Plastics are synthetic or semi-synthetic organic polymers that can be molded into solid objects. There are two main types: thermoplastics, which can be reshaped when heated, and thermosetting plastics, which set permanently. Common plastic processing methods include injection molding, extrusion, blow molding, calendaring, thermoforming, rotational molding, and laminating. Injection molding uses heat and pressure to force melted plastic into a mold cavity. Extrusion produces solid or hollow shapes of constant cross-section. Blow molding inflates a hollow tube of plastic against a mold cavity. [/SUMMARY]

2. PLASTICS : -
 Plastic is a material consisting of any of a wide range
of synthetic or semi-synthetic organic that are malleable and
can be moulded into solid objects of diverse shapes.
 Plastics are typically organic polymers of high molecular mass,
but they often contain other substances.
 They are usually synthetic, most commonly derived
from petrochemicals.
 The world's first fully synthetic plastic was Bakelite, invented in
New York in 1907 by Leo Baekelandwho coined the term
'plastics‘.

3. TYPES OF PLASTIC : -
1.THERMOSETTING PLASTIC: -
The molecules of thermosetting plastics are heavily
cross-linked. They form a rigid molecular
structure.
Although they soften when heated the first time,
which allows them to be shaped they become
permanently stiff and solid and cannot be
reshaped.
 Ex. Polyester resin and urea formaldehyde
Cross-linked molecules
Contd.

4. 2. THERMOPLASTIC: -
 Thermoplastics can be heated and reshaped
because of the ways in which the molecules are
joined together.
 The molecules of thermoplastics are in lines or
long chains with very few entanglements.
 When heat is applied the molecules move apart,
which increases the distance between them,
causing them to become untangled. This allows
them to become soft when heated so that they can
be bent into all sorts of shapes.
 Ex. Polyvinyl chlorides(PVC), Nylons, etc.
Contd.
individual monomer molecule

5. PROCESSING OF PLASTICS: -
1. COMPRESSION MOULDING
2. TRANSFER MOULDING
3. INJECTION MOULDING
4.EXTRUSION MOULDING
5. BLOW MOULDING
6.CALENDARING
7. THERMOFORMING
8.ROTATIONAL MOULDING
9.LAMINATING

6. 1. COMPRESSION MOULDING : -
Compression moulding is the forming process.
Compression moulding process is followed by two step first one preheating
and pressurizing.
Measured charge of compound placed between halves of split mold
Pressure is applied so that compound flows to fill mold cavity
 Compression moulding is generally used for thermosetting plastic.
 Example:- urea formaldehyde and phenol formaldehyde.

7. PROCESS DESCRIPTION

8. PARAMETERS : -
The quantity of charge ( moulding material ) put into the mould.
 Pressure of the moulding process:-
Range of pressure 2000-3000 psi ( 13.8-20.7 mpa ).
Mould temperature:-
Temperature range 300ºf to 375ºf ( 149⁰C- 191⁰C )
Cure time variables:-
The period required to harden thermosetting material to partial and complete
polymerization is called cure time. Cure times typically range from 1 - 5 min

9. 2. TRANSFER MOLDINGS : -
 It is similar to compression moulding.
 Thermoset polymers can be formed when a preset amount of material is placed in a
separate cavity and heated.
 A plunger moves the material into the shaped mould with high pressure.

10. 3. INJECTION MOULDING : -
It is a manufacturing technique for making parts from
thermoplastic and thermoset materials .
Injection moulding is a highly automated production process
for producing large quantities of identical items.
A measured amount of molten thermoplastic is driven by a
ram past a heating system into the mould.
The mould is split to allow finished object to be removed after
cooling.
Example : - Polystyrene, Nylon, Polypropylene, PVC,
Acrylonitrile Butadiene Styrene

11. PROCESS : -
 Plastic powder are fed from a hopper into a hollow steel barrel which
contains a rotating screw.
 The barrel is surrounded by a jacket of heaters which melt the plastic
material.
 The screw is forced back as the melted plastic collects at the end of the
barrel.
 Once a sufficient charge of melted plastic has accumulated a hydraulic
ram forces the screw forward injecting the thermoplastic through a sprue
into the mould cavity.
 This one is capable of exerting forces of up to 250 tonnes.
 Pressure is kept on the mould until the plastic has cooled sufficiently for
the mould to be opened and the component ejected.

