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Abrasive Wear
Wear caused by the continual contact, under pressure of hard particles
in the resins against the barrel lining, screw and valve components.
The abrasive particles may be fillers or reinforcements, such as
fiberglass, calcium carbonate, powdered metals and others.
Additive
A substance compounded into a resin to modify its characteristics
(i.e. intestates, stabilizers, plasticizers, flame retardants, etc.).
Adhesive Wear
Wear resulting from two metals rubbing against each other, such
as the screw flight lands and valve rings coming into contact with
the barrel lining during operation.
Amorphous
A term describing polymers having no crystalline structure.
Anneal
To heat an article to a predetermined temperature and slowly cool
it to relieve stresses. The annealing of metal components may reduce
their hardness.
Ball Check Valve
A device mounted at the discharge end of an injection screw used
to allow forward flow of plastic during recovery and no flow during
the injection stroke. This valving is accomplished by positioning
of an internal ball.
Barrel (Cylinder)
A cylindrical housing in which the screw rotates, including the
integrally formed special inner surface material, or replaceable
liner, if used. Also commonly referred to as a cylinder.
Barrel Shell (Backing Material)
The outer thick wall of the barrel made from metal backing material
to provide strength and to hold the lining.
Barrier Flight
A secondary flight of reduced outside diameter and usually designed
to separate melted polymer from solid polymer or to enhance melting
by having the polymer pass over it.
Bayonet Adapter
A cylindrical shaped part with holding pins that threads into the
thermocouple hole and retains a spring loaded thermocouple.
Bearing (HUB)
The portion of the screw immediately behind the flighted length
which prevents the escape of material and provides a seal between
the screw and the barrel.
Bell End
A flange at the discharge end of the barrel which provides added
strength to withstand internal pressure.
Bimetallic
A term used to indicate that a barrel is composed of two (or more)
metals, commonly used to refer to barrels which have a centrifugally
cast lining.
Blister Ring
A raised portion of the root between flights of sufficient height
and thickness to effect a shearing action of the polymer as it flows
between the blister ring and the inside wall of the barrel.
Blow Molding
A method of fabrication in which a warm plastic parison (hollow
tube) is placed between the two halves of a mold cavity and forced
to assume the shape of that mold cavity by the use of air pressure.
Pressurized air is introduced into the inside of the parison through
a blow pin thereby forcing the plastic parison against the surface
of the mold that defines the shape of the product.
Bore
The inside diameter of the barrel which houses the screw.
Breaker Plate (Extrusion)
A metal plate installed across the flow of the melt between the
end of an extruder screw and the die adapter with openings through
it such as holes or slots. It commonly supports a screen and also
reduces any swirling in the melt flow before it reaches the die.
Breaker Plate Recess (Extrusion)
The internal counterbore at the discharge end of an extruder barrel
that accepts the breaker plate and provides the seal and alignment
of the die adapter.
"C" Clamp Flange
A circular tapered flange at the discharge end of an extruder barrel
used to hold the die adapter. A similar shaped flange on the die
adapter and a "C" shaped clam accomplishes the closure.
Channel
With the screw in the barrel, the space between the flights bounded
by the root of the screw and the bore of the barrel.
Channel Area (Axial)
The cross-sectional areas of the channel measured in a plane through
and containing the screw axis.
Channel Depth
The distance in a radial direction from the bore of the barrel
to the root of the screw.
Channel Volume
The volume developed by the "axial area of screw channel"
in one revolution about the screw axis. The location of measurement
should be specified..
Channel Volume (Enclosed)
The volume of screw channel starting form the forward edge of the
feed opening to the discharge end of the screw channel. Also called
screw inventory.
Channel Width
The distance across the screw channel in a direction perpendicular
to the flight measured at the periphery of the flight.
Check Ring
The cylindrically shaped component of a non-return valve that reciprocates
in an axial direction. During injection, the ring shuts off against
the surface of the rear seat of the valve preventing the melt from
flowing backward toward the feed section of the screw. During screw
recover, the ring rests against the front seat (or stud in a three
piece valve) of the valve allowing melt to flow forward through
the valve to the discharge end of the barrel.
