The Basic Guide of Chrome Plating

Chrome plating a part generally consists of the following stages:

1. Degreasing to remove heavy soiling of the part.
2. Manual cleaning part to remove all residual traces of dirt and surface impurities.
3. Various pretreatments depend on the substrate to ensure proper adhesion.
4. Place the part in the chrome plating vat and allow it to reach the solution temperature.
5. Apply plating current for the necessary time to achieve the target thickness.

Typical Process of Chrome Plating

Chrome plating is available in two typical processes: hexavalent chromium and trivalent chromium.

Hexavalent Chromium

Hexavalent chromium is a conventional kind of chrome plating process that is primarily used for functional purposes. It is the most toxic chromium and is a proven human carcinogen. Toxic waste generated by the hexavalent chromium bath is hazardous waste and must be treated before disposal.

Trivalent Chromium

The main ingredient in trivalent chromium plating is chromium sulfate or chromium chloride. In specific applications and thicknesses, trivalent chromium plating can replace hexavalent chromium.

Trivalent chromium is far less toxic than hexavalent chromium. It is an environmentally beneficial solution to the conventional chrome plating process. However, Trivalent chromium’s usage and disposal of any waste are also strictly controlled.

The Steps of Chrome Plating

The first step in chrome plating is cleaning and degreasing the metal workpiece or object. After the workpiece or object has been meticulously cleaned to remove all traces of dirt, you can put it into a chromium anhydride container. Then, the container receives an electrical charge, causing a chemical reaction that makes the chromium adhere to the workpiece or object. In some cases, additional steps may be required, such as finishing and polishing.

Purpose of Chrome Plating

Chrome plating is commonly used for decorative uses or engineering purposes. Regarding decorative purposes, chrome plating provides a smooth and shiny appearance for the product. For engineering purposes, chrome plating can impart a very high degree of hardness to a metal’s surface. This high hardness can enhance wear resistance, provide anti-galling qualities, and improve corrosion resistance.  Chrome plating is an electrolytic technique used on materials such as ordinary steel, stainless steel, aluminum, and others.

Types of Chrome Plating

There are two types of chrome plating – decorative chrome plating and hard chromium plating. Let’s take a closer look at each.

Decorative Chrome Plating

Decorative chrome plating is intended to be aesthetically pleasing and durable. The standard thickness range of decorative chrome plating is between 0.002mm and 0.02mm. Because the decorative chrome layer is so thin, its durability is inferior to that of hard chrome plating.

Generally, the decorative chrome plating process begins with electroplating nickel, followed by chrome plating. Copper is sometimes electroplated instead of nickel. The nickel or copper level offers smoothness, corrosion resistance, and reflectivity. 

Benefits of Decorative Chrome Plating

Enhanced Visual Appeal: Decorative chrome plating creates a smooth and glossy surface, enhancing the part’s visual attractiveness.  Decorated chrome plating may raise the perceived worth of consumer products like kitchen utensils and equipment. Additionally, chrome plating enhances the appeal of automobiles and musical instruments.

Corrosion Resistance: Decorative chrome plating protects objects against corrosion caused by chemicals or other oxidizing agents. This decorative chrome layer benefits vehicle parts or other products used outside or in damp conditions.

Easy Cleaning: Because of its corrosion resistance, decorative chrome plating is simple to clean with ordinary home cleansers and chemicals. A smooth decorative chrome surface also prevents the accumulation of dirt and dust and retains its luster over time.

Some Wear Resistance: Decorative chrome plating can boost a product’s strength. However, due to its thinness, it is also susceptible to damage. For instance, a car accident might cause the decorative chrome layer on a bumper to shatter, exposing the underlying metal to corrosion and rust. Chrome-plated kitchen utensils can degrade when the thin chrome layer peels off over time.

Applications of Decorative Chrome Plating

Automotive Parts: Decorative chrome plating can be seen on many automotive parts, including bumpers, trim, rocker panels, door handles, and grilles. The application of decorative chrome plating improves the corrosion resistance of these parts, preventing them from rusting in the rain or snow. Decorative chrome also offers several finishing and buffing choices to boost its sheen and aesthetic appeal.

Tools: Applying decorative chrome plating improves durability and wear resistance on tools and hardware. Some tools include wrenches, sockets, pliers, and hex keys. Chrome-plated tools can withstand difficult situations without damage.

Instrument Hardware: Some instrument hardware is occasionally thinly plated with decorative chrome coating to improve beauty and longevity, such as guitars, clarinets, etc.

