plastics moulding methods ,types of plastic

1. Plastics
By surya teja

2. • Plastics are made from resin with or without fillers,
plasticisers and pigments. These are organic materials of high
molecular weight which can be moulded to any desired form
when subjected to heat and pressure in the presence of a
catalyst. ex:-acrylic,cellulose acetate,cellulose nitrate
,polyethylene,polysterane,poly vinyl chloride,polyvinyl acetate

3. Thermo plastic
• The thermoplastic variety softens on heating and hardens on
cooling, i.e., their hardness is a temporary property subjected
to change with rise or fall of temperature and can be brought
again to plastic stage on heating. These are formed by
addition polymerisation and have long chain molecular
structure. They can be remoulded, for use, as many times as
required. Examples are material resins— rosin, kopal, amber,
shellac; cellulose derivatives— cellulose acetate, cellulose
nitrate, nitrocellulose or celluloid, cellulose acetate-butyrate;
polythenic or vinyl resin—polyethylene

4. • Thermosetting plastic cannot be reused. They require great
pressure and momentary heat during moulding and finally get
hardened on cooling. The chemical reaction in this porcess
cannot be reversed. Once solidified they cannot be softened.
The thermosetting plastics acquire three-dimensional cross-
linked structure with predominantly strong covalent bonds
during polymerisation retaining strength even on heating;
under prolonged heating they fail by charring. Compared to
thermoplastics, they are hard, strong and more brittle. The
important thermosetting resins are phenolic resins or
phenoplasts (bakelite), amino resins, polyester resins, epoxy
resins and silicon resins. The principal uses are in electrical
equipments, plugs, sockets, switches, ash trays, knobs,
handles, etc.
Thermo setting plastics

5. Properties of plastics
• 1. Can be moulded to any desired shape or size and have high
tensile and compressive strengths.
• 2. Easy to work upon. 3. Light in weight and a few varieties are
glossy like glass. 4. Not attacked by insects and fungi. 5.
Available in desired colour and texture. 6. Require a little
maintenance. 7. Good electrical insulators and have low
thermal conductivity. 8. Shock absorbing material. 9. Can be
sawn, drilled and punched and welded easily.
• 10. High strength to weight ratio.

6. Properties of plastic
• 11. High resistance to weathering conditions. 12. Corrosion
resistance. 13. Decorative surface effect—painting or
polishing of the surface is not required. 14. High refractive
index. 15. Some varieties are as hard as steel. 16. Withstands
moisture, oil and grease well. 17. Inflammable. 18. High
coefficient of thermal expansion (about ten times of steel).
19. Deterioration under prolonged exposure to sun’s ultra
violet rays. 20. Low manufacturing cost, hence cheap.

7. Constituents of plastic
• Resin:-Synthetic resin, short for resin, is artificial synthesized
high molecular polymer. Therefore, different types of plastic
can be called after the name of the synthetic resin it is made
from.
• Synthetic resin, the basic raw material of plastic, takes up
30%-60% or more of its composition. It has the function of
agglutination, not only bindingitself together, but also the
other materials firmly together. As the type, property, and
amount of synthetic resin change, the physical and
mechanical properties of plastic also change. Therefore, the
main properties of plastic depend on the synthetic resin it is
made from.

8. Constituents of plastic
• (1) Filling Material
• It is filler for short. By adding filling material to the synthetic
resin, the flow between the chains of macromolecular
compound can be slowed down; the strength, stiffness, and
heat resistance of the synthetic resin can be improved; and
the cost of plastic can be lowered. The common inorganic
filling materials are talcum powder, diatomite, mica,
limestone powder, and glass fiber, etc. The common organic
filling materials are wood flour and wastepaper, etc..
• (2) Plasticizer
• The purpose of adding plasticizer is to improve the plasticity
and flexibility of plastic as well as to lessen the brittleness.

9. Constituents of plastic
• Plasticizer is either liquid with high boiling point and poor
volatilization or solid with low melting point. Plasticizer has
the disadvantage of reducing the mechanical properties and
heat resistance of plastics. The common plasticizers are
dibutyl phthalate (DBP), dioctyl phthalate (DOP), and
camphor, etc. .
• 3.)Lubricant :- is used to make the moulding of plastic easier
to prevent sticking of materials to the mould for a flawless
finish. The examples are stearates, oleates and soaps.

