Manufacturing

2. Introduction
Plastics is organic materials which is derived
directly from carbon.
Organic materials consist of carbon chemically
combined with hydrogen, oxygen and other
non-metallic substance.
These organic materials are prepared form natural
or synthetic resins.
Natural materials include Wood, coal petroleum,
natural rubber, animal fibres and food.
Synthetics include the large group of solvents,
adhesives, synthetic fibers, rubbers, plastics,
lubricants, dyes and cutting oils etc.
The plastics are synthetic organic materials, which
are also termed as “Polymers”.

3. Polymers
The term “polymer” is derived from the two Greek
words: Poly meaning “many” and meros meaning
“parts” or “units” thus polymers are composed of a
large number of repeating units called monomers.
The monomers are joined together end to end in a
polymerization reaction.
Polymerization
The process of linking together of monomers, that
is, of obtaining macromolecules is called
“polymerization”. It can be achieved by the
processing techniques. (Polymerization takes place
under suitable condition of temperature and pressure
and in the presence of a catalyst called an initiator).

4. Addition Polymerization
In addition polymerization, the polymer is
produced by adding a second monomer to
the first, then a third monomer to this
dimer, and a fourth to the trimor and soon
until the long polymer chain is terminated.
Polyethylene is produced by the addition
polymerization of ethylene monomers.
Many monomers will not polymerize with
themselves, but will co-polymerize with
other compounds.

5. Condensation Polymerization
In this process, two or more reacting
compounds may be involved and there is a
repetitive elimination of smaller molecules, to
form a by-product.
For example, in the case of phenol
formaldehyde (Bakelite), the compounds are
formaldehyde and phenol.
Metacresol acts as a catalyst and the by
product is water. There is also the growth
perpendicular to the direction of chain.

6. Addition to polymers: - One or more of the following
materials are added to the polymers to make them
processable plastics or plastics of desirable properties.
Catalysts or Accelerators: - These are added to accelerate
the chemical reaction during polymerization of plastics.
Fillers: - These are added to reduce the material cost
sometimes they are finally distributed to increase
strength, stiffness and thermal resistance. Common fillers
are wood flour, mica, quartz, carbon black, asbestos,
glass fibres etc.
Modifiers: - There are the chemicals added to plastics for
changing the properties of base resin.
Plasticizers: - These are added to improve the plastic
behaviour of the polymer. They are generally oily in
nature. Organic solvents, resins and even waters are used
as a plasticizers.

7. Stabilizers: - These are added to prevent the deterioration of
the plastics due to the action of heat and light.
Initiators: - They help in initiating or starting the reaction i.e.
polymerization.
Dyes and pigments: - They are the colouring agents, added
to impart different colours and shades to plastics.
Plastics
Plastics are the synthetic polymers. The term plastic is
related with plasticity. So in a certain phase of manufacture,
they are present in a plastic stage, which makes it possible
to impart any desired shape to the product.
Raw Material for Plastics
The raw material for plastic compounds are various
agriculture products and numerous minerals and organic
materials including petroleum, coal, gas limestone, silica
and sulpher. The natural resins are waxes, shellac, pitch,
bitumen resin, rubber etc. Synthetic resins are formed by
polymerization.

8. Properties of plastics
Lightness in weight because of low density (1 to 2g/cm3
)
Silent in operation
Easy workability
Low meting point
Highly resistant to abrasion
Good surface finish
Good thermal and electrical insulation
Good strength and rigidity
Good resistant to most of the chemicals
Good dimensional stability
Impermeable to water
Low fabrication cost
Can be made transparent or coloured.

9. Type of plastics
The plastics are classified in the following two groups
1. Thermosetting 2. Thermoplastics.
Thermosetting Plastics: - Plastics which are formed into
shape under heat (1270
C to 1800
C) and pressure which
results a permanently hard product. The thermosetting
plastics don’t soften on reheating and can not be
reworked. The common thermosetting plastics are alkyds,
,melamine, polyesters, phenols and urea.
Thermoplastics: - Plastics, which are softening under heat
and pressure. They remain soft at elevated temp and
become hard on cooling. They can be remelted repeatedly
by the successive application of heat. Common
thermoplastics are acrylics, poly-tetra-fluoro ethylene
(PTFE), polyvinyl chlorides (PVC), nylons, polyethylene,
polypropylene, polystyrene etc.

