Guill’s Chief Engineer, Denis Finn, provides this helpful glossary of useful terms, used in the extrusion
business worldwide.
● Extrusion Die assembly- also known as crosshead, inline tubing die, head, die. Connected to the
extruder by feed pipe/flange. Forms extrudate into desired shape.
● Tooling- comprised of two components—the tip and the die.
● Tip- defines ID of product for a tubing application or locates the substrate in a jacketing
application. Tips are also known as pins, mandrels,
● Die- defines OD of product. AKA bushing.
● Land length- straight section at end of the tool set.
● Gum space- distance between end of tip and back of die land.
● Draw down ratio- relationship between ID and OD of tooling vs. the ID and OD of the finished
product.
a. Linear draw- the ratio of the ID of the die and OD of the product. And the ratio between
the OD of the tip vs the ID of the product.
b. Area draw- ratio between the cross sectional area of the output of the tooling and the
cross sectional area of the finished product.
● Draw balance- ratio of the outer surface of the draw down cone to the inner surface of the draw
down cone.
● Concentricity- how well centered the OD of the product is to the ID of the product or the
jacketed substrate.
● Ovality- how round the OD your product is
● Dead spot- section of the flow where material is allowed to stagnate. Usually causes burning
and degradation issues over time.
● Balanced flow- uniform exit velocity over the cross section of the product. A well balanced flow
produces a higher quality product.
● Fish eye, gel, unmelt, comet- common terms for unmelted or non-homogeneous melt
● Melt fracture-surface defect in product caused by shear degradation (usually manifests as a
grainy/frosted appearance on the surface of the extruded part.)
● Die drool- particle buildup on the outside surface of tooling. Buildup can break off and cause
defects on finished products.
● Bulk residence time- amount of time polymer spends in the extrusion die assembly
● Shear- term to describe a force that the melt experiences as it is forced through the extrusion
die assembly.
● Viscous dissipation aka shear heat- frictional heat generated as a result of shear.
● Viscosity- resistance to flow
● Cold spot- section of extrusion die assembly that is not adequately heated resulting in
imbalanced flow or a thermoplastic freeze off
● Rheology- science of characterizing a fluid’s behavior
● Draw down cone- section of molten polymer as it draws down to its final product dimension.
● Calibrator- device to precisely establish and control the desired product dimensions
● Stripe-feature to identify or establish orientation of finished product.
a. Encapsulated- stripe between outside and inside surfaces of product
b. Embedded- surface stripe with established depth. Typically a percentage of the wall.
c. Surface- stripe only on surface of product.
d. Window- strip that goes through the wall from OD to ID.
● Surging- inconsistent melt output that results in product dimension variation..
● Coextrusion- any extrusion that uses two or more extruders.
● Wire line/pass line- distance between face of extruder to the center line of the crosshead.
● Direction of travel- a way to establish production line orientation.
● Recommended moisture content- a qualifier of how dry your polymer should be before you
process it.
● Substrate- the material that is being coated in a jacketing process. Can be wire, bundle of
strands, fibers, etc.
● Jacketing- covering a substrate with melt.
● Multi-lumen- a tube with multiple internal cavities.
● Melt probe- a device to directly measure pressure and/or temperature of the melt.
● Thermocouple- a device to measure temperature of the extrusion die assembly. Typically used
to control heater output.
● Heater bands- provide heat to the extrusion die assembly.
● Flow distributor- shapes the melt to achieve balanced flow.
For more information, please contact:
Denis Finn
Guill Tool & Engineering
10 Pike Street
West Warwick , RI 02893
(401) 823-7600
www.guill.com
dfinn@guill.com