Aircraft lockers benefit from strong adhesives

An aircraft maintenance company is using a flame retardant, bromine-free epoxy paste to reinforce mechanical fasteners on aircraft baggage lockers. Dean Palmer reports A leading aircraft maintenance company is using a new, low density, bromine-free, flame-retardant adhesive to reinforce mechanical fasteners installed in overhead baggage lockers and other honeycomb core parts on the aircraft. Cascade Aerospace is one of the leading aircraft maintenance companies in Canada. Among the latest products now being used at the company is Epocast 1633-A41/B, a low density, bromine-free, flame-retardant epoxy syntactic paste supplied by Huntsman Advanced Materials. Cascade switched to the new epoxy in response to recent environmental regulations governing the formulations used in flame-retardant epoxies. This lightweight syntactic is the result of several years' research at Huntsman, aimed at eliminating the chemical compounds octabromodiphenyl ether (OBDE) and pentabromodiphenyl ether (PBDE) that have typically been used by adhesives manufacturers to produce flame-retardant compounds. In addition to these improved environmental properties, Epocast 1633-A41/B epoxy syntactic products exhibit a compressive strength of 45MPa and are qualified to Airbus AIMS 08-08-001-04 and Boeing BMS 5-28, Type 18, Class 2 specifications. The syntactic paste used by Cascade is grey in colour although materials are also available in light blue, orange and black formulations. Because of their almost continuous, heavy usage, overhead lockers are one of the most frequently repaired aircraft components. Damage is found when the lockers are removed during the strip down on a fuselage inspection. While locker repairs are generally cosmetic, airlines want to keep interiors looking smart and pleasing to passengers. Paul Barnfield, support shop supervisor at Cascade Aerospace commented: "Epocast 1633-A41/B epoxy syntactic is one of the materials we use at Cascade to provide customers with high quality and reliability in aircraft repairs. During our maintenance on narrow body, commercial transport aircraft, we have found that it quickly produces high-strength reinforcement of honeycomb core for secure fastener installation." As part of its refurbishment programme on the lockers, Cascade reinforces honeycomb core at points that will be used to mount the locket in the aircraft. Using a manual dispensing gun, a technician fills a pre-drilled hole - covered with an insert tab - with Epocast 1633 epoxy resin and hardener. Syntactic paste is added until the material flows from the other side of the tab, indicating that the cavity is full and the reinforcement complete. The paste has a 2-5 minute work life and sets quickly at room temperature. After the epoxy syntactic cures, the insert tab is removed, excess epoxy is sanded over and the locker door is reinstalled. The unit is then repainted before being put back onto the aircraft. The 50ml dual cartridge used for dispensing the epoxy syntactic ensures thorough mixing of the components and neat dispensing of the paste with minimal waste. Cartridges can also be resealed and used again with a new nozzle. "A further benefit of the material is its formulation without bromine, which satisfies the latest environmental standards governing flame-retardant epoxies," Barnfield added.