10. Types of thermosetting Resins
Phenol formaldehyde (Bakelite): - The most
important and widely used phenolic resin is
phenol formalde-hyde. It is made by the reaction
of phenol with formaldehyde. (The phenol is
carbolic acid obtained as a by-product during
distillation of organic substance such as wood or
coal).
Properties :- Hard, rigid, scratch resistant;
resistant to heat, water, non oxidizing acids;
Excellent electrical insulating property, cheap.
Uses - Knobs, handles, plugs, cabinets, telephone
handsets, switches etc.

11. Urea formaldehyde :- It is obtained by the condensation of
urea and aqueous formaldehyde (urea is obtained by
mixing liquid carbon dioxide and liquid ammonia under
heat and pressure)
Properties: - Hard, rigid, durable, heat and scratch resistant,
wide range of colours.
Uses - Domestic electrical fittings such as switch covers,
plug tops, socket bases, lamp sockets, toilet seats,
tableware etc.
Melamine formaldehyde: - It is obtained by the
condensation polymerization of melamine and
formaldehyde (Melamine is obtained from calcium carbide).
Properties: - High dielectric strength, resistant to heat and
shock, Hard, good colour abilities, good resistance to
moisture etc.
Uses - Telephone sets, circuit breakers, switch panels etc.

12. Silicon resins :-
The silicon resins have silicon and oxygen chains to,
which are linked various organic groups such as methyl
side groups etc. These may be in the form of liquids,
semisolids, rubbers and solids.
Properties: - Resist high temperatures, excellent dielectric
strength.
Uses: -
Liquids: - Antifoaming agents, damping and hydraulic
fluids,high temp. Lubricants, water repellent for leather.
Semi solids: - Used as lubricants where very high and low
temperatures are encountered.
Rubbers: - Gaskets, insulation.
Solids: - High voltage insulator, high temp insulating
foams.

13. Epoxy resins :-
They are obtained by condensation polymerization
in the reaction of bisphenol (double phenol) and
epichloro-hydrin. These are cross linked by the
addition of a hardener.
Properties: - Good chemical and electrical
resistance, low shrinkage, good adhesion to metal
and glass, good resistance to wear and impact,
expensive.
Uses - Surface coatings, adhesive for glass and
metals, jigs and fixtures, laminating materials used
in electrical equipment.

14. Polyester resins :-
These are obtained by the reaction between a polyhydric
alcohol and a dibasic acid. They are divided into the
following three groups.
Saturated polyesters :- These are obtained by reacting
glycol with saturated dibasic acid. These are converted into
commercial fibres used for making terylene, dacron etc.
Unsaturated polyesters :- These are obtained by reacting
glycol with unsaturated dibasic acid (Maleic anhydride)
They are good resistance to temp. (up to 1450
C), water but
possesses low resistance to acids and alkalis.
These are used in safety hamlets, aircraft ,battery boxes,
motor car body components etc.
Alkyds :- These are obtained by reacting polyhydric alcohol
with Poly basic acid in correct proportions in the presence
of heat and catalyst (CO2
gas). These are modified by oil or
fatty acids.They are used in making good insulators, sheets,
rods, tubes, switches, Aircraft and automobile parts etc.

15. Furnace resins :-
These are obtained when waste farm products
such as cotton seeds, rice hulls are processed
with certain acids.
Properties :- Dark in colour, water resistant, good
electrical properties.
Uses :- Core sand binders, Hardening additives
for gypsum plasters.
Polyurethanes :-
These are obtained by treating di-isocynate and
diol.
Properties :- Excellent resistance to abrasion and
solvents.
Uses :- Coatings, films, foams, adhesives and
elastomers.

