EXTRUSION
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EXTRUSION:
 Continuous Process
 In principle, the plastic raw material is plasticated by means of a screw
plastication unit and the molten material is continuously pumped out through a
standard orifice (die) in order to take the shape and then the shape is set by
cooling/sizing system.
 Example:Film,Pipe,Tube, Profile, Monofilament, Box Strapping etc.
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CLASSIFICATION OF EXTRUDERS
1
Batch – Type
1.1
Ram Extruders
1.2
Reciprocating screw extruders
2
Continuous –Type
2.1
Screwless Extruders
2.1.1
Disk Extruders
2.1.2
Drum Extruders
2.1.3
Other Extruders
2.2
Screw Extruders
2.2.1
Single-Screw Extruders (SSE)
2.2.2
Twin-Srew Extruders (TSE)
2.2.3
Multi-Screw Extruders
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SINGLE SCREW EXTRUDER
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Single Screw Extruder
Parts & its functions
Screw Pump
:
Combination of Screw & Barrel
Hopper
:
Funnel like device, mounted on Hopper throat.
Holds a constant reserve of material.
Barrel
:
Cylindrical housing in which the screw rotates.
Hopper Throat
:
Circular opening at the feed end through which
the material enters the screw pump.
Drive System
:
AC/DC drives
Speed reduction gear box
Transmission system
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The Single-Screw Extruder consist of a screw rotating in
heated barrel or cylinder to which the material is fed.








Feed hopper
Extruder Screw and Barrel
Drive system (motor, gear box, transmission)
Thrust Bearing
Heating and Cooling Elements
Screen Pack and Breaker plate
Die
Temperature and pressure controls.
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Definition of terms
Compression Ratio
L/D ratio
-
is the ratio between the channel depth is the
feed zone to that of the metering zone.
-
Usually from 1.5 to 4:1
-
Length to nominal dia of screw
-
usually 20 to 22:1
Important Specification
Nominal dia of screw
Output(kgs/hr)
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Zones of Extruder & its Functions:
Feed Zone
Compression Zone
Metering zone
-
Transport the material from hopper to
compression zone.
-
Compacts, eliminates air gap
-
Transport the material from compression to
metering zone.
-
Softens the material
-
Melts, Mixes, the material pressurizes
and pumps the melt.
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Screw Nomenclature
P
W
L

is the screw pitch, distance between the centre of a two adjacent flights.
is the channel width
is the land width
is the helix angle, defined as an angle between the flight to the transverse plane of the screw
axis.
D
is the screw diameter, developed by rotating the flight about the screw axis.
R.D is the root diameter
Flight is the helical metal thread of the screw.
C
is the channel depth o radial distance form the bore of the barrel to the root
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SCREW TYPES
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Extruder Screws





General purpose screw
PVC screw
Nylon screw
Two stage screw/vented screw
Segmented screws is also available for special purpose
General purpose screw
PVC screw
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Nylon screw
P A SCREW
Two stage screw/vented screw
TWO STAGE SCREW
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Mixing elements
 Incorporated in the metering zone of screw
 Several designs
 Mainly to improve mixing, homogeneity
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THRUST BEARING


The screw fits into a thrust bearing located behind the feed hopper.
The function of the trust bearing is to absorb the thrust force acting on the
screw inside the extruder barrel
Typical Thrust Bearing as used in Single-Screw Extruders
Typical thrust bearing assembly – Single Screw Extruder



The bearing prevents the screw from moving backward.
Bearing life-time depends on the pressure and screw speed. For high speeds,
oversized being is needed.
For twin screw extruders several smaller bearings joined in one shaft is used.
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HEATING AND COOLING
ELEMENTS
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There are three methods of heating extruders:
1. Electric
2. Fluid
3. Steam Heating
Electric Heating
1. Induction Heaters
2. Cast-in Heaters
3. Band Heaters
i. Mica Insulated
ii. Ceramic Insulated
The electric heating is most commonly used due to :
1. Accuracy
2. Reliability
3. Easy to hook up.
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INDUCTION HEATERS
 AC Current passes through coil thus setting up a magnetic flux. Heat is
generated from the resistance offered to the eddy current set up by the flux.
 The barrel is heated directly by its resistance to the induced current
Schematic Arrangement Showing an Induction Heater in Section
Advantages :
Disadvantages :
 Accurate Control of Temperature.
 Relatively high cost.
 Good provision for cooling the barrel
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 No possibility for hot or cool
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CAST IN-HEATERS
The insulated heating elements are cast into semi-circular or flat aluminium
blocks, which are machined to match the surface to be heated
Cast-In
Resistance Heaters
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BAND HEATERS
They consist of Ni-chrome or other resistance wires mica or ceramic
insulated, then encased in steel cover.
MICA INSULATED
CERAMIC INSULATED
Flexible, supplied as a single piece.
Rigid, supplied in 2 halves
Can withstand a load of 23-31
KW/m2
Can withstand higher heating load
Shorter service life
Better services life
Less expensive
More costly
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FLUID HEATING SYSTEM
The heating fluid, that is most commonly used for extruders is oil. It may be
heated by any suitable means (mainly electrical). The heating system consists of
a heater a circulating pump, a surge tank, and a heat transfer channel in the
extruder barrel.
STEAM HEATING
The high specific heat and latent heat of vapourisation of water makes steam
an excellent heat transfer medium. However, this system is not frequently used
because of low maximum temperature that can be achieved, a need of working
with high pressure piping, frequent leaks of steam that require shutting down
of heating for repairs, and corrosion effects.
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COOLING SYSTEMS
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BARREL COOLING
 Barrel Cooling is needed to prevent overheating that may cause degradation.
 For small extruders fans that blow air over or around the barrel are used
 Other cooling system used include:
 Cooling channels inside the barrel wall
 Fins on the barrel or on the heaters to speedup heat transfer
 A water-fog spray over barrel.
 Continuous, controlled vaporization of liquid (Water)
 Copper tubing carrying cold water is sometimes used.
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HOPPER COOLING
 Water-cooling is used to cool the hopper throat to prevent bridging and to
protect the rubber parts present in the screw support assembly.
SCREW COOLING
 The cooling may freeze a layer of plastic on the screw root, reducing the
channel depth thus producing more shear at a cost of throughput.
 This may also reverse the required relationship between the friction coefficient
(low friction coefficient on the screw, high on the barrel), further reducing the
drag flow.
 Furthermore, there is a danger that the material staying a long time near the
screw root will degrade, contaminating the product.
 It is important to remember that the conveying ability of the screw is
controlled by the friction coefficient ratio : f(barrel) / f(screw) ó it is important
to maximize this ratio.
 Under normal circumstances the minimum value of the ratio that guarantees
conveying is 1.4.
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SCREW COOLING
 Screw cooling may be recommended to prevent decomposition of heat
sensitive materials
 However, it should be carried out using the cooling fluid at the temperature
above the softening point of the principal polymeric component.
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BREAKER PLATE
AND
SCREEN PACK
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BREAKER PLATE
Perforated circular metallic disc of about 4-5 mm thick.
Functions
- Support for Screen pack
- Converts the Spiral flow of melt in to stream lined laminar flow
- Holds back contamination and unmelted particles.
Fig.3.7
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SCREEN PACK
 Wire mesh 40,60,80
 Arrests the unmelted particles and contamination
 Helps in developing back pressure
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DIE DESIGN
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The role of a die is to form the melt into a desired linear product: fibres, films,
sheets, profiles, rods,etc.
The die is a channel, whose profile changes from that of the extruder bore to
an orifice, which produces the required form.
The dies can be classified using different criteria. For example, considering cross
section of the extrudate one may recognize dies to produce:

Solid Cross-Sections

Hollow Cross –Sections
Another classifications scheme is based on the die attachment to the extruder barrel:

Straight –through dies

Cross –heat dies

Offset dies
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SOLID CROSS - SECTIONS
 A Typical Die Design for extruding a solid rod is shown in fig.
 In the figure, DD is the diameter of die orifice, DB is the diameter of bore of
extruder barrel,  is the lead-in angle, and P is the die land.
 Because of the screen pack and breaker plate assembly, the pressure in the
extruder (PE) is reduced by the pressure loss across the assembly (PL).
 Since the die outlet is at atmospheric pressure, the working pressure is the die
pressure (PD) given by the difference: PD = PE – PL.
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HOLLOW SECTIONS
Hollow products like pipe or tubes are produced using the die design shown in
Fig.
 The outer diameter of tube is determined by the diameter of the outer die
ring orifice.
 The inner diameter is determined by the mandrel diameter
 To make the mandrel and outer die ring orifice concentric, centring screws
are provided.
 The mandrel is held in position by a spider. In the centre of the spider a
hole is drilled to supply air down the mandrel.
 To provide a smooth glossy extrudate, the die head is heated. A cold die
may cause blockage of the die.
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STRAIGHT – THROUGH DIES
 Those dies whose axes are arranged to be in line with the direction of
supply of melt.
 Spider, Mandrel is needed for tubes
 Used for the extrusion of pipe, rod, profiles and sheet
CROSSHEAD DIES
 Arranged with their axes at an angle of 908 (458 and 308 are also used) to
the melt feed.
 No need for spider assembly.
 Used for the production of insulated wires, cables
• OFFSET DIES
 Combination of both straight – through die and off-set die.
 Used for the production of pipe.
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EXTRUDATE SWELL
 Extrudate is contraction in the direction of extrusion and expansion in the
cross-section while emerging from the die is called Extrudate Swell.
 The phenomenon (previously called die swell) is illustrated in fig.
 Numerically, the extrudate swell is defined as the ratio of the outer extrudate
diameter (DE) to the other diameter of the die exit (DD), i.e., B = DE / DD
 When the melt emerges out of the die lips, there will be expansion in the
direction perpendicular to flow and contraction
in the direction parallel to
flow.
 Constrained molecules tends to relax at the die outlet. This leads to die swell.
 This is nullified by higher take off speed.
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Extrudate Swell may be reduced by :
 Decreasing the extrusion rate
 Increasing the melt temperature
 Increasing the die land
 Increasing the draw-down ratio.
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Die entry effect and exit
instabilities.
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MELT FRACTURE
 It is a die-entry effect
 In any converging flow there are tensile and shear forces
 If tensile stresses become large and if they exceed the tensile strength of melt,
the desirable smooth laminar flow is lost completely.
 The extrudate emerging from die exit will be of irregular shape. This
phenomena is called “Melt fracture”.
MELT FRACTURE
If die entrance is tapered
 Dead spots are eliminated
 Minimise development of tensile stresses and hence minimise distortion of
stream lines.
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SHARK SKIN & BAMBOOING EFFECT
Shark Skin
 Roughening of the surface of the extrudate
 The melt as it proceeds along the die channel, has a velocity profile with
maximum at the centre and zero at the wall.
 As it leaves the die lips, the material at the wall has to accelerate to the
velocity at which the extrudate is leaving the die.
 This generates tensile stress and if the stress exceeds Tensile strength, the
surface ruptures causing the visual defect - “shark skin”.

