The document discusses various joining, assembling, and surface modification methods for plastics, including mechanical connections, gluing, welding, machining, surface treatment, metallization, and coating processes. Some key joining methods discussed are vibration welding, spin welding, and ultrasonic welding, while common surface processes include flame treatment, corona treatment, and various vacuum metallization techniques. The advantages and disadvantages of different techniques are provided for joining, machining, and modifying plastic materials and components.

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JOINING & ASSEMBLING

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Methods of Joining &
Assembling
Gluing
Welding
Mechanical Connections

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Functions of Joining
For Permanent Joining
• Gluing
• Welding
For Disassembly
• Mechanical Connections

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Types of Mechanical
Connections
• Bolted Assemblies
• Self Tapping Screws
• Snap Fits
• Threaded Metal
Inserts
• Hook and Loop Type
Fasteners
• Moulded-in-Threads
• Boss Cap
• Push-on / Turn-on
Fasteners
• Rivets
• Press Fits

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The main mechanical connections
used for plastic assembly

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Types of Gluing
Solvent Bonding
Adhesive Bonding

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Adhesive bonding

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Solvent Bonding Advantages
• Homogeneous distribution of mechanical loads
• Good aesthetics
• Economic assembly
• Low weight, no heavy screws, bolts and nuts
• Heat sensitive constructions or materials, which
welding would distort or destroy, can be joined
• Good sealing and insulating properties.

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Solvent Bonding Limitations
• Entrapment of solvent in the joint
• Stress cracking or crazing
• Dissimilar materials can only be joined if both are soluble
in a common solvent or in a mixture of solvents
• Differences in thermal expansion of components are not
compensated if dissimilar materials are bonded
• Reproducibility/process control
• High solvent evaporation time due to its entrapment in
the polymer matrix
• No disassembly possible
• Assembly hazards such as fire or toxicity.

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Adhesive Bonding Advantages
• Application on various substrates like thermoplastics,
thermosets, elastomers and metals
• Homogenous distribution of mechanical loads
• Differences in thermal expansion of components can be
compensated for by using a thick adhesive layer
• Good aesthetics / no special requirements to hide the
bond.
• Economic assembly
• Low weight, no heavy screws, bolts and nuts
• Heat sensitive constructions or materials, which welding
would distort, can be joined
• No thermal stresses introduced
• Good sealing and insulating properties.

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Adhesive Bonding Limitations
• Long term behavior may not be very good
• Stress cracking or crazing of the plastic may
take place
• Dissimilar materials can only be joined if both
are compatible with the adhesive
• Reproducibility/process control
• Curing time can be high depending on the
adhesive
• No disassembly possible
• Assembly hazards such as fire or toxicity

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Welding
An effective method of permanently joining
plastics components together.

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Welding Principle
• Inter diffusion of Molecular Chains
• Phase Change from Solid to Liquid.
• Followed by Solidification Phase at the
Interfaces to be joined together.

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Uniqueness of Welding
• Good Aesthetics
• Clean
• Strong Bond

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Schematic representation of the
welding process

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Types of Welding
• Vibration welding
• Spin welding
• Ultrasonic welding
• Hot-plate welding
• Induction welding
• Laser welding
• Radio freq. welding
• Resistance welding
• Hot gas welding
• Staking

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Vibration Welding
• the two plastic parts to be joined are vibrated
(rubbed) against each other at a certain
frequency, amplitude and pressure which results
in frictional heating of the surfaces, causing the
polymer to melt at the interface.
• The molten polymer flows out of the weld-zone
giving rise to flash. When vibration stops, the
weld cools down and solidifies.

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Vibration welding process

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Vibration welding equipment

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Advantages of Vibration Welding
• Cost Effective
• Short Cycle Times
• Large Batch Sizes Possible
• Melted Polymer Not Exposed to Open Air
• Strong Bond

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Disadvantages of
Vibration Welding
• Welding Thermoplastic Elastomers is
problematic.
• Product is exposed to vibrations during
welding.
• Much flash is formed.
• 3D Contours can’t be welded.

