The Pultrusion Process
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 Pultrusion is a versatile manufacturing process for the continuous moulding of glass fibre reinforced composite materials into complex profiles. Pultruded glass reinforced sections are the most economic method of producing composite profiles with a constant cross-section. The range of shapes that can be produced are similar to those commonly made by thermoplastics or aluminium extrusion processes. Pultrusions are engineering composites which bridge the gap between the relatively weak ‘plastics’ materials, and the stronger metals to give a structural alternative to traditional engineering materials whilst retaining many attractive properties associated with plastics.
Although a range of fibre types and matrix resins can be used, the majority of applications employ E glass, S glass or carbon fibre reinforcement materials in either polyester, vinyl ester, epoxy or acrylic resin matrices. The glass fibre and resin matrix selection depends on the application. This is determined by the environment in which they are used. The majority of industrial glass reinforced plastics (GRP) use E glass reinforcements in either a polyester or vinyl ester resin matrix. Carbon fibre profiles have a higher modulus than GRP combined with a lower density giving greater stiffness and strength to weight ratios making them attractive in applications where weight and stiffness are paramount. Hybrid combinations of glass and carbon reinforced materials in vinyl ester resin matrix can offer an alternative to pure/100% glass reinforcement giving better mechanical properties at a lower cost than pure/100% carbon reinforcement.
Technical Information
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The technical data below shows a typical range of properties which reflect the variation in formulation possible by incorporating different reinforcing materials. The relatively high mechanical properties of Pultrusion are due to the large proportion of reinforcing fibres present, typically in the range 50 - 70%. Profiles which are reinforced entirely with rovings such as rods and other simple shapes generally have a high fibre content which confer the higher mechanical properties in the longitudinal direction shown in the Technical Data, however transverse properties of such materials will be relatively low.
For many shapes and applications the incorporation of reinforcements which give transverse properties, such as woven materials and multidirectional mats, is necessary. Because such materials do not pack so efficiently, the total fibre content is lower and the longitudinal properties reflect this reduction, together with the trade off in strength in the transverse direction, hence the lower figures in the Technical Data.
Although the situation is further complicated by the contribution due to the matrix resin, R.B.J. can generally select a suitable formulation and manufacturing route to meet your specific design requirements.
- Flexural strength = 275-700 MN/m2
- Flexural modulus = 14-34 GN/m2
- Tensile strength = 200-550 MN/m2
- Tensile modulus = 14-31 GN/m2
- Compressive strength = 96-206 MN/m2
- Izod impact strength = 50-100 ft lb
- Fire retardancy. Surface spread of flame (BS 476) to Class 1 or Class 2 can be attained. Low smoke, halogen free formulations are available.
- Density = 1.7-1.9 gm/cc
- Water absorbtion = 0.5-2%
- Barcol hardness = 40-70
- Specific heat = 940 J/kg K
- Thermal conductivity = 0.35 W/m K
- Co-efficient of thermal expansion = 7.2 x 10-6/K
- Heat Distortion Temperature = 100-200 °C
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