Glass polyester pultrusion

Glass, carbon, and aramid fibers are used as unidirectional or fabric mat reinforcements, with E-glass/ polyester being the most commonly used system. The limitation of pultrusion is that only constant cross-section parts can be fabricated. However, a variety of hollow and solid profiles of any length can be manufactured. 

It is reported that sandwich panels are being produced in the USA by pultrusion. In this process a plywood core is completely encased in a 3 mm thick glass polyester skin, resin penetrating the plywood during production to give increased bond strength and moisture resistance. 

The reinforcements amenable to RTM are similar to those used for pultrusion, except that they need not be continuous in nature. Thus, E-glass, S-glass, aramid, and carbon fibers are commonly used, as are discontinuous filaments such as wood fiber and polyesters. Even metal and ceramic fibers can be used in this technique. In one method, the preform is fabricated by spraying 12- to 75-mm-long chopped fiber rovings onto a preshaped screen. A binder sprayed with the fibers keeps them in place and holds the preform shape, which is then placed in the mold. 

Many different thermosetting polymers are used in pultrusion, eg, polyester, vinyl ester, epoxy, and urethane. Reinforcements must be in a continuous form such as rovings, tows, mats, fabrics, and tapes. Glass fibers are the low cost, dominant composition, but a ram id and carbon fibers are also used. 

Virtually any reinforcement-matrix combination feasible in any other composites application also may be used in pultrusion however, glass heavily dominates as reinforcement with 95 percent in the United States and 98 percent in Europe (see Table 11.1), whereas polyester resin dominates as matrix material with 79 percent in the United States and 66 percent in Europe [2]. 

Hybon 2011 Rovings. [PPG Industries/ Fiber Glass Prods.] Glass roving reinforcement for polyester and vinyl ester resin systems for pultrusion applies. 

In contrast to extrusion, in pultrusion a combination of liquid resin and continuous fibers is pulled continuously through a heated die of the shape required for continuous profiles. Shapes Include structural I-beams, L-channels, tubes, angles, rods, sheets, and so on, and the resins most commonly used are polyesters with fillers. Other resins such as epoxies and urethanes are used where their properties are needed. Longitudinal fibers are generally continuous rovings. Glass fiber material (mat or woven) is added for cross-ply properties. 

Figure 1.2 The effects of temperature on the dynamic mechanical behaviour of one polyester/glass fibre composite (isophthalic polyester Neste S 560 Z, E-glass, manufactured by pultrusion). The DSC method gives the Tg of the pure S 560 Z resin casting as 135°C. Owing to certain additives, the Tg of the FRP material in question could not be determined with DSC.

Vinyl ester resins are similar to unsaturated polyester resins in that they are cured by a free radical initiated polymerisation. However, they differ from the polyesters in that the unsaturation is at the ends of the molecule rather than along the polymer chain. Unlike polyesters, vinyl esters show a greater resistance to hydrolysis as well as lower peak exotherm temperatures and less shrinkage upon cure. Cured vinyl ester resins exhibit excellent resistance to acids, bases and solvents. They also show improved strain to failure, toughness and glass transition temperatures over polyesters. They can be used in filament winding, pultrusion, resin injection, vacuum moulding and conventional hand lay-up. 

Consider as an example a tension member manufactured from uni directional E glass fibres and polyester resin by the pultrusion process. The design criteria are hsted below ... 

Determine the maximum axial design compressive force that can be safely applied to the glass FRP section shown in Figure 4.1. It is manufactured from E-glass random mat plus roving and polyester resin, by the pultrusion process. 

These tubes are made by pultrusion with E-glass fibres and polyester resin. According to LERC the glass volume fraction is 50%, the Young s modulus is more than 20 kN/mm and the strength is more than 50 N/mm. ... 

Physical dimensions of many processed parts must be held to fairly close tolerances to ensure proper assembly of parts into a complete structure, as, for example, molded fender panels bolted to steel chassis cars, plastic screw caps for glass jars, etc. In general, the final dimensions of the processed part will differ from the dimensions of the mold cavity or the pultrusion die. Such differences are somewhat predictable, but are usually unique to the specific material and to the specific process. The dimensions of a mold cavity for a phenolic part requiring close tolerances will often be different from dimensions of a cavity for an identical polyester part. Both the part designer and the mold or die designer must have a full understanding of the factors affecting final dimensions of the finished product, and often need to make compromises in tolerances of both part and cavity dimensions (or even in plastic material selection) in order to achieve satisfactory results with the finished product. 

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