The variation in friction and leakage of some commonly used seal designs consisting of a combination of PTFE and elastomer components is considered for conventional hard chrome plated and HVOF (High Velocity Oxygen Fuel) coated countersurfaces. The study will show through experimental testing that the use of elastomer materials in the rod sealing of landing gear shock absorbers is valid as long as the surface texture is adequately specified and the coated countersurface is free from defects associated with the HVOF process. Frictional instabilities associated with operation in a short stroke regime are also discussed and real time measurements of the friction profile as a function of stroke are presented. It is shown that there is a critical velocity present for a given tribo-combination (seal-countersurface) and when exceeded, friction behaviour becomes fully transient as the instabilities at the stroke extremities appear to propagate over the stroke. The tests conducted within this study have evaluated two commonly used seal types for application within an aircraft landing gear shock absorber rod sealing arrangement. The use of coatings deposited using the HVOF process have been evaluated with these seals for replacing the conventional electroplated hard chrome surfaces and the following conclusions can be drawn: 1. Refinement of the surface texture parameters within the material ratio curve has allowed the use of elastomer components to be used with confidence on hard coatings such as WCCoCr and NiCrBSi countersurfaces for sliding tube components of landing gear. 2. Friction behaviour of reciprocating seals under conditions of short stroke application display large frictional instabilities that cause the friction force to become fully transient as the velocity is increased. 3.Leakage results for Seal 1 are very low when compared with Seal 2 which has very high leakage close to the limit of 1 drop per 25 cycles as specified by the SAE standards. Current work is underway to evaluate low temperature seal performance at temperatures down to -50 deg C static operation and -30 deg C for continuous dynamic sealing. The variation in leakage is particularly important at low temperature and this will be reported on in the future work as well as velocity-pressure measurements that are not discussed here.
Performance of rod sealing systems using chrome replacement coatings in landing gear shock absorbers, under conditions of short stroke reciprocating motion
Leistungsfähigkeit von Stangendichtungssystemen mit Chromsubstitutionsbeschichtungen in Stoßdämpfern von Flugzeugfahrwerken unter den Bedingungen einer oszillierenden Kurzhubbewegung
2009
18 Seiten, 14 Bilder, 3 Tabellen, 18 Quellen
Conference paper
English