Cast iron is a popular material for cookware, industrial parts, and other applications due to its durability, heat resistance, and low cost. While cast iron has an attractive matte gray finish when seasoned properly, some applications call for a shiny, chrome-like finish instead. The good news is that cast iron can be chrome plated through a process called electroplating.

Benefits of Chrome Plating Cast Iron

There are several reasons why chrome plating may be applied to cast iron parts and products:

Aesthetic Appeal

One of the main benefits of chrome plating cast iron is cosmetic appeal. The shiny chrome finish gives a clean, attractive look compared to the dark gray of unfinished cast iron. This makes chrome plating ideal for cast iron products where aesthetics are important, such as decorative hardware, appliances, automotive trim pieces, and plumbing fixtures.

Corrosion Resistance

Cast iron is prone to rusting when exposed to moisture and air. The chromium layer applied during chrome plating forms a protective barrier that greatly improves corrosion resistance. This makes chrome plated castings ideal for use in bathroom fixtures, outdoor furniture, automotive parts, and other applications where corrosion is a concern.

Hardness

Chrome plating can significantly increase the surface hardness of cast iron parts. Hard chrome plated layers measure 700-1000 HV on the Vickers hardness scale, over 10 times harder than standard cast iron at approximately 80 HV. This allows cast iron parts to better resist scratching, scuffing, and wear in high friction applications.

Lubricity

The slick surface of a chrome coating reduces friction between moving parts. This makes chrome plated cast iron a good choice for parts like gears, rollers, and piston rings where friction is problematic. The low friction surface facilitates smoother motion.

Cost Savings

In some applications, chrome plating cast iron is more cost effective than switching to a corrosion resistant alloy. Chrome plated cast iron parts can replace components made of more expensive metals or stainless steel alloys, saving on material costs.

Industries Using Chrome Plated Cast Iron

Chrome plating has allowed cast iron to expand into new applications across several major industries:

Automotive

Chrome plated cast iron parts are widely used in automobiles, trucks, and motorcycles. Common automotive applications include bumpers, grilles, trim pieces, valve covers, and piston rings. The chrome coating provides an attractive finish, while also preventing corrosion.

Plumbing

Many showerheads, faucets, and other bathroom hardware contain cast iron components that have been chrome plated. The corrosion resistant chrome finish allows these fixtures to withstand high humidity environments.

Furniture

Outdoor furniture made from cast iron can be chrome plated to prevent rusting and add a modern, eye-catching look. Wrought iron patio sets are often chrome plated for this reason.

Agriculture

Chrome plated cast iron fittings are installed in agricultural equipment to resist wear and corrosion from the elements. These parts include bushings, pulleys, gears, and soil engaging components.

Oil and Gas

Drilling equipment used in oil and gas operations, like drill collars and tool joints, rely on chrome plated cast iron for hardness and a low-friction surface. This reduces wear in abrasive wellbore environments.

The Electroplating Process

Electroplating is used to apply the chrome coating to cast iron parts. This involves submerging the part in a chrome plating bath and using electrical current to induce the chromium layer. Here are the key steps:

Cleaning

Before plating can begin, the cast iron part must be thoroughly cleaned to remove oil, rust, scale, and mold release agents from the casting process. An alkaline or acid solution is used in combination with rinsing baths.

Surface Preparation

A process called abrasive blasting is used to roughen up the surface and improve adhesion of the chrome layer. The cast part is bombarded with abrasive media like sand or glass beads traveling at high velocities.

Activation

Next, the part goes through an activation bath containing an acid like sulfuric acid. This etches the surface to further improve plating adhesion.

Plating

The activated part is submerged into the chrome plating electrolyte bath along with an anode. Electrical current causes chromium ions to deposit onto the negatively-charged cast iron cathode.

Rinsing

After plating to the desired thickness, the part is removed and undergoes several rinse baths to remove excess chromic acid.