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Spin Welding
• The two parts to be welded are pressed against
each other.
• One part is held fixed and the other rotates at
high speed.
• The friction between the two parts generates
heat which causes the polymer to melt at the
interface.
• The molten polymer flows out of the weld-zone
giving rise to flash. When rotation stops, the
weld cools down and solidifies.

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Spin welding equipment

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Advantages of Spin Welding
• Efficient, Simple Process
• Simple Equipment
• Short Cycle Times
• Large Batch Sizes Possible
• Melted Polymer not Exposed to Open Air
• Strong Bond

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Disadvantages of Spin Welding
• Welding Thermoplastic Elastomers is
problematic.
• Only Circular Contours can be Welded.
• 3D Contours can not be Welded.
• Relative Position of the Parts can not be
Adjusted.

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Ultrasonic Welding
• The process uses low amplitude and high
frequency vibrational energy.
• Parts to be joined are fixed firmly.
• Mating part is subjected to sinusoidal
Ultrasonic Vibrations of the order of 20,000
cycles per second.

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Ultrasonic welding process

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Equipment for ultrasonic welding

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Advantages of Ultrasonic Welding
• Cost Effective
• Short Cycle Times
• Large Batch Sizes Possible
• Melted Polymer Not Exposed to Open Air

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Disadvantages of Ultrasonic Welding
• Welding Thermoplastic Elastomers is
problematic.
• Product is exposed to vibrations during welding.
• Restricted to Small and Medium Size parts.

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Hot Plate Welding
Uses thermal energy to melt the welding
zone through conduction.

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Hot plate welding process

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Advantages of
Hot Plate Welding
• Cost Effective
• Large Batch Size is Possible
• Suited for Soft Materials
• No Electrical Fields, No Mechanical Vibrations.
• Strong Bond

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Disadvantages of
Hot Plate Welding
• Long Cycle Times
• Molten Polymer Expose to Open Air
• Weld Strength is Poor for Certain Heat
Sensitive Materials.

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Induction Welding
• Uses Inductive Energy to heat the Plastic.
• The bonding material melts and the parts
are joined under low pressure.

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Induction welding process

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Advantages of
Induction Welding
• Short Cycle Times.
• 3D Weld Surfaces are Possible
• Thermoplastic Elastomers can be welded.
• Can be used for highly filled materials
• Welding process is reversible (Repair,
Recycling).
• Tolerances on Part Dimensions not tight.

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Disadvantages of
Induction Welding
• Electro-magnetic Welding gasket Material is
required.
• Not well suited for parts containing
electromagnetic sensitive items (Metal Inserts).

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Hot Gas Welding
• Uses Hot Air or Nitrogen to Melt the Surfaces to
be joined.
• Process is extensively used for assembling large
parts.
• Suitable for field assembly and repair.

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Hot gas welding

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Hot gas welding process

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MACHINING OF PLASTICS

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Different Types of Cutting
• Sawing
• Laser Cutting
• Milling
• Turning & Boring
• Punching, Blanking and Die Cutting

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Different Types of Finishing
• Filing
• Sanding
• Grinding
• Polishing and Buffing

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SURFACE TREATMENT

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Uniqueness of
Surface Treatment
 Transforms the materials into more workable
substrates.
 Surface Treatment is a must before printing
for non-polar materials.

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Types of Surface Treatment
• Mechanical Abrasion
• Flame Treatment
• Chemical Etching
• Corona Treatment
• Plasma Treatment

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Different Types of Finishing
• Filing
• Sanding
• Grinding
• Polishing and Buffing

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METALLIZATION

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Uses of Metallization
 Enhances Reflectivity
 Improves Abrasion Resistance
 Has High Electrical Conductivity
 Provides Electromagnetic Shielding

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Types of Metallization
• Vacuum Metallization
• Plating
• Flame and Arc Spraying

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Types of
Vacuum Metallization
• Vacuum Evaporation
• Sputtering

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Vacuum Evaporation
• Metal usually Aluminum is heated to the point at
which it evaporates.
• The vapour is made to condense on the cold
plastic part.
• The process takes place in a vacuum in order to
allow, the metal to reach the plastic surface
without being oxidized.