If the conditions causing shark skin becomes more intensive, eg. Pressure at
the extruder becomes excessive or die temperature drops, the extrudate
“snaps back” -- “Bambooing effect”.
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a Die
EXTRUDER OUTPUT
 The simplest way to understand the operation of SSE is to mentally unwind
the screw into a long, straight channel of decreasing depth.
 Now the barrel is visualized as a flat metal slab placed above the screw
flights at the distance corresponding to the actual gap in the extruder,
between the barrel and the screw flights.
 In this schematic, the screw rotation inside the barrel is equivalent to
sliding the metal slab over stationery straight channel at an angle
corresponding to the pitch angle of the screw.
 The movement of the slab engenders three types of flow:
 Drag flow,
 pressure flow
 leakage flow.
The extruder throuhtput (Q) is given by the sum of the drag flow, the
pressure flow, and the leak flow, i.e., Q = QD - QP - QL Since both QP (the
pressure flow) and QL (the leak flow) will have opposite signs to QD (the
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drag flow)
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Drag Flow
 Drag Flow takes place by virtue of adhesion of the melt to the slab (barrel
wall).
 As shown in fig., the maximum melt velocity is at the barrel wall (the
same velocity as that of the wall), linearly decreasing to zero (screw is
stationery) across the screw channel depth.
 It is noteworthy that due to sliding of the slab at an angle, the polymer
drag flow in the straight channel is helicoidal.
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Drag Flow
QD =
2
2
D2 N h sin cos
Where
QD
D
N
H

=
=
=
=
=
Drag flow (in3/min.)
Barrel diameter (in.)
Screw Speed (rpm)
Channel Depth (in.)
Helix angle (17.8)
V = Pheripheral Speed of Boot Dia of Screw
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Pressure back-flow
 Pressure back-flow arises when a restriction, such as a die, valve or
breaker plate and screen is attached to the end of an extruder, which gives
rise to a pressure gradient in the channel.
 In the imaginary geometry, this is equivalent of blocking the end of the
straight channel.
 The drag flow generates the maximum pressure at this end.
 However, if there is a pressure at the channel end and only atmospheric
pressure at its entrance one must have a back flow through the rectangular
screw channel.
 For melts with simple rheological properties the velocity profile is
parabolic, as shown in fig.3.14 superposition of the drag and pressure
flow profiles leads to net flow also shown in figure.
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Pressure Back - Flow
QP
Where
QP
D
P
h


L
=
=
=
=
=
=
=
=
 Dh3 P sin2 
12 L
Pressure flow (in.3/sec)
Barrel diameter (in.)
Increase in Pressure (psi)
Channel Depth (in.)
Helix angle (17.8)
Viscosity (lb – sec/in2.)
Length metering section (in.)
V = Pheripheral Speed of Boot Dia of Screw
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LEAKAGE FLOW
 The imaginary geometry of the pressure flow in SSE provides also a simple
explanation of the leak flow.
 Imagine again the straight channel width a metal slab above the screw
flights at the over flight gap distance.
 If pressure is generated near the channel end, the material will not only be
pushed along the channel (as discussed above), but also across the over
flight gap ò this is known as the leak glow.
 The over flight (a radial clearance between the lands and the barrel) is
normally small, of the order of 0.13mm, thus the flow velocity is much
smaller than for the pressure flow.
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LEAKAGE FLOW
QL
Where
QL
D
P


S

L
 D23 tan P
10
SL 
=
=
=
=
=
=
=
=
=
Leakage flow (in.3/sec)
Screw diameter (in.)
Pressure drop (psi)
Flight clearance (in.)
Helix angle (17.8)
Flight Width (in.)
Viscosity (lb – sec/in2.)
Length metering section (in.)
V= Pheripheral Speed of Boot Dia of Screw
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Factors Affecting Extruder’s Output
S.
NO
FACTORS
CHANGE
OUTPUT
COMMENT
1
MATERIAL
1.1
Shear Viscosity
Increases
Decreases
1.2
Elongational Viscosity
Increases
Decreases
1.3
Additives
Increases
2
FEED
2.1
Uniformity of Pellets
Increases
Increases
Uninterrupted feeding is ensured
2.2
Sphericity of pellets
Increases
Increases
Easier Feeding
3
SCREW
3.1
Diameter
Increases
Increases
3.2
Channel Depth
Increases
Increases
3.3
Helix Angle (upto 30)
Increases
Increases
Output can either increase (Lubricating oil) or
decrease (Filler) depending on the type of additive.
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4
BARREL
4.1
Grooved
5
SCREEN PACK
5.1
Increases
Increases
No. and Size
Increases
Decreases
5.2
Back Pressure
Increases
Decreases
6
DIE
6.1
Cross Sectional Area
Increases
Increases
6.2
Land Length
Increases
Decreases
Grooved barrel in the feed section ensures higher
compression
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Barrel
 High grade steel cylinders
 Has to withstand up to 400 atm.
Iron Based Alloy
More hard & less corrosion
resistant
Complex non-ferrous alloys
less hard & more corrosion
resistant
 These expensive materials are used as liners in steel barrels.
 Barrels of Nitrided steel are also used.
 They are Cheap, hard, less resistant to corrosion.
Screw material
 Low carbon alloy steel
 Flight tips are hardened by flame hardening to prevent wear or nitriding the
entire screw.
 Chrome plated screws for vinyl polymers
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AND
 Special nickel alloy steel forCORPORATE
processing
of saran.
PLANNING
Twin Screw Extruders
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Twin Screw Extruder
 Two screws rotating inside a barrel.
 Intermeshing type are more popular.
 Different models/design available
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Basic Types

Co-rotating

Counter-rotating

Mainly used for preparation of master batches/colour concentrates

Co-rotating Twin screw - used for compounding all thermoplastics except
PVC.

