In May 1954 the world’s first film adhesive for aircraft structural bonding was created. Redux® 775 Film was a further development of the Redux®Liquid/Powder system, invented by Aero Research Ltd founder, Dr NormanDe Bruyne and George Newell. It is still manufactured today at the sameDuxford, UK site at which it was conceived (now part of Hexcel). The Redux® Liquid/Powder system had been invented in 1942. This groundbreaking discovery was not only a long-awaited solution for bonding early fibre-reinforced composites; it also gave previously unseen shear strength performance on aluminium substrates.
The Redux® Liquid/Powder system was readily accepted by the aerospace industry and the first bonded structural components in an aircraft successfully completed their maiden flight 60 years ago, in July 1944. The aircraft was theDe Havilland Hornet (and the Sea Hornet), whose wing structure reliedheavily on ‘Reduxed’ wood/metal components.
Experiments on converting the liquid/powder system into a film adhesive began in 1953. A so-called half-web was produced where a film of the liquidresole was coated onto polyethylene film, powder was applied to the phenolic coating and the excess was allowed to drop off, leaving a film which, bynatural pick-up of powder, had the required liquid to powder ratio. Two halfwebs were then consolidated together – powder face to powder face – to produce the Redux® Film.
Redux® 775 Film had the same adhesive properties as the originalLiquid/Powder system, with the added advantage of it being supplied in amore user-friendly, handleable form. The first aircraft to be built with Redux® 775 Film were the Handley Page Herald, Hawker Siddley 125, ArmstrongWhitworth Argosy, Bristol Britannia, Sud Aviation Alouette and SAAB’s Lansen and Draken aircraft. Although the product line has been rationalised, Redux® 775 Film has been used on a continuous basis since the 1960’s, particularly by the European aerospace industry.
A sample of the original batch of Redux® 775 Film has been preserved, at ambient temperature, and tests have been carried out over the years using lap-shear performance to determine the effect of ageing on the film. As the graph below demonstrates, there had been negligible deterioration in lap shear strength over the 50 years. One final set of lap-shear tests was carried out on June 7th on metal joints bonded with the remaining sample of adhesive. Hexcel was delighted that average results of 29.5 MPa were achieved from the original batch of 50-year old adhesive.
Research into adhesives for aerospace and industrial markets is still a key focus for Hexcel, who recently launched a range of paste adhesives to complement the Redux® films. Hexcel continues to focus on the development of improved RT cured pastes, providing comparable performance to high temperature cured film based products. Recognising the increasing demand for improved performance from film based products, Hexcel is focusing on achieving still higher temperature and peel performance materials to meet these needs.
Graph demonstrating lap shear strength from the original batch of Redux® 775 film adhesive. On the 50th anniversary the adhesive still performed above specification.
Photo: Simon Hirst, Lab Technician, carrying out final lap shear testing on the original batch of 50 year old Redux® 775 adhesive at Hexcel, Duxford.
Hexcel Corporation is a leading advanced structural materials company. It develops, manufactures and markets lightweight, high-performance reinforcement products, composite materials and composite structures for use in commercial aerospace, space and defence, electronics, and industrial applications.
Contact: Rachel Atkinson
Tel: +44 1223 838370
Rachel.Atkinson@hexcel-eu.com