Evaluation of Chrome Rod Alternative Coatings for Aerospace Sealing Applications Laboratory Hydraulic Seal and Rod Coating Testing

摘要

Several years ago Greene Tweed & Co. (GTC) conducted an evaluation of chrome rod alternative coatings for the U.S. Air Force. The result of that screening evaluation eliminated several candidate coatings and left tungsten carbide cobalt the clear, preferred coating. Since that time, various blends of tungsten carbide cobalt have been evaluated in numerous laboratory and flight test programs, and are rapidly gaining acceptance for OEM and reworked components. Several large aircraft manufactures now provide these coatings as standard on landing gear, flight control and utility hydraulic systems. The current evaluation, summarized in this report, was conducted for McClellan Air Force Base in coordination with the HCAT~(1) group. The HCAT group is a government and industry cooperative effort to research and evaluate alternative coatings for chrome plating. The group is currently headed by the U.S. Navy at the Naval Research Laboratory, coordinated and funded by all U.S. Military services. Industry participants include airframer, engine, landing gear and subsystem manufacturers. The current GTC test is in support of this effort and a logical continuation of the phase 1 screening program. This recent evaluation provides insight for long-term endurance and performance of current state-of-the-art sealing technology with these new coatings. The candidate coatings were evaluated for 50 million cycles. The stroke and load profile (duty cycle) is shown in Figure 1 and simulates a typical hydraulic flight control actuator. This duty cycle is a composite profile of commercial and military type aircraft. The performance criteria consisted of leakage, wear and life of both the candidate coatings and paired seals. The candidate coalings were tested concurrent with standard chrome as the baseline for comparison.