1._introduction_to_plastics_processing..ppt

CORPORATE TRAINING AND
PLANNING
INTRODUCTIONTO PLASTICS PROCESSING

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1.0 INTRODUCTION
 Plastics – The unique class of wonder materials – came into existence by
virtue of their superior performance and cost effectiveness over to
conventional materials.
 Over the years the applications spectrum of plastics have been
widened with the advent of new generation Polymers, blend alloys
and composites
 . Every day newer and newer application are being promoted in all the key
sectors of Indian Economy viz, Automobiles, Agriculture, Aerospace. Building
& Construction, Infrastructure, Telecommunication, IT, Medical & Bio Medical
engineering, Packaging, etc.
 This inturn necessitates the need for different types processing methods and
machinery to produce quality plastics products at affordable cost
 Today a host of processing methods and machinery are available to manufacture
plastics products meeting stringent quality requirements and cost to performance
balance.

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1.1 DEFINITION:
Plastics Processing – in a simple layman’s language – can be defined as the process of
converting the plastic raw materials into Semi-finished or finished products.
Raw Materials
(Powder/granules)
Semi-finished
or
Finished Products
Processing

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In a more technocrate way we may say “Get the Shape and set the Shape”.
Technique to get the shape and Set the shape varies depending on Process and
Material employed.
Principles:
 Deformation of a polymer melt (ex) Injection, Extrusion, Blow Moulding etc
 Deformation of a polymer in Rubbery state
Ex: Thermoforming
Vacuum Forming
Pressure Forming
 Deformation of a Suspension
Ex: PVC Plasticsol Processing / Coating
 Deformation of a Solution
Ex : Solvent Casting of CN Film
 Deformation of a low melt polymer / monomer
Ex: Acrylic Sheet Casting
 Preparation of GR Laminates
 Machined Structures
Secondary fabrication operation

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1.2 CLASSIFICATION OF PROCESSING METHODS
1. Primary Processing Methods:
u More importance by virtue of
o Extent of utilisation for Varied applications
o Growth Potential
Ex: Injection Moulding, Extrusion, Blow Moulding, Compression / Transfer
Moulding,
2. Secondary Processing Methods
u Lesser extent of utilisation
u Acts as supplementary to primary operation
Ex: Roto Moulding, Thermoforming, Coating, Casting, FRP Fabrication
Methods, Calendaring, etc.,

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Performance Requirements
Practical
Approach
Engineering
Approach
Material Selection
Properties Process Cost
Ideal Choice
Product Manufacture : A Simplified Flow Diagram
1.3 PROCESSING FUNDAMENTALS

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The process selection depends on several interrelated factors:
(1) Designing a part to meet performance and manufacturing requirements at the
lowest cost;
(2) Specifying the plastic;
(3) Specifying the manufacturing process, which requires
 Designing a tool ‘around’ the part,
 Putting the ‘Proper Performance’ fabricating process around the tool,
 Setting up necessary auxiliary equipment to interface with the main processing
machine
 Setting up ‘Completely integrated’ controls to meet the goal of zero defects;
(4) Purchasing equipments and materials, and warehousing the materials.

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COMPETITIVE PROCESSES
S.
N
o
Product
Inj.
Moulding
Extrusion
Thermo
forming
Blow
Moulding
Comp./
Transfer
Moulding
Roto
Moulding
1 Narrow neck
container
- - - 1 - -
2 Oil Barrels
Upto (200 ltrs)
- - - 1 - 1
3. Tanks (20000
ltrs)
- - - - - 1
4. Films,Profiles,
Pipes
- 1 - - - -
5 Housing, Auto
parts
1 - 2 2 2 -
6. Wider Neck
parts
1 - - - - -
7. Hallow
Containers
- - - - - 1
1. Best Process 2. Supplementary Process

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1. Setting up specific performance requirements;
2. Evaluating material requirements and their processing capabilities;
3. Designing parts on the basis of material and processing characterstics, considereing
part complexity and size as well as a product and process cost comparison
4. Designing and manufacturing tools (Moulds, Dies, etc) to permit ease of processing;
5. Setting up the complete line, including auxliliary equipment;
6. Testing and providing quality control, from delivery of the plastics, through
production, to the product
7. Interfacing all these parameters by using logic and experience and / or obtaining a
required update on technology.
Parameters that help one to select the right options are

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1.4 PROCESSABILITY:
 Processability means generally the ease or difficulty with which a plastic can be
handled during its fabrication into film, moulded products, pipe, etc.
 A plastic with good processability possesses the properties necessary to make it
easy to process the plastics into desired shapes.
 The main characterstics or properties which determine a plastic’s processability are
molecular weight, uniformity, additive type and content, and plastic feed rates.

