Brush plating is an electrochemical process that uses systems to electroplate, anodize, and electropolish localized areas on both OEM components and parts that need coatings for repair and dimensional restoration.
Brush systems are portable. Unlike their tank counterparts, brush plating systems use very small volumes of solution (usually only one or two gallons) 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. Brush plating requires different hand-held tools 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 tool and the other is connected to the part. 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 work surface is prepared using the same types of tooling and equipment that are 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?
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| Typical benchtop brush plating setup |
Flexibility and versatility. You can use this portable process virtually anywhere in the shop or out in the field. It can be taken right to the job site to perform operations such
as plating nickel onto localized areas of the international space station, touching up defective cadmium on aircraft landing gear, resizing worn stamping equipment, crankshaft bearing diameters, and repairing scores and pits in the valve stems at nuclear power plants.
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 the 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 to the plated part, 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. Because of the ability to accurately control deposit thickness, finish machining or grinding operations is 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
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| Plating Nickel on a node of the International Space Station. |
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 for 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 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.
Acceptance
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| Plating a pre-braze, sulfamate nickel deposit onto a turbine stator segment. |
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:
| MIL-STD 865 |
MIL-STD 865Selective
(Brush Plating)
Electrodeposition |
| MIL-STD 2197(SH) |
Brush Electroplating
On Marine Machinery |
| AMS 2439 |
Selective (Brush)
Nickel Plating
Low Stressed
Hard Deposit |
| AMS 2441 |
Selective (Brush)
Nickel Plating
Low Stressed
Low Hardness
Deposit |
| MIL-A-8625 |
Chromic (Type I)
Sulfuric (Type II)
Hard Coat (Type III)
Anodizing |
Brush plating is a valuable tool to include in your repertoire of coating processes
for OEM components and for the salvage and repair of parts used across a broad range
of industries. It is a flexible process that offers many advantages over competitive
processes. And because it is portable, it can save both time and money! PFD
