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Polymer Composites Poly E-410
Dr Atif JavaidPolymer & Process Engineering Department
University of Engineering & Technology, Lahore
Email:[email protected]
Lecture 5
14th February 2015
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Outline
Processing of Polymer Composites Prepregs Short fibre
composites
BMC Moulding SMC Moulding Cold Press Moulding
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Processing of Polymer Composites
Intrinsically linked to architecture of the composite
Producing PMC components involves a number of stages.
Constituent fibres & polymers produced.
Sized (coated) fibres available as unidirectional tows (3K, 6K,
12K, fibres) or rovings, woven fabrics or chopped strand mat.
Fibres can be combined with liquid resin; contact moulding (hand
lay-up) & left to cure.
Alternatively, intermediate produced;
Prepreg (pre-impregnated) (fibres pre-impregnated with partially
cured resin)
Sheet moulding compound, SMC (chopped glass fibres in
polymer)
Intermediate stored for later use.
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Reinforcement is pre-impregnated with resin
A-stage:soluble and fusible
B-stage:swollen but not dissolved by a variety of solvents
C-stage:rigid, hard, insoluble, infusible
safer than liquid resins
mixing done by suppliers > better quality
expensive relative to dry reinforcements
Prepreg (usually with epoxy resins)
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Pre-preg
finite shelf life: not use-by date
if out-of-date should not be used for applications which may
result in injury, loss or damage.
time the roll of the material is out of cold storage will reduce
its useful life (shelf life)
normal to allow the material to warm to ambient temperature
before use as condensation may form on cold material
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Pre-preg systems
cold-cure (not normally prepreg)
cure at ambient temperature
low temperature systems:
cure at ~60C, shelf life typically 3 months
medium temperature systems:
cure at ~120C, shelf life typically 6 months,
high temperature systems:
cure at ~180C, shelf life typically one year.
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Pre-preg
key considerations include:
Drape
formability to complex curvatures
Tack
stickiness
De-bulk
The process of removing air from a prepreg. Debulking
increases the density of the prepreg. every few layers form
a
stack and is subjected to vacuum in temporary bag or a
vacuum table.
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Short Fibre Composites - BMC Moulding
Economical process for high volume production of small-medium
components.
Bulk Molding Compound (BMC) is a pre mixed fiber reinforced
material that cures
under heat and pressure
Preform of moulding compound placed in the heated mould
cavity
Pressed into the finished shape.
Heat from mould initiates cure
Surface finish produced is excellent.
Mould - aluminium, cast iron or steel.
Electrical housings, car body panels, gas & electricity
meter boxes, car road
wheels, etc.
Styrene emission reduced since it is a closed mould process.
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Short Fibre Composites - SMC Moulding
High volume production of small-to-medium sized components.
Sheet moulding compound (SMC) is an intermediate material in
which resin &
reinforcement are already premixed
Sheet cut to a shape
Mould closed then heat applied to form & cure the part.
Process uses an accurate matched metal mould placed in a heated
press.
Automotive applications - car bumpers & car and truck body
panels.
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Short Fibre Composites - Cold Press Moulding
Intermediate process between contact moulding & hot press
moulding.
Reinforcement cut & placed in the mould.
Cold curing resin system poured in
Press closed causing resin to impregnate the reinforcement.
Exothermic heat generated during gelation together with pressure
provoke cure.
Once the moulding has cured, it is released from the mould.
Mould can be made of GRP or cheap metal.
Therefore inexpensive.
Automotive, industrial & electrical applications.
Tooling cost range covers small, simple to large, complex
moulds.
