References cited in this section

1. M. Rubinstein, Electrochemical Metallizing, Vinmar Press, 1987

2. J.C. Norris, Brush Plating: Part I, Metal Finishing, July 1988, p 44-48 Applications

In many cases, an operator brush plates only one part at a time. Nevertheless, selective plating is an effective and economical electroplating process when used in application for which it is designed. These include plating of parts that are too large to immerse in solution, plating a small area of a larger component, and touchup and repair of components, large or small, that would cost too much to strip and remanufacture. The largest parts ever plated are building domes and church steeples, up to about 1390 m (15,000 ft2), in copper, nickel, and gold. The smallest are cells on rotogravure rolls, 0.076 by 0.038 mm (0.003 by 0.0015 in.). The process can also perform at high production volumes, such as 4,000,000 parts/day for nickel-plated brass electrical contacts on alkaline batteries.

Cosmetic or decorative applications involve parts that range in size from jewelry to large exterior structural domes and lobby interiors.

Corrosion protection applications allow touchup of small rusted or corroded areas without disassembly. Examples include aircraft landing gears, virtually all kinds of machinery, mixing vats, and tanks. Parts too large to fit into plating tanks are almost always good candidates.

Repair of electronic parts is usually done with precious metals, such as gold, silver, and rhodium. Typical applications are repair of broken circuits and small circuit board contacts, and application of conductive coatings on high-

voltage sources. Selective plating minimizes scrap, allows immediate repair on site, and does not require immersion of the entire part in solution.

Restoration of large parts is a natural application for selective plating if the parts are permanent fixtures that cannot be removed or disassembled. The process makes it possible to repair and restore dimensions or apply a wear-resistant or corrosion-resistant surface to just about any part. Portable systems allow access to parts at great elevations and in remote areas, such as protecting the inside surface of a large mixing vessel and repairing critical equipment on ships at sea.

Specialized applications of selective plating involve unusual environments or the need for certain properties, such as conductivity or impact resistance. Examples include blocking radio frequency interference with a soft, radiowave-resistant material such as tin; plating aluminum to facilitate soldering; plating machinery components to ensure initial lubrication; and even plating test probes to resist extreme environmental conditions.

Following are examples of specific applications of selective plating and anodizing:

• Adhesive-bonded aircraft parts: anodizing (phosphoric acid) used to prepare aluminum skins and frames for adhesive repair of damaged skins

• Aircraft engine components: sulfamate nickel on high-temperature nickel alloys used as a prebrazing operation for second-stage turbine vanes, blades, and stator segments; also used for restoration of bearing area on turbine exhaust case, bearing housing and support, and cooling air duct

• Aircraft landing gears: cadmium touchup; on 2014 aluminum, hard coat on inner diameter of oil air strut used to accommodate press fit of bronze bearing

• Aircraft skins: anodizing (chromic acid or sulfuric acid) used to repair damaged chromic-acid and sulfuric-acid coatings, respectively

• Aircraft wheel: anodizing (sulfuric acid) used to correct a mismachined bearing bore

• Bus bars: silver on copper or aluminum used for electrical contacts

• Electric motors: nickel and copper used for dimensional restoration of motor shafts and bearing end caps; tin used for low-power motors to reduce vibration; and platinum, gold, or rhodium used to increase wear life and reduce arcing of commutators and slip rings

• Hydraulics: copper, nickel, cobalt, or chrome used to repair steel- or chrome-plated hydraulic components, often without disassembly

• Metal recovery systems: platinum coating used on titanium permanent anodes

• Missile launch rail: hard coat used on a 6061-T6 surface to bring dimensions into tolerance and provide wear resistance and corrosion resistance

• Mold repair: gold plating used on plastic molds where corrosive gases attack existing chrome; final plating of chrome used to repair rubber molds; copper, nickel, and cobalt used to repair other types of molds

• Printed circuit boards: gold over copper used on contact tabs, fingers, etc.

• Printing presses: copper, silver, nickel, cobalt, or chrome plating used to repair cylinders; in-press overhaul plating of side frame used for bearing retention and to correct out-of-concentricity condition

• Railroad axles: nickel used for dimensional restoration on bearing journals and sealing wear ring grooves

• Space shuttle manifolds: up to 0.5 mm (0.20 in.) of copper used to increase wall strength of a nickel-electroformed hydrogen-oxygen manifold for the prototype "Columbia" engine

• Steel mill coating line: cadmium, zinc, or nickel-zinc used to increase the thickness of the protective coating on steel sheet moving at 137 m/min (450 ft/min)

• Submarines: rhodium and gold used on copper slip rings

• Turbines: cobalt, nickel, nickel/cobalt, or chrome used to restore dimensions on bearing and seal surfaces; silver used to repair steam cuts on horizontal seal surfaces

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