16. Types of Thermoplastic resins :-
The following are the various types of thermoplastic
resins .
Cellulose derivatives : are as follows :-
Cellulose Nitrate :- It is obtained by reacting cellulose with
nitric acid in the presence of sulphuric acid, which acts as
dehydrating agents.
Properties :- Hard, Brittle, good colourability, good
resistance to moisture, highly inflammable.
Uses :- Pen bodies, toothbrushes, drawing instruments,
table-tennis balls, toys and toilet articles.
Cellulose Acetate :- It is obtained by reacting cellulose with
acetic acid in the presence of sulphuric acid.
Properties :- Transparent, wear resistance, easily moulded
and extruded, absorb moisture.
Uses :- Toys, knobs, radio panels, film for recording tape,
packaging, curtains and wrapping.

17. Cellulose acetate –
butyrate :- It is obtained by reacting cellulose with
acetic acid and butoric acid.
Properties :- Low moisture absorption, toughness,
good stability against heat and light, good
colourability.
Uses :- steering wheels, football helmets, goggle
frames, insulating tapes, pipes and tubes.
Ethyl cellulose :- It is obtained by reacting sodium
cellulose with ethyl chloride under pressure and
subsequent, precipitation in water, followed by
purification.
Properties :- Strong, tough, Moisture resistant and
good insulators.
Uses :- Jigs and fixtures, forming dies and moulded
components.

18. Polystyrene :- It is obtained by polymerization of
styrene in the presence of benzyl peroxide.
Properties :- Hard, brittle, low impact resistance, good
colourability, resistant to wear, dimensional stability
and insulating ability.
Uses :- Moulding of articles like toys, combs, buttons,
radio, television parts, refrigerator parts, battery cases
etc.
Polyethylene :- It is obtained by polymerization of
ethylene. It may be of low density or high density
depending upon the process.
Properties :- Resistant to moisture & chemicals,
inexpensive.
Uses :- Low-density polythene is used as film, bags.
High-density polythene is used for containers, bottles.

19. Polypropylene :- It is obtained by polymerization of
propylene in the presence of Zieglor-Natta catalyst.
Properties :- Excellent electrical properties, high impact
and tensile Strength, resistant to heat and chemicals.
Uses:- Hospital and laboratory equipments, toys ,furniture.
Vinyl resins :-Polyvinyl chloride (PVC) :- It is obtained by
heating a water emulsion of vinyl chloride in the presence
of small amount of benzoyl peroxide or hydrogen peroxide
under pressure.
Properties :- Hard thermoplastic, non-burning, weather
resistant .
Uses :- Rain water pipes, roofing sheets, safety halmets,
refrigerator components.
Polyvinyl acetate (PVA) :- It is obtained by heating vinyl
acetate in the presence of benzoyl peroxide as catalyst.
Uses :- Paints , lacquers, plastic emulsions, coating etc.

20. Polyamides :-It is produced by the reaction of a
diamine with an organic acid.
Properties :- Tough, stiff, whitish, high temp.
stability, good abrasion resistance.
Uses :- Light engineering components such as
gears, bushes, bearing.
Poly tetrafluoroethylene (PTFE):- It is obtained by
polymerization of water emulsion of tetrafluoro
ethylene under pressure in the presence of
benzoyl peroxide as catalyst. It is also called
Teflon or fluon.
Properties :- Extreme tough, low co-efficient of
friction, good electrical and mech. properties.
Uses :- Gaskets, packing, pump parts, tank
linings, asbestos fibres, and glass fibres.

21. Polymethyl methyacrylate (PMMA):-
It is obtained by polymerization of methyl
methyacrylate in the presence of acetyl
peroxide. It is popularly known as Lucite or
Plexiglass.
Properties :- Hard, rigid material, light
transmitting power, excellent optical properties.
Uses :- Lenses, aircraft light fixtures, bomber
noses, gun turrets, automotive appliances and
wind screens etc.

