Pultrusion process limitations

Joshi S. The pultrusion process in polymer matrix composites. In Advani S, Hsiao K-T, editors. Manufacturing techniques for polymer matrix composites (PMCs). Cambridge (UK) Woodhead Publishing Limited 2012. 

In contrast to the pultrusion process, the production speed and the maximum size of the profile are not limited by the required pulling forces. Due to the use of release films, there is no adhesion between the polymer and the surface of the mold. Furthermore, the friction between the release film and the tool is minimized because of the semi-continuous operating principle of the CCM process. 

Some disadvantages exist in the traditional thermosetting and thermoplastic pultrusion processes due to the limitation in different major aspects of the processes. However, studies conducted in various key features and problem areas, as listed in Table 12.1, of pultrusion process have resulted in better understanding and major advancements in the process. 

Phenolics are now growing into the FRP composite areas of hand lay up, open and closed mould techniques, pultrusion and filament winding. The driving force behind this recent growth is the concern over flammability and smoke generation of materials used in transportation and in certain types of construction. Use of phenolics is limited to those fabrication processes and sizes of structure which allow high temperature curing. 

For thermosets, the hollow part processes are filament winding and pultrusion. These processes are limited in shape and structure. There are three hollow part processes for thermoplastics (1) rotational molding, (2) twin sheet thermoforming, and (3) blow molding. 

Price (21) analyzed the thermorheological aspects of the processing of epoxy-carbon fiber and polyester-glass fiber. He used a heat transfer model for pultrusion and examined two limiting cases i) isothermal case with uniform die wall temperature and ii) adiabatic case where heat conduction was considered negligible. However no correlation between process variables and temperature profiles was discussed. 

Pultrusion is a continuous process that is easily automated production rates are relatively high, making it very cost effective. Furthermore, a wide variety of shapes are possible, and there is really no practical limit to the length of stock that may be manufactured. 

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