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Screw plays an important role in plastic machinery

Release time:2022-11-7

Screw is an important part of injection molding machine, which is used to transport, melt, compact, stir and pressure plastics. All these are completed by the rotation of the screw in the barrel. It can be seen that the screw plays an important role in the plastic machinery.

When the screw rotates, the plastic will generate friction and mutual movement on the inner wall of the barrel, the bottom of the screw groove, the screw edge advancing surface, and between the plastic and the plastic. The advance 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 molten film between the solid bed and the inner wall of the barrel shear, so that the solid between the molten film and the interface of the solid bed is melted. As the spiral shape of the solid bed moves forward, the volume of the solid bed gradually shrinks, while the volume of the molten pool gradually increases.

If the speed at which the solid bed thickness decreases is lower than the speed at which the depth of the screw groove becomes shallow, the solid bed may partially or completely block the screw groove, causing the plasticization to fluctuate, or because the local pressure varies greatly due to the melting speed, melt viscosity, melting temperature range, viscosity sensitivity to temperature and shear rate, corrosivity of high-temperature decomposition gas, and friction coefficient between plastic particles, In general, when processing some plastics with outstanding melt characteristics, the common universal screw will have a phenomenon that the shear heat of a certain section is too high. This phenomenon can generally be eliminated by reducing the screw speed, but it will inevitably affect the production efficiency.