Pultruding Polyurethane Composite Profiles: Practical Guidelines for Injection Box Design, Component Metering Equipment and Processing

Unsaturated polyesters and vinyl esters have been the workhorse resins in the pultrusion industry for a quarter century or more. In efforts to expand their markets and differentiate their products, however, pultruders are continually seeking out new materials and processes, which can mitigate some of the limitations of traditional resins such as brittleness or slow reactivity. During the past three years polyurethane resins, which exhibit superior strength and damage-tolerance relative to traditional polyester and vinyl ester pultrusion resins, have been successfully commercialized. Such advantages do not come without new challenges as polyurethane resins require their own unique material handling and processing methods. There is a perception in the pultrusion industry that these requirements present an insurmountable barrier for practical application of polyurethane resins. This paper aims to address this perception by providing a practical discussion of injection box design, material handling, component metering equipment, die design, and process conditions used for pultruding polyurethane profiles. Using the guidelines presented in this paper, manufacturers can be confident of running a robust pultrusion process with continuous line operation.