Aircraft operators will save on carbon wet-layup repairs of polymer composites under a committee's proposal that would be an industry first. After establishing the wet-layup-resin solution as an industry precedent, the Commercial Aircraft Composite Repair Committee plans to tackle a bigger materials issue: prepreg specifications for repair.
Participants say wet layup represents a good start.
``We operate Fokker, Douglas and Boeing aircraft, and each of the resin systems they specify has a different shelf life, mixing ratio and curing temperature,'' said Tony Lewis, productionforeman in USAir's composite shop in Winston-Salem, N.C., and newly elected CACRC chairman.
Use of one resin system, instead of four or five, will eliminate duplication, simplify procedures and lead to material commonality and more economical composite repairs, Lewis said.
An unusual cooperation exists among competitors, Lewis said: ``We have [original equipment manufacturers] working with airlines and suppliers and [regulatory] authorities.''
Committee members will vote in June or July on a standard specification applicable to wet-layup repair, according to Gerard Van Der Weijde, stress research specialist with Fokker Aircraft in Schiphol, the Netherlands, and coordinator of the CACRC repair material task group.
Material-qualification tests could begin in August at Tenax Fibers GmbH & Co. KG, according to Tenax's Bruno Degrigny. Tenax of Wuppertal, Germany, a unit of Tokyo-based Toho Rayon Co. Ltd., will supply carbon fibers.
Two resin companies are interested - Dexter Corp.'s Aerospace Materials Division and Ciba-Geigy Corp.'s Furane Aerospace Products Group. With Tenax, one or both of those companies could fund a program for its product. Each qualification will cost $200,000-$250,000.
Fabric will come from Cramer in Heek-Nienborg, Germany, if Dexter qualifies; or Ciba's Brochier unit in Decines, France, if Furane qualifies. Once tests are completed, aircraft makers and repair stations will include the system among qualified repair materials.
Dexter's widely used Hysol EA 9390 composite wet-layup resin qualified in 1988 under Boeing Co. material specification 8-301. Customers have been screening Furane's Epocast 89612 A/B resin system for nine months.
``We're moving to a two-part wet-layup resin and dry carbon fiber fabric and getting away from prepreg,'' said Michael Cichon, Dexter program manager in Pittsburg, Calif. ``We will provide the laminate and specimen preparation'' for the tests.
Manufacturers use prepreg for original flight articles but commonly turn to wet layup for repairs.
``The wet-layup systems will be high-performance materials designed to permit airlines to make excellent structural repairs without going near an auto-clave,'' said Tony Bonnington, head of manufacturing technology for Ciba Composites in Duxford, England.
Airline repair shops probably need less than 5 tons of wet-layup resins a year, he said.
Sections of the Air Transport Association, International Air Transport Association and Society of Automotive Engineers merged in 1991 to form CACRC, which met April 26-27 in Linkoping, Sweden, to discuss repair and material issues.
CACRC works to standardize terms, procedures and technician qualifications and to raise airline workers' awareness about how to work with composites.