The extrusion process is one that predates plastic itself but it’s one that has become synonymous with plastic applications today. To get the perfect extruded part, plastic manufacturers use several techniques, machines and methods.

To help extruders save money, yield higher quality products, and use equipment more efficiently, industry expert Allan L. Griff put together 10 important principles to keep in mind. We take a brief look at these principles in this three-part post.

The mechanical principle

The basic mechanics of extrusion are simple; a screw turns in a barrel and pushes the plastic forward. The intent is to multiply the force so that a great resistance can be overcome. Sir Isaac Newton explained that if a thing is not moving in one direction, the forces on it are balanced in that direction. So, the axial forces on the screw are balanced, and if it is pushing forward with great force on the plastic melt it must be pushing backward on something with equal force.

The thermal principle

Feed preheating and barrel/die heaters may contribute, and are critical at start up, but heat generated inside the barrel as the motor turns the screw against the resistance of the viscous melt is by far the most important source of heat for most systems.

The speed reduction principle

In most extruders, screw speed is changed by modifying motor speed. Motors typically turn at around 1750 rpm at full speed, but this is much too fast for an extruder screw. If it were turned that fast, it would generate too much frictional heat, and the residence time of the plastic would be too short to prepare a uniform, well-mixed melt. A typical reduction ratio is between 10:1 and 20:1.

Don’t miss part two of our post where we look at three more principles of extrusion.

Plastic & Chemical Trading together with our international partners deliver world class extrusion solutions to South Africa. If you’re in the market for a plastic manufacturing solution that can stand the test of time, contact Plastic and Chemical trading today.

Source: Allan L. Griff

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