Autoclave moulding prepreg

A vacuum is then drawn inside the cover membrane (to remove volatiles and porosity) while the pressure and temperature inside the autoclave are separately controlled (to provide even control of pressure across the surface, and thermal control of cure). Optimization of the application of pressure and vacuum will prevent the formation of dry laminates (which typically occurs when pressure is applied too early and low-viscosity resin is forced out) and porous laminates (when pressure is applied too late with high-viscosity cured resins). In general, consistent mouldings of high quality can be produced, but the process is slow and capital-intensive. 

Quality-control tests and important process variables 

Typical systems include epoxy carbon-fibre and epoxy glass-fibre prepregs for computer and aerospace applications. 

Blest et al. (1999) examine the modelling and simulation of resin flow, heat transfer and curing of multilayer composite laminates during autoclave processing. An empirical cure equation is used  

Elastomers can be prepared and processed using a variety of mixing and processing equipment, similarly to thermoplastic materials, and these will be addressed in this section. 

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A 177 C curing low micro-cracking/low moisture absorbing cyanate resin with a -128 to +121 C service temperature range (without post cure), formulated for press and autoclave moulding. Prepregs in all available fibres and fabrics can be manufactured via hot-melt or solution techniques, a. 1.19 j. 0.96 /o Tg (no post cure) 206"C (with post cure) 258 C... 

The following period between 1975 and 1985 was characterized by activities related to the development of prepreg systems for low pressure autoclave moulding, i.e. modification of the resin chemistries to achieve flow, tack and non-volatile cure. These requirements were dictated by the industry to meet the processing techniques already in place for epoxy and polyester resins. 

Autoclave moulding is typically used in the aerospace industry for the production of high-value composites from prepregs. The laminate, which is covered on both sides by a fine polyester cloth peel-ply (for enhancing the surface effect), is built up on the mould surface. The top surface of the laminate is covered by a porous release film and bleeder cloth. The whole assembly is then covered with a non-porous membrane, which is sealed to the mould, and then placed inside an autoclave as shown in Figure 6.19. 

Vacuum bag moulding (autoclave process) Prepreg is encased in flexible bag a vacuum is applied to draw the prepreg against a mould surface. Heat is applied. Process carried out in autoclave Very large structures prototypes short production runs high fibre content... 

Prepreg material with balanced warp/weft autoclave moulded ... 

Prepregs laid up at various fibre orientations, autoclave moulding, Vf = 62%. 

Prepreg draping and consolidation by vacuum or pressure bag moulding, autoclave... 

Scott and Heath (1992) [11] have reported that cost savings ranging from 25% to 40% are possible with liquid moulding raw materials when compared to prepreg. This is substantial as up to 50% of an autoclave component cost can be associated with the raw materials. 

As described in chapter 3.1 1ST and ITA already tested alternative ways to bring the B-staged prepreg inside of the concrete into the C-stage (Fig. 7). Thus, there is no further need to use a mould or autoclave process at all. This saves expenses. UV-, microwave or heat-curing systems are not favored by ISF and ITA, because cost intensive equipment would be needed as well as workers who have to deal with it on the construction side. 

For very large parts that cannot be accommodated in ordinary presses, the autoclave process can be used in conjunction with a vacuum bag [3]. In one example, prepreg is encased in a flexible plastic bag, which is situated in an autoclave (Fig. 2.2). A vacuum is applied to draw the bag against the mould surface and heat is applied. The process can be used to produce very large articles, but it can also be scaled down and has advantages for short... 

Layers of fibre pre-impregnated with resin (prepreg) are applied to a mould and rolled. A rubber bag is placed over the lay-up and the air is removed by means of a vacuum pump. Generally the mould is then placed in an autoclave, which applies further pressure and temperature to cure the resin, or simply in an oven. 

A rather common application of fibre reinforced polymers is car repair. This poor mans technology is translated to the "high tech" area. The most important difference is found in the addition of the word "advanced". For also in the aircraft industry composites is a sticky business. Prepregs are draped in moulds by hand, moreover, they are cured in expensive autoclaves. 

A 177 C cure toughened epoxy with a 126-138 C dry and 104 C, wet service temperature. Available in a broad range of tape, fabric and roving prepregs for the manufacture by press moulding or autoclave of... 

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