The screw is an important component of an injection molding machine, which functions to transport, melt, compact, stir, and apply pressure to plastics. All of this is achieved through the rotation of the screw inside the barrel, indicating that the screw plays a crucial role in plastic machinery.
When the screw rotates, plastic will generate 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 plastic and plastic. The forward movement of plastic is the result of this combination of motion, and the heat generated by friction is also absorbed to increase the temperature of plastic and melt it. The structure of the screw will directly affect the degree of these effects.
At the same time, the rotation of the screw causes a shear effect on the molten film between the solid bed and the inner wall of the barrel, thereby melting the solid at the interface between the molten film and the solid bed. As the spiral shape of the solid bed moves forward, the volume of the solid bed gradually decreases, while the volume of the molten pool gradually increases.
If the speed at which the thickness of the solid bed decreases is lower than the speed at which the depth of the screw groove becomes shallower, the solid bed may partially or completely block the screw groove, causing fluctuations in plasticization, or due to local pressure caused by the melting speed, melt viscosity, melting temperature range, sensitivity of viscosity to temperature and shear rate of various plastics, corrosiveness of high-temperature decomposition gas, and significant differences in friction coefficient between plastic particles. Generally, ordinary universal screws may experience excessive shear heat in a certain section when processing plastics with prominent melt characteristics. This phenomenon can generally be eliminated by reducing the screw speed, but it will inevitably affect production efficiency.