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1.5 PROCESSING METHODS:
 The type of process to be used depends on a variety of factors, including product
shape and size, plastic type, quantity to be produced, quality and accuracy
(Tolerances) required, design load performance, cost limitation, and time schedule.
 Each of the processes provides different methods to produce different products. As
an example, extrusion with its many methods produces films, pipe,sheet, profile,
wire coating, etc.
 Almost all processing machines can provide useful products with relative ease, and
certain machines have the capability of manufacturing products to very tight
dimensions and performances. The coordination of plastic and machine facilities
these processes.

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PROCESSING METHODS – An Overview:
Machine Operation Terminology
Terminology in the plastics industry regarding the operation of machinery is as follows:
 Manual Operation
Each function and the timing of each function is controlled manually by an operator.
 Semiautomatic Operation
A machine operating semi automatically will stop after performing a complete cycle of
programmed moulding functions automatically. It will then require an operator to start
another complete cycle manually.
 Automatic Operation
A Machine operating automatically will perform a complete cycle of programmed
moulding functions repetitively; it will stop only for a malfunction on the part of the
machine or mould, or when it is manually interrupted.
Depending upon the configuration of the part, economic viability and the part
tolerance, etc the process can be selected.

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An extruded parison tube of heated thermoplastic is positioned between two halves of an
open split mould and expanded against the sides of the closed mould via air pressure. The
mould is opened and the part ejected. Low tool and die costs, rapid production rates, and
ability to mould fairly complex hollow shapes in one piece.
BLOW MOULDING :
Description :
Limitations:
Generally limited to hollow or tubular parts; some versatile mould shapes, other than
bottles and containers.

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BLOW MOULDING

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Very widely used. High automation of manufacturing is standard practice. Thermoplastic
or thermoset is heated to plasticate in cylinder at controlled temperature, then forced
under pressure through a nozzle into sprue, runners, gates, and cavities of mould. The
resin undergoes solidification rapidly. The mould is opened, and the part ejected, Injection
Moulding is growing in the making of glass-reinforced parts. High production runs, low
labour costs, high reproducibility of complex details, and excellent surface finish are the
merits.
INJECTION MOULDING :
Description :
Limitations:
High initial tool and die costs; not economically practical for small runs.

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INJECTION MOULDING

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Widely used for continuous production of film, sheet, tube, and other profiles; also used
in conjunction with blow moulding. Thermoplastic moulding compound is fed from a
hopper to a screw pump where it is heated to plasticate then pumped out through the
shaping orifice (die) to achieve desired cross section. Production lines require input and
takeoff equipment that can be complex. Low tool cost, numerous complex profile shapes
possible, very rapid production rates, can apply coatings or jacketing to core materials
(Such as wire).
EXTRUSION :
Description :
Limitations:
Usually limited to sections of uniform cross section.

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EXTRUSION

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Thermoset compound, usually preformed, is positioned in a heated mould cavity; the
mould is closed (heat and pressure are applied) and the material flows and fills the mould
cavity. Heat completes polymerization and the part is ejected. The process is sometimes
used for thermoplastics, e.g. Vinyl phonograph records. Little material waste is attainable;
large, bulky parts can be moulded; process is adaptable to rapid automation.
COMPRESSION MOULDING :
Description :
Limitations:
Extremely intricate parts containing undercuts, side draws, small holes, delicate inserts,
etc.; very close tolerances are difficult to produce. Time consuming process.

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Widely used to produce Thermoset products with part complexity. Thermoset moulding
compound is fed into transfer chamber where it is then heated to plasticate; it is then fed
by a plunger through sprues, runners, and gates into a closed mould where it cures; mould
is opened and part ejected. Good dimensional accuracy, rapid production rate, and very
intricate parts can be produced.
TRANSFER MOULDING
Description :
Limitations:
High mould cost; high material loss in sprues and runners; size of parts is somewhat
limited.

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Dough-consistent thermoplastic mass is formed into a sheet of uniform thickness by
passing it through and over a series of heated or cooled rolls. Calenders are also utilized to
apply plastic covering to the backs of other materials. Low cost, and sheet materials are
virtually free of moulded-in stresses.
CALENDERING :
Description :
Limitations:
Limited to sheet materials and very thin films are not possible.

