| Japanese carmaker Mazda says
that a new plastic moulding technology it has developed can save between
20% and 30% of resin material in plastic parts with a similar saving on
weight.
The technique produces foamed plastics with regular sized bubbles but
uses a new foaming concept that allows the materials to be recycled afterwards
and has no adverse chemical reactions.
Mazda’s idea is to mix a “supercritical fluid” (SCF)
of an inert gas, such as nitrogen or carbon dioxide, in with the plastic
resin.
The SCF is produced by a combination of temperature and pressure that
takes the substance above its thermodynamic critical point, at which stage
it can diffuse as a gas through solid substances or dissolve other materials
like a liquid.
In its process, the SCF raises the fluidity of the plastic resin in liquid
form causing it to expand rapidly when it enters a mould, with even-sized
bubbles. This means less material is used.
Mazda has also used the idea in a “core-back expansion” moulding
technique, where the volume of the mould is increased after the material
has been injected, causing further expansion of the plastic inside the
mould and creating a lighter foam.
The group says it has produced multi-layer foamed plastics using this
technique, with an outer layer of more solid plastic that retains the
strength of the original and an inner core of lighter foamed material.
This would also enable materials to be tailored for the characteristics
needed rather than using conventional non-foam parts and could allow insulation
or acoustic properties to be built in.
Most plastic foaming techniques use thermal decomposition of organic or
inorganic compounds to produce the foam gas, and this can produce unwanted
chemical compounds inside the material.
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