Development of Cad Plating Replacement with Zinc Nickel on High Strength Steel Components
ABSTRACT: Landing gear components manufactured from high strength steel alloys require sacrificial protective coatings to perform safely in service. Cadmium has been the standard coating for such components for decades, but is a known carcinogen and has been targeted for elimination by the USAF. An experimental Zn-Ni coating was tested in Phase I as a replacement for cadmium. Results showed the Zn-Ni coating had comparable performance to cadmium in the areas of corrosion, fatigue, and hydrogen embrittlement (HE) testing. The main objective of this Phase II.5 project is to demonstrate and validate a full scale prototype LHE alkaline Zn-Ni production plating line to ensure operational robustness of the process, which has performed well in small scale prototype production line tests. Scale up testing is required to ensure that plating parameters, such as, current density, conformal anode requirements, bath agitation, plating bath stability, and coating uniformity are within specifications for landing gear parts in a full scale production process line. During the installation of the full scale production line existing equipment located at Hill AFB building 505 will be demolished, removed, relocated and rebuilt to accommodate the 3200 gallon LHE alkaline Zn-Ni production plating line. An initial site preparation meeting shall be conducted to organize the work flow to minimize down time of the current plating lines and relocation of equipment (i.e. perform major demolition, relocation, and installation work on long weekends when production is not operating Cd and iridite plating lines). Upon final installation, the Zn-NI plating line will be qualified IAW USAF-DRW-201027456 prior to production plating. Additionally quality conformance checks shall be performed during initial plating runs of landing gear components. BENEFIT: The USAF"s landing gear depot repair facility is located in building 507 at Hill AFB, UT. This facility uses a significant amount of cadmium during electroplating steel components. Although IVD aluminum has been used extensively as an alternative for limited landing gear components, it has several disadvantages: IVD is an external process Internal Diameters (ID), such as Axle ID"s, cannot be coated The IVD chambers are high maintenance equipment The IVD chambers are size limited several large landing gear components will not fit physically in the chamber The IVD chambers must be loaded with like-parts to produce specification results loading the chamber in this manner is not possible in an overhaul environment. The IVD coating is susceptible to Hydrogen Re-Embrittlement after exposure to aqueous cleaners. The lubricity of IVD aluminum is different from Cadmium, with a significantly different torque-tension relationship for threaded joints & fasteners. For these reasons, IVD aluminum coatings can never fully replace cadmium. However, the Zn-Ni electroplating process would be a drop-in replacement for the existing cadmium. Fully implemented, this would free up an entire section of the USAF landing gear facility currently dedicated to IVD operations. The Zn-Ni process also has far lower environmental impact compared with cadmium, and will enable the industry to cease cadmium usage. Ultimately, the results of this project will allow landing gear components to be plated with LHE alkaline Zn-Ni and comply with USAF environmental objectives as well as meet all performance requirements of the original designs.
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