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A predetermined amount of powdered thermoplastic material is poured into mould; mould
is closed, heated, and rotated in the axis of two planes until contents have fused to the
inner walls of mould; mould is then opened and part is removed. Low mould cost, large
hollow parts in one piece can be produced, and moulded parts are essentially isotropic in
nature.
ROTATIONAL MOULDING
Description :
Limitations:
Limited to hollow parts; production rates are usually slow.

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ROTATIONAL MOULDING

PLANNING
Heat-softened thermoplastic sheet is positioned over male or female mould; air is
evacuted between sheet and mould, forcing sheet to conform to contour of mould.
Variations are vacuum snapback, plug assist, drape forming, etc. Tooling costs are
generally low, large part production with thin sections possible, and often comes out
economical for limited part production.
THERMOFORMING
Description :
Limitations:
Limited to parts of simple configuration, high scrap, and limited number of materials from
which to choose.

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THERMOFORMING

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Liquid plastic which is generally thermoset except for acrylics is poured into a mould
without pressure, cured, and taken from the mould. Cast thermoplastic films are produced
via building up the material (either in solution or hot-melt form) against a highly polished
supporting surface. Low mould cost, capability to form large parts with thick cross
sections, good surface finish, and convenient for low-volume production.
CASTING
Description :
Limitations:
Limited to relatively simple shapes. Most thermoplastics are not suitable for this method.
Except for cast films, method becomes uneconomical at high volume production rates.

PLANNING
Reinforcement is placed in mould and is rotated. Resin distributed through pipe;
impregnates reinforcement through centrifugal action. Utilized for round objects,
particularly pipe.
CENTRIFUGAL CASTING:
Description :
Limitations:
Limited to simple curvatures in single axis rotation. Low production rates.
COATING
Process methods vary. Both thermoplastics and thermosets widely used in coating of
numerous materials. Roller coating similar to calendaring process. Spread coating
employs blade in front of roller to position resin on material. Coatings also applied via
brushings, spraying, and dipping.
Description :
Limitations:
Economics generally depends on close tolerance control.

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Excellent strength-to-weight. Continuous, reinforced filaments, usually glass, in the form
of roving are saturated with resin and machine-wound onto mandrels having shape of
desired finished part. Once winding completed, part and mandrel are cured; mandrel can
then be removed through porthole at end of wound part. High-strength reinforcements can
be oriented precisely in direction where strength is required. Good uniformity of resin
distribution in finished part; mainly circular objects such as pressure vessels, pipes, and
rocket cases.
FILAMENT WINDING :
Description :
Limitations:
Limited to shapes of positive curvature; openings and holes can reduce strength if not
properly designed into moulding operations.

PLANNING
Material, usually in form of reinforcing cloth, paper, foil, metal, wood, glass fibre, Plastic
etc., preimpregnated or coated with thermoset resin (sometimes a thermoplastic) is
moulded under pressure greater than 1000psi (7Mpa) into sheet, rod, tube, or other simple
shapes. Excellent dimensional stability of finished product; very economical in large
production of parts.
LAMINATING :
Description :
Limitations:
High tool and die costs. Limited to simple shapes and cross sections.

PLANNING
A variation of the conventional compression moulding, this process employs two metal
moulds possessing a close-fitting, telescoping area to seal in the plastic compound being
moulded and to allow trim of the reinforcement. The mat or preform reinforcement is
positioned in the mould and the mould is closed and heated under pressures of 150 –
400psi (1-3MPa). The mould is then opened and the part is removed after curing.
MATCHED-DIE MOULDING :
Description :
Limitations:
Prevalent high mould and equipment costs. Part often require expensive surface finishing.

PLANNING
Liquid thermoplastic material (Plastisol) is poured into a mould to capacity; mould is
closed and heated for a predetermined time in order to achieve a specified buildup of
partially fused material on mould walls; mould is opened and excess material is poured
out; and semifused part is removed from mould and fully fused in oven. Low mould costs
and economical for small production runs.
SLUSH MOULDING :
Description :
Limitations:
Limited to hollow parts; production rates are very slow; and limited choice of materials
that can be processed.

