Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

46.3 EXTRUSION

 

· 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,

  1. - white chalk, used as a filler
  2. - plasticizers, improve flexibility
  3. - stabilizers, improve light and heat resistance
  4. - pigments
  5. - 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,

  1. - 5 to 10 lbs of material per hour for each horsepower
  2. - the motor is geared down to drive the screw (often variable)

 

· Breaker plate,

  1. - at end of screw, and before extrusion die,
  2. - it increases back pressure for the screw
  3. - converts rotational to parallel flow
  4. - it stops unmelted plastic and debris

 

· Special heads can be used to coats wires, etc.