What is the Pultrusion Process?

Most people have a general understanding of the Extrusion manufacturing processes. However, outside the fiberglass composite industry, few may understand the term Pultrusion. The simple difference between the two is Push versus Pull. In the extrusion process, material is typically pushed through a forming die. In the Pultrusion process, material is physically pulled through the die by a pulling mechanism, hence the industry name . . . Pultrusion.

While the Pultrusion process, as a whole is simple in theory, it is somewhat complex in the actual manufacturing process. The first step in successfully producing a pultruded profile that provides the desired mechanical strength and physical requirements is the design and manufacture of the pultrusion die. Next, the preforming set-up for a specific product must be designed. This consists of a layout of the continuous strands of glass reinforcement, uni-directional roving, surfacing veils, resins, and internal chemicals that will be incorporated into the orientation of glass strand placement within the profile.

Once the die and preforming set-up arrive at the Pultrusion machine, the operators begin stringing the profile according to the specification of the particular product. Stringing the profile consists of pulling the glass reinforcements and surfacing veils through a series of preforming guides, then through the actual die itself. Once the raw reinforcements are pulled through the die and secured to the pulling mechanism, the required resin is added to injection manifolds, a wet out bath, or a combination of both.

As the glass strands pass through the injection manifolds and through the wet out bath, they are fully saturated with a thermo set resin that includes the fillers, catalyst, pigments and other chemicals. As the glass strands enter the back of the die they are under extreme pressure forcing out any air and excess resin from the reinforcement. Once inside the heated die, the part passes through various stages of controlled heat. The heat process causes the catalysts to react within the laminate allowing the layers of reinforcements to be mechanically fixed to each other resulting in a solidified laminated product exiting the die.

As the product exits the die, the profile continues its journey towards the puller. The puller consists of a caterpillar design that sandwiches the profile between a series of pads and is connected to a drive mechanism that keeps the laminate moving. This process is also referred to as a Continuous Laminating Process. Upon exiting the puller, the laminate passes through the final manufacturing stage, which is a cut-off saw where the product is cut to its final length.