Taking plating technology to the airplane

Taking Plating Technology to the Airplane By Derek Vanek February 1998 Amultitude of coatings are available today to protect or to enhance the performance of aircraft components. Uses include corrosion protection, increasing wear resistance...


Taking Plating Technology to the Airplane

By Derek Vanek

February 1998

Amultitude of coatings are available today to protect or to enhance the performance of aircraft components. Uses include corrosion protection, increasing wear resistance, improving electrical conductivity, enhancing lubricity, increasing hardness, or improving the adhesive bond between cemented parts. A majority of these coatings and deposits are originally applied to the individual components at facilities that use large tanks to electroplate or anodize.

Once the components are put into service and are subject to normal wear and tear, refinishing may be required. This usually consists of removing the damaged or worn component from the aircraft and sending it to the plating shop to be stripped and then replated or reanodized — even if the damage or wear is localized. In many cases disassembly is relatively simple, but in some instances it can be very time consuming — bordering on impractical.

One such instance is the damage that can occur to the chromic acid anodized coatings on aircraft skins. For example, the wing droop leading edge on the Falcon Jet HU-25A is chromic acid anodized using the Bengough Process. The coating may be damaged from in-service use or it may even be damaged during a routine maintenance operation.

In one case, an operator was removing corrosion products from cadmium-plated steel fasteners. In the process, they completely removed the anodized coating for up to 3/8 of an inch away from roughly 1200 fasteners that ran the length of the wings. The $150,000 option was to disassemble, strip, reanodize, and reassemble. The more attractive option was to selectively, brush chromic acid anodize the individual areas right on the wing.

Brush plating encompasses a family of portable electrochemical processes that are used on aircraft in both OEM and repair applications. This includes systems that are used for on-site electroplating, as well as portable anodizing and electropolishing. These systems are set apart from traditional tank finishing processes because they can be performed anywhere — in the shop or out in the hangar, and the parts can be plated or anodized without removing them from the aircraft.

How does it work?
Brush plating and anodizing operations, in their simplest forms, resemble painting. The operator soaks or dips the tool in a solution and then brushes or rubs it against the surface of the material that is to be finished. The tools are covered with an absorbent material that holds solutions so they can be applied to the work surface.

GraphicA portable power pack provides a source of direct current for all the processes. The power pack has at least two leads. One lead is connected to the tool and the other is connected to the part being finished. The direct current supplied by the power pack is used in a circuit that is completed when the tool is touching the work surface. The tool is always kept in motion whenever it is in contact with the work surface. Movement is required to ensure a quality finish.

Work surface preparation is usually accomplished through a series of electrochemical operations. These preparatory steps are performed with the same equipment and tool types that are used for the final finishing operation. Good preparation of the work surface is as important as movement of the tools to produce a quality finish.

Adhesion
The adhesion of brush electroplates is excellent and comparable to that of good tank plating on a wide variety of materials including steel, cast iron, stainless steel, copper, high temperature nickel-base materials, etc. When plating on these materials, the adhesion requirements of federal and military specifications are easily met. Limited, but occasionally useful, adhesion is obtained on metals that are difficult to plate such as titanium, tungsten, and tantalum.

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