Guide to Electro Plating Type and Process

Dec 12, 2022

What is Metal plating?

The plating process is a manufacturing process in which a thin layer of metal coats a substrate. Metal plating provides many benefits to products made from metal and other materials. This is mostly achieved through electroplating, which requires an electric current, or through electroless plating, which is in an autocatalytic chemical process. These techniques, as well as a few others, result in one or several of the following benefits:

Improved corrosion resistance
Decorative appeal
Increased solderability
Enhanced hardness
Reduced friction
Altered conductivity
Enhanced paint adhesion
Material deposition
Increased magnetism

Metal plating History

In 1805 the Italian chemist Luigi Brugnatelli successfully electroplated silver medals with gold. The inventions were kept secret by the French Academy of Sciences. 35 years later electroplating was “re-discovered” by Russian and English scientists working independently.

In 1940 the first patentfor electroplating was awarded. Factories in England started to mass-produced solver plated items such as utensils, brushes and teapots.

Their Effect on the End Product

Electroplating

Electroplating is the most common method of plating. Electroplating uses an electrical current to dissolve positively charged metal particles (ions) in a chemical solution. The positively charged metal ions are attracted to the material to be plated, which is the negatively charged side of the circuit. The part or product to be plated is then placed in this solution, and the dissolved metal particles are drawn to the surface of the material. Electroplating results in a smooth, even and rapid coating for the material that is plated, effectively changing the surface of the material. There are a number of different steps and processes that can be involved in electroplating, including cleaning, striking, electrochemical deposition, pulse electroplating, and brush electroplating.

Electroplating Effects

Electroplating is used to provide a protective coating, a decorative appearance, or to change the properties of a material for engineering. Electroplating improves the chemical, physical, and mechanical properties of the workpiece which affects the way it performs when machined. Plating the workpiece can be used to build it up from a smaller size, make it easier to machine, and to increase solderability, conductivity or reflectivity.

Electroless (autocatalytic) Plating

Electroless plating is so called because it is a plating method that does not use external electric power. Electroless plating involves a chemical reaction that induces metal atom reduction. In other words, the solution of metal ions (particles) when mixed with a reducing agent is converted into a metal solid when they come in contact with the catalyzing metal (which triggers the reaction). This results in the metal being plated with a solid layer of the plating metal.

Electroless Plating Effects

Electroless or autocatalytic plating is suitable for diverse sizes and shapes of materials and doesn’t require external electricity or plating baths, which reduces costs. However, electroless plating is slower, can’t create thick plates, and is more difficult to control than electroplating. The most common method of autocatalytic plating is electroless nickel plating. However, plating in silver, gold, and copper can also be applied with this technique.

Effects of electroless plating on the end product include protecting the base metal from corrosion, increasing the size of the workpiece, and altering solderability, reflectivity, and conductivity.

Immersion Plating

Immersion plating involves immersing one metal into a solution of metal ions from a more noble metal. The ions from the nobler metal are more stable, and so there is a natural ‘pull’ to displace the surface metal ions from the less noble metal with a thin layer of the nobler metal ions. Immersion plating is a slower process, and can only be used for plating less noble metals with nobler metals. Nobler metals are metals that are chemically inert. For example gold, platinum, or silver.

Immersion Plating Effects

Immersion plating results in only a thin coverage of plating, after which point the plating process will stop. Immersion plating also seems to be of poorer adhesion quality, where the plating doesn’t ‘stick’ as firmly to the base metal.

The effects of immersion plating on the end product include improved corrosion resistance, altered electrical conductivity, changed appearance, greater hardness, torque tolerance and modified bonding capabilities.

Common Metal Plating Types

Metal plating can give your items a fresh look and make them stronger, which extends their lifespans. You have several options when choosing which type of metal plating to go with to create the look and performance you want. Here are some of the most common types.

Chrome

Chrome plating gives metal a bright silver-toned finish that stands out. It's also a good choice for industrial projects because it reduces the risk of rust and increases the item's resistance to friction. Chrome plating is usually applied through an electroplating process that uses a chromic acid called hexavelent chromium.

