Metal plating is one of the widely used surface finishing processes. This technique offers many advantages to products manufactured from metals. Many manufacturers opt for this process because it offers benefits such as enhanced hardness, aesthetically pleasing appearance, better corrosion resistance, and improved magnetism.
There is a need to carefully select the plating metal. That is because certain metals work better with certain techniques.
What is Metal Plating?
This is a post-production process whereby a product is covered with a thin layer of metal through electroplating. In this case, the deposition of metal ions on the workpiece is achieved through the use of electric current. The outer layer can be nickel, copper, zinc, chromium, or other metal that improves corrosion resistance and aesthetics.
Benefits
These are some of the top benefits of metal plating:
Corrosion Resistance
Metal plating offers corrosion and rust resistance to metal components. This is because the extra layer protects the product against environmental contamination and harsh chemicals. In this way, it increases a product’s lifespan both aesthetically and functionally. The good thing about metal plating is that it increases the integrity of a component. Such components can be used in certain applications where corrosion is rampant.
Heat Resistance
By metal plating products, you can increase heat resistance. This is the case when you use metal with a high heat threshold such as silver. As a result, metal plating is quite popular in the automotive and aviation industries. This is because components used in these applications are subjected to extreme temperatures.
Improved Aesthetics
Other than increasing corrosion and heat resistance, metal plating improves the aesthetics of the product. For instance, antique and jewelry pieces are coated to enhance their visual appeal.
Enhanced Durability
The extra layer of metal enhances durability and minimizes the wearing of parts. By protecting parts from harsh environments, you can be assured the product will perform as expected. You should note that metal plating improves chemical resistance.
Disadvantages
Although metal plating enhances aesthetics and improves the lifespan of a product, it has some drawbacks. For instance, the process is time-consuming owing to the lengthy processes involved. Also, if it is not handled as required, it can result in defects. The coated product is subject to cracking and shipping when used in some environments.
Metal Plating Methods
The following are the common metal plating methods employed in various industries:
Electroplating
This metal plating process deposits a metal or an alloy on the surface of a workpiece. The technique uses electric current in an electrolyte solution. In this way, it dissolves ions which then get deposited on the surface of a part. The workpiece or part provides the negative charge to complete the circuit.
Electroplating is used to enhance the component’s physical, chemical, and mechanical properties. For instance, it creates a uniform and smooth coating. In addition, the thin coating provides the aesthetic appearance required on the component.
Electroless Plating
This technique does not utilize electrical current, hence its name. Rather, it is a chemical reaction whereby metal particles are converted to solid when mixed with reducing agents. This results in a solid plating that overlays the workpiece.
The good thing about this method is that it provides a fine finish. Moreover, it is cheaper because electricity is not used. Unfortunately, it is time-consuming and can result in thicker plates.
Electroless metal plating provides protection advantages and impacts the conductivity and solderability of the workpiece.
Immersion Plating
This technique dips the metal into a solution that contains ions of a noble metal. Since these ions are more stable, a natural “pull” takes place and displaces metal ions from the workpiece to create a thin, protective layer.
This process is slower as compared to electroplating and electroless plating methods. It is applicable when dealing with noble metals such as platinum, gold, and silver.
Plasma Spray Coating
If your parts or components are used in extreme temperatures, then you should go for plasma spray coating. That is because this method creates corrosion-resistant coating. However, it can alter the conductivity of your product.
The process starts by heating the plating metal to a high temperature with the use of a plasma flame. As soon as the plating metal melts, it is sprayed onto the workpiece and then cooled.
Common Plating Metals
Zinc
Zinc is widely used to create galvanized coating because it is inexpensive. Surface finishing providers use it through spraying and bath dipping. Through electrolysis, soluble zinc salts act as the cathode and metallic zinc as the anode.
The sherardizing process produces a ductile coating whose uniformity and thickness can be controlled easily. This process helps to coat smaller hardware items, such as nails and screws.
For larger items, molten zinc can be applied through dipping. In some cases, trace amounts of aluminum are added to increase fluidity.
Although zinc coatings can be porous, the coating’s ability to protect the product from corrosion is not compromised.
Cadmium
In some cases, cadmium is used as an alternative to zinc and used to coat some automotive components. In the aviation industry, it is preferred because of its natural lubricity and advanced protection characteristics. Since it can withstand the adverse effects of salt and fresh water, it is suited for marine applications.
Since cadmium has safety concerns, it is rarely used for metal plating. As a result, most manufacturers have opted for zinc-nickel alloy.
Chrome
Chromium plating is mainly used for aesthetic purposes. Even then, it improves the hardness and corrosion resistance of parts. This explains why it is ideal for industrial applications. With hard chrome plating, it is possible to restore tolerances on worn components.
Chrome plating being an electroplating technique uses chromic acid. In some cases, chromate can be applied over zinc to provide extra protection.
Nickel
When it comes to metal plating, nickel is quite popular. It is widely used in electroless plating. This material is used to coat household parts, such as shower fixtures and cutlery.
Nickel plating is commonly used on metals such as aluminum and copper, but can also work on a range of metals. For electroless plating, it is advisable to use nickel phosphorous alloy. Phosphorous helps to enhance corrosion and hardness resistance.
Copper Plating
This is another widely used plating metal suitable for applications that need improved conductivity. In most cases, it is used as a coating pre-treatment for following metal plating. Low material cost and high plating efficiency make copper an expensive metal for plating.
Tin
Tin is mainly used to coat steel for applications in food and beverage industries. Other than enhancing corrosion resistance, it is non-toxic and creates a coating that makes steel weld easily.
Considerations for Metal Plating Finishes
Parts that are plated offer several benefits that range from better functionality and improved aesthetics. However, there are certain considerations for metal plating finishes that you should pay attention to before the metal plating process.
Material Conditions
You have to ensure the metal is in a plating-ready condition. For instance, a metal with heat treatment scales, oil, and grease buildup can pose challenges during the plating process. All these buildups must be eliminated through pre-treatment processes. Some of the techniques used include acid pickles, vapor blasting, and chemical descaling.
Thickness Tolerance
Inadequate or excessive coating thickness can result in plating issues. There is a need to determine the right thickness range. Remember that:
- Electroplating produces uniform coatings. Thus, tight thickness tolerances are not a problem.
- Electrolytic plating can result in the settling of finishes in certain areas.
- Specify the areas of a product that should have tight plating thickness.
- Always take into account recesses, corners, and geometric considerations.
Surface Roughness
It is important to pay attention to the texture of the part’s surface before plating. Fortunately, a surface roughness chart can help you. Smooth surfaces tend to provide better plating results.
Strength or Hardness Specifications
Metal plating results in improved strength and hardness of parts. Therefore, there is a need to take into account the existing hardness and strength of the part. The metal and method you choose for plating should work towards achieving the desired specifications.
Thread Inclusion
If you are including threading on your parts, it is vital to take it into account. Usually, plating parts such as hydraulic fittings and screws are thicker as compared to flat surfaces. By factoring this, you can ensure threaded parts fit together and meet important specifications.