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Principle of vacuum
evaporation metallization

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Sputtering
• Vacuum coating process in which the
coating material displaced by impact with
inert gas plasma.

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Sputtering Process
• A high voltage electric field is created between
the fixture of the plastic part and a negative
electrode, the metal target.
• Metal target (Aluminium or an Alloy) serves as a
donor of metal atoms.
• Positively charged gas ions are attracted by the
negative metal electrode and are accelerated.
• Charged gas ions gains kinetic energy and hits
the negative electrode.
• The metal ions escape from the solid metal
target and the plastics part is covered with thin
metal layer.

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Sputtering

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COATING PROCESS

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Types of Coating
• Extrusion Coating
• Calender Coating
• Fluidized Bed Coating
• Electrostatic Bed Coating
• Electrostatic Powder Gun Coating
• Transfer Coating

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Extrusion Coating
Extrusion film coating is a technique in
which a hot film of plastics is placed on a
substrate and allowed to cool.

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Extrusion Coating

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Advantages of
Extrusion Coating
• Multilayer plastics may be placed on substrate.
• No solvents are needed.
• Thickness applied to substrate may be varied.
• Uniform coating thickness on wire and cable.
• Cellular coatings may be placed on substrate.

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Disadvantages of
Extrusion Coating
• Extrudates are hot melts.
• Equipment is expensive.

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Calender Coating
• Calendered films may be used as a coating on
many substrates, in a method similar to
extrusion coating.
• The hot film is squeezed on to the sub-strate by
the pressure of the heated gauging rollers

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Calender Coating

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Advantages of
Calender Coating
• High-speed continuous process.
• Precise thickness control.
• Pressure-sensitive and heat-reactive hot
melts may be used.
• Coatings are stress-free.
• Short runs are relatively economical.

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Disadvantages of
Calender Coating
• Equipment cost is high.
• Additional equipment needed for flat
stock.

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Fluidized-Bed Coating

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Advantages of
Fluidized Bed Coating
• Uniformity of Thickness.
• Thermoplastics and some thermosets may
be used.
• No solvents needed.

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Disadvantages of
Fluidized Bed Coating
• Substrate must be heated above plastics
melt or fusion temperature.
• Primer may be needed.
• Thin coatings are hard to control.
• Continuous automation of line is difficult.
• Post cure is needed.
• Surface finish may be uneven(Orange-peel).

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Electrostatic-Bed Coating

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Advantages of
Electrostatic Bed Coating
• Thin, even coats are easily applied.
• No preheating needed.
• Process is readily automated.
• Reduced overspray.
• Improved finish quality.

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Disadvantages of
Electrostatic Bed Coating
• Thick coatings need preheating of substrate.
• Small openings or tight angles are hard to coat.
• Dust recovery system may be needed.
• Only ionic resins or plastics can be used.
• Post cure is generally needed.
• Substrates may require special preparation.

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Electrostatic Powder
Gun Coating

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Advantages of
Electrostatic Powder
Gun Coating
• Thin, even coats are easily applied.
• No preheating necessary.
• Process is readily automated.
• Short runs and coating of odd-shaped
pieces are practical.
• Lower equipment cost than electrostatic bed
coating.

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Disadvantages of
Electrostatic Powder
Gun Coating
• Thick coatings need preheating of substrate.
• Small openings or tight angles are hard to coat
• Dust recovery system may be needed.
• Only ionic resins or plastics can be used.
• Post cure is needed.
• High labor cost.
• Thickness harder to control.

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PRINTING ON PLASTICS

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Types of Printing
 Pad Printing
 Screen Printing
 Flexographic Printing
 Rotogravure Printing
 In Mould Decoration

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Advantages of
Pad Printing
• Simple Process
• Cheap Process
• Multi-Colour Printing Possible
• Recommended for Flat Surfaces

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Pad Printing Process
First Method:
• The pad is first pressed on to a transfer plate
covered with a layer of ink deposited by a roller.
• Pad picks up the ink from the plate and pressed
on to the part to be printed.
Second Method:
• The pattern is etched in a cliché plate.The
rubber pad with flat surface is pressed on to the
cliché plate and picks up the design. The pad is
pressed on to the part.

