KNOWLEDGE & UNDERSTANDING OF PLASTICS
Types of plastic, Marking Out, Cutting & Finishing
ESSENTIAL INFORMATION
Oil is the main source of plastics. Companies Marking Out
like ICI change oil into plastic granules. Acrylic sheet comes with a protective coating. Try to
Plastics are a modern group of materials.
The granules are produced in many colours leave this on for as long as possible.
Designers make good use of them because
and are sold to manufacturers who use
they have many important properties. They
heat and machining to shape them into
can be colourful, lightweight, strong, hard
Mark
out
bends,
holes
everyday products.
or flexible, non-toxic, need no surface finish
Types of Plastic
and cuts with a spiritbased fineline pen on the
protective coat.
and can be easily formed. They are also
insulators and some can be recycled.
There are two main types of plastic:
Thermosetting plastics are
heat resistant. They are
ideal for pot handles and
light switches. A product
made from thermosetting
plastic will not soften with
heat.
Thermoplastics - Most of
the plastics you work with
in school are thermoplastics. They go soft when
heated and can be bent or
formed into shapes. You
will probably make a
model with clear or
coloured acrylic sheet This
is a thermoplastic.
Everyday products made from thermoplastics include
polypropylene chairs, toothbrushes and telephones. Curves are cut using a
fine-toothed coping
saw or abrafile.
Finishing
The edge is done by 1. Filing
2. using wet and dry abrasive paper,
3. polishing the edge with finishing paste.
Cutting
Straight cuts can be scored
with a plastic cutter and
snapped in a vice or over
the edge of a bench. Line
up with the edge of the
bench. Hold firmly and
snap.
KNOWLEDGE & UNDERSTANDING OF PLASTICS
Drilling
Forming
Acrylic cracks easily
but can be lightly
punched with a centre
punch
A vacuum forming machine heats the plastic
over its entire area.
The soft plastic is then
sucked over the wooden mould and allowed
to cool.
A step drill is designed
to drill plastics without cracking them.
The diameters increase
in steps.
The mould sits
in the machine
and has sloping
sides, rounded
corners and
small vent
holes to let the
air through.
Shaping
The strip heater
heats the acrylic
along a narrow
strip. This causes
the acrylic to soften
and allows easy
bending.
Drilling, Shaping, Forming & Joining
ESSENTIAL INFORMATION
Designers know that plastics can
be used to produce intricate detail
on colourful high quality products.
Forming plastics using heat makes
this possible and opens up all sorts
of possibilities for the designer.
This is why plastic is one of today's
most important materials .
Joining
Joining plastics can be tricky. Epoxy resin can be used
but for best results an acrylic cement is used. It is
watery and should be applied with an applicator. It
seeps into and bonds neat clean joints. Work in a
well-ventilated area.
Oven heating
Once cool the acrylic retains
its new shape. Reheating thermoplastic would make it
return to its original shape.
This is known as plastic
memory
Bending is made easier using a
wooden former.
An oven can be used to heat acrylic to 160°. The soft
plastic is easily formed in a wooden former.
Dip
coating
puts a protective
polythene coat on
metals. The metal
is heated and held
in a fluidiser. The
fluidiser contains
a polythene powder which is
blown by air. The plastic melts onto the hot metal.
Dip coating is used on tools such as pliers. It insulates, protects and makes the product feel good.