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.

⒈ Plasticizing pressure: (back pressure) When a screw injection machine is used, the pressure on the top of the screw when the screw rotates and retreats is called plasticizing pressure, also known as back pressure. The magnitude of this pressure can be adjusted by the relief 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 product quality and the type of plastic. If these conditions and the rotational speed of the screw remain unchanged, increasing the plasticizing pressure will strengthen the shearing. The effect is to increase the temperature of the melt, but it will reduce the efficiency of plasticization, increase the reverse flow and leakage flow, and increase the driving power.

Pressure curve in injection molding

In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the mixing of the colorant is uniform, and the gas in the melt can be discharged. In general operation, the decision of plasticizing pressure should be as low as possible on the premise of ensuring the quality of the product. The specific value varies with the variety of plastic used, but usually rarely exceeds 20 kg/cm 2 .

⒉Injection pressure: In the current production, the injection pressure of almost all injection machines is the top of the plunger or screw to the plastic.

The applied pressure (converted from the oil circuit pressure) shall prevail. The role of injection pressure in injection molding is to overcome the flow resistance of plastic flowing from the barrel to the cavity, give the melt filling rate and compact the melt