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Pad printing

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Screen Printing
• A Stencil containing a design is placed in
frame covering the holes in the screen
where no ink is desired.
• Ink is placed on the screen.
• By a squeeze the ink is forced through the
screen on to the part.
• Part is allowed to dry.

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Screen printing

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Flexographic Printing
• High Speed Printing
• Used for Printing on Films
• Recommended for Frequent Changes
• Multi-Colour designs can be produced
simultaneously.

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Flexographic Printing Process
• A rubber plate is attached to the plate roller.
• The plate roller picks-up the ink and
transfers it onto the film.
• Film after printing is passed through hot air
for drying.

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Flexo Graphic Printing

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Rotogravure Printing
This method of printing is recommended on films for long runs. In this method
the roller itself will be engraved. Ink is applied to the entire surface of the
roller and a device called a doctor blade is used to scrape the plate and
remove all excess ink. The ink left in the sunken areas of the roller is
transferred directly on to the film.

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DIP MOULDING

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Dip Moulding Process
 Process in which heated moulds are
immersed in plastisol.
 Plastisol sticks to the hot mould and the
part is formed.
 Parts are stripped from the mould

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Types of
Dip Moulding Machines
• In line Machines
• Rotary Machines
• Advanced Machines
• Dual Path Machines

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In-Line and Chain Machines

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Rotary Machines

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Advantages of Dip Moulding
• Low tooling costs typically a fraction of injection
molding
• Quick and inexpensive prototypes
• Short lead-times on custom tooling weeks
versus months
• No internal stress molded into parts
• Large parts can be made without significant
tooling investment.
• Multi-Dipping capabilities allow us to design
products with two colors or materials on one part
- typically used for making products with durable
inside liners and more consumer friendly
exteriors.

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Limitations of Dip Moulding
• Internal dimensions, tolerances are
often much higher than on injection
molded parts.

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Applications of
Dip Moulding
• Handle Grips
• Caps
• Plugs
• Handles
• Bellows
• Boots
• Closures

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Dip Molding Applications

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CASTING PROCESS

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Casting
• Liquid Resins or Molten Plastics mixed
with Catalyst is poured in to moulds.
• Allowed to Polymerize or Cool.
• Parts are removed.
• Finishing Operations are done as
desired.

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Product Range
• Sheets
• Rods
• Tubes
• Table Tops
• Sinks
• Fancy Buttons
• Watch Crystals
• Furniture Parts etc.

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Types of Casting
 Simple Casting
 Solvent Casting
 Hot Melt Casting
 Rotational Casting
 Slush Casting

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Solvent Casting
• Solvent Solution of Plastic Poured on to a
Stainless Steel Belt.
• Solvent is evaporated by addition of heat.
• Film deposit on the belt is stripped and
wound on roller.

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Advantages of
Solvent Casting
• Additives for heat stabilization and for
lubrication are not needed.
• Films are uniform in thickness and optically
clear.
• No orientation are stress is possible with
this method.

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Hot Melt Casting
• Used for potting and encapsulation.
• Electrical parts to be protected from
hostile environments are placed in
moulds and hot resin is poured over
the components.
• When cooled, the plastic provides
protection for the part.

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Slush Casting
• Pouring dispersions of PVC or Plastisols
in to heated hollow open mould.
• Material solidifies as it strikes the walls of
the mould.

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Applications of
Slush Casting
• Hollow parts of dolls
• Rain Boots

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Rotational Casting
• Plastics Powders or Monomers are placed
in one half of the mould.
• Keep the other half and the mould is
placed in an oven.
• Mould is rotated bi-axially.
• The plastics fuses as it touches hot mould
surface.

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Applications of
Rotational Casting
• Ice Chests
• Boxes
• Large Commercial Containers