Pultrusion refers to a continuous or uninterrupted process that utilizes fiber reinforcements or other resin matrices to produce cross-sectional materials. Pultrusion is a combination of two terms, ‘pull’ and ‘extrusion.’ The procedure involves pulling the raw materials, unlike extrusion, which works by pushing.
It was unveiled to the public in 1951, so it has not been on the market for long. People associate pultrusion with W. Bandit Goldsworthy.
He is acknowledged as the inventor of this process because he promoted the dissemination of pultrusion knowledge. He died in 2003. Even after his death, the process continues to develop, grow, and improve up to date.
Pultrusion Process
As mentioned above, Pultrusion involves pulling of fiberglass through the liquid resin for reinforcement. Some types of resin include polyester, phenol, vinyl ester, epoxy, and polyurethane.
The resin soaks and permeates the unfinished product. The material spools, and reinforcements are fed into the machine, known as a tension roller, to start the process. The roller begins by shaping the materials into the various forms of the final product.
A surface veil may be included in this step to prevent erosion or fiber bloom. It also makes fiber resistant to corrosion and to ultraviolet radiation. At this point, pigments to impart and enhance the final color of the product may as well be added.
With the attachment of the resin base, the combination of the resin and the fiberglass is then passed through a heated and molded die using a specific pulling device. The process is known as polymerization.
The heated die is vital in the pultrusion process because it helps create a hard, die-shaped product. The product is then heated to form and durable, rigid, reinforced structural form.
The final product of the firm profiles is then moved along a pull mechanism. The profiles are cut to appropriate lengths using a cutting saw, and the pultrusion process ends with a final product of fiberglass-reinforced polymer.
Raw Materials Used in the Pultrusion Process
Resin
Many types of thermosetting and thermoplastic resin systems are used in the pultrusion process, and they include the about to be mentioned:
- Unsaturated vinylester
- Epoxy
- Unsaturated polyester
- Phenol-resins
- Methacrylate resins
- Polyurethane
- Thermoplastics
Unsaturated Polyester Resin
During pultrusion, various types of unsaturated polyester resin are used. They are usually preferred due to their viscous nature, which makes them easy to fill with kaolin, chalk, or ammonium polyphosphate.
Methacrylate Resin
You can get a wide variety of at least 5 types of Methacrylate resin. It has more benefits than the other standard types of resin.
Some of the many advantages include the following:
- They have a high filler content of aluminium trihydrate (ATH), up to 200 parts. That means it complies closely with the strict fire safety standards.
- Efficient flame-retardant properties become evident when ATH and ammonium polyphosphate are present.
- Methacrylate Resin is exceptionally reactive, which means that the pultrusion process speed will be relatively high.
- It has a low shrinkage attribute, and this entails that the material has a good quality surface, with no exothermic cracks.
- Another advantage is that you can add pigment to the methacrylate surfaces without any difficulty
Phenol Resins
Phenol resin is the oldest type of resin system. The procedure used to produce the material involves condensing phenols and formaldehyde.
During the making process, there is a high risk of cracks and pores because water is released during curing. So, phenol resin is likely to cause problems throughout the pultrusion procedure.
It is less flammable, though it has a high flue gas emission rate. Moreover, it is not possible to add pigment to this type of resin.
Polyurethane
Polyurethane has been successfully used in the pultrusion process since the early 2000s. It is highly resistant to impact and fatigue.
Additionally, it has a lower shrinkage rate than unsaturated polyesters. Polyurethane profiles are typically used when high-performance structures are required.
Thermoplastics
Thermoplastic-based profiles exhibit high surface slip, but exposure to heat can cause deformation.
They are incredibly resistant to abrasion. Most manufacturing industries utilize Polyethylenes, polyamides, and polypropylenes as matrix materials.
Fiber Reinforcements
The glass, carbon, and aramid fibers highly determine the strength and the rigidity of the end products of the profiles.
Reinforcing Glass Fiber
Glass fiber reinforcements are usually very crucial during the pultrusion process. The silane size typically surrounds the glass filaments, enhancing cross-linking with the matrix. During pultrusion, smooth roving, monofilament, and textured roving are typically used.
Woven or Non-woven Fabrics
The above reinforcement materials are usually used to enhance the strength of the transverse section. The combination of fiber and non-woven fabrics with versatile layers is created.
Advantages of the pultrusion process:
- Pultrusion is a fast and economical method for impregnating and curing various materials.
- The process ensures exact control of the resin content
- The fiber cost is usually minimal, since a large portion of the material comes from the baskets.
- It is easy to close the impregnation area of the resin, and this prevents explosive emissions
- The lamination structural properties are very beneficial as the fibre profiles are not bent, and therefore, a high volume of fibre fractions can be found.
- The pultrusion process produces lightweight profiles, and this results in the minimization of the shipping cost. A profile with more than 2000m2 of Z200 can be transported by a usual 40ft container, while one person can manually carry piles with short lengths, and this reduces the cranes’ time.
As above mentioned, the pultrusion manufacturing process is cheaper, convenient, and efficient compared to other alternatives in the market.
It also produces high-quality and error-free composites, which ensures that the client goes home with a satisfactory smile. As a result, it has become popular and in demand in recent years.
