will reduce the plasticizing speed. In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the color mixture uniform and the gas in the melt discharged. In general operation, the plasticizing pressure shall be determined as low as possible on the premise of ensuring good product quality. The specific value varies with the type of plastic used, but it rarely exceeds 20kg/cm2.
2. Injection pressure: In current production, the injection pressure of almost all injection machines is based on the pressure applied on the plastic by the top of the plunger or screw (converted from the oil pressure). The role of injection pressure in injection molding is to overcome the flow resistance of plastic from the barrel to the cavity, give the molten material the speed of mold filling and compact the molten material.
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