219
8
5 Temperature of the mould—The temperature of the mould
is set in gradients, and processability depends upon the
wetting of the reinforcement, followed by the gelling of the
resin, and finally by the curing of the composite. The
temperature zones must be strictly regulated for optimum
properties of the composite.
5 Extraction speed—The speed of extraction decides the
residence time during the pulling process in pultrusion.
Therefore, the processability of the pultruded composite
depends upon the speed of extraction.
? Example 8.2 suggests the processing technology for the
fabrication of (a) moulded thermoplastic furniture, (b) hollow
seat frame for aircraft, (c) boat hull, and (d) radome for aircrafts.
v Answer
(a) Moulded thermoplastic furniture—It can be moulded
through an injection moulding process.
(b) Hollow seat frame for aircraft—The most suitable process
would be pressure bag technology.
(c) Boat hull— It may be fabricated using vacuum bag
technology. A wooden or steel mould may be used for this
process. A foam core is also used to increase the stiffness
and bring down the density of the boat hull.
8.1.7 Vacuum-Assisted Resin Transfer Moulding
(VARTM)
5 Processing Technology—Vacuum-assisted resin transfer
moulding (VARTM) is a closed moulding process for batch
production. In this technology, the reinforcement is placed in
the cavity of a matched die mould that has injection and outlet
port(s). Continuous strand mats and woven reinforcement are
laid to dry on the core of the mould. Preformed glass reinforcements are often used for complex mould shapes. The mould is
closed and clamped. A vacuum is applied from the outlet port
to evacuate air trapped in the reinforcement. A vacuum also is
used to enhance the resin flow and reduce void formation.
From the injection port, a low-viscosity resin mixed with
hardener is injected at a high pressure. In the case of two
component systems of resin, metered mixing equipment is
used to control the resin/catalyst or hardener ratios that are
mixed through a motionless/static mixer and injected into the
injection port. The VARTM process is shown schematically at
. Fig. 8.11. For an optimum surface finish, a gel coat may be
applied on the mould surface prior to moulding. Once the
mould is completely filled with the resin, the resin will start
coming out from the outlet port. Initially, the resin may come
out with some air bubbles that had been trapped in the
reinforcement. Later, clear resin starts coming out, and at this
8.1 · Closed Mould Processing Technologies
8
5 Temperature of the mould—The temperature of the mould
is set in gradients, and processability depends upon the
wetting of the reinforcement, followed by the gelling of the
resin, and finally by the curing of the composite. The
temperature zones must be strictly regulated for optimum
properties of the composite.
5 Extraction speed—The speed of extraction decides the
residence time during the pulling process in pultrusion.
Therefore, the processability of the pultruded composite
depends upon the speed of extraction.
? Example 8.2 suggests the processing technology for the
fabrication of (a) moulded thermoplastic furniture, (b) hollow
seat frame for aircraft, (c) boat hull, and (d) radome for aircrafts.
v Answer
(a) Moulded thermoplastic furniture—It can be moulded
through an injection moulding process.
(b) Hollow seat frame for aircraft—The most suitable process
would be pressure bag technology.
(c) Boat hull— It may be fabricated using vacuum bag
technology. A wooden or steel mould may be used for this
process. A foam core is also used to increase the stiffness
and bring down the density of the boat hull.
8.1.7 Vacuum-Assisted Resin Transfer Moulding
(VARTM)
5 Processing Technology—Vacuum-assisted resin transfer
moulding (VARTM) is a closed moulding process for batch
production. In this technology, the reinforcement is placed in
the cavity of a matched die mould that has injection and outlet
port(s). Continuous strand mats and woven reinforcement are
laid to dry on the core of the mould. Preformed glass reinforcements are often used for complex mould shapes. The mould is
closed and clamped. A vacuum is applied from the outlet port
to evacuate air trapped in the reinforcement. A vacuum also is
used to enhance the resin flow and reduce void formation.
From the injection port, a low-viscosity resin mixed with
hardener is injected at a high pressure. In the case of two
component systems of resin, metered mixing equipment is
used to control the resin/catalyst or hardener ratios that are
mixed through a motionless/static mixer and injected into the
injection port. The VARTM process is shown schematically at
. Fig. 8.11. For an optimum surface finish, a gel coat may be
applied on the mould surface prior to moulding. Once the
mould is completely filled with the resin, the resin will start
coming out from the outlet port. Initially, the resin may come
out with some air bubbles that had been trapped in the
reinforcement. Later, clear resin starts coming out, and at this
8.1 · Closed Mould Processing Technologies