Cooking Utensils: Decorative chrome plating can strengthen the corrosion and heat resistance of metal cooking utensils like tongs, knives, spatulas, spoons, and forks. Chrome-plated kitchen utensils are simple to clean and offer durability for extended usage. Shiny chrome cooking equipment is highly appealing to both home cooks and chefs.

Hard Chrome Plating

Hard chrome plating, also known as industrial chrome or engineered chrome plating, applies an extremely thick layer of chromium to generally steel-made engineering parts. It is an electroplating process that involves immersing the part in a chromic acid solution and depositing a chromium layer on the surface. Standard hard chrome thickness is between 0.02mm and 0.04mm.

Hard chrome plating extends the life of the parts and provides excellent corrosion and wear resistance for pricey metal objects. It is also used to prevent parts from seizing and to boost their durability. Another outstanding property of hard chrome plating is its ability to expand chemical inertness, particularly oxidation resistance.

Benefits of Hard Chrome Plating

Superior Hardness: Hard chrome plating is harder than most industrial abrasives and metallic coatings. It is very hard, measuring between 65 and 69 HRC (also based on the base metal’s hardness). Hard chrome plating may withstand rigorous industrial applications and high stresses.

Durable Thickness: Thick hard chromium plating protects machine components from wear during regular operation or in hostile environments, such as when exposed to corrosive chemicals.

Low Friction: Hard chrome plating generates less friction when in contact with carbons, metals, graphites, and polymers. Hard chrome plating decreases friction and heat between equipment components when applied to moving parts.

Wear Resistance: Due to its high hardness and low friction, hard chrome coating resists wear and abrasion even under high mechanical contact stress. Hard chrome parts can get long-term durability.

Oxidation Resistance: Hard chrome plating provides exceptional oxidation resistance, which makes it essential in the chemical, pharmaceutical, and food and beverage industries.

Easy Re-plating: If hard chrome plating becomes damaged or wears away over time, it is simple to remove with stripping chemicals and re-plate. Replating can be repeated to increase the lifespan of equipment components significantly.

Applications of Hard Chrome Plating

Automotive Industry: Hard chrome plating is also used in the automotive industry, especially for shock absorbers, cylinders, or other parts prone to work under high cycles for a long time. Hard chrome plating can meet the durability and lubricity requirements of such components.

Aerospace Industry: In the aerospace industry, we can also see hard chrome-plated components like landing gear and aluminum piston heads. The use of hard chrome plating extends the life of the various parts, makes them resistant to wear, and ensures that they don’t weigh too much.

Gears: The low friction properties of hard chrome plating provide gears with wear protection and lubrication benefits, enhancing performance and extending service life.

Filling Material: Hard chrome plating is an excellent filling material to ensure that some worn parts return to their original dimensions.

The Difference Between Hard Chrome and Decorative Chrome Plating

Understanding the differences between hard and decorative chrome plating will help you choose the suitable method for your project. Below I will explain their differences in three aspects – thickness, property, and applications.

Thickness

The main distinction between hard chrome and hard decorative plating is the chrome plating’s thickness on the finished product. Hard chrome plating is thicker than decorative chrome plating. Decorative chrome plating is primarily used for aesthetic appeal and as a protective layer. Hard chrome plating has several industrial uses because of its strength, wear resistance, corrosion resistance, and other advantageous properties.

Property

Hard chrome plating provides materials with increased hardness and strength. Additionally, it offers reduced friction, wears resistance, and long-lasting durability. On the other hand, decorative chrome plating enhances the visual appeal of your component. It also possesses a degree of wear resistance, albeit not as much as hard chrome plating.

Applications

Although Decorative chrome and hard chrome plating have the same chrome manufacturing process, their applications are distinct. Hard chrome plating is ideal for industrial applications and high-stress conditions. On the other hand, decorative chrome plating provides the desired look and protection for many consumer products.

How to Remove Chrome Plating?

Like other surface treatments, the chrome plating coat may become damaged or wear down over time. That’s why we need to know how to remove chrome plating from plastics and metals. There are many ways to remove or stripe the chrome plating layer from the substrate, such as using specialized machinery and chemical solutions.

Specialized Machinery

The first method is using various specialized machines to remove chromium. Although this method is the most expensive, it is also the most efficient. Some specialized devices include an abrasive blaster and ultrasonic cleaner. 

Using an Abrasive Blaster

Abrasive blasting is abrading materials using a spray of fine-grain powder or small pellets. An abrasive blaster is equipment that aids in abrasive blasting. Such equipment is frequently available at vehicle body shops and construction firms. Long-term abrasive blasting can remove the chrome finish from an object, but you may need further touch-up work for the object’s hard-to-reach areas.