Brass

Brass plating is a good choice for steel light fixtures and other indoor decorative items. Items plated in brass don't have a strong resistance to corrosion, so it's best to choose another finish for outdoor furniture and other metals that will be exposed to the elements. Brass is a great alternative to gold. Great for lighting and furniture manufacture pieces.

Nickel

Nickel plating is popular for household items and gives them a sleek, modern look. Nickel is commonly used on aluminum, stainless steel, and copper items, though it can bond to other metals as well. The process for plating items with nickel is electroless, which makes it a simpler, more environmentally-friendly choice. Nickel is great for table and chair legs.

A high phosphorous nickel alloy can increase the strength and rust resistance of the items it's applied to. It is a great alternative to silver.

Gold

Gold plating gives items a classic, rich look and is often used on metal light fixtures, high end furniture, and other decorative and luxury items. Unlike gilding, gold plating involves applying the finish by submerging the item in a gold bath instead of applying gold-colored foil. This type of plating is very resistant to oxidation.

Gold plating also increases electrical conductivity, which makes it a good choice for electrical connectors and component cables.

Silver

Silver plating is another option if you're looking for a timeless, yet modern finish. Like gold, silver increases electrical conductivity and adds an appealing decorative touch, but it's less expensive than gold is. Silver does have a tendency to crack or peel when it's exposed to high humidity, so it's best used on items that will be in drier environments. Silver is great for light fixtures and hotel furniture.

Bronze

Bronze is a plating type best suited for indoor projects because it's not as resistant to rust as other plating types. Standard bronze finishes have a coppery color and are well-suited to steel items.

Oil-rubbed bronze is another type of bronze plating that has a darker, brushed appearance. If you're looking for a popular, darker finish for a brass or copper item, oil-rubbed bronze is a good choice. Great for table ends, sculptures and outdoor metal decorative pieces.

Copper

Copper plating is an expensive option that gives metal a bronze-colored hue, though it can also be blackened for an antique or vintage appearance.

While copper plating can stand on its own, it's also used as a pre-treatment for other metal plating types, such as nickel and chrome, because it makes it easier for subsequent coatings to stick to the metal. Copper is a great metal for hotel décor, huge metal frames, car parts and screws.

Tin

Tin plating gives metals a silver appearance that has more of a grayish undertone than most silver and nickel finishes. Items coated in tin can have a matte or bright finish. This plating type is an excellent choice for outdoor furniture, metal fencing, and food preparation and serving items due to its excellent rust resistance.

Tin is a very common metal, which lowers production costs.

Zinc

Like tin, zinc is available in abundance, which keeps costs lower than some other plating types. Zinc plating gives metal a bluish gray appearance and is common on small metal parts that might be exposed to moisture. Screws, bolts, and other small parts coated in zinc are less likely to rust than many other finishes.

Typical Steps In Electroplating Process

The process shown below takes about 90 minutes to complete. This is the process for plating steel aerospace parts with cadmium.

Cleaning: the surface must be free of contaminants for bonding to take place.

Suspended parts in a vat of boiling chemical solvents. The hot vapor comes in contact with cold metal and condenses, dripping down into vat along with any contaminants, leaving the parts clean and dry.

Rinsing and dry (if needed)

Acid cleaning and etching: Sandblasting with aluminum oxide will roughen up the surface so that the plating metal adheres better.

Sandblasting parts with aluminum oxide powder to etch the surface and improve adherence of plating metal

Rinsing (if needed)

Conversion Coating or Plating

Hanging part to be electroplated on the copper frame. Copper Wire suspends part from top and continues to bottom creating an electrical circuit through the part to be welded.

The electroplating tank is filled with water and chemicals to help conduct electricity. The sides of the tank are lined with bags or balls of plating metal. The support frame holding the part is connected to a negative terminal of the electrical source. The metal that is to be plated is connected to the positive terminal. A DC current of up to 6 volts dissolves the plating metal which travels through the water, attaching to the negatively charged piece to be plated. The process can take just a few minutes for thin plating to several hours for thick plating.

Water Rinsing (1 minute)

Chemical Rinsing to make parts more rust resistant

Rinse in Hot Water