Brush electroplating is a process where a metal coating is applied using a brush or pad connected to a power source.
The plating solution is supplied through the brush and applied directly to the surface.
It is used for repair work, selective plating, and coating specific areas.

Brush electroplating

Brush electroplating (also called selective electroplating or tampon electroplating) is a specialized electroplating process in which a brush or absorbent pad soaked with electrolyte solution is moved over a specific area of a workpiece while electric current deposits a metal coating.

Unlike tank electroplating, the object does not need to be immersed in a plating bath. The coating is applied only where required, making this process ideal for localized repair, selective coating, and maintenance work.

Definition

Brush electroplating is an electroplating process in which a metal coating is deposited onto selected areas of a workpiece using a handheld brush, electrolyte solution, and direct current.

Principle of brush electroplating

Brush electroplating also works on the principle of electrolysis.

During the process:

The workpiece acts as the cathode
The brush acts as the anode
The brush is covered with an absorbent material soaked in electrolyte
Electric current causes metal ions to move and deposit on the workpiece surface

As the brush moves continuously over the area, metal builds up layer by layer.

Main components of a brush electroplating setup

1. Brush or plating tool

The brush is usually made of:

Graphite
Stainless steel
Conductive materials

It is covered with:

Felt
Cotton
Absorbent fabric

Functions:

Carries electrolyte
Transfers current
Applies coating locally

2. Electrolyte solution

Contains dissolved metal salts.

Examples:

Nickel solution
Copper solution
Gold solution
Silver solution
Zinc solution

Function:

Provides metal ions for coating.

3. Workpiece (cathode)

The component to be coated acts as the cathode.

Examples:

Shafts
Machine parts
Mold surfaces
Aircraft components

Connected to the negative terminal.

4. DC power supply

Provides direct current for electrolysis.

Voltage and current are adjusted according to coating requirements.

5. Connecting cables

Provide electrical connection between the power source and system components.

Working process of brush electroplating

Step 1: Surface preparation

The workpiece surface is cleaned thoroughly.

Contaminants removed include:

Grease
Oil
Oxides
Dirt
Rust

Methods:

Degreasing
Mechanical polishing
Chemical cleaning

Surface preparation is critical for good adhesion.

Step 2: Masking (if needed)

Areas that should not be plated are covered.

Materials used:

Tape
Protective coatings
Masks

Purpose:

Ensure only selected regions are plated.

Step 3: Electrolyte application

The absorbent brush is soaked in electrolyte solution.

Step 4: Current application

Direct current is switched on.

At the anode:

M → M⁺ + e⁻

At the cathode:

M⁺ + e⁻ → M

Metal ions deposit on the workpiece.

Step 5: Brush movement

The operator moves the brush continuously over the target area.

Purpose:

Uniform coating
Avoid overheating
Maintain even deposition

Step 6: Rinsing and finishing

After plating:

Surface is rinsed
Dried
Polished if required

Metals commonly used in brush electroplating

Examples:

Nickel
Copper
Gold
Silver
Zinc
Chromium
Tin
Cadmium

Selection depends on application requirements.

Applications of brush electroplating

Repair and maintenance

Used to repair:

Worn shafts
Bearings
Machine parts

Aerospace industry

Used for:

Aircraft repair
Component restoration

Mold repair

Used to restore:

Dies
Molds
Tool surfaces

Electronics

Selective coating of:

Connectors
Contacts

Decorative applications

Localized gold or silver coating

Advantages of brush electroplating

1. No large plating tank required

Portable equipment can be used.

2. Localized coating possible

Only desired areas receive plating.

3. Suitable for repair work

Can restore worn surfaces.

4. Portable process

Can be used at installation sites.

5. Lower chemical consumption

Uses smaller amounts of electrolyte.

6. Minimal disassembly

Large components often do not need removal.

Disadvantages of brush electroplating

1. Not suitable for large-area coating

Large surfaces become time consuming.

2. Requires skilled operator

Movement affects coating quality.

3. Lower productivity

Not ideal for mass production.

4. Coating thickness variation possible

Uneven motion can produce inconsistent deposition.

Comparison: Brush vs Tank electroplating

Feature	Brush electroplating	Tank electroplating
Process area	Localized	Entire object
Equipment	Portable	Fixed tanks
Chemical use	Lower	Higher
Production volume	Small	Large
Repair work	Excellent	Limited
Automation	Low	High

Conclusion

Brush electroplating is a portable and selective electroplating process used mainly for repair, maintenance, and localized coating applications. It is especially useful where complete immersion is difficult and only specific areas require metal deposition.