Clearance (Screw/Barrel)
The difference in the diameters of the screw and the bore (diametral
clearance) or, more commonly, one-half the diametral clearance,
referred to as radial clearance.
Coefficient of Thermal Expansion
The fractional change in dimension (sometimes volume) specified
of a material (plastic, metal or other materials) per a unit change
in temperature.
Color Concentrate
A measured amount of die or pigment combined into a predetermined
amount of resin, serving as a carner to for a color concentrate.
The concentrate is then added to the bulk of the resin in measured
quantity to achieve a predetermined color in the finished plastic
product.
Compression Ratio (Channel Depth)
The factor obtained by dividing the channel depth in the feed section
of the screw by the channel depth in the meter section (or the depth
of the last complete flight). This Channel Depth ration is commonly
referred to as the Compression Ratio. In constant lead screws this
value approximates, but is greater than the volumetric compression
ratio.
Compression Ratio (Volume)
The factor obtained by dividing the developed channel volume of
the screw at the feed opening by the developed volume of the last
full flight prior to discharge. This is not the commonly used definition
of compression ratio (see Compression Ratio - Channel Depth)
Compression Section
See Transaction Section
Concentricity
The term to describe two circles or cylindrical shapes having a
common center and common axis, such as the inside and outside diameters
of the flighted surface and bearing surface of a screw. Deviation
from concentricity is referred to as "Runout".
Conical Transition
Transition where the depth charge is accomplished with a conical
shaped root surface (interrupted by the screw flights).
Core
An internal hole extending longitudinally from the shank through
a portion of the screw for the circulation of a heat transfer medium
or installation of a heater.
Corrosive Wear
Wear caused by the attack of various acids on the surface of screws,
barrels, valves and other processing components. Acids formed in
the processing of plastic erode and pit the metal surfaces. The
acids come from the polymers themselves or from flame retardants,
forming and coupling agents.
Counterbore
The recessed area in the discharge end of an injection barrel which
acts as a pilot to assure the concentric fitting and seal surface
of the end cap to the barrel.
Crystallinity
A state of molecular structure in some polymers that denotes uniformity
and compactness of the molecular chains forming the polymer.
Cycle
The complete, repeating sequence of operations in a process or
part of a process. In molding, cycling time is the elapsed time
between a certain point in one cycle and the same point in the next.
Cylinder
See Barrel
Diameter (Barrel)
The nominal inside diameter of an extrusion or injection barrel.
See Bore.
Diameter (Screw)
The nominal outside diameter of a screw. See Flight Land.
Die
The metal orifice mounted to the discharge end of a extruder barrel
through which the melt flows to form a desired extrudate. Commonly
includes the die block and die adapter which holds the die block.
Die Adapter
Part of an extruder die which holds the die block.
Die Block
Part of an extruder die which contains the orifice through which
the melt flows to form an extruded product.
Dispersive Mixing
The mixing of a fluid (melted polymer) with a solid (unmelted polymer,
pigment and agglomerates above a certa size, etc.) which exhibits
a yield port. Dispersive mixing is involved in the final melting
of a polymer or breaking down a pigment in the manufacture of a
color concentrate.
Distributive Mixing
The mixing of a fluid (melted polymer) and other components (such
as liquid color concentrate) where all components are fluids and
do not exhibit a yield point. Distributive mixing is aimed at achieving
thermal and color uniformity where no solids breakdown is required.
Endcap
The device that bolts to the discharge end of an injection barrel
and adapts the injection nozzle.
Endcap Bolts
The bolts used to attach the endcap to the injection barrel.
Extrudate
The stock or melt as it emerges from the discharge orifice (die)
in a desired product form, such as film, pipe, coating on wire and
others.
Feed Housing
A separate components of an extruder barrel assembly which contains
the feed openings, water cooling channels and, in some cases, a
grooved interior lining. It is capable of withstanding high pressures
(15,000 PSI or more), especially if it is grooved, and may incorporate
a thermal barrier between it and the barrel to which it is attached.
Also referred to as feed throat.
