Brush plating, also known as "selective plating" is an electrochemical process with systems that are used to electroplate, anodize and electropolish localized areas on both OEM components and parts that need coatings for repair and dimensional restoration.

Brush plating systems are portable. Unlike their tank counterparts, brush plating systems use very small volumes of solution (usually only 1-2 gal) and hand-held tools to apply the deposits and coatings onto localized areas. These hand-held tools are covered with an absorbent material that is saturated with a solution and then brushed or rubbed against the part.

As with tank plating, which has different baths for the various operations involved, brush plating requires different hand-held tools to be used for each different solution in the operation.

A portable power pack (rectifier) provides the direct current required for all the processes. The power pack has at least two leads. One is connected to the plating 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 plating tool is touching the work surface.

The work surface is prepared by conducting a series of preparatory steps that are performed with the same types of tooling and equipment used for the final finishing operation. As with a tank plating process, brush plating requires good preparation of the work surface to produce an adherent deposit.

Why Use Brush Plating?
Flexibility and Versatility. You can use this portable process virtually anywhere in the shop for out in the field. It can be taken right to the job site to perform operations such as plating nickel onto the ID of a large gear sprocket, touching up defective cadmium on aircraft landing gear, resizing worn stamping equipment, plating crankshaft bearing diameters and repairing scores and pits in valve stems at nuclear power plants. It is very easy to mechanize or automate for production plating or anodizing applications.

Save Time and Money. Because you can take the process to the part, you can eliminate the shipping costs and reduce the turnaround time to have a completed part. You are not at the mercy of the tank plater’s schedule. Additionally, you can minimize disassembly/reassembly, and you may not have to take the part out of the system in order to apply the coating or deposit.

Other Methods Will Not Work. Brush plating offers several advantages over its biggest competitors—tank plating, flame spray and welding.

Masking is Minimized. Extensive masking is required in order to plate or anodize a localized area on a large component in a tank. Brush plating requires only minimal masking of the area adjacent of that to be plated, thus reducing processing time. Quite often, parts are even physically too large to fit into a tank.

No Heat is Involved. Both flame spray and welding operations develop tremendous amounts of heat that can distort the part. Brush plating and anodizing do not, and, because of the ability to accurately control deposit thickness, finish machining or grinding operations are not always needed. In many cases, parts can be plated right to the desired thickness and then put into service.

The Evolution of Brush Plating
Brush plating has come a long way from the early days of tank plating when it was a common practice to touch up bad spots on plated parts using solution saturated rags wrapped around pieces of pipe. Today, brush plating and anodizing systems are used to selectively apply engineered deposits and coatings in very precise thicknesses for both OEM and repair applications.

Brush plating and anodizing are now completely divorced from their tank counterparts, although some of the equipment and terms still resemble those used in tank processes. Tools, equipment and solutions, however, cannot be used interchangeably between brush and tank systems.

Since it is more difficult to control temperature and current density in portable finishing processes than in tank processes, it was necessary to develop complete, integrated portable finishing systems for commercial applications. These systems were developed to be used by operators who are not familiar with tank finishing techniques.

Today, brush plating systems are available for electroplating, anodizing, hard coating and electropolishing. These systems vary in their degree of sophistication and coating capabilities.

Small pen-type systems apply only flash deposits on small areas. Larger, more sophisticated systems use power packs with outputs up to 500 amps and are capable of producing excellent quality finishes and high thicknesses on large surface areas. Automated systems are also available for high-volume production applications.

Acceptance
In 1956, the first North American commercial specification was issued for brush electroplating. This formal recognition of a portable process as a viable alternative to tank processes was an important milestone in the development and acceptance of brush plating processes. Government specifications, MIL-STD 865 and NAV-SHIPS 0900-038-6010, were issued in 1969 and 1970, respectively. With more than 100 commercial specifications now documented for brush plating alone, it is clear that brush plating processes have gained widespread acceptance.

Companies manufacturing, using and repairing products such as aircraft, electric motors, dies and molds, ships, pumps, valves, printing presses, paper mills, railroads and power generation and transmission equipment have embraced brush plating by writing specifications and approvals for its use.

The following specifications are representative of the current acceptance of brush plating processes:

Summary
Brush plating is a valuable tool for plating OEM components, as well as for the salvage and repair of parts used across a broad range of industries. It's a flexible process that offers many advantages over competitive processes. And, because it's portable, it can save both time and money. PFD