Injection device: The injection device mainly realizes plastic mixing during the injection molding process. Measurement. Functions such as injection and pressure maintenance and contraction. The screw injection device is the most commonly used, which combines the screw molding and injection plunger into one screw. Essentially, it should be referred to as a coaxial reciprocating rod injection device. When it is working, 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, and there is also heat generated by shearing inside. As the temperature rises, it becomes molten. As the material at the front end of the heating cylinder is stored, the reaction force (back pressure) generated by these materials pushes the screw backward, and the limit switch is used to limit its retreat amount. When it retreats to a certain position, the screw stops rotating, thereby determining (measuring) the amount of injection for one time.
After the material inside the mold cools down, once the product is taken out, the mold is closed again and enters the injection process. At this time, the hydraulic cylinder (injection cylinder) of the injection device applies force to the screw, which becomes an injection rod under high pressure, injecting the molten material at the front end into the mold from the nozzle. The screw injection device is composed of a screw, a material barrel, a nozzle, and a driving device. Injection screws are generally divided into three stages: feeding, compression, and metering, with a compression ratio of 2-3 and a length to diameter ratio of 16-18. When the melt is ejected from the nozzle, due to the injection force on the pressurized melt being afraid of the reaction force, a portion of the melt will flow back to the rear through the screw groove. To prevent this phenomenon, install a check valve at the end of the screw. For rigid polyvinyl chloride, a conical screw head is used.
The barrel is the part that contains the screw, and it is made of heat-resistant material. Made of high-pressure resistant steel. Install an array of electric heating coils on the periphery of the barrel to heat the materials inside the barrel, and use thermocouples to control the temperature to ensure that the plastic has a suitable temperature. The nozzle is the transitional part connecting the material barrel and the mold, and it is equipped with an independent heating ring because it is an important part that directly affects the melting state of the plastic. Generally, open nozzles are used for injection molding of low viscosity polyoxymethylene. Then a needle valve nozzle is used.
The rotation of the screw can be driven by an electric motor or a hydraulic motor, and the reciprocating motion of the screw is achieved through hydraulic pressure.