Feed Opening
A hole through the feed section of the barrel for the introduction
of feed material into the barrel. Also referenced to as feed hole
or feed port.
Feed Port
See Feed Opening
Feed Section (Screw)
The portion of the screw which receives the material to be processed
and conveys it to the transition section of the screw. The feed
section normally has a constant channel depth and constant root
diameter.
Filler
An insert substance added to plastics for the purpose of improving
physical properties or process ability, or to reduce the cost of
material.
Flange
A short external section of the barrel, with a large diameter,
through which bolt holes have been placed to either assist in mounting
the barrel to the machine, or to which an end cap, die adapter or
other member is fastened. It may also add strength to that section
of the barrel.
Flight
The helical metal thread or raised portion of the screw.
Flight Angle
See Helix Angle.
Flight Cutback
The portion of the screw at the discharge end that is not flighted.
This is normally included for calculations as part of the flight
length.
Flight Depth
The distance in a radial direction from the land of the screw flight
to the root.
Flighted Length
Overall axial length of the flighted portion of the screw, from
the start of the feed pocket to the front end of the register or
(in the case of extruder screws or smear head screws) the point
where the mot diameter begins to decrease. Flighted length does
not include valves.
Flight Face
The face of the flight extending from the root of the screw to
the flight land. The rear face is the side toward the feed section
and the front face is the side toward the meter end of the screw.
Flight Hard Surface
A screw flight having its periphery harder (or more wear resistant)
than the base screw metal achieved by flame hardening, induction
hardening, heat treating, depositing of hard facing metal, or other
means.
Flight Land
The surface at the radial extremity of the flight constituting
the periphery or outside diameter of the screw.
Flight Land Width
The distance across one flight land in a direction perpendicular
to the flight. Commonly referred to as flight width.
Flight Lead
The distance in an axial direction from the center of a flight
land to the center of the same flight land after one complete turn.
This is not flight pitch in a mufti-flighted screw.
Flight Pitch
The distance in an axial direction from the center of a flight
land to the corresponding point of an adjacent flight land.
Front Radius
The radius at the intersection of the front or pushing side of
the flight and the screw root. Usually this radius is smaller than
the rear radius and may change from one portion of the screw to
another.
Front Seat (Valve)
A separate wear resistant component of a non-return valve that
limits the forward travel of the check ring.
Grooved Liner (Or Barrel)
A liner whose bore is provided with longitudinal grooves, usually
for several diameters in the feed section only.
Heater Bands
The electrical heating elements mounted on or around the barrel,
adapters, dies. nozzles! etc.
Heating Zone
A portion of the barrel length having independent temperature control
of the heater bands.
Helix Angle
The angle of a screw flight at its periphery relative to a plane
perpendicular to the screw axis.
It is calculated as: Helix Angle = Arctangent ( Lead) Pi x D)
Hopper (Feed)
A funnel-shaped container mounted directly on the barrel over the
feed opening to hold a reserve of material to be processed.
Hygroscopic
A term applied to polymers in their pellet or powder form indicating
a tendency to absorb moisture from air.
Injection Pressure
The pressure of the injection screw against the melted plastics
material (expressed in PSI), excluding any loss of pressure due
to frictional drag of the screw, equal to the force acting upon
the injection piston.
Injection Rate
The injection rate is the calculated rate of displacement of the
screw (or plunger), expressed in cubic inches per second, computer
at the injection pressure specified.
Inlay
A hard surface portion of a flight land not extending across the
full flight width.
Involute Transition
The transition where the depth change is accomplished with a root
surface which remains parallel to the screw axis but changes its
depths.
L/D Ratio (Screw)
The ratio of the working flighted length of the screw (distance
from the front edge of the feed opening to the forward end of the
screw flight when the screw is in the forward position) to Its outside
diameter. In practice, the ratio calculation is simplified to dividing
the flighted length of the screw by its nominal diameter.
Lead (Screw)
The distance measured parallel to the screw axis from one edge
of the top of a screw flight to the same edge of the same flight
after one complete turn. It is not the distance measured to the
next screw flight in a multiflighted screw. (For this see PITCH)
Liner
The wear resistant removable sleeve(s) in the barrel.
