2012 Issue

48 must be periodically replaced. During a landing gear’s lifespan, it is routinely sent back to the shop, disassembled, stripped of paint and cadmium, and inspected. Before being returned to use, the cadmiumplating is replaced. All that stripped cadmiummust also be disposed as hazardous waste. Cadmium’s corrosion protection virtues have outweighed its hazardous vices, be- cause no alternative was as effective and versatile. (Other alternatives have been developed, but they all include limita- tions such as line-of-sight application.) LHE Zn-Ni (Low Hydrogen Embrittlement Zinc-Nickel) electroplating has challenged cadmium’s performance and versatility. Zinc-Nickel plating has been used as a corrosion prevention coating for over 20 years in the automotive industry. Unfortu- nately, those early incarnations of the zinc- nickel coating process caused hydrogen embrittlement in the high-strength steels used for landing gears. Hydrogen embrittlement occurs when the tiny hydrogenmolecule is absorbed into the crystalline matrices of high-strength steel. The intrusive molecule can then cause brit- tle fracture under tensile stress. Hydrogen embrittlement is a concern when electro- plating most metals onto high-strength steel — including cadmium. To mitigate hydrogen embrittlement, cadmium is pro- cessed so that the metal is deposited in a porous film. Then the part is hustled into a bake oven, and the hydrogen is driven out of the metal’s matrices with heat. The LHE Zn-Ni process creates a purplish coating that is porous enough for the hydrogen to escape during a bake. And it performs as well as or better than cadmium in corrosion tests. LHE Zn-Ni’s ability to match or exceed cadmium’s qualities has been extensively tested. Over six years ago, the USAF Land- ing Gear Engineering Group and Hill’s De- pot Repair EngineeringGroup teamedwith ES3 in Layton, UT and Boeing on a Small Business Innovative Research (SBIR) project to evaluate Dipsol’s new LHE Zinc-Nickel electro-plating process as a cadmium re- placement. ES3 conducted corrosion and processing tests using small plating tanks at Boeing and a prototype production line at Hill AFB. Testing included fatigue (ASTM E4, ASTEM E380, ASTM E467), hydrogen embrittlement (ASTM F 519-93), re-embrit- tlement (ASTMF 519-93), liquidmetal/solid metal embrittlement (LME/SME) (ASTM F 519-93), corrosion (ASTM B 117-94), SO 2 corrosion (ASTMD1654-92), General Prop- erties and Paint Adhesion (AMS-QQ-P-416), and Brush Plating (MIL-STD-865). Then they repeated the tests several times to ensure statistically significant results. With the completion of preliminary testing, evaluation, and development, Hill AFB has awarded ES3 a contract to install a full-scale LHE Zn-Ni electro-plating line in their electroplating facility. Once installation is completed, landing gear components from multiple aircraft will be plated with LHE Zn-Ni and observed in a 24-month field service evaluation. Aircraft stationed at coastal locations with aggressive cor- rosive environments will be selected to provide the best possible evaluation. After testing is completed, parts from fighters, bombers, and cargo planes will be switched one-by-one from cadmium to LHE Zn-Ni. The switch will reduce worker exposure to carcinogenic cadmium, reduce potential for cyanide gas release, and reduce cadmium hazardous waste. And one day, it may even eliminate them. The Zn-Ni project has been recognizedwith several prestigious awards including the General Bernard P. Randolph Engineering Team Award and the General Thomas D. White Sustainability Award.  Ruth Schaefer works as a chemical process engineer in Landing Gear Maintenance at Hill AFB. She has a BS and MS in Chemical Engineering from the University of Wyoming. She spentayearworking intheNavynuclearshifttestengineering departmentatthePugetSoundNavalShipyardbeforemoving to Utah to work in Explosives Research & Development at Thiokol (now ATK). Dave Frederick is the lead engineer for all projects dealing with testing at the Landing Gear Test Facility (LGTF) at Hill AFB. He provides lead consulting for material and process concerns pertaining to all AF landing gear components. He has a BS in Chemical Engineering from the University of Wyoming. GO GREEN | continued from page 47 C-5 Galaxy Nose Landing Gear Test plating landing gear components with Zn-Ni