22. Synthetic Rubbers or Elastomers :-
Styrene rubber :- It is produced by copolymerization of
butadiene (75%) and styrene (25%)
Properties :- High abrasion resistance, high load bearing
capacity and resilience.
Uses :- Motor tyres.
Nitrile rubber :- It is a cop`olymer of butadiene and
acrylonitrile.
Properties :- Excellent resistance to heat, sunlight, oils, acids
and salts.
Uses :- conveyor belts, aircraft components, hoses, gaskets,
automobile parts.
Polychloropropene rubber :- It is made by polymerization of
chloropene, a chlorinated butadiene. It is also known as
neoprene.
Properties :- Resistant to oils, heat and light.
Uses :- Hoses, gaskets, conveyor belts, adhesives etc.

23. Butyl rubber :-
It is made by copolymerisation of iso-butylene with small
amount (1 to 5%) of isoprene.
Properties :- Excellent resistance to heat, abrasion and
chemicals, good electrical insulating properties.
Uses :- Cycle, automobile tubes, hoses, tank linings, high
voltage wires and cables etc.
Polysulphide rubber :-
It is made by the reaction between sodium Polysulphide
and ethylene dichloride.
Properties :- Good resistance to mineral oils, fuels,
solvents and sunlight.
Uses :- Hoses, gaskets, cable coverings, oil tank linings
etc.

24. Fabrication of Plastics :
There are various methods of producing components
from the plastic materials, which are supplied in the
granular, powder and other forms.
Various plastic processing methods are :
Compression Moulding
Transfer Moulding
Injection Moulding
Extrusion Moulding
Blow Moulding
Casting
Slush casting
Calendering
Laminating
Thermoforming.

25. Compression Moulding :-
This method is mostly used for thermosetting plastics but can also
be applied to some of the thermoplastic materials.
In compression moulding, a material normally in powder or
preform shape, is loaded directly into the hot die cavity. Pressure
from 150 to 700 kg/cm2
is applied, held for a curing period and then
the finished part is ejected.
It is most economical when it is applied to small production and
parts produced require close tolerances, high impact strength and
low mould shrinkage.
Compression moulding equipment is usually simple, It consist of a
hydraulic or pneumatic press with parallel platens that apply the
heat and pressure.
The moulds are usually made of tool steel and are polished to
chrome plated to improve material flow and product quality. The
moulds are heated by variety of means, inducing electrical heaters,
steam, oil and gas.
Typical compression molded parts include gaskets, seals, knobs,
gears and handles for kitchenware’s.

26. Compression Moulding

27. Transfer Moulding :-
In compression moulding, the material does not flow
into intricate parts of the complex moulds and also
the pressure required is very high because the
material is introduced in the mould in the solid state
and has to plasticise and flow with in the mould itself.
In order to overcome this difficulty, transfer-moulding
process is used.
In this, the heat and pressure is applied to the
thermosetting material in a chamber outside the
mould and when this thermosetting material becomes
fluid, it is transferred to the mould through sprue and
gate under pressure. The mould is held under
pressure until the product is completely cured.

28. Transfer Moulding

29. The charge material (Thermosetting material) is frequently
preheated to shorten the cycle and minimize erosion of
the cavity, plunger, runner and gates.
It is used when the product requires good tolerance,
finish and excellent detail. It can also be used when
inserts are to incorporated into the product to improve
the strength or used to provide threaded cavities or holes.
The products made by this process includes electrical
switchparts etc., Gear, wiring devices, household
appliances, under hood automotive parts etc.
The disadvantages of transfer moulding are :
The wastage of material is rather higher than with
compression moulding
The mould cost is also higher than for compression
moulding.

30. Injection Moulding :-
Injection moulding is the most widely used process for high
volume production of thermoplastic resin parts.
In this process, the granules of dry raw material (powdered
plastic compound) are fed by gravity from a hopper into a
cavity that lies ahead of a moving ram or plunger. As the ram
advances, the material is forced into a heated chamber,
where it is preheated. From there it is forced through a
torpedo section, where it is melted and superheated (200 to
3000
C).The heated material is then forced through a nozzle
which is mounted against the mould. After feeding the
material into the mould, it is allowed to cool. When sufficient
hardening takes place, the mould is opened and produced
part is ejected out by ejector pins.
Some injection moulding machines uses the screw instead of
ram (plunger). This screw rotate and reciprocate axially, to
control the flow of material and to provide the pressure.

