Metal plating is a process whereby a layer of metal is coated on an object that is made of a different type of metal. The purpose behind plating is to give a more pleasing look or to add the appearance that the object may actually have a greater value. This process can also become beneficial because the exterior metal may be more resistant to corrosion, protecting it from the elements.
Consider silver plating for a moment. This is often done for decorative purposes, where adding a layer of silver to sink or cadmium helps give the appearance that jewelry, for example, is much more valuable. Oddly enough, this process is even used in making money. The penny has an exterior plating of copper wrapped around a zinc interior.
This is an interesting science experiment if you would ever like to check it out. Using a common nail file, you can shave away a little bit of the copper exterior and then place the penny inside a glass that contains hydrochloric acid. Come back the next day and you are going to find a paper thin piece of copper which is the exterior of the penny. The zinc combines with the hydrochloric acid to become zinc chloride, completely gutting out the zinc in the process.
What Is Needed in Metal Plating?
To perform metal plating, there are some components and substances that are needed. The first of these are cleaning products, that help to prepare the metal surface for the plating process. Most often, there are three cleaning processes that are used:
- oxide removal
- electro polishing
- alkaline cleaning
There are also products that are used to finish and protect the exterior layer once the metal plating process is completed. These include:
- chromate conversion
Types of Plating
There are actually three different types of metal plating processes that can be used.
In the electroplating process, an electrical current is used to create a chemical reaction. This causes the metal ions to become reduced, giving greater control of the plating process.
In this type of process, I chemical reaction is created that reduces the metal atoms. This is often used in a non-conductive process where no electricity is required. The problem with this particular type of plating is that it is difficult to control the parameters, and the plating bath has a limited lifetime. Examples where this coding process are used include:
- black oxide
The use of this type of coating process adds thickness to the metal without creating a direct connection between the process metal and that of the substrate.
#3 Immersion Plating
This type of process is often referred to as a displacement reaction. Where this most frequently occurs is where one metal ion reduces to combine with a different metal ion to create a new substrate. An example of this type of displacement reaction is what was discussed earlier with the penny in hydrochloric acid. This is a very common form of plating, which has numerous applications. These include:
- protecting surfaces
- creating decorative coatings
- creating a coating that could be used for connectivity, reflectivity, or other similar properties
- used to protect unusual metals
- the creation of alloy metal plating
Methods of Plating
There are different types of plating methods that are important to know if you want to know how the plating process works. These include:
#1 Rack Plating Method
The first of these is the rack plating method. This technique is most commonly used in situations where the metal that is going to be plated is hung on some type of frame or rack. This is one of the most versatile methods, because it gives the labor the ability to focus on particular areas and to rents easily.
#2 Barrell Plating
Barrel plating gets its name from the fact that the plating process actually occurs in a closed barrel. This process is employed when the laborer is electroplating smaller parts and there is a very small degree of processing that is required. The rinse water that is used is high, and the drying out rates are also high.
#3 Manual Plating
While this is one of the best grades of plating, the challenge with it is that it is all performed manually by a trained technician. This ensures that the plating is conducted properly, as the technician especially trained to accomplish this goal. However, because no automation is conducted, it also requires the technician to monitor the entire process.
#4 Automated Plating
This process can be either semi-automated or completely automated. In the automated operation, the only role of the employee is to rack an unranked the pieces during the metal plating operation. In the semi-automated process, it requires that the employee manually control the rails and the hoists. If this process is used for larger parts, lower production rates often follow.
How Electroplating Process Works?
To properly perform metal plating, we will look at one example. In the electroplating process, the entire process can take no more than 90 minutes to complete. This process is often used for plating aerospace parts with cadmium.
Step 1: The first step is that the surface must be freed from all contaminants that are bonded to the metal. This is accomplished by using one of the cleaning solvents that was mentioned before.
Step 2: If needed, rinsing and drying are performed
Step 3: The next step is to sunblast the metal surface with aluminum oxide. This roughens the surface so that the metal plating will adhere to the surface of the metal better during the plating process.
Step 4: If needed, the rinsing process is conducted again. Note: There is no issue with rinsing the surface again, even if it is not necessary.
Step 5: Now is the point where coating or plating is done. This can be conducted using one of the four plating processes mentioned in the previous section.
Step 6: Water rinsing should be conducted for one minute.
Step 7: To prevent rust, a chemical rinse should be used.
Step 8: Finally, one more water rinse should be performed. This should be done with very hot water to remove any chemicals or byproducts that may be on the metal.
Metal plating is one of the most important processes in working with metals, simply because it has such a wide array of uses. One who is skilled in this work can be sure that they will always find work.