JEC COMPOSITES MAGAZINE - Issue #35 - September 2007 - 38

Innovative Prepreg Systems temperature, but with the part now out of the mould and with no risk of distortion. This concept was first exploited in the LTM® tooling systems. The resins developed for this purpose exhibited resistance to extremely high temperatures, but their inherent brittleness made them totally unsuitable for structural applications. ACG’s determination to move forward into other arenas brought about further developments to this pioneering system, introducing toughness and allowing low-pressure processing, all essential characteristics that have made prepreg technology a reality for the marine industry. That’s not to say these materials were perfect; material is stored frozen to maximize life, but the reactivity of a particular prepreg system and its minimum curing temperature are inextricably linked. Therefore, low-temperature curing means a short working life, which in turn limits the project size or dictates the speed at which you must work. This was less than ideal, but some early projects did show that these materials were attractive to the marine industry. This was reflected in a number of boats built at that time, including an 18ft Skiff, an Ultimate 30 and an Open 50. Race boats are not the only specialist area producing extreme one-offs. LTM® systems have also found use on a number of high-profile aerospace projects, including Scaled Composites’ Spaceship One and Global Flyer. Laminating process Typical curing conditions require 120°C and a pressure of 3 to 6 atmospheres (bar). ACG autoclave While an autoclave remained the ultimate route to producing high-performance components, it was seen as a barrier to the wider adoption and application of composite materials in other industries. Innovative resin formulation has always been at the heart of ACG technology; a modern Formula One race car could feature up to eight different resins within its structure. ACG has always manufactured “standard” 120°C curing prepregs, but an early advancement in this area led to a unique technology known as “step ahead” curing. This technology is centred on the company’s Low Temperature Moulding (LTM®) processing resins. These resins are formulated to cure at low temperature and can be transformed by further heat treatment into highly robust structures. These resins develop a higher level of performance in terms of mechanical and thermal characteristics than would be expected from a particular curing condition. This enhanced stability allows initial curing to take place at 50-60°C, thereby utilising relatively low-cost tooling. The cure can then continue to a much higher level with stability still running ahead of the cure SpaceShipOne. (left) Male moulded hull. (right) “Net processing” Interest in high-performance composites was growing and there was an obvious need for more user-friendly, low-temperature, lowpressure moulding solutions. That’s when ACG’s Variable Temperature Moulding (VTM®) system came onto the scene. The basic chemistry is derived from the LTM® system, offering optimised low-temperature, low-pressure processing, flexible cure temperatures between a modest 65°C and 120°C with “step ahead” cure and a working life of one month. The VTM® does not need an autoclave and resin rheology is controlled to optimise fibre wet-out, but not at the expense of excessive resin bleed. The myth still persists that resin must be bled from a component to maximise properties. ACG has always advocated “net processing” – what goes in comes out, resin content and material properties remain predetermined and controlled. Why buy resin just to throw it away? JEC Composites Magazine / No35 September 2007

JEC COMPOSITES MAGAZINE - Issue #35 - September 2007

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #35 - September 2007