New Arc Wire Approvals for Aircraft Power Plant Overhaul

Arc spray systems are increasingly used in the overhaul of aircraft engine components and auxiliary power units. The increasing use of arc spray over plasma for metallic coatings has created a demand for new wire approvals. The chemistry is already established as a powder and it is a matter of conversion to a wire and the arc spray process. The increasing popularity of the arc spray process is due to its superior bond strength and microstructure that exceed those of plasma. In one case, there is a two and one-half percent porosity requirement for the arc spray and up to 15% is allowed for plasma. This density approaches HVOF quality requirements. This paper will discuss some historical background of the process, what is approved and then move on to the new materials that are submitted for approval. Microstructures and bond strengths will be presented and some information about a proprietary method to solve a coating problem in the aircraft overhaul industry of long standing. The paper will also discuss new advances in arc spray systems and materials, which makes these systems amenable to replacing plasma sprayed coatings.

Some Notes on Aircraft Overhaul and Maintenance

Commercial aircraft, in common with all public transport, must be subjected to routine inspections and regularly overhauled in the interest of both safety and economy.Aircraft maintenance and overhaul are not just the domestic concern of the organisation doing the work. There must be adherence to Standards approved by the Air Registration Board on behalf of the Ministry of Civil Aviation; and these Standards are the national interpretation of some of the directives issued by the International Civil Aviation Organisation as part of the international agreements regulating air safety. The regulations are neither rigid nor detailed, but they exist for the protection of air travellers against the remote chance of an operator failing to maintain airworthiness. In particular, they call for regular maintenance checks and, to procure annual reissue of the Certificate of Airworthiness, an annual overhaul or its equivalent.