Working principle of injection mould

Injection mould is an important method of thermoplastic products production, except for a few thermoplastics, almost all thermoplastic products can be produced by injection mould method.Injection mould is achieved by injection mould machine. At present, there are many types of injection machine, and in order to adapt to the continuous update of plastic products, the structure of the injection machine has been improved and developed. But no matter what kind of injection machine, its basic role has two, heating molten plastic, so that it reaches the viscous flow state; Pressure is applied to the viscous plastic to shoot it into the mold cavity.

The working process of the injection machine is: first, the moving mould and the fixed mold are closed, and then the hydraulic cylinder piston drives the screw according to the required pressure and speed, and the plastic which has been melted and accumulated at the end of the barrel is shot into the mold cavity through the nozzle. Now the screw keeps turning. When the molten plastic is filled with the mold cavity, the screw still maintains a certain pressure on the melt (i.e. pressure preservation), to prevent the plastic flow back, and to the cavity due to the cooling shrinkage of the plastic needed. After a certain period of pressure retention, the pressure of the piston disappears and the screw begins to rotate. At this time, the plastic falling into the barrel from the hopper is transported forward with the rotation of the screw. In the process of plastic conveying to the front end of the barrel, the plastic is heated by the heater and the influence of the screw shear friction heat and shape gradually rising until melting into viscous flow state, and establish a certain pressure. When the melt pressure of the head of the screw reaches to overcome the resistance of the piston back of the injection hydraulic cylinder, the screw rotates at the same time, and the melt at the front end of the barrel increases gradually. When the screw falls back to a predetermined position, it stops rotating and retreating. The above process is called premolding.During the premolding process, or for a slightly longer period of time, the molded plastic cools and hardens in the mold. When the plastic parts are completely cooled and hardened, the mold is opened, and the plastic products are pushed out of the mold under the action of the push mechanism, which completes a working cycle.

Compared with plunger injection molding, screw injection molding can make the plastic in the barrel to get good mixing and plasticizing, improve the molding process, improve the quality of plastic products. At the same time also expanded the range of plastic injection molding varieties and the maximum amount of injection, for heat sensitive plastic and poor liquidity of plastic and large, medium plastic products, generally available screw injection machine injection molding. From the injection molding process can be seen that the injection mould cycle is short, high productivity, can be controlled by microcomputer, easy to achieve automatic production, plastic products precision is easy to ensure, wide range of application.