Counter rotating - preferred for PVC.
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TWIN SCREW EXTRUDERS SHOWING THE TWO SCREW
ARRANGEMENTS
Co - Rotating
Counter - Rotating
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Comparison between Co-rotating and Counter rotating
Sl.No.
Co-rotating
Counter rotating
1
Both screws either turn clock-wise
or counter clock-wise.
One screw turns clockwise and other
counter clockwise.
2
More complete self wiping
Less self wiping
3
Less
likelihood
stagnation
4
Better mixing
Less than co-rating
5
Total shear is more
Less shear compared to co-rotating and
single screw extruder
6
Mostly for compounding of TP
Mainly for PVC compounding
7
Positive pumping
Positive pumping
8
Less power
single screw
of
material
consumption
than
More likelihood of material stagnation
Less powjer consumption than
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AND screw.
PLANNING
APPLICATIONS OF EXTRUSION
1. Film:
Blown film, Cast film, Co-extruded films, BOF.
Material Used: PP,PVC, LDPE, HDPE, PET, Nylon etc.
2. Pipe/tube
Material: HDPE, LDPE, LLDPE, PVC etc.
3. Sheet
Material: HDPE, ABS, HIPS, PC etc.
4. Monofilament
Material: PP, Nylon etc.
5. Extrusion Coating/Lamination
Coated Playing Cards, Wrapping and LDPE laminated Woven sacks
Material: LD,PP,HDPE
6. Box Strapping
Material: PP, HDPE etc.
7. Tape/Woven Sack
Material: PP, HDPE
8. Wire Coating/Covering
Primary/Secondary insulation
Material: LDPE, PVC (Primary insulation) Nylon (secondary insulation)
9. Profiles (Door and window)
Material: PVC
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BLOWN FILM EXTRUSION
 Upward blown film
-
LD,HD,PVC, Nylon etc.
 Downward blown film
-
PP (Mainly to get clarity)
Process outline
 Melt emerging from extruder is inflated by air pressure (3 to 4 kgs/cm2)
 Bubble is properly stabilized and cooled
 Wound on the winder
 In Blown Film Extrusion a tube of plastic material is extruded out of the die,
while hot it is blown into a bubble, then cooled.
 The bubble is inflated by air pressure contained in between the die and the
seating provided by the nip rolls.
 The bubble is flattened by a pair of collapsible frames before it passed
through the nip rollers.
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The film blowing operation can be accomplished theoretically in any of the
following conditions:
 Horizontal
 Vertically Upward
 Vertically Downward
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 Choice of any one or the other
of the three methods is dictated
by the plastic material and
process limitations.
 The horizontal direction is very
rarely used.
 The vertical upward blowing is
preferred, e.g. for PE and PVC.
 The vertical downward blowing
is used for the manufacture of
high clarity PP film.
 This process requires water
quenching of the bubble for fast
cooling which is rendered
convenient by this position.
BLOWN FILM TERMINOLOGY
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BLOWN FILM DIES
Advantages:
SIDE FEED DIE
1.
Low initial Cost
2.
Adjustable die opening
3.
Will handle low flow materials
Disadvantages:
1.
Mandrel deflects with extrusion rate,
necessitating die adjustment
2.
Die opening changes with pressure
3.
Non-uniform melt flow
4.
Cannot be rotated
5.
One weld line in film.
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CENTRE FEED DIE
Advantages :
1.Positive die opening
2.Can be rotated
3.Will handle low flow resins
Disadvantages:
1.High initial cost
2.Very hard to clean
3.Two or more weld lines in film
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SPIRAL FLOW DIE
Advantages:
1.No weld line in film
2. Positive die opening
3. Easy to clean
4. Can be rotated
5. Improved Film Optics
Disadvantages:
1. High head pressure
2. Will not handle low flow resins
without modification
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DEFINITION OF TERMS

Blow Ratio is the ratio between maximum diameter of the bubble
(DBMmax) to that of die diameter (DD):
BR = DBMmax / DD
Blow ratio indicates the maximum amount of stretching in the crosswise
direction for a particular material. For Polyethylene BR = 2 : 1.

Lay Flat Width is the width of the flattened lay flat tubing :
LFW = (  DD / 2 ) BR
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
Draw Down Ratio is a measure of the extent of thinning of the web
without rupturing it. It is defined as a ratio of the die orifice gap to the
film thickness at the nominal blow ratio BR = 1, given by the product
of the measured film thickness and blow ratio:
Draw Down Ratio =
Die Gap
Film Thickness X Blow Ratio

Freeze Line Height is the height from the die face at which the melt
freezes. The freeze line height affects the optical property of the film
since molecular relaxation takes place at freeze point, thus:
 Higher the freeze line height, poor will be the optical properties.
 Lower the freeze line height Brittleness of the film increases.
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EXTRUSION – BLOWN FILM
Process Variables

Melt Temperature

Back pressure

Internal Air pressure

Efficient cooling

Single lip/Dual lip cooling ring

Take off speed

Blow Up Ratio (BUR)
Typical Converter film
2:1
Shrink film
4:1
Commercially viable combination
1. Low LFW and Low Thickness
2. High LFW and High
Thickness
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TRAINING AND
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BLOWN FILM EXTRUSION
MELT STRENGTH RELATED EFFECTS
Higher melt strength – Stiffer film allows more air to be blown against the
bubble without causing bubble instability. Hence higher output.
Recycled materials – low melt strength. Hence low speed of operation and
low output.
Reduction in melt temperature will increase output. With Internal Bubble
Cooling (IBC) the rate can increase 25-50%.
LDPE/LLDPE blends – highest rates can occur when BUR is about 2.2 to
2.8. Low BUR – not much surface area to cool hence low output rate.
CORPORATE TRAINING AND
PLANNING
CORPORATE TRAINING AND
PLANNING
FLAT FILM - EXTRUSION
Chill-roll system for Flat-Film Extrusion Line
The Melt emerging out of the die lips strikes the chrome
chill roll where it solidifies.
plated
Subsequently the film is pulled through nip rolls .
Trimming blades trims-off the thicker edges. Then the film is wound
CORPORATE TRAINING AND
on the winder.
PLANNING
FLAT FILM DIES
Basically two types of dies.
 T -type
 Coat Hanger / Fish Tail Type
Coat hanger dies ensures no
stagnation of melt. Hence preferred
for Heat sensitive material like
PVC.
CORPORATE TRAINING AND
PLANNING
COMPARISON BETWEEN BLOWN FILM & CAST FILM
BLOWN FILM
CAST FILM
1. Tougher than Cast Film
2. More Stiffer
1. Less Toughness
2. Less Stiffer
3. Cheaper
3. More Costlier Process
4. A High output Tubular
film requires high tower &
Bigger building to
accommodate
5. Easily changeable film
width by changing air
pressure
4. Requires less space.
5. Not so easy
6. Excellent gloss & clarity
6. Less gloss & clarity
CORPORATE TRAINING AND
PLANNING
TUBULAR-QUENCH
It involves the downward extrusion of a tubular extrudate from
an Annular die
Followed by Quenching on water–covered converging boards
Which causes rapid crystallization which enhances the optical
property.
The tube is inflated with air to give a film of required lay-flat
width and thickness.
It is widely recommended for PP film.
CORPORATE TRAINING AND
PLANNING
Fig:Tubular Quench Process
 Tabular quench film process For
PP
Cooling water
Collapsing
Board
Water level
Nip Roll
CORPORATE TRAINING AND
PLANNING
ORIENTATION OF FILMS

Orientation of film by stretching it under heat is widely applied to films
such as PP,PS, PA and PET to improve clarity, impact strength, and
(particularly of PP) barrier properties.

