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Pultrusion is a continuous process for manufacture of composite materials with constant cross-section. Reinforced fibers are pulled through a resin, possibly followed by a separate preforming system, and into a heated die, where the resin undergoes polymerization. Many resin types may be used in pultrusion including polyester, polyurethane, vinylester and epoxy.
The technology is not limited to thermosetting polymers. More recently, pultrusion has been successfully used with thermoplastic matrices such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET) either by powder impregnation of the glass fiber or by surrounding it with sheet material of the thermoplastic matrix, which is then heated.
Ecological cleanness of manufactured products, in contrast to composites on thermosetting resins base, as well as practically unlimited possibilities of recycling (processing) after the resource depletion appear to be forcible arguments in favor of reinforced thermoplastics. For these reasons the industrial output and use of the given materials in highly industrialized countries have increased by 8-10% per year in recent decades.
Pultrusion technology of manufacturing of fiber composites with polymer matrix appears to be energy-efficient and resource-saving.
For economic and environmental reasons the matrix of thermoplastic polymers is more preferable, but due to the high viscosity of melts it is difficult to achieve high productivity and high quality of fiberfills impregnation.
Products manufactured under this technology, are widely used in the following industries:
- In agriculture and chemical industry for manufacturing of chemically resistant to aggressive media slatted floors with enhanced strength characteristics used in the construction of livestock facilities, chemical plants, etc.;
- in construction industry for the production of glass-fiber reinforcement, profiles, carcasses, stiffening bars for PVC-windows, etc.;
- in aerospace industry for manufacturing of structure components of aircraft;
- in sports and tourism industry for manufacturing of equipment having enhanced strength properties: skis, ski poles, tent and hovel constructions, etc.;
- in electrical power engineering for manufacturing of dielectric structures, fiberglass rods used in composite insulators and as supporting structures for elements of signaling blocks, and fiberglass profiles used in manufacturing of transformers and electric motors;
- in commercial production, using grains of long-fiber molding material (LLM) as a raw material for subsequent manufacturing of structures and products with enhanced strength and chemical properties;
- and in many other industries and plants, using mechanisms, structures and materials, which meet high standards of chemical, dielectric and strength stability.
1 - Continuous roll of reinforced fibers/woven fiber mat
2 - Tension roller
3 - Resin Impregnator
4 - Resin soaked fiber
5 - Die and heat source
6 - Pull mechanism
7 - Finished hardened fiber reinforced polymer
The first pultrusion patent in the United States was issued in 1951. W. Brandt Goldsworthy is widely regarded as the inventor of pultrusion.
The design of pultrusion machines varies. Two often used types are reciprocating (hand-over-hand) and continuous (cat-track).