Pultrusion process materials

Figure 7.87 Schematic diagram of a typical pultrusion process. Reprinted, by permission, from M. Schwartz, Composite Materials Handbook, 2nd ed., p. 4.46. Copyright 1992 McGraw-Hill.

As pointed out in the beginning of the chapter—and perhaps also noticeable from the process description earlier—the pultrusion process at first appears rather simple and straightforward however, several intricacies arise on closer inspection. The key technology issues of pultrusion of thermoset-matrix composites are usually considered to be resin formulation, temperature control, material guidance, and die design (not in order of importance). It is typically the skill in these areas that distinguishes a successful pultruder from his hapless competitor. 

Batch, G. L., and Macosko, C. W., Computer Aided Analysis of Pultrusion Processing. AIChE Conference on Materials in Emerging Technologies, Minneapolis, August 1987. 

Different TP pultrusion processes are used. As an example Thermoplastic Pultrusion Technologies (TPT), Yorktown, VA, USA, uses a hot-melt injection process for pultruding RP thermoplastic. Unlike TS pultruded profiles, TP profiles can be postformed and reshaped. Higher continuous use temperatures are possible with some TP matrices, and line speeds are faster with raw materials usually costing less. 

Pultrusion—Process for the manufacture of composite profiles by pulling layers of fibrous materials, impregnated with a synthetic resin, through a heated die, thus forming the ultimate shape of the profile. Used for the manufacture of rods, tubes and structural shapes of constant cross-section. 

C Koppernses, S Nolet, JP Fanned. Method and Apparatus for Wetting Fiber Reinforcements with Matrix Materials in the Pultrusion Process Using Continuous In-Line Degassing. U.S. Patent No. 5073413, Dec. 17, 1991. 

Astrom, B.T. and Pipes, R.B. (1991) Correlation between modelling and experiments for a thermoplastic pultrusion process. Proceedings of the Vlllth International Conference on Composite Materials, ICCM-VIll (eds S.W. Tsai and G.S. Springer), Honolulu, Hawaii, USA, July 15-19, Section 13-A-1-13-A-10. 

Table 8.1 Properties of reinforcement materials for the pultrusion process...

The selection of a suitable thermoplastic matrix material mostly depends on the desired mechanical properties and the desired long-term service temperature. Depending on the application area, there are other decision criteria known from thermoset matrix materials, which can be of major interest, for example the chemical resistance or the water absorption properties. In contrast, thermoplastic composites are normally featured with an improved toughness compared to their thermoset competitors. Table 8.2 gives an overview on properties of different common polymers which are used for the pultrusion process. 

The pull-off unit, which pulls the composite material through the whole pul-trusion unit, is a mechanism located behind the pultrusion die. Because the constructive implementation is of least importance for a successful pultrusion process, it can be any mechanism that pulls the composite through the process. However, there are only two versions of pull-off units in practice -a continuous and a reciprocating unit. ... 

Like the pultrusion process, the selection of a suitable thermoplastic matrix material mainly depends on the desired mechanical properties and the desired long-term service temperature. The range of usable matrix materials starts with standard polymers such as polyethylene (PE) or polypropylene (PP) and ends with high performance polymers such as polyetherimide (PEI) or poyletheretherketone (PEEK). Recent developments have shown that the processing of reactive thermoplastic materials is possible as well (CBT). For some physical properties of common matrix materials see Table 8.2. °... 

By means of the described technology properties, both processes are suitable for mass production. Nevertheless, there is a preferred field of application for both technologies. Unidirectional reinforcement fibers are best suited for the pultrusion process. In contrast, the CCM process is independent of the fiber orientation, thus it doesn t matter if unidirectional or multidirectional reinforcement materials are used. The assessment of the rates of production (= process speed) against the circumferences of the profiles, which are in contact with the tools surface (see Fig. 8.34), defines relevant process parameters and emphasizes the preferred field of application. Thus the circumference characterizes the profile shape. 

Larock, J. A. and Hahn, H. T., Pultrusion processes for thermoplastic composites . Journal of Thermoplastic Composite Materials, 2, 216-228, 1989. 

The microwave assisted pultrusion process (Methven et al, 2000) is an innovative variant of the pultrusion process. Microwave heating (Metaxas and Meredith, 1983) characterized by a high frequency electromagnetic energy source is a fast, instantaneous, non-contact and volumetric heating, and therefore, very interesting for materials processing. 

Carlone and Palazzo (2008) developed a computational modelling of microwave assisted pultrusion. This model is based on an electromagnetic submodel, meant to evaluate the electric field distribution and the heat generation rate due to the microwave source and on a thermochemical submodel, used to determine the temperature and degree of cure distributions. The performed simulations revealed the relevance of design of the microwave cavity, the curing die, and the importance of the dielectric properties of the materials in microwave pultrusion process. 

Carlone, P. and Palazzo G. S. (2008), Numerical modelling of the microwave assisted pultrusion process . International Journal of Material Forming, 1, 1323-1326. 

Chen, X., Xie, H., Chen, H. and Zhang, F. (2009), Optimization for CFRP pultrusion process based on genetic algorithm-neural network . International Journal of Material Forming, 3 (Suppl 2), S1391-S1399. 

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