Electroplating and chrome plating are two common industrial processes used to coat metal objects with a thin layer of metal. But while both techniques involve running an electric current through a solution to deposit metal, chrome plating refers specifically to the electroplating process using chromium, while electroplating can use various metals.

Electroplating

Electroplating is a general term referring to any process that uses electric current to coat a conductive surface with a thin layer of metal. It’s an electrochemical process where metal ions in solution are reduced onto a cathode surface, building up a uniform metal coating.

The part to be plated forms the cathode (negative electrode) in the electrolytic cell solution. When current is applied, positively charged metal ions in the solution are attracted to the negatively charged part. These ions precipitate out of the solution, bonding to the part’s surface atomically and forming a thin metal coating.

Electroplating has been used commercially since the 1840s. It serves both decorative and functional purposes across a wide range of industries including automotive, aerospace, medical, electronics, and more. Reasons for electroplating include:

Decorative finish – Electroplated coatings like nickel, chrome, and brass provide an attractive, shiny surface.
Corrosion protection – Coatings like zinc, nickel, and tin protect the base metal from corrosion damage.
Wear/abrasion resistance – Hard electroplated coatings like chromium increase wear and abrasion resistance.
Electrical conductivity – Copper electroplating improves electrical conductivity.
Lubricity – Silver plating provides a low friction surface.

Almost any conductive metal can be electroplated including gold, silver, nickel, copper, chromium, zinc, tin, and cadmium. The process steps are similar regardless of the specific metal being applied.

Electroplating Process Overview

Electroplating involves multiple steps to prepare the part, plate the part, and finish the plated surface. Here is a general overview:

Surface preparation – The part surface is thoroughly cleaned to remove oils, dirt, oxides. This ensures good adhesion.
Activation – The part undergoes activation to remove any remaining surface oxides and create an atomically clean surface.
Electrocleaning – The part is electrocleaned which applies an electric current in a detergent bath to further clean the surface.
Electroplating – The part is immersed in a solution containing the metal to be plated. Electric current reduces metal ions onto the part surface.
Post-treatment – Any final finishing steps are performed like rinsing, drying, lacquering, grinding, polishing.

The specific process parameters like temperature, current density, and plating time depend on the metal being plated and the desired coating properties.

Electroplating Uses

As mentioned above, electroplating serves both decorative and functional purposes. Here are some of the most common applications:

Decorative chrome plating on faucets, fixtures, automotive trim
Corrosion resistant zinc plating on nuts, bolts, marine components
Wear-resistant hard chromium coatings on hydraulics and machine parts
Silver plating on electrical contacts and conductors
Copper plating on EMI shielding and heatsinks
Gold plating on electronics to protect copper traces

Electroplating allows almost any metal to be deposited as a uniform coating onto parts of any size and geometry. It is an economical and efficient way to enhance properties like corrosion protection, wear resistance, solderability, reflectivity, and electrical conductivity.

Chrome Plating

Chrome plating refers specifically to the electroplating process using chromium as the plating metal. It is by far the most widely used type of decorative electroplating. Items covered with a chrome coating have a characteristic mirror-like, shiny surface.

The chrome plating process is very similar to other electroplating operations. But it has some additional steps to produce the desired appearance and properties. It also relies on a chromium plating solution rather than zinc, copper, nickel, etc.

Chrome Plating Process

Here are the key steps involved in chrome electroplating:

Surface cleaning – The substrate is degreased and cleaned thoroughly to remove oils, scale, rust, etc.
Activation – The surface undergoes activation in an acid bath to remove any oxides and prepare for plating.
Copper plating – A layer of copper is applied to provide good adhesion for subsequent nickel and chromium layers.
Nickel plating – A layer of nickel is plated over the copper to provide a smooth surface for chrome deposition.
Chrome plating – The part is immersed in a chromium plating bath and current applied to deposit the chrome layer.
Rinsing and drying – The chrome plated part is rinsed thoroughly and allowed to dry.
Polishing and buffing – Final hand polishing and buffing enhances the mirror finish of the chrome plating.

The chrome layer is typically only 0.2 to 2 microns thick, so the copper and nickel underlayers help provide corrosion protection. The bright chrome finish also oxidizes quickly, so a clear topcoat lacquer is often applied for durability.

Chrome Plating Benefits

Here are some of the advantages offered by chrome electroplating:

Excellent decorative finish – Provides a bright, mirror-like surface with high reflectivity.
Good corrosion protection – The chrome coating resists corrosion and oxidation over underlying substrate.
High hardness – Chrome plating has a typical hardness of 60-70 HRC, increasing wear life.
Lubricity – The slick surface has low friction, facilitating movement of mechanisms.
Uniform coverage – Electroplating allows coating of complex shapes.
Abrasion resistant – The hard chrome surface resists damage from rubbing and abrasion.
Cost effective – Chrome plating is relatively affordable compared to other decorative finishes.

Chrome’s advantages have made it the most widely used finish for items like automotive trim, plumbing fixtures, door handles, fasteners, medical equipment, and many other items.

Key Differences Between Electroplating and Chrome Plating

Now that we’ve provided overviews of general electroplating and specific chrome plating processes, let’s look at some of the key differences between the two in more detail:

Metals Used

Electroplating can apply coatings of almost any metal including nickel, copper, tin, silver, cadmium, gold etc.
Chrome plating exclusively uses chromium to deposit the chrome finish.

