Pultrusion process profiles

In the pultrusion process, continuous fibers are impregnated by the thermoset precursors and are pulled through a heated die where the cure takes place this produces continuous profiles of different shapes at a rate of the order of 1 m min-1. 

To produce pultruded products with consistent and high quality, it is important to tailor and control the pultrusion process. To achieve a uniform degree of cure in the cross-section of a product, control of the temperature profile inside the pultrusion die is an essential aspect. Also, to achieve consistent fibre wetting, controlled flow and pressure build-up must... 

Initial modelling on predicting velocity profiles in pultrusion dies was carried out by Gorthala et al. (1994). Here a two-dimensional mathematical model in cylindrical co-ordinates with a control-volume-based finite-difference method was developed for resin fiow, cure and heat transfer associated with the pultrusion process. Raper et al. 

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. 

The pultrusion process by which the profiles are made lends itself exceptionally well to the inclusion of some pigment paste in the resin formulation. This allows brightly coloured profiles to be made, affording visually pleasant structures. 

The pultrusion process has a low labour requirement and it can manufacture large amounts of profile with high glass-to-resin ratio, using continuous roving at a competitive cost. 

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. 

Tooling for the profile processes. Extrusion and pultrusion, the profile processes, require steel dies because they build up back pressures behind the die. However, the tooling costs for these processes are relatively low because the shapes manufactured with them are normally... 

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. 

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. 

Figure 8.35 illustrates clearly that the pultrusion process is the preferred choice for the production of profiles with small circumference at high line speeds. In contrast, the reachable line speeds with a CCM press are lower, but independent of the profiles shape. That means that profiles with a huge circumference can be produced as fast as those having a smaller circumfer-... 

A mathematical relationship between the DOC profile across the cross-section of a pultruded part and the die-heater temperatures was established by Li et al. (2002b).The relationship was employed to optimize the die-heating profile such that a near-uniformly cured component could be obtained finally. The algorithm was implemented for simulation of pultrusion process using the three-dimensional finite element/nodal control volume (FE/NCV) approach developed by Joshi and Lam (2001). 

Michael, B. (Airbus operations GMBH) (2011), Pultrusion process for production of a continuous profile. Patent Application Publication, US2011/0049750A1, 3 March 2011. 

Pultrusion. The pultrusion process makes structural profiles of any shape continuously from composite materials (6-9), just as they would be extruded in aluminum. It is a one-step process that converts raw stock into finished product at rates up to 4.5 m/min. 

Fig. 10. Time-temperature profile for pultrusion process and development of conversion along the process. Temperature, conversion. From Ref. 55.

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