31. Injection Moulding

32. The injection moulding has the following
advantages over the compression moulding.
It is a faster method
It is most economical method for mass
production of single product.
The metal inserts can be easily cast with the
product.
The products having complex shape or thin
walls can be easily moulded.
The material wastage in low because the
runners and sprues can be grinded and
reused.
The process can be easily mechanized i.e.
easily automated.

33. Extrusion Moulding :-
Extrusion means the continuous flow of material through
a die. In this process, the powdered polymer or
monomer is fed by a screw along a cylindrical chamber.
As the powder moves towards the die, it is heated and
melts. It is then forced through the die opening of
desired shape. Hooper is used to feed the powdered
material into the cylindrical chamber. The cylindrical
chamber is heated by electricity, oil or steam. A rotating
screw is used for carrying, mixing and forcing the
material through the die.
Extrusion process is used for the thermoplastic material.
This method is mostly used for making long tubes, rods,
pipes, ropes etc. The extruded shape (outcome of the die
opening) is carried through a cooling medium by a
conveyor. Cooling is done by the following means.

34. Extrusion Moulding

35. By exposure to air at room temperature.
By passing through a liquid bath at a controlled
temperature.
By jet of compressed air.
Rapid cooling must be prevented because it
causes warpage and sets some internal strains in
the finished pieces.
Advantages :-
Low initial cost.
Continuous production.
High uniaxial strength
Intricate profiles can be produced.
Material thickness can be accurately controlled.

36. Blow Moulding :-
This process is applied to only thermoplastic material for
making thin walled hollow articles such as bottles and
floatable objects. In this process a heated closed end
thermoplastic tube is placed in the mould and air pressure is
applied to inflate it i.e. the tube will expand to the walls of the
cavity. After the product is cooled sufficiently, the mould is
opened and the product is removed.
In this process, the mould is in two halves. The cylinder or
tube of plastic material (known as parison) is heated and
placed between the jaws of a split mould.
When the mould is closed, it pinches off the parison and the
product is completed by air pressure which forces the
material against the mould surfaces. The mould should be
properly vented to eliminate the poor surface finish.

37. Blow Moulding

38. Casting :-
It is similar to metal casting process but in this case poured
liquid is plastic instead of metal. In this process products
are produced without the application of pressure. The
plastics are heated to a suitable temperature and then the
molten resin is poured into the moulds. The moulds are
made up of lead. After proper curing and hardening, the
products are removed from the moulds. The liquid resins
such as polyesters, silicon's, phonetics, acrylics and some
cellulose derivatives are used for pouring. Different types of
moulding such as open moulding, centrifugal moulding,
shell moulding, slush moulding is used to produce the
products. Casting process is generally used when there is
not sufficient justification for making the expensive dies. So
it is used when the number of parts to be produce are
limited.

39. Slush Casing :-
In this casting method, the slurry is prepared from
the thermoplastic resin and then this slurry is
poured into the preheated mould. A uniform layer
of the resin sets all along the surface of the mould
because of the heat of the mould. When the layer
of the desired wall thickness is set, the extra
material is drained off. Extra heat is now applied
for proper curing of the resin. After proper cooling
(chilling)or hardening of the product takes place.
Then the product is removed from the mould. This
method is used to make the product where
appearance is important and not the wall
thickness such as toys and artificial flowers etc.

40. Calendering :-
It is the process of producing film or thin sheets by
squeezing a thermoplastic material between the
revolving rolls or cylinders. The thermoplastic
material is composed of resin, filler, Plasticizers
and color pigment. The thickness is gradually
reduced and is controlled by a combination of
squeezing and altering the speed of the finished
rolls. The finished product is cooled by passing
through water-cooled rolls (chilling rolls). The
products produced by Calendering are vinyl,
polyethylene, cellulose acetate films and sheets,
vinyl floor tiles etc.

