REINFORCEMENTS AND RESIN SYSTEMS
Roving is made up of fiberglass unidirectional filaments, which are manufactured in continuous rolls. Roving is always present in pultruded products comprising 50% to 70% of the total glass content. In addition to supplying the necessary strength to pull the profile, roving supplies the product with high tensile, flexural properties and is a big contributor to the overall section stiffness.
Generally, fiberglass roving is used in pultrusion to achieve the required properties. In special structural applications where more stiffness is required, graphite roving can be used. Conversely, polyester roving may be used in applications where more flex is needed.
Continuous strand mat is the remainder of glass reinforcement used in the pultrusion process. Typically, it is 30%-50% of the total glass content. Unlike hand-laid-up or press-molded processes that use short chopped fibers, the pultrusion process must have a multidirectional mat that has good pull strength to facilitate getting it to the die after it has been wet-out with the resin. This continuous strand mat is designed specifically for the pultrusion process and offers good wet-out characteristics, conformability to a variety of shapes, and good physical properties including the required pull strength.
Generally, fiberglass continuous strand mat is used to obtain the desired transverse properties of the product. Whereas the roving ties the composite together in the longitudinal direction, the mat is responsible for tying the composite together in all directions, but mainly in the transverse direction. Although continuous strand mat is suitable for most applications, a variety of products such as woven roving, stitched roving, and woven fabrics can be used in custom applications to increase the desired transverse properties.
Veils are used to enhance the surface of pultruded profiles. Most widely used today are synthetic veils. A veil is added to the outside of a profile just prior to entrance of the die. As a result, the finished profile has a resin-rich surface that aids in resistance to ultraviolet (UV) degradation and makes the profile more hand-friendly. Since the veil brings more resin to the surface and the resin is the ingredient that gives the corrosion resistance, adding the veil increases the corrosion resistance.
All standard structural shapes are manufactured using a surface veil as well as UV inhibitors to protect against UV degradation.
Generally, two types of resins are most often used in the pultrusion process. They are isophthalic polyester resin and vinylester resin. Each resin is available in a fire retardant version as well as non-fire retardant. In selecting the proper resin, one must consider the environment in which the product will be used. Generally, polyester resin will be adequate to handle most environments. However, the vinylester will handle the more severe applications where better chemical resistance is needed. It is a good idea to check the resin corrosion guide for proper selection of system.
Standard structural shapes are stocked in three series: standard polyester, fire retardant polyester and fire retardant vinylester resin systems.
Standard Polyester (ST) Resin System
Standard structural shapes are manufactured using isophthalic polyester resin. This resin system is olive green in color and contains UV inhibitors. Polyester resin exhibits good corrosion resistance, good dielectric properties, low thermal conductivity, and excellent mechanical properties.
Fire Retardant Polyester (FR) Resin System
This resin system exhibits the same characteristics as standard polyester along with a fire retardant rating of 25 or less when tested in accordance with ASTM E-84 and exhibits low smoke generation. Products manufactured using this resin system are gray and yellow in color.
Fire Retardant Vinylester (VE) Resin System
Being fire retardant, this resin meets a rating of 25 or less when tested per ASTM E-84 and has low smoke generation. It is produced in beige and yellow. This system exhibits excellent corrosion resistance and is capable of higher service temperatures than polyester resin systems.
Generally, these resin systems cover most applications, and can be custom mixed to meet more stringent requirements for a specific application.