Plastic Moulding
Multi-component moulding
When one part is moulded around another of a different colour,
separation for recycling becomes impractical. This requires a shift
in thinking towards minimising start up and reject levels.
Balancing supply of components is also crucial since both shortages
and overmake of the insert cause waste.
Handling of off cuts in plastics
processing
Care is needed to set up collections and recycling systems for
plastics materials which are processed by cutting or moulding after
extrusion. Incorporation or regrind may be limited by process
factors and off-cuts to component ratios need to be redesigned to
work within these limits.
Regrind in injection moulding
In injection
moulding, care is again needed in handling rejects. The problem is
often cross contamination of colours or different materials, which
can lead to excess materials which cannot be recycled.
Design of sprues and runners in injection
moulding
Sprues and runners should ideally be minimised to reduce re-melting
costs and should be designed for recycling within the process.
Sprue systems which are removed downstream can be recycled but this
is more difficult to manage due to the delay and distance involved,
especially where colours must be segregated for reuse.
It is now common to design hot-runner systems which leave no
sprue but this must be thought of at the component design stage and
not left to the mould design stage.