© Copyright G.R.P.Technology 2018 - Adelaide Australia
Plastics -There is almost an infinite number of plastic materials 'out there'. We will try to deal here with the
common used ones - the property differences and methods of processing. If you are an inventor or developer we
can help you with your project.
Fit for purpose ?
Let's do a fast track sieve test here .........
Inside or Outside ?
If the product is to be used outdoors then you have some real issues to deal with...
UV resistance - in places like the US & Australia this can be really big issue, as compared to countries like the UK
where UV is not anywhere near as severe. UV resistance costs $.
UV can degrade the colour and the surface of the product. A more specialised plastic and/or coating can
overcome this problem but this will come at a cost.
Temperature
Particularly if the product is outside what temperature will it be exposed to ?
Plastics at lower temperatures will get brittle
and the impact resistance will decrease.
At higher temperatures the product may wilt
under load and discolour and degrade.
Fire Resistance
Should the product be resistant to fire ?
Does it have to meet a specific regulation ?
This feature can very much limit the choice of
materials.
Chemical Resistance
There are big variations in chemical resistance
of plastics and you should not that as the
temperature increases the chemical resistance
can reduce.
A useful chart for chemical resistance can be
found here from Miller Plastics Inc.
Physical & Mechanical Properties
What are the extremes of properties for this
application ?
For example - impact strength, Flexural
strength, tensile strength, wear resistance,
thermal properties - temperature, coefficient of
expansion (which may be different than the
material you MAY fix it to)
Thermoplastic v's Thermoset Plastics
The difference between the two is....
A thermoset is a material that goes on a one
way journey. Usually the application of heat,
reaction or catalyst drives a chemical reaction
that is not reversible. The material cross links
to give a cured polymer that has a three
dimensional structure.
A thermoplastic softens
where heated but does
not cure or set. As it gets
hotter it can be pumped
into a die cavity to form a
product and when
cooled can be removed
from the die. No
chemical cross linking
occurs. This means the
product reprocessed
again into another
product - recycled -
again and again.
There are a vast number
of variations in the
formulation of these
materials. Components
such as fillers,
reinforcements,
pigments, light
stabilisers, impact
modifiers, fire retardants,
bends of other resins,
are used to tailor a
compound to give the
sorts of properties
required in the end
product.
Here above is a list of some of the better known thermoplastic and thermosetting resins.
Common Plastic Processes and videos
These are the common processes that are used for plastics
Injection Molding
Pellets of plastic are heated and pumped into a die to mould the product, the die is cooled and the part ejected.
To show you how this works watch a video ….. click here to view
Vacuum Forming
A sheet of plastic is heated to a critical temperature and a vacuum is used to suck it down onto a mould. The
product is then cooled and trimmed to size.
For an explanation, click here
Extrusion
Here pellets are heated and pumped through a die to give a continuous shape which is cooled and cut to length.
To see a video of this process click here
Blow Molding
The way to make a plastic bottle - the story of the process in video form is here on YouTube
Laminating with Resin
Epoxy laminating - click here
Polyester - how to fibreglass - click here
This should give you a general summary of the subject, talk to us if you want more detail.