Screw is an important part of injection molding machine. Its function is to transport, melt, compact, mix and press plastic. All these are completed by the rotation of the screw in the barrel, which shows that the screw plays an important role in the plastic machinery.
When the screw rotates, the plastic will produce friction and mutual movement on the inner wall of the barrel, the bottom surface of the screw groove, the advancing surface of the screw edge and between the plastic and the plastic. The forward movement of plastics is the result of this combination of movements, and the heat generated by friction is also absorbed to raise the temperature of plastics and melt them. The structure of the screw will directly affect the degree of these effects.
At the same time, the rotation of the screw makes the film between the solid bed and the inner wall of the barrel shear, so that the solid between the film and the solid bed interface melts. As the spiral shape of the solid bed moves forward, the volume of the solid bed decreases gradually, while the volume of the molten pool increases gradually.
If the decrease speed of the solid bed thickness is lower than that of the shallow depth of the spiral groove, the solid bed may partially or completely block the spiral groove and cause the plasticization to fluctuate, or because of the local pressure, the melting speed, the melt viscosity, the melting temperature range, the sensitivity of the viscosity to the temperature and shear rate, the corrosiveness of the high temperature decomposition gas, and the friction system between the plastic particles There is a great difference in the number. Generally speaking, the phenomenon of high shear heat will appear when the general screw processes some plastics with outstanding melt characteristics. This phenomenon can be eliminated by reducing the screw speed, but it will inevitably affect the production efficiency.