Basic HTML Version
The
EXTRUDER
TIMES
Continued...
Intake Zone
The Two popular methods of feeding an extruder are starve-feeding and force-feeding.
During force-feeding, a reserve of material is maintained in the hopper of the extruder
and material is “positively displaced” or “forced” into the extruder. Starve-feeding is the
condition when an extruder is fed at a rate less than the capacity of the screw. The
hopper remains empty and functions as a conduit to avoid material from spilling. Starve
feeding is the more popular method for feeding due to several advantages that will be
discussed later.
The modular design of the extruder screw assembly provides an option for a wide
selection of screw elements for configuring in the ‘intake zone’. The popular twin-screw
elements
2
are Single Flight Element (SFE), Schubkanten (SKE), Special Schubkanten
Element (SSKE), Normal Right-hand Screw element (RSE), Deep flight SK element (DSK),
and the newly invented Single Flight ‘V’ shaped (SFV) element.
Free Volume is the space available in a unit length (= diameter) of the extruder. This is
obtained by removing the space occupied by screw elements inside the 8 shaped barrel.
Conveying Efficiency is the ability of the element to move the material forward in the
extruder. It is 100%, if all the material moves forward at the completion of each turn of
rotation.
CONFIGURATION OF
SCREW ELEMENTS IN
EPZ!
A N O V E R V I E W
TABLE OF INTAKE ZONE ELEMENTS
ELEMENTS
NOMENCLATURE GEOMETRY &
PROFILES
CONVEYING
EFFICIENCY
FREE
VOLUME
TENDENCY TO
BREAKUP AND
COMPACT
CHARACTERISTICS
POTENTIAL USE
Single Flight
‘V’ Element
Highest
Medium Medium All Types
Right Handed
Screw Element
Low
Medium Medium Pellets
Deep Flight
Schubkanten
Low
Highest
Medium Tri-lobed Force-fed Powders
Schubkanten
Element
High
High
High
Powders, Mix of Powders
and Granules
Special
Schubkanten
Element
Low
Highest
Medium Bi-lobed Force-fed Extruders
Single Flight
Elements
Medium Low Low
Alloys & Blends with different
melt characterization
FEEDING
Nearly all twin-screw extruders are starve-fed,
although the degree of screw filling can vary,
depending on the requirements of the process.
MELT ING
All extruders melt plastic by heating it, but the
melting process is different in co-rotating and
counter rotating extruders. In a co-rotating
extruder, the plastic is subjected to intense
shearing and deformation in the kneading
blocks.
Melting (also called fusion) should be nearly, but
not fully, complete before the material leaves
the compression section and enters the vent
section. Insufficient fusion will allow powder to
enter the vacuum system, while complete fusion
will interfere with the removal of gas and vapor
at the vent.
Source: Handbook-TSE by SPE.
INTAKE
ZONE
MELTING
ZONE
VENTING
ZONE
MIXING
ZONE
VACCUM
[VENTING] ZONE
METERING
ZONE
FLEX YOUR RISK MUSCLE
Bull's-eye every time? If so, you're standing too close
to the target. As comedian Woody Allen puts it, "If
you're not failing every now and again, it's a sign
you're not doing anything very innovative." Everyone
has a "risk muscle" You keep it in shape by trying new
things. If you don't, it atrophies and you're no longer
able to take chances.
HOW CAN YOU EXERCISE YOUR RISK MUSCLE?
source: Roger von Oech's Creative Whack Pack.