Published 5/1/2011

Touching Up: Selective Brush Plating in the Field

Selective brush plating is much more than just a touch-up repair process. Hundreds of applications are using the selective brush plating process to provide surface enhancement coatings to aircraft OEM applications.

Edited by: PF Editorial Team

Touching Up

A Sifco SP30 ZPower Pack is used in the field to brush plate parts in the aerospace and defense industry.

Helicopter Axle with 2 journals selective brush nickel plated

Brush-plated nickel sulfamate is used on an AE 3007 2nd stage vane as a prebraze coating on high temperature material aircraft components as required by General Electric, Pratt & Whitney and Rolls Royce.

F35 Fuel Fitting component, where small bores are selective brush nickel plated prior to brazing.

Common Uses

The process is known to be portable, fast, easy to use, reliable, environmentally friendly and requiring minimal masking. It is used in many aircraft OEM applications including landing gear, engines, instruments and accessories, hydraulics and avionics. These applications require adding metal to existing surfaces for a variety of reasons. Five of the most common uses are:

Enhancing corrosion protection
Improving braze characteristics with a flash of nickel
Improving surface properties
Restoration of tolerance conditions
Repairing aluminum components

The Process

Brush plating is a contact method of electroplating in which metals are deposited onto localized areas using an absorbent pad-wrapped anode saturated with a proprietary plating solution (selective anodizing can be accomplished using a similar technique). Brush techniques are suitable for simple geometric shapes such as outer diameters, interior diameters and flat surfaces.

The basic items needed are a portable rectifier (power pack), plating tools, masking materials and solutions. For electroplating, the part becomes the cathode and is connected to the negative terminal of the power pack. The positive terminal is connected to a “tool” handle, and an anode that is wrapped with an absorbent material that provides insulation and wear resistance as the tool moves over the part. The appropriate solution -- which can be fed with a pump -- completes the electrical circuit. The deposition rates can be about 0.035 inches/hour, which means quick plating of the part.

Base material specific procedures have been developed to ensure excellent adhesion of the deposit onto all of the commonly used metals, but identifying the substrate is crucial as the appropriate preparatory procedure is determined by both the substrate and the plating solution selected. Mild steel, high alloy steels, cast iron, copper, nickel, aluminum, and stainless steels all require different preparatory treatments.

The surface is prepared only where the plating is required. Masking fixtures can be used for repetitive or high volume applications. The area to be masked must be cleaned to ensure that masking materials will adhere. Grease and soil are removed with a solvent; steel wool, emery paper, wire brushing, or sand blasting is used to remove scale, rust or tarnish. The parts are then ready for electrocleaning, etching, desmutting, and/or activation in accordance with supplier procedures.

The variety of available selective plated deposits provides alternatives for excellent corrosion protection and hardness and wear resistance depending upon the deposit plated. In most cases the deposits meet or exceed all the performance requirements of federal, military and commercial specifications for tank plating. There are also comparable standards written specifically for brush plating.

In addition, work continues on advancing the selective brush plating process by developing and improving deposits and the process itself through advancements in plating onto titanium and the development of a cobalt chromium carbide metal matrix deposit used in high temperature applications.

Scott Peterson is SIFCO Applied Surface Concepts’s aerospace market manager. For more information, contact them at 800-765-4131, or at sifcoasc.com.