13. 4. EXTRUSION MOULDING: -
 Continuous process used to produce both solid and hollow products that have a
constant cross-section.
 Ex: - Window frames, hose pipe, curtain track, garden trellis.
 Thermoplastic granules are fed from a hopper by a rotating screw through a
heated cylinder.
 The tapered screw compacts the plastic as it becomes elasticised. The die which
is fitted to the end of the extruder barrel determines the cross-section of the
extrusion.
 Thicker cross-sections are extruded more slowly as more time is required for the
initial heating and subsequent cooling of the larger quantities of material which
are involved.
 As the extrusion leaves the die it is cooled by passing through a cooling trough
containing cold water.

15. 5. BLOW MOULDING: -
 Blow Moulding is an automated process that is used extensively to make
bottles and other lightweight, hollow parts from thermoplastic materials.
 A hollow length of plastic, called a parison, is extruded down between the
two halves of the mould.
 The mould closes
 Compressed air is blown into the inside of the parison which inflates it,
pushing the soft plastic hard against the cold surfaces of the mould.
 The mould is then opened the moulding ejected and the waste (called
flash) is trimmed off with a knife.
 Example : - high density polythene and low density polythene are used.

16. 1. 2.
3. 4.

17. Blow Moulding Process
Extrusion
Blow
Moulding
Injection
Blow
Moulding
Stretch Blow
Moulding

18. 6. CALENDARING : -
 It is a intermediate process where the extruded plastic sections are reduced to
sheet.
 Only used for thermoplastics.
 Involves rolling out a mass of premixed plastics material between large rollers to
form a continuous and accurately sized film.
 The process begins with the ingredients being blended and fluxed in a mixing mill
at approx. 100°c.
 Nip rollers control the thickness of the sheet material can be gradually reduced in
thickness.
 Rolls of semi-rigid PVC which will be used to manufacture transparent A4 folder
'pockets'.

19. Example: -
1. Flexible PVC :- Rainwear, Shower curtains, Tapes, etc.
2. Rigid PVC: - Credit cards, Lamination

20. 7. THERMOFORMING: -
 Process used to shape thermoplastic sheet into discrete parts.
 Basic principles: -
i. Heat a thermoplastic sheet until it softens.
ii. Force the hot and pliable material against the contours of a mold by using
either mechanical, air or vacuum pressure
iii. Held against mold and allow to cool, and plastics retains its shape
 This can be done by: -vacuum and pressure forming.
 Lower pressures are required to thermoform.

22. 8. ROTATIONAL MOULDING : -
 Rotational moulding is a process used for producing hollow plastic products.Such
as road cones and storage tanks up to 3m³ capacity.
 A measured weight of thermoplastic is placed inside a cold mould.
 Heated to a temperature of 230-400 c whilst being rotated around both vertical
and horizontal axes.
 The mould moves into a cooling area or chamber where it is cooled by air or
water jets.
 The hollow moulding can be removed as soon as it is cool enough to hold its
shape.

23. The rotational molding
(roto-molding or roto-
casting) process. Trash
cans, buckets, and plastic
footballs can be made by
this process.
90% of rotational
mouldings are made from
polyethylene

24. 9. LAMINATING: -
 Layers of materials are bonded with a resin into a strong solid structure, often
with heat and pressure.
 This can be done in following ways: -
 Gravure coating
 Wet bond laminating
 Dry bond laminating
 Solvent less laminating
 Extrusion laminating
 Example: -Foil, Snack food bag, Saran- coated nylon, Metallized propylene, etc.

25. Extrusion die
Chill roll
Substrate A
Substrate B
Strip-off roll
Pressure
roll
Nip roll
Extrudate Three ply
laminate
Extrusion laminating Dry bond laminating
Gravure coating