THE PLASTICS EXTRUSION OPERATING
MANUAL
by Allan L. Griff, Consulting Engineer
Outline of Contents
Introduction to Extrusion --mechanical and
thermal principles, variables, typical values.
Drive System -- motors, speed reduction and
variation, thrust bearings.
Screws and Barrels -- three-zone concept, L/D,
pitch, compression ratio, clearances, materials of construction,
special designs: Maddock, barrier, pins, grooves, vents and twin-screw
systems.
The Head Zone -- screens and changers,
breaker plates, safety devices, measurement of pressure and melt
temperature, static
mixers, gear pumps.
Extrusion Dies -- materials, heating, need to
reduce resistance.
What Happens Inside the Barrel -- feed zone:
perfect bite and overbite, use of barrel heat to control wall friction,
starve feeding, grooved barrels, bulky feed.
What Happens Inside the Barrel -- compression zone:
melting mechanism, backflow over the flights, solid bed theory, surging
and use of the motor ammeter.
What Happens Inside the Barrel -- metering zone:
final mixing and melting, drag flow and pumping capacity, melt density,
blue-screw syndrome, melt pressure measurement.
What Happens in the Head and Die -- concept of
resistance, back-pressure, streamlining, die lines, die temperature
control, dimension control, swell, drawdown, orientation.
Setting Conditions -- think in zones, not
profiles; what controllers and microprocessors do.
Maintenance -- 12 key areas (motor, heaters,
screw, etc.), cleaning small parts.
Safety -- dangers from heat, electricity,
moving parts, weight, other hazards.
Start-up, Material Change and Shutdown --
preheating, full or empty screw, watch vital signs, purges, disassembly
and cleaning, screw removal.
Common Problems -- surging, poor mixing,
roughness, overeating, moisture, air, contamination.
Materials for Extrusion -- explanation of melt
index, quality tests for incoming materials.
Directory -- websites and phones of over 350
suppliers of new and used equipment.
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