Basic PS film in its non-oriented form is brittle and has only a limited use
as a dielectric in capacitors. When biaxially oriented, the film is tough and
can be thermoformed into crystal clear tubs, trays and larger items such as
cake covers.

The largest application of orientation techniques, however, is in the
manufacure of PP films and the various processes will be illustrated mainly
with respect to this film.

The main processes can be divided into linear and tubular.

The principle of the linear type can be illustrated by considering the twostage process shown in fig 3.27 (a) and (b).
CORPORATE TRAINING AND
PLANNING
(a) Sequential Orientation Process using a Stemer – forward draw first.
CORPORATE TRAINING AND
PLANNING
(b) Sequential Orientation Process using a Stenter –Sideways draw first.
CORPORATE TRAINING AND
PLANNING
MULTI-LAYER FILM
The process is carried out by Co-extrusion.
It involves the extrusion of two or more layers of different or
similar materials using Two or more extruders and Input
combining adapter.
CORPORATE TRAINING AND
PLANNING
POLYMER LAYER COMBINATON
CARRIER LAYER usually, LDPE, HDPE, LLDPE, PC, PET, EVA
etc’
BENDING LAYER Or TIE LAYER:
These materials adhere to different types of Polymers.
Ex:
Ionomer: Good adhesion to LDPE, PA, EVA and LLDPE
EVA: Good adhesion to LD, LLDPE, PA, PC, PET.
Barrier Layer:
PA, PET, PVDC(Best), EVOH
CORPORATE TRAINING AND
PLANNING
Film Blowing, Mono- and Multi-layer
and Double Bubble Film Blowing
3-layer 2 extruders
3-layer 3 extruders
5-layer 3 extruders
5-layer 4 extruders
7-layer 4 extruders
7-layer 5 extruders
FILM BLOWING
There are two techniques of
making film. One is the cast film
process. The other is the blown film
process. The difference in qualities is
that the blown film is more christalline
than the cast film
AXON manufacture CORPORATE
machinery
for AND
TRAINING
PLANNING
both processes
Blown Film Co-Extrusion
Barrier properties is the main reason to go for multi layer film
Three layer Co-Extrusion
Five layer Co-Extrusion
CORPORATE TRAINING AND
PLANNING
MULTILAYER BLOWN FILM
Please check below a number of layer-designs from 2 layer up
to 7 layers. The glue-layers are of great importance where two
different polymers are not compatible
3-Layer head for 2 extruders
-Layer head for 3 Extruders
CORPORATE TRAINING AND
PLANNING
CORPORATE TRAINING AND
PLANNING
CORPORATE TRAINING AND
PLANNING
Multilayer Film Dies
 Two types of dies:
1.Feed Block
2.Multimanifold
 In Feed Block the melt streams are brought together and flow
out the die
 In Multimanifold the melt spreads independently and meet at
the die exit
 Two types of process
Oscillating Platform
Oscillating Haul-Off
CORPORATE TRAINING AND
PLANNING
MULTI LAYER FLAT FILM DIES
Multimanifold threelayer flat-film die
Feed Block
CORPORATE TRAINING AND
PLANNING
Three layer Blown
film Die with internal
bubble cooling
CORPORATE TRAINING AND
PLANNING
5- Layer
Blown film
Die with
Radial melt
distributor
CORPORATE TRAINING AND
PLANNING
COMPARISON BETWEEN FEED BLOCK AND
MULTICHANNEL DIE SYSTEM
SELECTION
CRITERIA
FEED BLOCK
MULTICHANNEL DIE
Investment cost
Relative by low
High.depending on
number of layers
Number of layers
Nearly unlimited upto
9 layers possible
Limited usually 2 or 3
layers
Handling
Relatively easy no
regulation of individual
layers
More expensive
because individual
layers have to be
regulated
Thickness variation on
individual layer
+10%
+5%
Permissible viscosity
difference in
components
1:2 to 1:3
Larger than 1:3
Flexibility
Better easy variation
number and position
of layers by exchange
of ports
Low, number of layers
are pre set.
CORPORATE TRAINING AND
PLANNING
Fig:Oscillating
Platform
CORPORATE TRAINING AND
PLANNING
Fig:Oscillating Haul-Off
CORPORATE TRAINING AND
PLANNING
Advantages of Multi-layer Film
Two to seven layers depending on the application.
It possesses good barrier properties against gas and
moisture.
High tensile,impact and tear strength.
Good stiffness,optical,carrier and printing properties.
 e.g. LDPE/HDPE/LDPE,LLDPE/LDPE..etc.
CORPORATE TRAINING AND
PLANNING
Sheet Extrusion
Sheet is produced by forcing molten thermoplastic through a long horizontal
slit die. The extruded hot web passes around metal cooling rolls and is then
cut up or rolled up.
Material used :
HIPS is the most important sheet material. HDPE, PVC, ABS are also used.
Sheet grades usually have high melt viscosity.
CORPORATE TRAINING AND
PLANNING
Process Line
 The sheet leaving from the slit die is picked up by vertical stack of three rolls.
 The polishing rolls are usually chrome-plated and provided with temperature
control by circulating oil. The polishing rolls imparts a good surface to the
product without warpage. The temperature of the top rolls should be as high
as possible without sticking, while the bottom roll should be just cool enough
to prevent distortion.
 From the polishing rolls the sheet passes along a conveyor, which consist of
free running rollers.
 The sheet is pulled by the pulling rolls are covered with elastomer. Their
speed is adjusted to be slightly less than that of the polishing rolls to allow for
shrinkage that takes place as the sheet cools.
 The sheet is cut into desired dimensions by means of razor blades (thin
sheets), shear cutting device (Standard sheets), or circular saws (thick sheets).
CORPORATE TRAINING AND
PLANNING
Sheet Extrusion Line
CORPORATE TRAINING AND
PLANNING
SHEET EXTRUSION ON 3-ROLLER CALANDERS
CORPORATE TRAINING AND
PLANNING
Dies
Dies used in sheet extrusion are similar to that of flat film dies. Various crosssection of a flat sheeting die is shown in fig
Various Cross-Sections of Flat Sheeting Dies: Circular,
Tear drop, Angular and Flat Teardrop
CORPORATE TRAINING AND
PLANNING
Extrusion coating
 The plastic is coated over a substrate like paper, by extruding
die downward between two rolls.
through a slot
 Substrate is fed between the molten plastic and the roll and is joined with the
plastic by pressure between rolls without the use of an adhesive.

