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.