Sealing

Finally, a sealant may be applied to prevent the chromium layer from oxidizing or tarnishing. The chrome plated cast iron component is now complete.

Chrome Plating Equipment

Specialized equipment is required for commercial or high-volume chrome plating operations. Here are some of the key components:

Rectifier – Provides DC power for the electrolytic process. Controlled voltage and amperage settings optimize plating results.
Anodes – Blocks or baskets made of lead alloy suspended in the tank to serve as the positive electrode.
Plating Tanks – Typically constructed of plastic or stainless steel. Contains the chromium plating solution. May use heaters and agitation systems.
Rinse Tanks – Additional tanks for clean water rinsing between process steps. Flowing rinses prevent solution contamination.
Hoists – Used to lower and raise parts in and out of tanks. Keeps hands safely out of the corrosive baths.
Filtration – Removes contaminants and replenishes chrome ions to maintain solution quality.
Air Knives – Blow excess solution off parts between tanks for cleaner rinsing.
Fume Extractors – Pull dangerous chromic acid vapors away from the plating area.

Proper safety precautions are critical when working with electroplating chemicals and electric current. Workers wear non-conductive gloves, aprons, and eye protection.

Chrome Plating Cost

The cost of chrome plating cast iron can vary based on several factors:

Part size – Larger parts require more chrome plating solution and electrical power, increasing process costs.
Production volume – High volumes benefit from economies of scale compared to low volume job shop work.
Surface area – Intricate parts with greater surface area necessitate longer plating times.
Number of sides – Extra setups are needed to plate multiple sides of a part.
Surface preparation – More extensive pre-plating work like abrasive blasting adds cost.
Thickness – Thicker chrome layers take longer to deposit, increasing cost.
Specifications – Aerospace and military applications often have more stringent standards.

Typical chrome plating costs range from $100-200 per hour for job shop work. High volume production with automated equipment can bring part costs down around $5-20.

Quality Control

To ensure proper chrome layer thickness and performance, plating shops use several quality control measures:

Hull cell testing – Checks solution strength and settings.
Thickness testing – Measures plating thickness on finished parts.
Adhesion testing – Confirms proper layer bonding.
Corrosion testing – Evaluates corrosion resistance with salt spray tests.
Hardness testing – Verifies surface hardness using microindentation or scratch tests.
Bend testing – Checks ductility and adhesion by bending plated parts.
Appearance – Visually inspect for proper coverage and color.

Reputable plating shops will provide documentation of these quality checks. This ensures the plating meets required specifications.

Advantages of Chrome Plated Cast Iron

To summarize, here are some of the main benefits that make chrome plating a popular finishing choice for cast iron components:

Attractive chrome plating appearance
Improved corrosion resistance
Increased surface hardness and wear resistance
Lower friction from slick chrome surface
Cost savings versus stainless steel alloys
Expanded applications across industries

So whether the goal is an eye-catching finish, extending part life, or preventing rust, chrome plating offers an effective solution for upgrading the performance of cast iron. Careful process control and quality checks ensure optimal plating results. With the right preparation and plating procedure, cast iron can gain all the benefits of a durable, attractive chrome finish.

References

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Safranek, W. H. The Properties of Electrodeposited Metals and Alloys. American Electroplaters and Surface Finishers Society, 1986.
Legg, Keith O. “Chrome Plating.” SFSA Technology Training, Southern Fastening & Supply Inc, 1997, pp. 1–30.
Chrome Plating. American Electroplaters and Surface Finishers Society, no. 6, AESF, 1999.
“Hard Chrome Plating.” Industrial Chrome Plating, American Plating Power, www.americanplatingpower.com/industrial-chrome-plating/. Accessed 14 Feb. 2023.
Chromic Acid Anodizing of Aluminum (MIL-A-8625) – A Guide to Process Selection and Optimization. Metal Finishing Suppliers Association, no. 88-8, MFSA, 1988.