10. Constituents of plastic
• 4.)Catalyst :-is added only in the case of thermosetting
plastics to accelerate the polymerisation of fusible resin
during moulding operation into cross-linked infusible form.
• 5.)Blowing Agent:- Sodium bicarbonate and ammonium
carbonate are sometimes added to plastics to produce porous
articles.

11. Fabrication of Plastics.
extrusion

12. • Extrusion:
•
• Using this processing it is possible to produce a wide range of different
forms of plastic,
• such as tubes, sheets and films, structural parts, etc. 1º Step: Plastic
pellets are placed in
• a feed hopper which feeds into the system. 2º Step. A turning screw
pushes the plastic
• into the barrel where heaters increase the temperature and a melted
polymer is obtained.
• 3º Step. The melted plastic is forced through a shaping die. Depending on
the particular
• shape of this element, a continuous shape is formed and pulled out of the
extrusion
• machine. 4º Steep. Solidification by cooling

13. Injection molding

14. Injection molding
• Plastics pellets flows, due to gravity, from the feed hopper
onto a turning screw. It is converted into a melted plastic by
the action of heaters situated along the barrel. The screw
moves the molten plastic forward, forcing the plastic through
a gate into the cooled mould. The mould is opened once the
plastic has solidified and the piece is pushed from the mould
by automatic ejector pins. After we get the manufactured
piece,the mould is closed and clamped and the process begins
again.

15. Compression molding

16. Compression molding
• This is a similar process to extrusion. In compression
moulding, plastics pellets,
• sometimes called moulding powder, are placed in the feed
hopper and pushed to the
• gate by the action of the turning screw. It is heated and
compressed while it passes
• through the barrel. After the gate, the molten charge is
quickly transferred to a press
• where it is moulded while still hot. The part is removed after
sufficient cooling.

17. Blow molding

18. Blow moulding
• Plastic grocery bags, bottles and similar items are made using
this processing.
• As in compression processing, plastic pellets are melted and
the plastic is forced
• through a gate into the blow pin camera. The plastic
substance is expanded and cooled
• by being made to flow around a massive air bubble. After a
few seconds, the mould is
• opened and the manufactured product is ready.

19. Blow moulding

20. Polymerization and condensation
• Polymerization is the process by which small molecules are
joined together to form very long chains. Condensation:
process by which a covalent bond forms between two or more
different types of molecules and a by-product, such as water,
is released; significantly alters the properties of the
components.

21. Poly vinyl chloride
• Polyvinyl chloride plastic is a kind of common building plastic
made fiom the polymerized vinyl chloride monomer. Polyvinyl
chloride plastic has better chemical stability and aging
resistance, but poor heat resistance. It may decompose and
metamorphose if the temperature exceeds 100°C. Usually, it
should be used at temperature of below 60-80°C. By adding
different amounts of plasticizer, hard and soft polyvinyl
chloride plastic can be made.pvc is used in wall
coverings,gutters,floorings,cables and wiring,windows etc;

22. Reinforced plastics
• Glass Fiber Reinforced Plastics It has the properties of light
weight, water resistance, high strength, corrosion resistance,
and decorativeness. It is suitable to be used as lighting and
decorative sheet.
• Synthetic fiber reinforced film It is the main raw material
used in building aerated house. It has the properties of light
weight, airtight, heat insulation, and easiness to be
transported. It is suitable for the exhibition hall, gymnasium,
agricultural greenhouse, temporary granary, and other kinds
of temporary buildings.

23. Plastic laminate
• Plastic laminate is a composite building material made from
kraft paper, resin, and adhesives. Multiple layers of kraft
paper are soaked in resin, then pressed together at high levels
of temperature and pressure to form a single sheet. Plastic
laminate adhesive or resin is then used to add a decorative
paper or melamine top layer. Finally, a protective urethane
top coat, or wear coat is added to enhance strength and
durability. Sheets of plastic laminate may be bonded to a
wood or composite base using plastic laminate glue,
adhesives, or resin. The laminate-topped base is then used as
a countertop, floor finish, or wall paneling. The sheets of
laminate themselves can also be used as a decorative finish
material is a wide variety of applications.

24. Polythene sheets
• Polyethylene (abbreviated PE) or polythene is
the most common plastic.its primary use is in
packaging.PE is usually a mixture of organic
compounds (C2H4)nH2 ,they only differ in the
value of n.