41. Calendering

42. Laminating :-
It is the process of bonding together a variety of
materials by heat and pressure to form a single
piece. This single piece is known as laminates. So
laminating plastic comprise sheets of paper,
fabric, asbestos, wood etc. which are first
impregnated or coated with resin and then bonded
together by heat and pressure to form the single
piece. This single piece has improved properties
i.e. it is hard, strong, impact resistant, unaffected
by heat or water and has good machining
characteristics. Because of these improved
properties , laminating plastics can be used for the
fabrication of gears, handles, bushings, furniture
and many other articles.

43. Laminating

44. High pressure process :-
Phenolics, melamines, ureas and silicon are the
most commonly used resins in high pressure
laminates.
Firstly the resonoid material (e.g. phenol
formaldehyde) is dissolved by a solvent (e.g.
alcohol) to convert it into a liquid vanish.
Rolls of fabric paper are passed through this
liquid bath for impregnation.
It is then squeezed through a set of rollers.
They are then passed through a drier which
evaporates the solvent.
The sheets are cut into convenient sizes and
staked together to make up the desired thickness
of the final sheet.

45. These are then pressed by hydraulic press at
about 1800
C and under high pressure (8 Mpa to 14
Mpa)Under action of heat and pressure, a hard
rigid plate having desirable properties are formed.
It is a continuous process as shown in figure
below.
For the production of tubes, the paper or fabric is
rolled on a steel mandrel of desired diameter and
then placed with in the steel mould for the final
processing.For the production of rods, the
impregnated material is rolled and heated inside
the cylindrical moulds, followed by grinding to
size.High pressure laminations are mainly
composed of cotton cloth paper, asbestos and
glass fabrics. Heavy cloth laminates are used for
gear blanks, cams and other industrial purposes

46. Low pressure process :-
Low pressure laminating also called reinforced plastic
moulding require the much lower pressure than that
required for high pressure laminating (only 3 Mpa).
The commonly used thermosetting resins are
phenolic, furane, silicones, epoxies and polyesters.
The reinforcing materials used are glass fibres,
asbestos, nylon, cotton etc.
Some of the processes used for low pressure
laminates are as follows:-
(a) Contact Moulding :- In this process, the layers of
reinforcing material are coated with catalyzed resin
and placed one over the other on a prepared form.
Spray gun is used instead of hand operation to
accelerate the process.

47. Advantages :-
It is simplest of all the methods.
It requires minimum equipment.
the mould cost is low
no size limit of products
more flexible i.e. changes in designs are easy.
Pressure bag Moulding :- In this method. The resin
impregnated of rubber. A pressure plate is secured to the
top of the mould. The air or steam pressure is applied
between the beg and the plate so that the bag expand
against the workpiece.
Advantages :-
It provides dense and void less products.
The cylindrical shapes can be easily made.
The cores and inserts can be used easily.
It retains the advantages of contact moulding.

48. Vacuum bag Moulding :- In this process, the
lay-up of resin impregnated material is placed over
the form mould. It is covered by a bag made of
cellophane or polyvinyl film. The vacuum is drawn
through the ports provided in the mould. This
causes that the atmospheric pressure acts on the
bag and forces the layup against the form.
Advantages :-
It gives better surface finish.
There is less air entrapment and less voids.
It retains the advantages of contact moulding.

49. Autoclave forming :- This process is the
modification of either the pressure method or
vacuum bag method. In this method, lay-up has
been made and covered with a plastic film .Then
the entire assembly is placed in a steam or hot air
autoclave at 0.35 to 0.8 M pa.
Advantages :-
It provides dense and void free moldings.
Effective air removal.
Undercuts are possible.

50. Matched die Moulding :- In this process, dies are
used. The dies are usually made of steel for small
parts and cast Iron for larger parts. It is used for
large production. If the production is less, dies are
made from plastic or wood.
Advantages :-
The products have greater accuracy.
It produces the high strength and good surface
finish products.