There are a few points to keep in mind when using abrasive blasting to remove chromium:

1. When blasting your chrome, you should use a medium with a rather fine grain to avoid damaging the underlying metal.
2. While chipping off tiny pieces of chrome with an abrasive blaster, the airborne dust and sediment created can be harmful. So you should wear the necessary protective gear, such as goggles and masks. 

Using an Ultrasonic Cleaner

You also use an ultrasonic cleaner to remove chrome plating. Ultrasonic cleaners employ high-frequency sound waves to remove dirt, grime, and other deposits off surfaces. They are typically used for cleaning delicate electronic parts or jewelry.

Ultrasonic cleaners function to remove chrome plating by causing the chromium particles to vibrate at a high frequency. This procedure separates the chromium from the metal surface, causing the chrome to flake off. Moreover, the restricted size can only make ultrasonic cleaner to remove chrome from relatively small materials.

Chemical Solutions

Using chemical solutions is a less expensive method of removing chrome than specialized machinery. But you must handle chemicals with considerable caution due to their toxicity. And don’t forget to wear protective clothes and gloves.

Using Hydrochloric Acid

Hydrochloric acid, also known as muriatic acid, is a strong and corrosive acid. The corrosive property of hydrochloric acid is beneficial for removing chrome from metals. A 30-40% concentration acid solution should be enough to remove chromium.

Following is the process to remove chrome using hydrochloric acid:

1. Create a 30% acid solution by combining 1/3 part hydrochloric acid and 1 part water in a vat designed for chemical mixes like a heavy-duty plastic bucket. Alternatively, you can purchase a pre-mixed acid solution of sufficient concentration.
2. Immerse the chrome-plated object in the solution until the chrome comes off.
3. After removing the chrome, remove the object from the bucket and rinse it off with soap and clean water. Leave to dry.

Using Sodium Hydroxide

Sodium hydroxide, or lye, is a caustic and fundamental chemical. It is an effective way to remove chrome plating from metal. But it is worth noting that using sodium hydroxide would be extremely dangerous if the base metal is aluminum. Because when the sodium hydroxide is mixed with water to form a solution, it can corrode the aluminum and give off hydrogen gas.

Proceed as below:

1. Combine 8 to 12 fl ounces (approximately 227ml to 355ml) of sodium hydroxide with 1 gallon (3.785L) of water in a vat. Note using a vat made of neutral material, such as a heavy-duty plastic bucket.
2. Thoroughly submerge the chrome-plated object in the solution. This process may take a long time, so check frequently to see whether the chrome has begun to peel.
3. After removing the chrome, take the object from the bucket. Then clean the object with soap and water before drying. 

Perform Reverse Electroplating

Performing reverse electroplating involves a live current, sulphuric acid, and chromic acid. Therefore, reverse electroplating is dangerous for removing chrome plating using chemicals.

This method should only be undertaken by professionals familiar with electricity and chemicals. Performing reverse electroplating would produce toxic and carcinogenic chemicals. Also, the live current poses a significant danger of electrocution.

Below are the steps of reverse electroplating:

1. The chromic and sulphuric acid are mixed in water with a 100:1 ratio to make the solution.
2. The mixture is heated. For decorative chrome, maintain the solution temperature between 95 and 115 ℉. Hard chrome requires temperatures between 120 and 150 ℉.
3. It is needed to send a negative charge from a DC power source into the chromic plating solution via wire.
4. Attach the positive cathode to the stripping item and immerse it in the solution. You can successfully remove positively charged external chromium from objects.
5. Rinse the object with agitated running water. And have garbage processed and disposed of professionally.

Conclusion

Chrome plating refers to electroplate chromium as a coating on other metals. Chrome is a natural element and a type of silvery-white metal with a little blue hue; it easily passivates in the air and produces a thin film on the surface. 

The chromed layer provides corrosion resistance, increases surface hardness, simplifies cleaning operations, and enhances the appearance. The chrome plating process is appropriate for various commercial and industrial applications.

LEADRP can serve as your manufacturing partner for high-quality chrome plating services. Our experienced professionals and advanced tooling will satisfy your needs for the product. Contact us today, and let’s discuss your project.

References

Chrome plating – From Wikipedia

A brief guide to the chrome plating process – From The Surface Engineering Association

What is the Difference Between Hard Chrome and Decorative Chrome Plating? – From Hard Chrome Specialists

How to Remove Chrome Plating – From wikiHow

What Is Chrome Plating? – From Monroe