• 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
- 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)
- 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.
