46.3 EXTRUSION

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The basic process - plastic is melted and pushed through an extrusion die with a desired cross section. The plastic leaves the die in roughly the right shape. It is then passed through a sizing and cooling apparatus. Finally, for wound product, it passes through pullers, and onto a spool.

Basically a screw, like that described in injection molding is used to melt the plastic and generate pressures.

Some additive for plastics are,

- white chalk, used as a filler

- plasticizers, improve flexibility

- stabilizers, improve light and heat resistance

- pigments

- lubricants minimize sticking and improve flow

Typical extrusion conditions are, [Source, unknown]

The typical extruder barrel is between 20:1 and 28:1 for length to dia., and typical pressures are 10 to 20 ksi.

Typical motor characteristics are,

- 5 to 10 lbs of material per hour for each horsepower

- the motor is geared down to drive the screw (often variable)

Breaker plate,

- at end of screw, and before extrusion die,

- it increases back pressure for the screw

- converts rotational to parallel flow

- it stops unmelted plastic and debris

Special heads can be used to coats wires, etc.