Material used LDPE & PVC
PP, HDPE, Ionomer etc. are also used.

Equipment compresses of

Pre treatment unit

Coating unit

Take off & winding
CORPORATE
TRAINING
ANDfor Extrusion Process
Sketch
of PLANNING
Paper
Coating
Dies
 Coat hanger die
 ‘T’ type die
Manifold T-die : (a) Die Body, (b) Manifold,
(c) Adjustable Lip and (d) Clamping Screw
Coat-Hanger Die : (a) Die Body, (b) Manifold, (c) Fixed Jaw,
(d) Movable Jaw, (e) Choker
Bar, (f) TRAINING
Clamping
Screw and (g)
CORPORATE
AND
PLANNING
Jaw Adjusting
Screw
Wire Coating/Cable Covering
Unit comprises of

Un wind unit (For conductor)

Pre treatment unit

Wire coating unit


Cooling Trough
Take off/ wind up.
Steps Involved

Wire/conductor is unwound & straightened by Tension

Control Unit.

Pre treated to promote adhesion of molten plastic

Then passed through the Cross head die of the coating

Coated wire is then cooled by passing through cooling trough

Wound on the winder
CORPORATE TRAINING AND
PLANNING
unit
Wire Coating Extrusion Line
Diagram of a production line for the coating of wire or cable with plastic. The conductor
to be covered unwinds at the left, is preheated, passes into the crosshead die (center). The
extruder is behind the die, and feeds it with molten plastic, which coats the conductor. The
finished product is cooled, tested and wound up at the right.
CORPORATE TRAINING AND
PLANNING
Die used

Tubing die
USED MAINLY FOR PRIMARY
INSULATION

Pressure die
USED MAINLY FOR SECONDARY
CORPORATE TRAINING AND
INSULATION
PLANNING
Dies
T-TYPE
DIE
COAT
HANGER
TYPE DIE
( Widely Used)
Coat Hanger type of Die is much more stream lined
than T-type Die
CORPORATE TRAINING AND
PLANNING
Tube/Pipe Extrusion
Wall thickness & flexibility/Rigidity differentiates between tube/pipe
Pipes are produced by horizontally extruding molten polymer
through
an annuler opening into several sizing, cooling devices that stabilizes the
final dimension.
Comprises of
Extruder
Die
Sizing device
Cooling bath
Cater puller
Cutter or winder
CORPORATE TRAINING AND
PLANNING
DIES USED
STRAIGHT THROUGH
OFF SET DIE
CORPORATE TRAINING AND
PLANNING
Sizing Equipment - Methods
Vacuum Trough

Widely used

With the help of vacuum, Pipe is stabilized and sized to retain the shape
Sizing Sleeve

Methods fixes the outside pipe diameter as it hardens by contact
water cooled metal sleeve.
with a
FLOATING PLUG SYSTEMS- USED FOR
RIGID PIPES OF MEDIUM AND LARGE
SIZES
TO PREVENT LOSS OF AIR PRESSURE
FLOATING PLUG SYSTEM IS USED
CORPORATE TRAINING AND
PLANNING
Extended Mandrel

