Adiabatic Extrusion
A method of extrusion in which
the sole source of heat is the conversion of the drive
energy through the viscous resistance of the plastics mass
in the extruder.
Barrel
The portion of the extruder
surrounding the screw or plunger.
Barrel
Liner
A sleeve forming the internal
surface of the barrel.
Compound
Plastics material as prepared
for a further manufacturing operation particularly for
extrusion, moulding or calendering.
Compression
section
Part of the transition section
in which there is a reduction in screw channel volume.
Cooling
tank
A tank commonly containing water
through which extrusion is continuously passed for cooling.
Crosshead
die
An extrusion die which produces
an extrudate the axis which is at an angle to that of the
extruder barrel.
Cure
The process of cross-linking a
plastics material.
Decompression
section
In a two-stage extruder that
part in which there is an increase in screw channel volume.
Die
A part or assembly of parts
held, contained or fitted to the extruder head to form the
melt to the desired profile.
Die
plate
In moulds, the main support for
the punch or mould cavity.
Discharge
section
The flighted portion of the
screw at the discharge end in which the melt is forced
towards the die.
Draw
down
Reduction of thickness of
plastics emerging from the die by control of haul off speed.
Drive
The entire system used to supply
mechanical energy to the screw.
Dry
blend
A free flowing mixture of resin
or compound and other ingredients as prepared for a further
manufacturing operation particularly for extrusion or
moulding.
Embossing
The production of embossed film
or sheeting.
Embossing
roll
A roll having a patterned
surface used to produce embossed sheeting.
Extrudate
The product of an extrusion
process.
Extruder
head
A component which may be
attached to the discharge end of the extruder barrel to
house the die.
Extruder
size
The nominal inside diameter of
the extruder barrel.
Extrusion
A continuous shaping of plastic
material by forcing it, as a melt, by pressure through a
die.
Extrusion
coating
A method of coating in which
molten plastics is fed direct from an extruder die into a
nip-roll assembly together with the substrate.
Extrusion
pressure
The pressure of the melt at the
discharge end of the screw.
Gelation
(compounding)
A stage in compounding material,
at which it first becomes a coherent mass.
Haul
off or caterpillar
A device for taking away
extrudate continuously from the die.
Heating
zones
Parts of the barrel, head and
die arrange for independent temperature control.
Internal
mixer
A mixer consisting of specially
shaped rotors operated in a closed chamber.
Length-to-diameter
ratio (L/D ratio)
Effective screw length divided
by the screw diameter and commonly expressed as a ratio to
unity.
Masterbatch
A compounding ingredient resin
and additives with the additives present in higher
concentration than are required in the final plastics
material.
Matting
The process of rendering a
polished surface uniformly dull.
Melt
Extrusion material when heated
to a plastic condition.
Metering
section
The flighted portion of the
screw at the discharge end, in which the melt is forced at a
controlled rate towards the die.
Outer
die ring
The part of tubing die which
shapes the external surface of a tube.
Post
cure
To continue the cure of a
moulded article by a subsequent heating process.
Processing
aid
An additive to, or a component
in, a resin to facilitate processing.
Ram
extruder
A machine consisting essentially
of a barrel with means of temperature control, in which a
plunger operates to force material as a melt to a die.
Ram
pressure
Used colloquially for the total
force applied by a hydraulic ram, equal to the hydraulic
pressure multiplied by the ram area.
Screen
pack
Wire gauzes supported by the
breaker plate and used for filtering the melt and increasing
back pressure.
Screw
A helically grooved rotating
member housed in the barrel of a screw extruder.
Screw
diameter
The diameter developed by the
rotating flight land about the screw axis.
Screw
extruder
A machine consisting essentially
of a barrel with means of temperature control and housing
one or more rotating Archimedean screws which convey
plastics materials from feed aperture and deliver it as a
melt under pressure to a die.
Take
up (extrusion)
A device for reeling extruded
material.
Torpedo
(extrusion)
A device at the discharge end of
the screw for completing mixing and homogenising of the
melt.
Transition
section
The flighted portion of the
screw between the feed and discharge sections in which the
extrusion material becomes a melt.
Travelling
saw
A saw which travels with the
extrudate while cutting it to length.
Twin
screw extruder
An extruder with a pair of
screws working together in a common barrel.
Two-stage
extruder
A screw extruder so designed
that the pressure of the extrusion material drops
substantially, part way along the screw.
Two-stage
screw
A screw for use in a two stage
extruder comprising a decompression section before the final
metering section.
Vacuum
sizing
A process using a sizing die
with vacuum applied to the external surface of the extrudate.
Vacuum
tank
A cooling tank operating under
reduced pressure to control the dimensions of the extrudate.
Vent
A hole or groove in a mould
provided to allow air or volatile matter to escape during
the moulding operation.
Vented
extruder
A two-stage screw extruder
having an opening part way along the barrel for the removal
of air and volatile matter from the plastics material.
Weld
line
A mark formed by union of two or
more streams of material flowing together.
