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What is Pultrusion?

Pultrusion is a mature processing technology that was originally conceived in response to growing demand for fibre-reinforced composites with good mechanical and physical properties. Pultrusion is an automated, continuous production process for manufacturing fibre-reinforced plastic profiles that guarantees constant quality and short delivery lead times.

The main advantage of this technology is the high glass fibre strand content of the profile, up to a maximum of 70% by weight, which makes the profiles extremely strong. The maximum profile height is 30 centimetres and the maximum width is 1 metre. Furthermore, any desired length can be produced using this technology.

This production method for reinforced polyester profiles makes it possible to match the material properties and structural characteristics required by design engineers. The fibre reinforcement, the type, the number and orientation of the fibres are the main variables, and these variables have a considerable effect on the mechanical properties of the profiles.

You tell us your requirements, we analyse the design parameters and put forward a suitable proposal. We produce what you specify!

Pultrusion in general

Pultrusion is a continuous production process for manufacturing fibre-reinforced plastic profiles subject to tight quality monitoring. It allows accurate dimensional control of the pultrusion profile’s cross-section. Pultrusion is suitable for all kinds of fibres. Furthermore, several types of fibre can be combined. The ability to achieve a high fibre content (up to 70% by weight) results in high specific stiffness and strength.

This advanced processing technology was created to satisfy growing demand for glass fibre-reinforced plastic with excellent mechanical and physical properties.

Minimum CO2 emissions and the low level of energy consumption during production make the profiles extremely sustainable and more environmentally friendly than comparable steel and aluminium products, thereby achieving a good ecological balance.
krafton® has been a recognised expert in this field for decades and manufactures an extensive range of FRP profiles, such as angle profiles, tube profiles, bar profiles, H and I profiles and many special custom profiles.

krafton®’s pultrusion process in 6 steps

krafton® has a track record of more than 40 years in processing polyester, and has more than 25 years’ experience with pultrusion processes. Our company is an acknowledged specialist in this field. Every day, we produce first-class FRP profiles. We are proud of our pultrusion lines and our well-organised production facility for fibre-reinforced plastic profiles. So we are happy to explain our pultrusion process steps.

1. Insertion of the glass fibre reinforcements

The process starts with insertion of the glass fibre reinforcements. Reel winding frames are located at the front of the machine. These frames hold reels of glass fibre thread. Approximately 2.1 kilometres of glass fibre thread, e.g. 9600 TEX, are wound on each reel.

2. Travel through the impregnation bath

The glass fibre threads, and possibly glass fibre matting, pass through the impregnation bath where they are coated with polyester resin. The liquid synthetic resin is mixed with a hardener, colourant, fire retardants and other additives.

3. Travel through the infeed plates

The infeed plates guide the glass fibre threads and mats to the right position in the mould to ensure the correct glass fibre content. The glass fibre threads enhance linear tensile strength and the mats give the material transverse tensile strength. The amount of glass fibre material depends on the profile’s design specifications and properties.

4. Travel through the heated mould

Next, the resin, fibres and mats are pulled through a heated mould. The profile is formed and cured in the hot mould. Halfway through the mould, the material is already starting to harden. Once it leaves the mould, it is fully cured and can be subjected to mechanical load. The profile requires no further processing. The mould is made from wear-resistant steel and assembled from several parts. The inside of the mould is chrome-plated. The programmable computer controls all machine operations. This is where the throughput speed, cutting length and the different temperature profiles in the mould’s heating system are set. The moulds used by krafton® accommodate a maximum width of 1 metre. We have moulds for all profile types and dimensions, ranging from small bar profiles and angle profiles to wide bridge decking elements. We use our own moulds for the standard profiles. We also design custom moulds for customers. These moulds remain the property of the customer and are used to produce their unique and, in some cases patented, custom profiles on our pultrusion machine.

5. Pultrusion of the profile

A dual gripping and pulling system alternately clamps and pulls the profile. The clamps are shaped to exactly match the outside of the profile and are clad with soft plastic to avoid damaging it. Pultrusion is a continuous process with the added advantage of good quality control. The dimensions of the pultrusion profile’s cross-section are controlled within tight tolerances. Pultrusion is suitable for all kinds of glass fibres. Different types of fibre can also be combined. As a result, a high fibre content (up to 70% by weight) can be achieved, resulting in high specific stiffness and strength.

6. Cutting the GRP profile to length

The cross-cut saw moves at the line speed and cuts the profile to the desired length. Because the saw moves synchronously with the profile, the saw cut is perfectly perpendicular. A diamond-coated saw blade is used for maximum service life. A dust extractor is fitted to the saw unit.