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Validation of HVOF Thermal Spray Coatings as a Replacement for Hard Chrome Plating on Hydraulic/Pneumatic Actuators

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Cost and performance rept.

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Electrolytic hard chrome EHC plating is a technique that has been in commercial production for over 50 years. It is a critical process that is used both for applying hard coatings to a variety of aircraft components in manufacturing operations and for general re-build of worn or corroded components that have been removed from aircraft during overhaul. Chromium plating baths contain chromic acid, in which the chromium is in the hexavalent state, with hexavalent chromium hex-Cr or Cr6 being a known carcinogen. During operation, chrome plating tanks emit a hex-Cr mist into the air, which must be ducted away and removed by scrubbers. Wastes generated from plating operations must be disposed of as hazardous waste and plating operations must abide by U.S. Environmental Protection Agency EPA emissions standards and Occupational Safety and Health Administration OSHA permissible exposure limits PEL. High-velocity oxygen-fuel HVOF thermal spray technology can be used to deposit both metal alloy coatings and ceramicmetals cermets such as tungsten carbidecobalt WCCo that are dense and highly adherent to the base material. Previous research, development and validation efforts had established HVOF thermal spray coatings as the leading candidates for replacement of hard chrome. This led to industry acceptance of HVOF WCCoCr and WCCo in place of hard chrome for landing gear, to the point that landing gear on most new aircraft designs are now specified with HVOF. In addition, in overhaul operations these coatings can be built up to thicknesses needed for dimensional restoration, as is currently done with EHC. HVOF systems are commercially available and installed in several depots, and there are numerous commercial vendors supplying the OEM community. Although HVOF coatings are now coming into wide use for landing gear, their qualification as an acceptable replacement for EHC plating on actuators has not been adequately demonstrated.

Subject Categories:

  • Economics and Cost Analysis
  • Coatings, Colorants and Finishes
  • Test Facilities, Equipment and Methods

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