Pultrusion

Introduction

The pultrusion process is a proven manufacturing method for obtaining high quality composite profiles with consistently repeatable mechanical properties. Pultruded products are essentially composed of high performance fibres (glass, carbon, or aramid) individually or in combination, embedded in a polymer matrix (polyester, vinylester, epoxy or phenolic). Some of the features of the pultrusion process include:

• Complex shape and unlimited length capabilities
• Precise positioning of reinforcements
• Low scrap rates
• Wide choice of reinforcements and resins

click here to view large flash image

The Pultrusion Process 

The Pultrusion process starts by pulling/drawing continuous reinforcements (in rovings or mat / roving forms) through a resin impregnation system. Each fibre is coated with a specially formulated resin; 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 coated fibres are passed through preforming guides to align reinforcement and preform the part to the desired shape before entering the heated die. The shape and dimensions of the end product are ultimately determined by the die cross section. The temperature of the die is carefully controlled to ensure that the composite is fully cured, the rate of reaction is controlled by heating and cooling zones in the die.

The fully cured section can be cut to length downstream of the pulling mechanism (either a moving carriage with adjustable clamps or a caterpillar puller system) by a circular saw 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.

Pultruded Profiles A pultruded composite profile consists of: Reinforcing Materials These provide the load bearing component and the required mechanical properties - strength, modulus and impact resistance.  The choice of reinforcement used is determined by the technical demands placed on the pultrusion.  Glass fibre is the most commonly used reinforcing material giving the pultrusion light low weight, high stiffness and excellent durability. Both unidirectional fibres and multidirectional mats can be combined to provide a profile with the optimum mechanical properties for the required application. For higher performance requirements, carbon fibres can be used. This enables even stiffer and lighter profiles to be produced. The use of aramid fibres will produce a profile with excellent toughness. Matrix Materials The resin matrix binds the composite together and imparts enhanced properties such as corrosion resistance, excellent fire and smoke properties, high temperature performance etc.

Resins Available

- Polyester is suitable for most industrial applications.
- Vinylester affords improved corrosion resistance and physical properties. 
- Epoxy offers superior thermal stability and corrosion resistance.
- Modar® improves fire performance and smoke emissions.
- Phenolic maximises fire performance and is offered as an alternative to Modar®

Surface Mats

These improve the surface finish and offer improved performance for chemical and weather resistance.

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.
 

Why Pultrusion?

Pultrusion is used for the production of either solid or hollow constant cross section profiles. One of the greatest attributes of the pultrusion process is that a wide range of materials can be used to provide a broad spectrum of composite properties.

The key benefits of pultrusions include:

• Consistent quality
• Low weight
• High strength & stiffness
• 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
• Pigmentability

 

Characteristics of Pultrusions Exceptional Strength & Stiffness 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. Low Weight 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.

Maintenance Free 
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 makes pultrusions very effective as a thermal break.

Electrical Characteristics
Glass fibre pultrusions are electrically non-conductive, making them ideal for electrical insulating applications.

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 CAT scanners.

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 on-site positioning and reduction in structural strengthening and foundation design requirements.

Dimensional Stability and Accuracy
The coefficient of thermal expansion is similar to steel and significantly less than aluminium. 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.

Temperature Performance
Continuous exposure to temperatures up to 65 Celsius is well within the capacity of Fibreforce standard profiles. Custom designed profiles can withstand considerably higher temperatures. 

Fire
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.

Fabrication 

Pultrusions can be easily fabricated by:

• Machining
• Drill
• Punch
• Saw
• Laser Cut
• Water Cut
• Grind
• Jointing
• Adhesive Bond
• Bolt
• Rivet
• Any combination of above