Lining
The internal wear resistant portion of an extrusion or injection
barrel. The lining may be metallurgically bonded to the inside diameter
of the barrel shell or be removable liners that are press or shrink
fit into the barrel shell bore.
Melt
Plastic material in a molten condition.
Melt Channel
The channel in a barrier screw designed to collect and convey forward
the melted polymer.
Metering Section
The portion of the screw at the discharge end with a constant flight
depth and having a length of at least one turn of the flight.
Mixing Section
An area of the screw with special geometry designed to enhance
-distributive and/or dispersive mixing in the melted polymer:.
Nitriding (Gas)
The surface hardening of certain alloy steels by heating the steel
in an atmosphere of nitrogen (ammonia gas) at approximately 9500F.
A very hard (70+Rc) case depth of .007" to .0 15" results
which is wear resistant. Process is commonly used for barrel inside
diameters, screws and valve components.
Nitriding (ION)
The surface hardening of certain alloy steels by heating the steel
(to approximately 600 OF) in an atmosphere of hydrogen gas, adding
an electrical charge to the steel and nitrogen gas, allowing a bombardment
of the positively charged steel by hydrogen and nitrogen gas ions.
This creates a hard (70+Rc) wear resistant, case hardness to a slightly
greater and more uniform depth than gas nitriding with less distortion
or contamination of the workpiece. Process is commonly used on screws
and valve components.
Non-Return Valve
A device mounted at the discharge end of an injection screw that
uses a sliding ring to allow flow of plastics in one direction only.
On screw recovery it allows flow forward. On injection stroke it
allows no flow and makes the screw perform like a plunger.
Nose Cone
The conical surface at the discharge end of an extrusion screw.
Nozzle
A device that threads into the endcap and adapts the nozzle tip
to the endcap.
Nozzle Tip
A device that threads into the injection nozzle and adapts between
the nozzle and the sprue bushing of the injection mold.
Overall Length (Screw)
The total length of the screw parallel to the screw axis. It includes
the flighted length, the shank and any nose cone, but not the non-return
valve.
Parison
The hollow tube of molten polymer which is pinched at one or both
ends and inflated in a blows mold to make a hollow part. See Blow
Molding.
Pilot (Barrels)
A cylindrical portion at the rear end of an extruder barrel used
to locate the barrel with the feed throat.
Pilot (Screws)
An internal cylindrical surface at the front end of an injection
screw used to accurately locate a non-return valve or other portion
that attaches to the screw.
Pitch
The distance measured parallel to the screw axis from one edge
of the top of the screw flight to the same edge of the adjacent
flight. In the case of a mufti-flighted screw the pitch is less
than the lead.
Plasticizing Capacity
The maximum quantity of a specified plastic material that can be
raised to a uniform and moldable temperature in a unit of time.
This capacity is generally expressed in pounds per hour (or ounces
per second) as calculated from the recovery rate.
Pocket
A place where a screw flight is initiated, usually starting from
a cylindrical area or another flight. A feed pocket exists on most
screws and is located at the intersection of the bearing and the
beginning of the flight.
Polymer
A high-molecular weight organic compound, natural or synthetic'
whose structure can be represented by small repeat units (monomers)
forming chemical bonds with the same or other monomers. If two or
more monomers are involved, a copolymer is obtained.
Press Fit
An interference fit, characterized by constant bore pressure throughout,
achieved by mechanically forcing the entering piece into the receiving
piece by use of a press or similar machine. Barrel liners may be
press fit into the prepared barrel shell.
Pressure Tap
A hole designed to accept a pressure transducer or pressure gauge.
Pump Ratio
The ratio obtained by dividing the depth of the second metering
section by the depth of the first metering section on a two-stage
screw.
Pushing Side
The flight face of the screw flight that faces the discharge end
and runs from the front radius to the top of the flight land. This
surface is commonly close to being perpendicular to the axis of
the screw.
Raised Register
A register that has a larger diameter than the adjacent root diameter.
This is sometimes supplied on injection screws having metering depths
too deep to match the rear seat of a standard non-return valve.