Method uses a water cooled extended mandrel

Provides additional internal cooling and internal support
Sizing plate

Method involves pulling the pipe through a series of brass plates

Mainly for small dia pipes/tubes.
CORPORATE TRAINING AND
PLANNING
Extrusion of Mono filaments
 Mono filaments are wise like polymer strands of dia 0.09 to 1.52 mm.
 Usually they have circular cross-section.
 The polymer melt from extruder is pumped out through a multi-hole die, quenched,
stretched/oriented and annealed to get the filament of enhanced properties.
The production process comprises of
 Extrusion
 Filament forming
 Stretching (orientation)
 Annealing
 Winding
CORPORATE TRAINING AND
PLANNING
Orientation Systems
A
C
Liquid-bath method
Heated Point method
D
B
Air - Oven method
CORPORATE TRAINING AND
PLANNING
Cold Drawing
Extrusion -- Box- Strappings
The process sketch is similar to Monofilament line except the die – A slotted
die is used in place of multi-hole monofilament die
Plastic Strappings, made of PP/HDPE replace iron
flexibility.
because of their
Process outline
Plasticated melt from an extruder is pumped out through a slot die
Quenched in water bath
Bath temperature
- 800C for PP
- 900C for PA-6
Passed through a orientation system and stretched to about 8 times in order
to improve tensile properties.
Annealed in an annealing chamber to relieve the stresses
Wound on winder.
CORPORATE TRAINING AND
PLANNING
CORRUGATED PIPES
 The characteristics of corrugated plastic pipes depend on profile and
material.
 Corrugated pipes have either parallel ring grooves or a continuous
helical groove.
 The pipes design can be single walled or twin walled.
 Most common
fluoropolymers.
thermoplastics
are
PVC,
PE,PP,
 The most important advantages are
 Considerable raw material savings
 High pressure resistance with good flexibility.
 High impact strength
CORPORATE TRAINING AND
 Good hydraulic characteristics
PLANNING
PA
and
Process
Essentially IIIr to extrusion of pipes except that the die and
the calibration units are specially designed to produce corrugation on
the pipes.
The cylindrical part of the pipe die head extends into the closed area
of a revolving mould block chain. The plastic tube is pressed against
the profiled, revolving mould block halves by internal air pressure or
by vacuum calibration.
As it passes through the forming machine, it is cooled by contact
with the mould blocks, and by that time it reaches the end of the
chain, the tube must be sufficiently cooled to leave the rotating
mould blocks in a stable form.
CORPORATE TRAINING AND
PLANNING
a--Pipe die head with Insert
c-- Shaping die
b--Compressed air inlet
TRAINING AND
dCORPORATE
-- Sealing
stopper
PLANNING
e -- Vacuum connection
In order to let the pressure or vacuum sizing become effective,
the molten tube must be brought over a special extended outer die ring
as close as possible to the moulding chain –inlet. Otherwise the tube
would be blown off in pressure sizing and fail in vacuum sizing.The
extended position of the outer die ring cannot be heated separately. So
that it must be made of a material of high thermal conductivity.
CORPORATE TRAINING AND
PLANNING
Double walled corrugated pipe
production:
The manufacturing process is the same as with
standard corrugated pipes, but when the first tube has been
formed, the second tube is laid smoothly on the inner
surface of the still plastic corrugation and welded to the first
with the aid of a sizing mandrel.
CORPORATE TRAINING AND
PLANNING
Double Walled Corrugated Pipe Production
a -- Die for coextrusion
b --Through flow guide
c --Mandrel extrusion for inner layer
d -- Shaping die
CORPORATE TRAINING AND
PLANNING
Applications of Corrugated pipes are:
 Conduits for cable protection, TV,Telephone, Glass fibre, power,
control and computer lines, automobiles, machines and planes,
protective pipes and conveyor pipes.
 Drain pipes for fields, streets, squares and houses.
 Pipes for vacuum cleaners, washing machines, dish washers,
medical application – drip irrigation, hoses for fields, hot houses
and plantations.
 Protection pipes for district heating, domestic connection lines,
structural and civil engineering.
 Large size pipes for sewage, waste water, control shafts and
conveyor pipes.
Corrugated pipes are produced with diameters form 3\5 to
CORPORATE TRAINING AND
2000mm.
PLANNING
POST EXTRUSION FORMING
Inline postforming with extruder : Embossing one or
both sides with shallow or deep patterns
CORPORATE TRAINING AND
PLANNING
INLINE FIXED / ROTATING RINGS USED TO TWIST EXTRUDATE
CORPORATE TRAINING AND
PLANNING
INLINE VACUUM/PRESSURE FORMER FOR PLASTIC SHEEET WITH MATCHED, WATER COOLED FORMING
MOULDS ON CONTINOUS CONVEYOR SYSTEM
AN INLINE COIL FORMER CAN PRODUCE TELEPHONE CORDS, SPRINGS, ETC.,
USING EXTRUDED ROUND, SQUARE, HEXAGONAL, AND OTHER SHAPES
CORPORATE TRAINING AND
PLANNING
TROUBLE SHOOTING
PROBLEM
CAUSES (S)
SOLUTION(S)
General Considerations
Surging
Gels
(Contaminants that look like
small specks or bubbles)
Resin bridging in hopper
Eliminate bridging
Incorrect melt temperature
Correct melt temperature
Improper screw design
Check design
Rear barrel temperature too low or
too high
Increase or decrease rear
temperature
Low back pressure
Increase screen pack
Improper metering length
Use proper screw design
Melt temperature too high
Lower melt temperature
Not enough progression in screw
use new screw
Bad resin
Check resin quality
Melt temperature too low
Increase melt temperature
Die gaps too narrow
Heat die lips
Melt fracture
(Rough surface finish)
Increase die gaps
CORPORATE TRAINING AND
PLANNING
Use processing aids
Bad colour
Bubbles
Overheating
Die lines
Colour concentrate incompatible with resin
Ensure melt index of
concentrate base
Wet material
Dry thoroughly
Overheating
Decrease temperature; check
thermocouples
Shallow metering section
Use proper compression-ratio
screw
Improper screw design
Use lower-compression screw
Restriction to flow
Check die for restrictions
Barrel temperature too low
Increase temperature
Scratched die
Refinish die surface
Contamination
Clean head and die
Cold polymer
Check for dead spots in head;
adjust barrel and head
temperature to prevent
freezing
Flow lines
Overheated material
Decrease temperature
Poor mixing
Use correct screw design
Contamination
Clean system
CORPORATE TRAINING AND
Improper temperature PLANNING
profile
Adjust profile
Blown Film
Wrinkles
Dirty collapsing frame
Clean frame
Too much web tension
Adjust tension
Improperly designed air ring
Use new air ring
Gauge variations
See gauge variations
Insufficient cooling
Use refrigerated air