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Effect of polymer properties on Process Technique

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1.6 EFFECT OF POLYMER PROPERTIES ON PROCESS
TECHNIQUE
(1) Water absorption of Raw materials,
(2) Physical form of raw material,
(3) Thermal stability of polymer,
(4) Flow properties,
(5) Adhesion of melt to metal,
(6) Thermal properties affecting, Heating and cooling of melt,
(7) Compressibility and shrinkage,
(8) Frozen in Orientation.
When processing thermoplastic melts the following factors should be taken into
account in order both to process efficiently and obtain quality products.

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Water / Moisture is the greatest enemy for processing of plastics.
 Hygroscopic Materials
 Absorption phenomena - Ex: Nylon, POM, PC.
 Adsorption phenomena - Ex: HIPS, PS, ABS.
 All these materials should be pre-dried.
 Non-Hygroscopic material - Ex: PVC, Polyolefins, etc.
 Need not be predried. Except when completely wet during monsoon.
WATER ABSORPTION

PLANNING
Actions Necessary
1. Use granules as soon as the bag is opened.
2. Pre-drying ovens, Hopper drier, Dehumidifying drier can be used.
3. For PC - Dehumidifying drier preferable
Physical form of Raw Material
 Powder form, granular form, lumpy/slab form
 Slab Form - Calendering,Compression Moulding
 Granular Form – Preferred - Uniform pellet size ensures even and faster feeding.
 Powder Form - Difficulty in feeding - But savings in cost because of the ability to
avoid pelleting stage - Special feeder attachment essential to ensure proper feeding.

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Thermal stability of polymers
 PVC thermally sensitive material - Little higher melt temp. may lead to depredation - HCL is
released - This can leads to corrosion and harmful to human being. PID Temperature
controller can be used.
 PMMA, POM upon depredation liberates MMA & formaldehyde respectively - MMA
volatilize and cause bubbles - Formaldehyde gas causes “eye-irritation”.
 PVC & POM (acetal) should never be processed one after the other. This may lead to
explosion
Adhesion of melt to metal:
 Wetting of the polymer melt against the metal wall of processing equipment can
lead to strong adhesion of polymer to metal. Ex: difficulty in removing PVC - Mix
from two roll mill.
 PC has a strong adhesion to metal. It can take away the skin of the barrel if not
properly purged

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THERMAL PROPERTIES AFFECTING HEATING AND COOLING
In the case of polymer melts the specific heat varies with temperature. For crystalline
polymers such as POM, NYLON etc. latent heat of fusion and sp.heat should be taken in to
account. i.e Total heat content (Enthalpy) =LH of fusion + sp.heat.
POLYMER PROCESS TEMP 0C ENTHALPY / KJ / KG
PS 200 310
LDPE 200 500
HDPE 260 810
PP 260 670
Because of higher enthalpy PP requires more cooling time than LDPE and PS.

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COOLING SHRINKAGE AND COMPRESSIBILITY
When polymers are in molten stage the vibrations of the molecules results in the polymer
chain being pushed apart so that the volume occupied by a given polymer mass is higher
than when the material is solid.
POLYMER
DENSITY AT 20
C(G/CC)
DENSITY AT PROCESS
TEMP (G/CC)
LDPE 0.923 0.746(210c)
PP 0.905 0.765(210c)
PMMA 1.180 1.105(210c)
SPVC 1.48 1.390(190c)
Because polymer melts are compressible moulding shrinkage is much less than the above
fig.

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FROZEN-IN ORIENTATION
 When polymer melts are being shaped by either injection moulding or Extrusion the
long polymer chains tend to be elongated or uncoiled in the direction of flow.
 After shaping, the melt is usually cooled rapidly and there is seldom time for the
oriented molecules to return to a random coiled shape by the process known as
relaxation.
 Some orientation is thus “Frozen-in” the product. Such stressed parts are very weak.
Hence annealing is must.

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PROCESS SELECTION CRITERIA FOR PLASITC PRODUCTS
Introduction:
With the advent of New Generation Polymers, blends alloys and composites,
over the last decade, the application spectrum of plastics has been widened.
Today with the result, the plastics have penetrated deeply in all the key sectors
of economy which includes
Automobiles Telecommunication
Aerospace Defence
Biomedical Building & Construction etc
In the liberalized economy the survival of plastic industries largely depends
upon timely delivery, quality, cost and cost / performance balance of plastics
products.