Rear Radius
The radius at the intersection of the rear or trailing side of
the flight and the screw root. Usually this radius is larger than
the front radius and may change from one portion of the screw to
another.
Rear Seat
A flat, ring shaped portion of a non-return valve that abuts the
front vertical face of an injection screw and seals the flow of
plastic by contact with the rear conical shaped end of the check
ring.
Recovery Rate
The weight (or volume) of a specified moldable material discharged
from the screw per unit of time, when operating at 50% of injection
capacity, as determined by SPI test procedure. The rating is normally
expressed as ounces r cubic inches) per second.
Register
The cylindrical portion of an injection screw at the most forward
end accurately machined to match the rear seat of the non-return
valve.
Relief
An area of the screw shank of lesser diameter than the outside
diameter and located between the bearing and the spline or keyway.
Resin
Any of a class of solid or semi-solid organic products of natural
or synthetic origin, generally of high molecular weight with no
definite melting point. In the broadest sense the term is used to
designate any polymer that is a basic material for plastics. Most
resins are polymers.
Retainer
The larger part of a no n-return valve that threads into the injection
screw. The forward portion retains the front seat or the sliding
ring. The front end of the retainer is usually torpedo or conical
shaped and usually is fluted.
Ring (Valve)
See Check Ring.
Rockwell Hardness
A common method of expressing the degree of hardness of a material
by testing its resistance to indentation, under pressure, by a diamond
or steel ball. Results are expressed on various scales, the most
common of which is the "C" scale, identified as Rc, which
is used to compare the hardness of barrel linings, screw surfaces
and valve components. A similar test, Brinnell hardness test, expresses
results on a somewhat different scale and is identified as HB.
Root
The surface of the screw between the flights, usually a cylindrical
or conical shape, of a diameter smaller than the outside diameter
of the flights.
Screen Pack
A woven metal screen or equivalent device installed across the
flow of melt between the tip of an extruder screw and the die and
supported by the breaker plate. It is used to strain out contaminants
or to increase the back pressure or both.
Screw
A helically flighted shaft which rotates within the barrel to mechanically
work and advance the material being processed.
Screw Axis
A reference line of infinite length drawn through the center at
the rear of the shank and the center of the discharge end.
Screw Channel
See Channel.
Screw Diameter
The dimension defined by the cross-section of the screw bounded
by its flight lands. Although it is usually expressed as a nominal
diameter (such as 3 1/2") its actual diameter could be 3.490"
to 3.492".
Screw Inventory
See Channel Volume (Enclosed)
Screw Speed
The number of screw revolutions per minute (RPM).
Sealing Ring
A round ring used in place of a breaker plate to seal between an
extruder b barrel and the die adapter.
Shank
The non-flighted portion of the screw at the drive end.
Shear Ring
See Blister Ring.
Shot.
The yield from one complete Injection molding cycle, including
the part, runner systems and flash.
Shot Capacity
The maximum volume of material which an injection molding machine
can produce from one forward motion of the screw. Commonly expressed
in ounces.
Shrink Fit
An interference fit, characterized by a constant bore pressure
throughout, achieved by heating the larger receiving piece to allow
the smaller mating piece to enter. In some cases, barrel liners
are shrink fit into the prepared barrel shell. See also Press Fit.
Sleeve
See Liner.
Smear Tip
A conical device used in place of a non-return valve at the discharge
end of an injection screw. This smear tip is generally used with
high viscosity, heat sensitive materials where a non-return valve
would cause degradation.
Solids Channel
The channel in a barrier screw that is connected to the feed channel
and is designed to contain and convey forward unmelted polymers.
Square Pitch
A screw flight where the pitch is equal to the nominal screw diameter,
i.e., 3 1/2" diameter screw with a 3 1/2" lead
Surging
A pronounced fluctuation in extruder output over a short period
of time without a deliberate change in operating conditions.
Swing Gate
A hinged device mounted at the discharge end of an extruder barrel
and used to support the die adapter.
Swing Gate Flange
A flange at the discharge end of an extruder barrel using bolts
to attach the die adapter to the barrel.