Increase flow of Air
Reduces output
Fold, creases
Blocking
Port lines
Splitting
Misalignment between nip rolls and die
Check alignment
Excessive stretching between nip and roller
Reduce winding speed
Nip assembly drive not constant
Adjust or replace drive
Inadequate cooling
Use better cooling method
Excessive winding tension
Adjust tension
Excessive pressure on nip rolls
Adjust pressure
Bad resin
Check resin
Melt temperature too low
Increase melt temperature
Die too cold or too hot in relation to melt temperature
Adjust die temperature
Excessive orientation in machine direction
Increase Blow-up ratio
Degraded resin
Reduce melt temperature
Poor resin choice
CORPORATE TRAINING AND
PLANNING
Ensure resin is suitable
Die lines
Nick on die lip
Chande die
Dirty die
Clean die
Inadequate purging
Increse purging time between resin
changes
Gauge variations
(machine direction)
Check temperature
Surging
Check hopper for bridging
Inconsistent take-up speed
Check take-up speeds
Gauge variations
(transverse direction)
Printing problems
Adjust gap
Non-uniform die gap
Centre air ring on gap
Insufficient treatment
Use properly treated film
Additives interfering with ink
Use resins with no interfering
additives
Erratic treatment
Reduce slip levels to about 600
ppm for water-based inks
CORPORATE TRAINING AND
PLANNING
Sheet
Poor gauge uniformity
Melt flow is not stable
Use gear pump to stabilise flow
Viscosity not stable
Poor mixing
Use static mixer
Clean hopper
Streaks
Contaminated System
Check screw and die;
Clean if necessary
Total discoloration
Excessive regrind
Check amount of regrind used
Discontinuous lines
Too much moisture
Increase resin drying
Use hot regrind
CORPORATE TRAINING AND
PLANNING
Pipe and Tubing
Poor output
Improper die or screw design
Ensure die and screw are designed for
desired output
Insufficient vacuum
Increase vacuum
Excessive moisture
Maintain normal percentage of moisture
in compound.
Gases entrapped
Reduce temperature
Water inside pipe
Stop water access
Mandrel heat too high
Check mandrel heat
Stock temperature too high
Reduce temperature slowly
Mandrel is coated with material
Clean mandrel
Screw clearance set improperly
Adjust clearance
Puller drive slipping
Adjust or replace puller drive
ID blisters
ID burn streaks
ID grooves
ID wavy surface
CORPORATE TRAINING AND
PLANNING
Material hung up on die
Clean die
Temperature too high
Reduce temperatures slowly
OD burn streaks
Too much air pressure on puller
Reduce air pressure
OD uneven
circumference
Insufficient air pressure
Check air pressure and all
connections
OD discoloured
Stabiliser level too low
Check stabiliser level
Air bubbles adhering to pipe in flotation
tank
Install wiper in tank
Improper adjustment of spray rings that
surround water tank.
Readjust spray rings
Air supply too high
Adjust air supply
Insufficient water supply
Increase water supply
Pipe hot when measured
Allow pipe to cool before
measuring
Mis-adjusted die bushing
Adjust die bushing to achieve
uniform thickness
Wrong die set-up
Use correct set-up
OD pock marks
OD oversized
Wall too thick
CORPORATE TRAINING AND
PLANNING
QUESTIONS
1.
Which type of die is preferred for sheet extrusion.
2.
What is TDO and MDO?
3.
What is TQ PP?
4.
Tubular quench film process is used for
a.
5.
LDPE
b. NYLON
d. PP
In extrusion process the function of screen pack is
a.
To filter contamination.
c. Developing backpressure.
6.
c. LLDPE
b. Arrest unmelted particles.
d. All the above.
The relationship between MFI and viscosity is
a.
Directly proportional
c. Inversely proportional
b. Equal
d. None of the above
7.
State the effect of grooved barrel on output of an extruder
8.
What is barrel?
9.
Mention any one material for making corrosion resistance barrel.
10. What is helix angle?
CORPORATE TRAINING AND
PLANNING
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
State the helix angle for PVC screw.
Name the blown film dies.
How the thrust bearing is rated?
State true or false:
Co-rotating twin-screw extruder is preferred for PVC compounding
What is the other name for two stage screw?
What is the other name for “die swell”?
PP blown film is produced by _____________ process (mention specific
name.)
State the compression ratio for nylon screw.
The effect of backpressure in extrusion is to
a. Improve mixing
b. Reduce mixing
c. Increase Viscosity
d. None of the above
Classify extruders.
Name the different extruder screws.
State any two merits of Twin-screw extruder
Name the different co extrusion dies
State the different types of Twin screw extruder.
Why PP blown films are always produced by downward extrusion process.
CORPORATE TRAINING AND
PLANNING
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
The cut of an extruder ________ (increase / decrease) with increase in Back
Pressure.
How an extruder is specified?
Name the coextrusion blown film dies.
Define LD ratio.
Define Compression ratio.
The mixing elements are incorporated in
a. Feed zone
b. Compression Zone
c. Metering Zone d. None of these
What is melt fracture?
What is shark skin?
What is Bambooing?
Define Blow Ratio?
Define Blow Up Ratio?
What do you mean by FLH?
Name the different wire coating dies?
State the Compression Ratio for Rigid PVC Screw.
State the Compression Ratio for Nylon Screw.
Nominal dia of screw = Root dia + 2
What is Barrier screw ?
State the electrical heating systems used in extruders.
State the electrical heating systems used in extruders.
CORPORATE TRAINING AND
Compare the two types of band heaters.
PLANNING
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
State the purpose of hopper cooling.
State the purpose of screw cooling.
State the functions of breaker plate.
State the functions of breaker plate.
State the equations to find out output of an extruder.
What is draw down ratio?
State any two merits of blown film over cast film.
State the various orientations systems used in monofilament extrusion.
What is fish eye? Suggest remedies.
Name any two applications for corrugated pipes.
CORPORATE TRAINING AND
PLANNING
REFERENCE :
1.
Extrusion of Plastics – Fisher
2.
Extrusion of Plastics – Allan Griffth.
3.
Plastics Extrusion Technology – Friedhelm Hensen
4.
Plastic Materials and Processing – A. Brent Strong
5.
Tools and Manufacturing Engineers Handbook (T meh)
6.
Polymer Processing – D H Morton – Jones
7.
Plastics Processing Data Handbook (Second Edition) – Dominick Rosato
8.
Plastics Technology Handbook – Manaschanda, Salil K. Roy
9.
Principles of Plastics Extrusion - Brydson and Peacock
10.
Handbook of Plastics Materials and Technology Irvin Rubin.
CORPORATE TRAINING AND
PLANNING
CORPORATE TRAINING AND
PLANNING