1 Individual strands of fiber are fed into a die where they will be soaked in resin and formed into their final profile.
2 A finished tube emerges through the cutter, ready to be cut to length.
– Offers a 75 to 80 percent weight reduction on steel and 30 percent on aluminum.
– Greater dimensional stability than its metal counterparts.
– Can be colored without the problem of chipping because the color is added to the polymer itself.
– Surface decorations can be applied to mimic grain and other textures.
– Nonconductive and noncorrosive.
– A drawback with pultrusion is that the design is restricted to profiles with a constant cross-section.
Volumes of production
Depends on the size and complexity of the shape—around 1,500 feet is a typical minimum run.
Unit price vs. capital investment
The cost is lower than that for some molding processes, injection (see p.196) and compression molding (see p.174), for example, but higher than for, say, hand lay-up molding (see p.152).
Speed
Depends on size, but, as a rule of thumb, it is possible to achieve 20 inches per minute for a profile measuring 2 by 2 inches, 4 inches per minute for chunky shapes and 40 inches per minute for narrower sections.
Surface
The surface finish can be controlled to a degree, depending on the reinforcement and polymer.
Types/complexity of shape
There are no problems with undercuts in pultrusion. Virtually any type of shape that can be squeezed through the die can be made, bearing in mind that the shape must have a constant thickness.
Scale
The maximum size for profiles is typically 47 inches wide, although there are specialist machines that make larger components. Minimum wall thickness is approximately 1/10 inch. The size of the manufacturing plant dictates the limit to the length of the pultrusion.
Tolerances
Vary depending on the profile, but on a standard box-section, with a wall thickness of 1/5 inch, the tolerance is ±1/75 inch.
Relevant materials
Any thermoset polymer matrix that can be used with glass and carbon fiber.
Typical products
Applications for pultrusions are varied and include permanent and temporary structural components for industrial plants, vandal-resistant indoor and outdoor public furniture, and fairground and exhibition stands. Smaller-scale applications include electrically insulated ladders, ski poles, racket handles, fishing rods, and bicycle frames. Perhaps surprisingly, pultruded plastics have a resonance similar to certain woods, which has led to them being used as replacements for hardwood frames for xylophones.
Similar methods
Extrusion (p.96) and PulshapingTM (p.102).
Sustainability issues
Parts can be produced with thin wall thicknesses as a result of the fiber reinforcement, which minimizes material use without compromising strength. However, as the process is entirely automated and heat intensive, energy use can be quite high in relation to the fairly slow cycle speed. The combination of materials makes the composites nonrecyclable.
Further information
www.exelcomposites.com
www.acmanet.org/pic
www.pultruders.com
PulshapingTM
PulshapingTM is one of the newest additions to the manufacturing world and the processing of composites. Developed by US-based Pultrusion Dynamics, Inc., it addresses one of the biggest problems—the constant, unvarying cross-section along the whole length—in the pultrusion process (see p.99). PulshapingTM allows designers to modify a cross-sectional shape in three dimensions during continuous processing of components in fiber-reinforced plastics. For example, a round profile can be a constant cross-section along the majority of its length, and can then be transformed to a square at one end and an oval at the other, using appropriate tooling. A particular advantage of this process is that it can, for example, allow tube ends to be shaped with threaded fasteners or expansion–reduction couplings joints.
– Shares the many advantages listed for pultrusion (see p.99).
– The added advantage is that the geometry can be changed at selected locations along the continuous length of a component.
– Although the geometry can be altered along the length of the component, this is restricted to a repeat pattern. A continuous curved shape or continuous taper cannot be executed with this method.