The screw is an important part of the injection molding machine. Its role is to transport, melt, compact, stir, and apply pressure to the plastic. All of this is accomplished by the rotation of the screw in the barrel, and it can be seen that the role of the screw in the plastic machinery is decisive.
When the screw rotates, plastic will generate friction and mutual movement between the inner wall of the barrel, the bottom of the screw groove, the thrust surface of the screw edge, and plastic and plastic. The forward movement of plastic is the result of this combination of movements, and the heat generated by the friction is also absorbed to increase the temperature of the plastic and melt the plastic. The structure of the screw will directly affect the extent of these effects.
At the same time, the rotation of the screw causes shearing of the melt film between the solid bed and the inner wall of the barrel, thereby melting the solid between the melt film and the solid bed interface. As the solid bed spirals forward, the volume of the solid bed gradually shrinks, and the volume of the bath gradually increases.
If the solid bed thickness decreases at a rate lower than the shallower depth of the groove, the solid bed may partially or completely block the groove, causing plasticization to fluctuate, or due to partial pressure due to the melting speed of various plastics, the melt Viscosity, melting temperature range, sensitivity of viscosity to temperature and shear rate, corrosiveness of pyrolysis gas, and friction coefficient between plastic particles are very different. Common general purpose screw in common sense has outstanding characteristics in processing some melts. In plastics, there will be a certain period of high shear heat, this phenomenon can be eliminated by reducing the screw speed, but this will inevitably affect the production efficiency.