The extruder screw is perhaps the single most important component in an extrusion machine. The screws are machined out of a solid rod with thread that is used for conveying plastic material within the extrusion barrel.
The design of the screw itself is an engineering marvel. A single screw has 4 major functions:
- Conveyor – use or conveying plastics resin through the extruder.
- Imparting heat energy – the screw creates pressure and grinds the material thus producing heat that is used to melt the plastic material.
- Mixing – used for mixing material with colorant to create an uniformly mixed colored resin.
- Compacting – to build pressure within the extruder and to expel trapped air before the molten resin is being pushed through the die (or mold).
Does one screw fit all types of plastic material? No! General purpose screws are used for more common materials like PP and PE. Specially designed screws are available for corrosive material like PVC, and there are also screws for highly abbrasive materials like Nylon and PC.
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