Composite materials have become a regular feature of our daily lives over the last thirty years. As experience and confidence in composite materials has grown, their use has extended from decorative and functional applications to structural ones,
Some of the Major composite markets include:
- Motor vehicles
- Rail transport
- Wind turbine blades
- Sports goods such as fishing rods, ski poles and tennis rackets
- Storing and transporting corrosive liquids
- Boats and marine
Advantages of Composites
The properties that attract the attention of designers to composite materials are:
- Low density
- High strength
- High stiffness
- Corrosion resistance
- Wear resistance
- Low heat transmission
- Good electromagnetic transmission
- Low sound transmission
There are many production methods available to the designer who is considering the use of a composite material including:
- Contract moulding
- Hand lay up
- Filament winding
- Resin transfer moulding
- Injection moulding
- Press and prepreg moulding
- Centrifugal moulding
The aerospace industry has been a major user of composite material for structural applications for many years now. More recently civil engineers and the construction industry have started to recognise the potential of these materials in providing solutions to the many problems associated with the deterioration and corrosion of infrastructures.
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Advantages of Pultrusions
Pultruded composite profiles are composed of high performance fibres (glass, carbon, or aramid) individually or in combination, embedded in a polymer matrix (polyester, vinylester, epoxy or phenolic). Pultruded fibre reinforced composites are considered to be one of the highest performing composite materials. These materials have been recognised as the materials for the future and their use is expected to grow throughout industry.
The pultrusion process is a proven manufacturing method for obtaining high quality FRP profiles with consistently repeatable mechanical properties.
Some of the features of the pultrusion process are:
- Complex shape and length capabilities
- Precise positioning of reinforcements
- Low scrap rates
- Wide choice of reinforcements and resins
Pultrusion successfully combines a number of elements which can provide a wide variety and combination of properties and characteristics required by the final application of the product.
Pultrusion is a method of manufacturing either discrete or continuous lengths of fibre reinforced composites by pulling resin impregnated fibres through a series of forming guides.
They then pass through a heated die to cure the resin system, thus producing a rigid cured composite as it exits the die. The shape and dimensions of the end product are determined by the die cross section.
Pultrusion is an ideal process for the production of either solid or hollow constant cross section profiles.
The Pultrusion Process
The process starts by pulling continuous reinforcements through a resin bath to wet out the fibres. The process is controlled to ensure full wetting out of the fibre reinforcement. Excess resin is then removed to expel any trapped air and to compact the fibres. The impregnated reinforcement is passed through preforming guides to align the reinforcement before entering the heated die.
The temperature of the die is carefully controlled to ensure that the composite is fully cured.
Pulling is achieved using either a moving carriage with adjustable clamps or a caterpillar puller system. The fully cured section can be cut to length after the puller system, or if size and shape permit, be wound onto a drum as a continuous length.
The only limitations on length for cut sections are storage and transportation.
Pullwinding combines the two techniques of pultrusion and continuous filament winding resulting in a profile with excellent hoop strength, longitudinal strength and modulus, with a smooth surface finish.
The combination of reinforcement and resin needs to be selected in order to provide a range of properties to fit the design requirements.
Some properties are determined primarily by the resin and others by the reinforcement.
The benefits of pultrusions include:
- Consistent quality
- Low weight
- High strength
- Good surface finish
- Continuous length
- Excellent corrosion properties
- Electrical and thermal insulation
- Maintenance free
- Non magnetic
- Fire retardant properties
- Excellent creep and fatigue performance
- Transparent to radio frequencies
Characteristics of Pultrusions
On a weight for weight basis, pultrusions are stronger than steel, By varying the type and orientation of the reinforcements, various mechanical properties can be obtained and tensile strengths in excess of 1000 MPa are achievable.
Considerable design freedom can be achieved by tailoring the material properties to suit the application.
Weighing up to 80% less than steel and 30% less than aluminium, pultrusions offer an alternative choice, where weight saving is a requirement.
The high strength to weight ratio of pultrusions offers the designer many advantages over conventional materials and makes pultrusions the obvious choice for offshore, transport, aerospace, building and Civil engineering applications.
Highly Corrosion Resistant
Pultrusions have good corrosion resistance when subjected to a wide variety of corrosive chemicals and environments.
Most profiles have a synthetic surface veil, which provides a resin rich layer enhancing the already excellent corrosion resistance of the material.
The excellent corrosion properties of the material have resulted in a material that requires little or no maintenance.
Low Thermal Conductivity
Pultrusions have a low thermal conductivity 1/250 of aluminium and 1/60 of steel – this
characteristic makes pultrusions very effective as a thermal break.
Glass fibre pultrusions are electrically nonconductive, making them ideal for electrical
It is possible to introduce a degree of conductivity for the purpose of static dissipation for example anti static gratings for offshore applications.
Pultrusions are transparent to radio waves, microwaves, and other electromagnetic
frequencies. This makes them suitable for use in aerial masts and in various radome applications.
These properties also extend to medical applications such as transparency to x-rays and
non magnetic properties for use in CATscanners.
Ease of Installation / Design
The lightweight nature of pultrusions can result in major cost savings. These stem from savings associated with installation including more economical transportation, handling and on site positioning and reduction in structural strengthening and foundation design
Dimensional Stability and Accuracy
The coefficient of thermal expansion is similar to steel and significantly less than aluminium:
|10 -6/ oC|
|Steel||11 – 14|
A fully cured pultruded profile is resistant to stretching, warping or swelling over a wide range
of temperatures and physical stresses.
Correctly designed profiles will not deform or acquire a permanent set under prolonged fatigue loading, high stress or operational impact
Continuous exposure to temperatures up to 65 Celsius is well within the capacity of Pultrex standard profiles. Custom designed profiles can withstand higher temperatures
Pultrusions are not readily combustible, and combinations of resin matrix and fibre reinforcement can be formulated to meet extremely rigorous fire safety demands. Modar® based systems offer superior fire performance with exceptionally low smoke and toxicity levels, whilst phenolic resins will maintain some structural integrity at very high temperatures.
Pultrusions can be easily fabricated by Machining – Drill, Punch, Saw, Laser Cut, Water Cut, Grinding
Jointing – Adhesive Bond, Bolt, Rivet Any combination of above