184
7
5 Form of reinforcement—Only fabrics and chopped strand mats
(CSM) are processable by contact layup technology. The
processability of composites having a curvilinear or 3-D profile
is governed by the ability to drape the reinforcement on the
contoured surface. The drapeability of CSM and satin weave
fabrics is the best, while for plain weave fabrics, it is the least.
The descending order of drapeability of the reinforcement is
CSM → eight-harness satin weave fabric → six-harness satin
weave fabric → four-harness satin weave or twill weave
fabric → plain weave. The satin weave of a harness more than
eight is difficult to handle; therefore, only up to an eight harness
satin weave fabric is used. The drapeability of CSM is the best
because there is no interlacing point, and strands of fibres (e.g.
glass fibres) are loosely bonded. Therefore, CMS provides the
maximum pliability leading to a maximum drapeability [10].
On the contrary, plain weave has interlacing points in close
proximity; therefore, it is not pliable but is stiff and not
drapeable.
5 Shape and profile of the product—Sharp edges and undercuts do
not favour the processability of composites by contact layup
technology. Albeit, undercuts in the product can be processed
by using split moulds, but this makes the moulding process
complicated and costly. Contact layup offers a good finish on
only the surface of the composite, which is in contact with the
mould.
7.1.2 Spray Layup
5 Processing Technology—The spray layup (spray-up) process
is also called the chopping process and is similar to the hand
layup process. The spray-up process is used for making
boats, storage tanks, transportation containers, bathtubs,
bathroom fittings, etc. in a large variety of shapes and sizes.
A laminate with chopped fibres has good conformability,
and its processing is faster than hand layup in moulding
complex shapes.
Similar to contact layup technology, in this process, RT
curable resins (such as epoxy or polyester) only are used. In the
spray-up process, the thickness and consistency is controlled
manually; therefore, this process is more operator-dependent
than compared to hand layup. Although the production rate
per mould is low in the spray-up process, the consistency in
quality of the composite product is good. However, it also is
feasible to produce substantial production quantities using
multiple moulds. In this process, a gel coat is first applied on
the mould prior to the spray-up of the laminate system.
Continuous fibres, glass rovings, and resin are mixed with
hardener and are fed through a chopper gun. The resin-saturated fibre strands on the mould are shown in . Fig. 7.3. Then
the compacting rollers are applied on the laminate sprayed on
the mould to saturate the fibres with resin and to make the
Chapter 7 · Processability in Open Mould Processing of Polymeric Composites
7
5 Form of reinforcement—Only fabrics and chopped strand mats
(CSM) are processable by contact layup technology. The
processability of composites having a curvilinear or 3-D profile
is governed by the ability to drape the reinforcement on the
contoured surface. The drapeability of CSM and satin weave
fabrics is the best, while for plain weave fabrics, it is the least.
The descending order of drapeability of the reinforcement is
CSM → eight-harness satin weave fabric → six-harness satin
weave fabric → four-harness satin weave or twill weave
fabric → plain weave. The satin weave of a harness more than
eight is difficult to handle; therefore, only up to an eight harness
satin weave fabric is used. The drapeability of CSM is the best
because there is no interlacing point, and strands of fibres (e.g.
glass fibres) are loosely bonded. Therefore, CMS provides the
maximum pliability leading to a maximum drapeability [10].
On the contrary, plain weave has interlacing points in close
proximity; therefore, it is not pliable but is stiff and not
drapeable.
5 Shape and profile of the product—Sharp edges and undercuts do
not favour the processability of composites by contact layup
technology. Albeit, undercuts in the product can be processed
by using split moulds, but this makes the moulding process
complicated and costly. Contact layup offers a good finish on
only the surface of the composite, which is in contact with the
mould.
7.1.2 Spray Layup
5 Processing Technology—The spray layup (spray-up) process
is also called the chopping process and is similar to the hand
layup process. The spray-up process is used for making
boats, storage tanks, transportation containers, bathtubs,
bathroom fittings, etc. in a large variety of shapes and sizes.
A laminate with chopped fibres has good conformability,
and its processing is faster than hand layup in moulding
complex shapes.
Similar to contact layup technology, in this process, RT
curable resins (such as epoxy or polyester) only are used. In the
spray-up process, the thickness and consistency is controlled
manually; therefore, this process is more operator-dependent
than compared to hand layup. Although the production rate
per mould is low in the spray-up process, the consistency in
quality of the composite product is good. However, it also is
feasible to produce substantial production quantities using
multiple moulds. In this process, a gel coat is first applied on
the mould prior to the spray-up of the laminate system.
Continuous fibres, glass rovings, and resin are mixed with
hardener and are fed through a chopper gun. The resin-saturated fibre strands on the mould are shown in . Fig. 7.3. Then
the compacting rollers are applied on the laminate sprayed on
the mould to saturate the fibres with resin and to make the
Chapter 7 · Processability in Open Mould Processing of Polymeric Composites