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9/8/98 AC 43.13-1B (6) Epoxy adhesives are a two-part synthetic resin product, and are acceptable providing they meet the requirements of para- graph 1-4a. Many new epoxy resin systems appear to have excellent working properties. They have been found to be much less critical of joint quality and clamping pressure. They penetrate well into wood and plywood. How- ever, joint durability in the presence of ele- vated temperature or moisture is inadequate in many epoxies. The epoxy adhesives generally consist of a resin and a hardener that are mixed together in the proportions specified by the manufacturer. Depending on the type of ep- a. Properly prepared wood surfaces. b. Adhesive of good quality, properly prepared, and properly selected for the task at hand. c. Good bonding technique, consistent with the adhesive manufacturer’s instructions for the specific application. 1-6. PREPARATION OF WOOD SUR- FACES FOR BONDING. It is recommended that no more time than necessary be permitted to elapse between final surfacing and bonding. Keep prepared surfaces covered with a clean plastic sheet or other material to maintain cleanliness prior to the bonding operation. The mating surfaces should be machined smooth and true with planers, joiners, or spe- cial miter saws. Planer marks, chipped or loosened grain, and other surface irregularities are not permitted. Sandpaper must never be used to smooth softwood surfaces that are to be bonded. Sawn surfaces must approach well-planed surfaces in uniformity, smooth- ness, and freedom from crushed fibers. It is advisable to clean both joint surfaces with a vacuum cleaner just prior to adhesive applica- tion. Wood surfaces ready for bonding must be free from oil, wax, varnish, shellac, lacquer, enamel, dope, sealers, paint, dust, dirt, adhe- sive, crayon marks, and other extraneous mate- rials. a. Roughening smooth, well-planed sur- faces of normal wood before bonding is not recommended. Such treatment of well-planed wood surfaces may result in local irregularities and objectionable rounding of edges. When surfaces cannot be freshly machined before bonding, such as plywood or inaccessible members, very slight sanding of the surface with a fine grit such as 220, greatly improves penetration by the adhesive of aged or polished oxy, pot life may vary from a few minutes an hour. Cure times vary between products. CAUTION: Some epoxies may have unacceptable thermal or other hidden characteristics not obvious in a shop test. It is essential that only those products meeting the requirements of paragraph 1-4a be used in aircraft re- pair. Do not vary the resin-to- hardener ratio in an attempt to alter the cure time. Strength, thermal, and chemical resistance will be adversely affected. Read and observe material safety data. Be sure to follow the ad- hesive manufacturer’s instructions re- garding mixing, open and closed cur- ing time, and usable temperature ranges. to 1-5. BONDING PRECAUTIONS. Satis- factory bond joints in aircraft will develop the full strength of wood under all conditions of stress. To produce this result, the bonding op- eration must be carefully controlled to obtain a continuous thin and uniform film of solid ad- hesive in the joint with adequate adhesion and penetration to both surfaces of the wood. Some of the more important conditions in- volve: Par 1-4 Page 1-5PDF Image | AFS-640
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