2. Principle
• The molten plastic material under suitable condition is forced
through the die/ orifice which impart the desired shape/
profile to the extrudate. Or
• The plastic material is melted with the application of heat
and extruded through die into a desired shape.
3. Working
• The plastic material in compounded form is fed through the
hopper into the barrel / cylinder having provision for heating
for softening the plastic material.
• The hot plastic charge is further worked through the cylinder
by a helically flighted revolving screw.
• The temperature of the plastic material rises owing to the
frictional heat produced by the compression of the charge
between the rotating screw and the cylinder surface.
• During the movement of plastic material from hopper to the
die, the plastic material passes through three zones named
feed zone, compression zone and metering zone.
4. Working
• Each zone contributes in its own way to the overall extrusion
process.
• The feed zone receives the plastic material / charge from the
hopper and send it over to the compression zone. No heating
takes place in the feed zone.
• In compression zone, the plastic material melts due to the
heat conducted from the heating source and is compressed
by the working of the screw.
• The pasty molten plastic material is then sent to the metering
zone, where it acquires a constant flow rate imparted by the
helical flight of the screw.
5. Working
• The pressure built up in the metering zone enables the plastic
melt to enter the die and emerge out of it with the desired
profile.
• The extruded material of the desired profile emerging the die
is quite hot and has to be cooled rapidly to avoid deshaping.
• The extrudate is accordingly carried over a conveyor belt
through a tub containing cold water.
• During this process, the material dissipates heat to the water
and gets set.
• The product formed is cut to the desired length or wound
onto the roll.
8. References
• Plastic engineering handbook by Joel Frados.
• Polymer extrusion by hanser publication.
• Polymer processing by DH Morton Jones.
• Hand book of plastic technology by W.S. Allen/ P.N. Baker.
• SPI Plastics Engineering Handbook by Michael L. Berins.
• SBP Handbook of Plastics.