51. Vacuum Forming:-
Vacuum forming, is the shaping of hot sheets or strips of
thermoplastic materials into a desired shape. The used
sheets are produced by either extrusion, calendering or
pressing. The sheet is clamped into a frame. Then it is
heated with electric heaters, until it begins to sag. Vacuum
is then applied through small holes in the mould and the
plastic sheet is rapidly pulled tightly against the mould.
Then the frame is raised and the part is removed.
Fig (a) Only vacuum is used for drawing the sheet into
the mould.
Fig (b) The formed mould presses down the heated sheet,
forming it partially, followed by pulling the vacuum through
the mould to complete the forming.
Fig (c) A cored plug is used to push the heated sheet into
the mould.
Fig (d) Heated sheet is pulled down by vacuum and then
male plug is moved down to get the required contour.

52. Vacuum Forming

53. Machining of Plastics :-
Machining of plastics is essential when the
accuracy needed is more than that of produced by
moulding methods. Sometimes machining is also
essential when tapped holes are required in the
products.
Following care should be taken while doing the
machining of plastics.
Use cutting fluid to remove the heat.
While doing turning, maintain light cuts, high
cutting speeds and low feed rates.
Cutting tool used should have larger clearance
angles.

54. Some of the operations used for plastics are as
follows :-
Sawing :-While doing sawing, coarse-tooth
hecksaw blades should be used but for brittle
materials (e.g. acrylics) fine tooth saw can be
used.
Turning :-High speed steel cutting tool with large
clearance angles can be used for turning of
plastic. Maintain light cuts, high cutting speeds
and low feed rates.
Drilling :- While doing drilling in plastic, standard
high speed drills with 200
helix angle can be used.
Reaming :-The helical flute reamers having sharp
cutting edges are used for the reaming of plastic
products.

55. Tapping :-
High speed steel ground thread taps can be
used for the tapping. While doing tapping,
material has the tendency to pushed away
rather than cut, this should be avoided by
using the little bit oversize taps.
Threading :-
The threading can be done by using single
point cutting tool in a centre lathe.
Sometimes high speed steel dies are also
used to produce the threads.

56. Joining of plastics :-
Plastics can be joined by the following methods :
By Welding :- Plastic products can be joined by welding
but the workpiece (plastic) material should not be
inflammable. Hot gas welding, friction welding and
ultrasonic welding can be used to obtain the various joints.
By Solvent :- In this method, the solvent is applied to the
plastic surface to be joined which dissolve the edges and
produce tacky surfaces. Then they are joined together.
By Adhesive :- By using adhesive, plastic can be used to
metals and non metals.
By fasteners :- Various fastening devices such as bolts,
screw, nuts rivets etc. can be used for the fastening of the
plastic sheets.

57. Thermoplastics Applications
Acrylics Synthetic fibers, lenses, windows.
Cellulosics Spectacles, toothbrushes, type
writer key handles.
Nylons (Polyamides) Gears, bushings, synthetic fibres,
engine parts
Polyesters Bottles, synthetic fibres, machine
parts.
High Density
polyethylene.
Drums, pipes, bags, insulation
Low Density
polyethylene
Bottles, carrier bags, insulation
Polyvinyl chloride
(PVC)
Piping, sheets, cable insulation,
flooring, footwear etc
Polystyrene : Cabinet, toilet seats, radio and
TV cabinets.

58. Thermoplastics Applications
Phenols Fuse boxes, lamp holders,
handles etc.
Aminos Laminates, crockery, resins,
coatings etc.
Alkyds Circuit breakers, switch gear
etc.
Furan Equipment, floorings, foundry
moulds
Vinyl esters Tanks, ducts, piping
Unsaturated
polyesters
Building panels, car bodies,
ducting, coating etc.

59. Design Considerations :-
Try to locate the parting surface of the mould in
one plane.
Try to avoid undercuts.
Thick sections should be avoided for greater
economy and faster cooling.
Plastic wall must not be too thin or weak
Sharp corners should always be avoided.
Adequate radii and fillets should be provided to
eliminate sharp edges.
Holes should be cored wherever possible to avoid
machining, but smaller holes should be drilled.

60. Inserts, if used, should be strong enough to
sustain mould pressure.
Due allowance for shrinkage must be provided.
Transition between thick and thin sections should
be gradual.
A draft upto 10
is normally needed to enable easy
removal of products from the moulds.
Long cored holes should be avoided, as far as
possible.
Try to avoid tolerances closer than 0.125 mm.