Chrome plating is a popular metal finishing process used to apply a thin layer of chromium onto metal objects. The shiny chrome layer improves aesthetics, enhances corrosion resistance, facilitates cleaning, and increases surface hardness. But what exactly goes into chrome plating?

Chrome Plating Process

Chrome plating involves electroplating a thin layer of chromium onto a metal substrate. The metal object to be plated serves as the cathode in the electrolytic process while the chromium source serves as the anode.

When an electric current is applied, chromium ions in the plating solution deposit onto the positively charged workpiece. The chromium ions are attracted to the object’s surface, where they bond and build up the chrome layer atom by atom.

The key steps in a typical chrome plating process include:

Surface preparation – Thorough cleaning and activation
Plating – Immersing parts in chrome plating bath
Post-treatment – Rinsing, drying, polishing

Proper cleaning and surface activation before plating ensures the chromium deposits evenly and adheres properly. The plating step applies the chrome layer to the desired thickness. Finally, post-treatment removes contaminants and adds final finishes.

Required Materials and Equipment

Chrome plating requires a range of materials, solutions, and equipment to carry out properly. Here are the key items needed:

Plating Tank and Rectifier

Plating tank – Holds plating solution, made of non-conductive plastic or lined steel
Rectifier – Provides DC current for electroplating process

Anodes

Lead anodes – Pure lead anodes supply chromium ions
Titanium anodes – Alternate for creating hard chrome deposits

Plating Solutions

Chromic acid – Provides Cr3+ ions for chromium deposition
Catalysts – Accelerate plating rate; sulfuric acid commonly used
Additives – Refine deposit appearance and properties

Cleaners and Activators

Alkaline cleaners – Remove grease and organic soils
Acid solutions – Activate surfaces for plating; sulfuric acid commonly used

Rinsing Aids

DI water – Removes residuals from parts after each process step
Rust inhibitors – Prevent oxidation between process stages

Handling Fixtures

Racks, baskets, hooks – Suspend parts in tanks during processing
Cathode fixtures – Hold parts and conduct plating current

Safety Gear

Eye and face protection
Acid-resistant gloves, aprons
Fume extractors and respirators

Testing Instruments

Amp meters – Monitor plating current and solution conductivity
Thickness gauges – Ensure proper plating thickness

Step 1 – Surface Preparation

Thorough surface preparation is vital for effective chrome plating. The object’s surface must be completely clean and activated prior to plating to allow even chromium deposition.

Cleaning

All oils, grease, dirt, and organic contaminants must be removed from the surface. Cleaning methods include:

Manual cleaning – Removes gross contamination like dirt and grease
Emulsion cleaners – Soaps suspend and remove oils and organic soils
Alkaline cleaners – Hot alkaline solutions remove oils and soils
Electrocleaning – Uses electrolysis to loosen surface contaminants
Solvent cleaning – Emulsifiable solvents remove oils and other carbon-based soils

Parts are usually cleaned by immersion in a sequence of cleaning solutions with intermediate water rinses. Agitation helps boost soil removal.

Activation

This step etches the surface and removes any remaining metallic and organic contaminants. It creates an active metal surface optimized for plating.

Activation is accomplished using:

Acid dips – Sulfuric or hydrochloric acid solutions activate surfaces
Electrocleaning – Uses anodic current and alkaline solution to clean/etch
Anodic etching – Removes oxides and impurities using reverse plating current

Proper activation exposes a pristine reactive surface for chromium deposition.

Step 2 – Plating

With a prepared surface, the next step is plating. This is where the chrome layer is actually applied onto the object’s surface.

Chrome Plating Solution

The plating solution contains:

Chromic acid – Provides Cr3+ ions for chromium deposition
Catalyst – Accelerates plating rate; sulfuric acid commonly added
Additives – Improve solution conductivity and deposit qualities

The solution temperature is kept around 50-60°C to facilitate proper plating. Lead anodes supply chromium ions into the bath during plating.

Plating Method

The object is immersed in the plating tank and allowed to warm to the solution temperature.
Plating current is applied, typically ranging from 10-1000+ amps depending on part size.
As current flows, chromium ions deposit onto the positively charged workpiece.
Plating continues until the chrome layer reaches the desired thickness.
Solution is agitated to provide even deposition.

Key plating factors like current, time, temperature, and agitation are controlled to achieve a uniform chrome layer with the required thickness and properties.

Step 3 – Post-Treatment

Once plated, the workpiece undergoes several post-treatment steps:

Rinsing

The part is thoroughly rinsed with water to remove plating solution dragout.
Rust inhibitors may be added to prevent oxidation.

Drying

Drying prevents water spots. Parts may be air dried or force dried.

Polishing

Buffing and polishing can enhance the chrome’s luster and smoothness.
Techniques include mechanical polishing, electropolishing, or chemical brightening.

Coatings

A lacquer or wax coating is sometimes applied to prevent tarnishing.

Proper post-treatment removes contaminants and adds final finishes to maximize aesthetics and durability.

Key Process Variables

There are several key process variables that can be adjusted to refine the chrome deposit:

Current density – Measured in amps/ft2. Determines plating rate.
Time – Plating duration to achieve desired thickness.
Temperature – Typical range is 35-65°C. Affects plating speed and deposit structure.
Agitation – Keeps solution moving to provide even deposition.
pH – Keeps plating solution stable; adjusted with catalysts.
Additives – Modify deposit brightness, hardness, internal stresses, etc.

Careful control of these parameters allows plating operators to tailor the chrome coating properties as needed.

Quality Control Testing

Rigorous quality control testing ensures a consistent, high-quality chrome plating process:

Thickness testing – Micrometers or eddy current gauges verify plating thickness meets specifications.
Adhesion testing – Tape or bend tests assess coating adhesion to the substrate.
Corrosion testing – Salt spray tests check chromium corrosion resistance.
Hardness testing – Microhardness indenters measure chrome layer hardness.
Appearance – Visually inspected for proper luster, smoothness, and uniformity.

Plating bath chemical concentrations are also continually analyzed using titration and analytical lab techniques.

Applications of Chrome Plating

Chrome plating provides many benefits that make it a versatile metal finishing process suitable for a broad range of applications:

Decorative plating – Enhances aesthetic appeal of surfaces with an attractive chrome finish. Used extensively on automotive trim and accessories.
Engineering plating – Improves wear and corrosion resistance. Common on hydraulic cylinders, shafts, and other high-wear components.
Mold plating – Facilitates mold release and improves mold life. Ideal for plastic injection molds.
Restoration work – Can repair worn or damaged surfaces. Allows salvaging of valuable equipment and parts.

From tiny intricate parts to large industrial equipment, chrome plating is an effective and reliable metal finishing solution across many industries.

Conclusion

Chrome plating requires the right combination of materials, equipment, and process controls to produce high-quality chromium coatings. Thorough cleaning and activation, optimized plating parameters, and consistent quality testing are essential. With the proper steps in place, this versatile plating process can provide exceptional aesthetics, surface protection, and durability enhancement for all types of metal components and products.