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With the availability of host of plastic raw materials and a wide range of
plastic processing methods and technologies, it is a difficult task for the
processor to select a suitable cost effective process for a specific product.
Although in some cases one or more processes may be suitable for producing a
specific plastics product A plastics processor can select a specific process
keeping in mind the key parameters such as cost, quality and cost/performance
balance.
In this presentation, a few selected case - studies were made for the benefit of
plastic processors.

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Process Selection Criteria
The following parameters play a key role in selecting the best suited process
to produce a specific product for a specific application.
1. Material Processibility - Limitations
2. Volume of production
3. Size & shape of the product (configuration)
4. Cost to performance balance
5. Quality

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Material Processibility Limitations
If a specific material is suitable for a particular application, then material
processibility will decide the specific method of Processing / Production.
Case :1
Product : PET bottle
Process : Blow Moulding
Specific process : Injection stretch Blow moulding
Not possible by : Extrusion Blow moulding or Extrusion Stretch blow
moulding
Reason:
PET material used today does not have the required hot melt strength to
hold/self support a parison.

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Case: 2
Product : PTFE sheets
Process : Compression moulding following by sintering process.-The sintered
sheets are subsequently machined to the required dimension.
Other Conventional Process:
Extrusion - Not possible.
Reason:
PTFE exhibits - very high melt viscosity above its melting temperature. Hence only
best suited process is compression moulding followed by sintering.

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Configuration of Product
- Size & shape governs the process selection.
Case 1:
Narrow neck containers like Shampoo bottles, Pharmaceutical
containers, soft drink bottles will have to be produced by Blow moulding only.
Case 2:
Hollow containers such as Tanks (20,000ltrs) will have to be produced by
Roto moulding inspite of higher initial cost on plant & machinery.

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Case 3:
Product : FRP Boat
Raw materials : Fiber glass material, Polyester resin and other
additives
Process : 1. Hand lay-up 2. Spray up
Most suitable process:
If volume of production is less then hand lay up. If more then spray up
technique. Spray up technique calls for higher initial investment.

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Cost / Performance Balance
If more than one process is suitable for producing a product based
on performance, then cost plays a crucial role in process selection.
Case: 1
Product : 200 litres chemical container
Material : HDPE
Process : 1. Blow Moulding 2. Roto Moulding

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Sl.
No.
Parameter Blow Moulding Roto Moulding
1.
Specific Process
Accumulator
Blow Moulding
Three arm
rotomoulding
2. Volume of Production High Low
3. Initial investment on
plant & machine
High Moderate
4. Performance Good Good
5. Cost/performance Best good
Hence accumulator type blow moulding process can be selected.

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Case - 2
Product : FRP pipe
Material : Glass fiber, Polyester resin & other additives
Process : 1. Limited lengths & high strengths - Filament winding
2. Continuous lengths & high strength - pultrusion
3. Centrifugal casting - Batch process
If medium strength and relatively stress free pipes are required with better optical
properties, then centrifugal casting is the best method.

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Case: 3
Product : PVC Flexible sheet
Material : Compounded PVC with additives such as plasticizer, stabilizer,
colourants etc.
Process : 1. Calendering 2. Extrusion
Suitable process : Calendering
Reason : Wider width, cost effectiveness
Case: 4
Product : Acrylic sheet
Material : PMMA
Process : 1. Casting 2. Extrusion

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Sl.
No.
Parameter Casting Extrusion
1. Mechanical Properties Lower Higher
2. Optical properties High Low
3. Initial investment Low High
4. Stress built-up
Almost stress
free
Stress built-up
due to
orientation.
Since optical properties are very essential based on cost/performance & quality
casting process is best.

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Quality
Mainly due to quality reasons, inspite of higher cost of manufacture, certain products
are produced by a specific process only.
Case:1
PVC - gramaphone records - even today produced by compression moulding.
Reason: Stress-free moulding
Case:2
Product: PP Blown film
Process: Only downward extrusion process should be used instead of upward blown
film process.
Reason:
PP, being a crystalline polymer,in order to get transparency, the film emerging out of
die lips needs to be quenched.The best /economical way of quenching is to dip in
water which is possible only in downward extrusion. So due to quality reason this
process is selected.

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Case:3
Product : Plastic float
Material : PP/HIPS
Processes:
1. Roto Moulding
2. Injection Moulding - Two halves and then joining by vibration welding.

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Sl.
No.
Parameter Roto Moulding Injection Moulding
& Welding
1. Initial Investment Moderate High
2. Quality Good Moderate
3. Production rate Low High
4. Low volume / prototype Best -
5. High volume Production - Best

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