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 GRP profiles. We are proud of our pultrusion lines and our well-organised production facility for glass 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.