When Dalian injection moulding works, the plastic in the hopper falls into the heating barrel by its own weight. Through the rotation of the screw, the plastic moves forward along the screw groove. At this time, the material is heated by the external heater of the heating barrel. At the same time, there is heat generated by shearing inside, and the temperature rises to a melting state. With the storage of the material at the front end of the heating barrel.
The reaction force (back pressure) produced by these materials pushes the screw backward, limits its backward amount by using the limit switch, and stops the screw from turning when it falls back to a fixed position, thus determining the injection quantity at a time. After the material in the mould is cooled, once the product is taken out, the mould is closed again and the injection process is carried out.
At this time, the hydraulic cylinder (injection cylinder) of the injection device exerts force on the screw. Under high pressure, the screw becomes the injection rod, and the melt at its front end is injected into the mould from the nozzle. The screw injection device is composed of screw, barrel, nozzle and driving device. Injection screw is generally divided into three sections: feeding, compression and measurement. The compression ratio is 2-3 and the length-diameter ratio is 16-18.
When the melt is ejected from the nozzle, because the injection force on the pressurized melt is afraid of reaction force, part of the melt will flow backward through the groove of the screw。 To prevent this phenomenon, a check valve is installed at the end of the screw。 For rigid polyvinyl chloride, the conical screw head is used。 The barrel is the part that holds the screw。 It is heat-resistant。