90% of rotational mouldings are made from polyethylene (PE), used mainly to manufacture hollow shaped products such as footballs, road cones and storage tanks up to 3m³ capacity.
SHABEEL KAHLID 21
ATEEQ AHMAD 31
Classification of material
What is plastic? Or why plastic are called
plastic made of??
Types of plastic
Why Design with Plastics
CLASSIFICATION OF MATERIALS
Materials used in the design and
manufacture of products
Layers of lens
aluminium & acrylic
What is plastic
The word plastic itself comes from the Greek word plasticos,
which means to be able to be shaped or molded by heat. As
we will see, shaping plastics by using heat is a basic part of
nearly all plastics manufacturing processes.
plastic made of…?
Plastic is made by combining long chains of small carbon
molecules known as monomers to for a polymer. Monomers
are atoms of general petroleum chemicals such as crude oil
and natural gas. There are different types of monomers
such as styrene and vinyl chloride which is used to make
Natural plastics - these are naturally occurring
materials that can be said to be plastics
because they can be shaped and moulded by
heat. An example of this is amber, which is a
form of fossilised pine tree resin and is often
used in jewellery manufacture.
Synthetic plastics - these are materials that
are derived from breaking down, or ’cracking’
carbon based materials, usually crude oil, coal
or gas, so that their molecular structure
changes. This is generally done in
petrochemical refineries under heat and
pressure,. It is further divided into two
The majority of common plastics are thermoplastics.
Thermoplastics can be heated and reshaped because of the
ways in which the molecules are joined together.
This can be repeated many times (as long as no damage is
caused by overheating).
USES OF PLASTICS (THERMOPLASTICS)
Here are some common products made from thermoplastics.
Low density polythene
Initially set by heat
USES OF PLASTICS (THERMOSETS)
Thermosets have different qualities to thermoplastics.
Most modern plastics are derived from natural
materials such as oil, coal and natural gas with crude
oil remaining the most important raw material for their
production. The starting point for the production
process is the distillation, in petrochemical refineries, of
the raw material into fractions (different parts).
The heavy fractions give us lubrication oils and the
heavy oils used for heating fuels. The lighter fractions
give us gas, petrol, paraffin and naphtha. The chemical
building blocks for making plastics come mainly from
DISTILLATION FROM CRUDE OIL.
The start of making plastics is to subject naphtha to a cracking process in which
complex organic chemical compounds are separated into smaller molecules,
dependent on their molecular weight. These smaller molecules include ethylene,
propylene, butene and other hydrocarbons. The compounds produced through
the cracking process are then further refined to produce the base plastic
WHY DESIGN WITH PLASTICS?
Low electrical and thermal
Easily formed into complex shapes,
can be formed, casted and joined.
Wide choice of appearance, colors
Continuous process used to produce both solid and hollow products that
have a constant cross-section. E.g. window frames, hose pipe,
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 crosssection of the extrusion.
Materials used in Extrusion
This extrusion is part of a window seal made from thermoplastic elastomer
Powder or granules from a
hopper into a steel barrel with a
rotating screw. The barrel is
surrounded by heaters The
screw is forced back as 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
Pressure is kept on the mould
until the plastic has cooled
for the mould to be opened and
the component ejected.
Normally thermoplastics are used in this
process although a few thermosetting plastics can also
be injection moulded.
Toy made from high impact polystyrene (HIPS).
1. Mould is attached to a platen
(support plate). The platen and
mould are then lowered and a
rigid thermoplastic sheet
material is clamped onto an air
tight gasket and usually
heated from above.
2. Once the thermoplastic sheet is
softened enough (reaches a
plastic state) then air is blown in
to raise the sheet in a slight
bubble before the platen is raised
bringing the mould into contact
with the plastic.
3. trapped air remaining
between the platen and the
heated plastic sheet is then
evacuated by a vacuum pump.
Atmospheric pressure acting
over the top surface completes
the forming process by
pressing the plastic sheet onto
4. Once the plastic sheet has
cooled down to below it's freeze
point the air flow is reversed to lift
the forming off the mould and the
1. The mould is charged with a
measured amount of powder or
granules ready to be compressed.
Sometimes plastic charge is first
compacted into a shape called a
2. When the two halves of the
mould are brought together the
plastic material is forced under
compression to flow rapidly around
the cavity. heat from the platens
causes the plastic to cure resulting
in a permanent change in shape.
The component is
ejected from the
mould and any
formed at edges
(flash) is removed.
Typical thermosetting plastics used in
compression moulding are urea
formaldehyde and phenol formaldehyde.
DISADVANTAGES OF USING PLASTICS
Low useful temperature range (up to 600 F)
Less dimensional stability over period of time
hardens and become brittle over time
Sensitive to environment, moisture and chemicals