Pultrusion is a manufacturing process used to create continuous lengths of fiber reinforced polymer (FRP) composites with constant cross-sections. This process is cost-effective and very efficient, making it appealing for use in a wide range of applications. Pultruded composite shapes (profiles) exhibit similar performance characteristics of standard metal shapes, but offer distinct advantages over these materials. Here we discuss how pultrusion works to help you better understand the process and its benefits.
Pultrusion is one of the first composite manufacturing processes developed and has been used since 1951. It has consistently evolved to meet the diverse needs of the industries it serves. This method of manufacturing creates consistent cross-section FRP profiles that closely resemble the steel profiles typically used in construction. It is analogous to extrusion, but this process pulls fiber reinforcement through a die. Pultruded FRP composite sections are used to quickly and easily construct corrosion-resistant, lightweight and electrically non-conductive alternatives to steel structures. Examples of typical uses include decking and planking, structural profiles and plates, bridge components, grating and more.
There are a wide number of reasons why engineers and users may opt for pultruded FRP composites rather than more traditional materials. FRP is lightweight and offers immense flexibility, functioning well as both small components and large infrastructure. In addition to serving the construction and automotive industries, FRP is often the material of choice for applications within the consumer goods, marine, electric and wastewater treatment sectors.
Although FRP can be produced using a variety of manufacturing methods, pultrusion is a popular choice due to its cost-effectiveness, energy efficiency, affordability, eco-friendliness and minimal waste production. It is the best method for situations requiring large quantities, rapid production and continuous manufacturing.
Pultrusion is an eco-friendly manufacturing option, producing significantly fewer pollutants than many alternatives. It is also cost-effective and highly efficient, giving it widespread appeal. The pultrusion manufacturing process consists of the following four steps:
The pultrusion process involves pulling the fiber reinforcement through a heated die. These materials are typically either continuous strand mats or rolls of filament (otherwise known as rovings). The first step of this process is feeding these raw materials into the pre-forming guide. This must be done very carefully, as inaccuracy can have a negative impact on the final profile. There a large number of fiber inputs coming together to create the part. A tension roller within the guide shapes the materials.
Once brought together in the guide, the reinforced fibers undergo resin impregnation. Traditionally this is done by moving the fibers through a wet-out bath of polymer. The wet-out baths typically consist of a resin, pigments, fillers, and a curing catalyst. In some cases, the resin is injected into the heated die.
After passing through the wet-out bath, the reinforced fibers pass through a heated die. This is the step where the fibers begin to solidify into their final shape, as the heat initiates the cross-linking process within the impregnated reinforcements. A key consideration during this step is the temperature. A low temperature can result in a weak composite profile, while a temperature that is too high can cause the composite to crack.
Near the end of the heating process, the temperature of the resin will become higher than the temperature of the die. This begins the separation process. Manufacturers use a pulling mechanism to remove the cured profile from the die. Once separated, the profiles can be cut to the appropriate lengths and undergo secondary processing if necessary.