Electroplating allows choosing a metal coating based on the desired properties – corrosion protection, wear qualities, conductivity, etc. Chrome plating is primarily for the bright decorative finish chromium provides.

Base Metals

Electroplating is used on steel, iron, copper, and other alloy substrates depending on the application.
Chrome plating is mostly done on brass, copper, or stainless steel substrates to maintain the bright finish.

The substrate metal influences the pre-treatment and surface activation steps needed prior to plating. Different base metals have different surface properties and reactivities.

Adhesion Strength

Electroplated coatings like nickel or copper have relatively low bonding strength to the substrate.
Chrome plated finishes adhere more strongly to substrates due to the high-temperature process used.

The weak atomic-level bonding of electroplated coatings makes them more prone to damage like peeling or flaking over time. Chrome’s higher processing temperatures create stronger cross-linking between layers for better adhesion.

Corrosion Protection

Electroplating with metals like zinc, nickel, or tin provides active corrosion protection of the base metal.
Chrome plating provides more limited corrosion protection, mostly as a physical barrier over the substrate.

Electroplated zinc and nickel coatings actively protect the base metal through sacrificial or passivation mechanisms. Chrome plating alone is permeable to corrosion, so copper and nickel underlayers are needed for corrosion resistance.

Durability

Electroplated coatings like nickel and copper provide moderate durability against wear and abrasion.
Chrome plated parts have excellent durability due to the hardness of chromium and its strong adhesion.

The thin chrome layer is very resistant to damage from rubbing, scraping, and general wear stress. It maintains its smooth polished appearance much longer than standard electroplated finishes.

Cost

Electroplating with metals like zinc or nickel is relatively inexpensive.
Chrome plating has higher costs due to greater process complexity and expensive chemicals.

Electroplating with common metals uses fairly simple cyanide or sulfate bath solutions. Chrome plating requires additional copper and nickel plating stages along with chromium bath chemistry and polishing/buffing steps.

Use Cases

Electroplating has a wide array of applications from corrosion protection to wear resistance to conductivity.
Chrome plating is primarily used decoratively for the bright chrome finish it provides.

Electroplating’s versatility allows it to serve many functional purposes across industries. Chrome plating is less common for technical applications, as other electroplated metals often perform better while being less expensive.

Electroplating Equipment

Electroplating and chrome plating rely on similar equipment setups to apply metal coatings. Here is an overview of typical equipment components used in electroplating processes:

Power Supply

Provides the electric current that facilitates the ion reduction reaction depositing the metal coating. Supplies like rectifiers provide low voltage, high amperage DC power.

Anodes

Insoluble anodes made of the plating metal are immersed in the plating solution. As current is applied, metal from the anode dissolves to replenish the solution with positively charged ions.

Plating Bath

Contains the aqueous solution of metal salts, complexes, or cyanides used to supply metal ions for the coating process. Tanks are typically constructed of non-conductive materials like plastic or fiberglass.

Workpiece Fixture

Holds the part to be plated suspended in the plating bath. Fixtures ensure proper orientation and contact with the electric current. Rotating racks help agitate the solution.

Filtration System

Filters like cartridges or diatomaceous earth beds continually clean the plating solution by removing particulates and impurities. This maximizes solution life.

Heating/Cooling System

Maintains a constant optimum temperature in the plating bath through heaters, chillers, cooling coils, etc. Precise temperature control is critical for uniform plating thickness.

Proper cleaning, rinsing, and drying stages may also be incorporated in a complete electroplating line. Automated systems with programmable hoists allow high-volume throughput for production environments.

Electroplating Safety Considerations

Working with electroplating baths and solutions comes with a variety of safety hazards. Here are some key risks to keep in mind:

Electric shock – High voltage DC power supplies pose a serious shock hazard. Ensure connections are insulated and operators wear proper PPE.
Chemical exposure – Plating solutions often contain toxic elements like cyanides that can harm skin, eyes, respiratory system. Proper protective equipment is mandatory.
Fume inhalation – Heated plating tanks release corrosive acidic mists that damage lungs. Ensure proper ventilation and exhaust systems.
Fire hazard – Flammable vapors from cleaning/degreasing agents and hydrocarbon buildup present an explosion risk. Implement strict precautions around electrical equipment.
Equipment damage – Metal objects falling into tanks can crack plating solution tanks. Use non-conductive tanks and avoid metallic tools near baths.
Solution contamination – Prevent any contamination of plating chemistry by oil, grease, dirt, solvents, or other chemicals. This can ruin entire batches.

Following safety protocols like PPE, ventilation, hazard training, and good housekeeping is critical when working with electroplating or chrome plating systems.

Key Takeaways – Electroplating vs Chrome Plating

Electroplating uses electric current to deposit metal coatings of almost any type onto conductive objects.
Chrome plating refers to the specific electroplating process using chromium to apply a decorative chrome finish.
Electroplating serves functional purposes like wear resistance or corrosion protection. Chrome plating is primarily decorative.
Electroplating can coat base metals like steel, iron, copper and alloys. Chrome plating is mostly done on brass, copper, or stainless steel.
Chrome plating provides better adhesion strength and durability compared to standard electroplating.
Electroplating is relatively simple and inexpensive. Chrome plating involves more complex processes and higher costs.
Both techniques rely on similar equipment – power supplies, anodes, plating baths, workpiece racks, and filtration systems.

References

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