214
8
8.1.4 Pressure Bag and Vacuum Bag Moulding
5 Processing Technology—Pressure bag or vacuum bag moulding
technologies are the economic offshoots of the autoclaving
process because the costly processing equipment (such as the
autoclave) is not used. Instead, a hot air circulation oven is
used. Pressure bag or vacuum bag moulding also differs from
autoclaving technology because either pressure or a vacuum is
applied along with the heat, whereas in the autoclaving process,
all three can be applied simultaneously.
The schematic of the vacuum bag process is shown in
. Fig. 8.7. In a vacuum bag process, the composite layup or
prepreg on a mould is placed in the bag in the same manner as
it was placed in the autoclaving process described earlier. Once
the bagging is complete, a vacuum is applied, and the mould is
placed under the vacuum in the oven for curing the composite.
In the case of a pressure bag process, the bagging is done in
the similar way, but here the pressure is applied inside the product
in such a way that the composite layup or prepreg presses against
the walls of the mould cavity. The schematic of this process is
shown in . Fig. 8.8. Later, the mould is placed under pressure in
the oven for curing of the composite. The pressure bag technology
is used for tubular confined structures in general. This technology
is popular for both thermosetting and thermoplastic matrices.
In vacuum bag technology, a flexible film (PVA, nylon,
mylar, or polyethylene) is placed over the wet layup. The wet
layup is made by using either thermosetting prepregs or a hand
layup process. The layup is placed inside the mould, then the
edges at the end of mould and film are sealed, and finally the
vacuum is applied. For the vacuum bagging process, a release
film is placed over the laminate. This is followed by a bleeder
ply of non-woven cloth of nylon, polyester, or other material
that absorbs excess resin from the laminate. A breather ply of a
non-woven fabric is placed over the bleeder ply to enable a
uniform suction of air. After that, a vacuum bag is mounted
Point to Ponder…
Pressure bag technology is used
for making carbon or Kevlar
fibre-reinforced nylon composite hollow frames for sports
bicycles. The damage tolerance
of these frames is good.
. Fig. 8.6 World’s largest autoclave [12]
Chapter 8 · Processability in Closed Mould Processing of Polymeric Composites
8
8.1.4 Pressure Bag and Vacuum Bag Moulding
5 Processing Technology—Pressure bag or vacuum bag moulding
technologies are the economic offshoots of the autoclaving
process because the costly processing equipment (such as the
autoclave) is not used. Instead, a hot air circulation oven is
used. Pressure bag or vacuum bag moulding also differs from
autoclaving technology because either pressure or a vacuum is
applied along with the heat, whereas in the autoclaving process,
all three can be applied simultaneously.
The schematic of the vacuum bag process is shown in
. Fig. 8.7. In a vacuum bag process, the composite layup or
prepreg on a mould is placed in the bag in the same manner as
it was placed in the autoclaving process described earlier. Once
the bagging is complete, a vacuum is applied, and the mould is
placed under the vacuum in the oven for curing the composite.
In the case of a pressure bag process, the bagging is done in
the similar way, but here the pressure is applied inside the product
in such a way that the composite layup or prepreg presses against
the walls of the mould cavity. The schematic of this process is
shown in . Fig. 8.8. Later, the mould is placed under pressure in
the oven for curing of the composite. The pressure bag technology
is used for tubular confined structures in general. This technology
is popular for both thermosetting and thermoplastic matrices.
In vacuum bag technology, a flexible film (PVA, nylon,
mylar, or polyethylene) is placed over the wet layup. The wet
layup is made by using either thermosetting prepregs or a hand
layup process. The layup is placed inside the mould, then the
edges at the end of mould and film are sealed, and finally the
vacuum is applied. For the vacuum bagging process, a release
film is placed over the laminate. This is followed by a bleeder
ply of non-woven cloth of nylon, polyester, or other material
that absorbs excess resin from the laminate. A breather ply of a
non-woven fabric is placed over the bleeder ply to enable a
uniform suction of air. After that, a vacuum bag is mounted
Point to Ponder…
Pressure bag technology is used
for making carbon or Kevlar
fibre-reinforced nylon composite hollow frames for sports
bicycles. The damage tolerance
of these frames is good.
. Fig. 8.6 World’s largest autoclave [12]
Chapter 8 · Processability in Closed Mould Processing of Polymeric Composites