217
8
5 Processability Parameters—The following are the processability
parameters for processing polymeric composites using a
contact layup process.
5 Type of matrix resin—Only thermoplastic matrices are
processable by injection moulding technology. Matrices
that degrade at their melting temperature are not processable by injection moulding.
5 Melt flow index (MFI)—The matrix should have high MFI
(in excess of 20 g/minute). This enables the filling of the
cavity at low pressures.
5 Form of reinforcement—Only short fibres, whiskers, and
particles can be reinforced in the composite using injection
moulding technology. The processability of fabricreinforced composites is not feasible.
5 Size and shape of the product—Products having undercuts
and a thick section (>3 mm) are difficult to injection
mould.
5 Injection pressure—Injection pressures that are lower than
the locking pressure are only processable. The injection
pressures are calculated based on the projected area of the
product.
5 Design of injection mould—The high heat capacity of the
mould material restricts the rate of production in injection
moulding. In order to improve the processability of the
composite, cooling the injection moulds is required to be fast.
8.1.6 Pultrusion
5 Processing Technology—Pultrusion is a manufacturing process
for producing continuous lengths of composite with regular
and constant cross sections. In this process, a preform of
reinforcement is passed through resin and into the moulding
die. The moulding die has a heating mechanism to cure the
thermosetting resin. The cross section is determined by the
opening profile of the die.
Raw materials used are a liquid resin mixture (containing
resin, fillers, and additives) and reinforcing fibres, yarns,
rovings, or fabrics. The pultrusion process involves pulling
these raw materials through a heated metallic (e.g. steel) die
using a pulling device. Therefore, this process becomes
continuous. The continuous strand fibreglass roving, mat,
cloth, etc. are impregnated in a resin bath, and then it is pulled
through a steel die by a powerful tractor mechanism. The
heated steel die consolidates the wet reinforcement, sets the
shape of the stock, and controls the fibre/resin ratio. Therefore,
the profile that comes out of the mould is a hardened and
cured composite with regular cross sections. The pultrusion
process is used for the bulk manufacturing of beams, bars,
I-section and hollow cross-sectional members, etc. A hybrid
composite profile is achieved by using hybrid fabric stakes,
foams, etc.
8.1 · Closed Mould Processing Technologies
8
5 Processability Parameters—The following are the processability
parameters for processing polymeric composites using a
contact layup process.
5 Type of matrix resin—Only thermoplastic matrices are
processable by injection moulding technology. Matrices
that degrade at their melting temperature are not processable by injection moulding.
5 Melt flow index (MFI)—The matrix should have high MFI
(in excess of 20 g/minute). This enables the filling of the
cavity at low pressures.
5 Form of reinforcement—Only short fibres, whiskers, and
particles can be reinforced in the composite using injection
moulding technology. The processability of fabricreinforced composites is not feasible.
5 Size and shape of the product—Products having undercuts
and a thick section (>3 mm) are difficult to injection
mould.
5 Injection pressure—Injection pressures that are lower than
the locking pressure are only processable. The injection
pressures are calculated based on the projected area of the
product.
5 Design of injection mould—The high heat capacity of the
mould material restricts the rate of production in injection
moulding. In order to improve the processability of the
composite, cooling the injection moulds is required to be fast.
8.1.6 Pultrusion
5 Processing Technology—Pultrusion is a manufacturing process
for producing continuous lengths of composite with regular
and constant cross sections. In this process, a preform of
reinforcement is passed through resin and into the moulding
die. The moulding die has a heating mechanism to cure the
thermosetting resin. The cross section is determined by the
opening profile of the die.
Raw materials used are a liquid resin mixture (containing
resin, fillers, and additives) and reinforcing fibres, yarns,
rovings, or fabrics. The pultrusion process involves pulling
these raw materials through a heated metallic (e.g. steel) die
using a pulling device. Therefore, this process becomes
continuous. The continuous strand fibreglass roving, mat,
cloth, etc. are impregnated in a resin bath, and then it is pulled
through a steel die by a powerful tractor mechanism. The
heated steel die consolidates the wet reinforcement, sets the
shape of the stock, and controls the fibre/resin ratio. Therefore,
the profile that comes out of the mould is a hardened and
cured composite with regular cross sections. The pultrusion
process is used for the bulk manufacturing of beams, bars,
I-section and hollow cross-sectional members, etc. A hybrid
composite profile is achieved by using hybrid fabric stakes,
foams, etc.
8.1 · Closed Mould Processing Technologies