What is the role of screw in plastic machinery?


The screw is an important part of the injection molding […]

The screw is an important part of the injection molding machine. Its function is to convey, melt, compact, stir and press the plastic. All of these are accomplished by the rotation of the screw in the barrel. It can be seen that the role of the screw in plastic machinery is pivotal.

When the screw rotates, the plastic will produce friction and mutual movement between the inner wall of the barrel, the bottom surface of the screw groove, the screw flight advancing surface, and the plastic and the plastic. The forward advancement of the plastic is the result of this combination of motions, and the heat from friction is absorbed to raise the temperature of the plastic and melt it. 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 molten film between the solid bed and the inner wall of the barrel, thereby melting the solid between the interface between the molten film and the solid bed. As the spiral shape of the solid bed progresses forward, the volume of the solid bed gradually decreases, while the volume of the molten pool gradually increases.

If the rate at which the thickness of the solid bed decreases is lower than the rate at which the groove depth becomes shallow, the solid bed may partially or completely block the groove, causing fluctuations in plasticization, or due to local 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 high-temperature decomposition gas, and friction coefficient between plastic particles are very different. Generally speaking, ordinary general-purpose screws have outstanding characteristics in processing certain melts. There will be a phenomenon of excessive shear heat in a certain section of plastics. This phenomenon can generally be eliminated by reducing the screw speed, but this will inevitably affect the production efficiency.