Thermocouple
A device, consisting of two dissimilar metallic conductors in contact.
that produces an electrical current whose magnitude depends upon
the temperature of the junction. The resulting temperature measurement
feeds into a pyrometer to help monitor and control the temperature
of a barrel or nozzle. The thermocouple is housed in a steel tubing
adapter.
Thermocouple Hole
A machined hole in a barrel, nozzle or adapter designed accept
the thermocouple adapter.
Thermoplastic
A material that will repeatedly soften when heated and harden when
cooled. Typical thermoplastics are the styrenic polymers and copolymers,
acrylics, cellulosics, polyethylene, polypropylene, vinyl's, nylons
and various fluorocarbon materials.
Thermoset
A material that changes as a result of a chemical reaction to heat
and pressure, catalysts or ultra-violet light, from a soluble, fusible
stage to an insoluble infusible and cured condition. Typical thermoset
materials are unsaturated polyesters (BMC), aminos (melamine and
urea), alkyds, epoxies and phenolics.
T.I.R.
An abbreviation used to identify tolerances with respect to concentricity.
Total indicator Reading is standard terminology for drafting and
machinist work to describe the deviation in concentricity of a measured
surface from a selected surface as shown on a dial Indicator. Also
known as F.I.M. (Full Indicator Movement).
Torpedo
See Nose Cone.
Trailing Side
The flight face of the screw that faces the feed end and runs from
the rear radius to the top of the flight land.
Transducer
A device for transferring power generated in one system to another
system. Various types of electronic transducers are used in connection
with molding and extruding equipment to measure, monitor and/or
control linear position, pressure, temperature, speed and other
factors. See separate MCMD publication covering Electronic Transducers
Used By the Plastics Industry.
Transition Section
The portion of the screw between the feed section and the metering
section in which the flight depth decreases in the direction of
discharge. This section is sometimes referred to as the compression
section.
Twin Barrel
A dual cylindrical housing in which two extruder screws rotate
side-by-side, including a nitrided inner surface or a centrifugally
cast bimetallic lining for resistance to wear. There are two major
types of twin barrels: one, which provides for the intermeshing
of the two extruder screws and; a second, in which the two extruder
screws do not intermesh. Intermeshing, counter-rotating twin screw
extruders are commonly used in profile extrusion of thermally sensitive
materials, such as PVC. Intermeshing and non-intermeshing, counter
and co-rotating twin screw extruders are used in a variety of specialty
polymer processing operations.
Two-Piece Barrel
A cylindrical housing in which the screw rotates, that is construction
of two sections. One section, which extends the full length of the
varrel, consists of an outer shell (typically constructed of annealed
alloy steel) with a full outside barrel diameter over the majority
of its length, then tapering abruptly to a much smaller diameter
over the final one-fourth (approx.) of As length at the discharge
end of the barrel. This section commonly has a centrifugally cast,
bimetallic lining for resistance to wear. The second section, is
an outer shell with full outside barrel diameter (construction of
heat treated alloy steel), which is shrink fit over the smaller
diameter of the first section and welded to the larger diameter
of that section at its taper area. The second section provides added
yield strength to the barrel at its discharge end.
Two-Stage Screw
A screw for a vented barrel consisting of a feed, transition and
meter section, followed by a decompression section (or vent section)
located under the vent to allow the escape of volatiles without
vent bleed. The decompression section has a deep channel and is
usually several diameters in length, followed by a second transition
and meter section. Frequently, two-stage screws are longer (24 to
32:1 L/D) than standard screws, although two-stage screws may be
as low as 20:1 L/D.
Vent Bleed
The unplanned escape of melt through the vent during the operation
of vented barrel processing.
Vent Deflector
A barrel with a vent which utilizes a two-stage screw to accomplish
the removal of volatiles from the material being processed.
Vent Hole
See Vent Port
Vent Port
An opening through the barrel wall, intermediate in the injection
or extrusion process, to permit the removal of air, water vapor
and volatile matter from the material being processed.
Vent Stack (Chute)
A device surrounding a major portion of the vent deflector designed
to prevent any material that might escape through the vent port
during start up from collecting on the barrel, heater bands or wiring.
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