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Gear Refurbishment, An Economical Approach for Aerospace Overhaul & Repair
A program to repair gear teeth was initiated for AlliedSignal's Power by the Hour customers. Repair turnaround times were becoming more critical as the availability of new gears for the gas turbine engine overhaul and repair depot became scarce. We decided to partner with Air Gear Industries International because they are an FAA/JAA approved repair facility and have had considerable experience in the refurbishment of aerospace gearing. Most other gear manufacturers did not want to participate because of the paperwork and liabilities involved in obtaining FAA approval for FAA repairs. Also, because of the small number and variety of gears, it would not be economical for a production facility to participate in this program. Power gears of AGMA quality Q11 - Q13 were chosen to begin the program because the need was greatest and it would be the most rewarding even though it would also be the most challenging since minimum stock removal would be paramount to a successful rework. A number of gears from the Coast Guard fleet of helicopters were reviewed and based on knowledge of the manufacturing stock removal, blueprint case depth, and Material Review Board actions, it was concluded that most of the gears were reworkable. Working together with Air Gear, an acceptable procedure for rework ensued including the establishment of inspection requirements. The refurbishment procedure was often more involved than just reprofiling the gear teeth. It also included honing, chrome plate and regrind of bearing journals, and unbolting and rebolting of two gears. In addition, a marking procedure for tracking and repair limits had to be established. A 150 hour or 1000 cycle engine test was also required before final approval could be issued. To accommodate AlliedSignal's requirements for quality and delivery, Air Gear used their specialized grinding machines which they had developed for gear refurbishment. These machines can be dedicated for individual parts and be available and ready whenever a part is received. With a long term commitment from AlliedSignal, Air Gear could justify dedicating these machines to the work at hand. With the success achieved in the Coast Guard program we have gone forward onto the regional fan jet program, the ALF 502/507 engine which has even more stringent requirements for gear tooth stock allowance and profile tolerances.
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