In Cleveland, metal finishing is the process of applying a coating (or finish) to a metal object. This article describes some of the processes used to finish metal.
Benefits of Finishing
Finishing is the last step (with the exception of packaging) in the production of a metal object. Three of the benefits of finishing are described as follows:
- A finish can provide a corrosion-resistant coating. For example, nickel (first) and chromium (second) are plated onto steel to prevent rusting. Chromium can be polished, so any rust that shows through can be polished away.
- A finish can provide a wear-resistant coating. If a metal object is made out of a metal that is subject to wear, a coating of another metal can be applied to protect the object from wear. Use of wear-resistant, protective coating allows the bulk of the object to be made out of a less expensive metal, and a relatively thin and more expensive metal is used to provide protection.
- A finish can provide a decorative coating. Jewelry is oftentimes plated with silver or gold just to provide a decorative finish. Chrome is plated to steel because it looks good and protects the steel from corrosion.
Priming and Painting
A coating of primer is applied to a metal surface to protect it from corrosion, and a coating of paint is applied to give it the desired color. Sometimes a clear coat is applied to protect the paint. The paint adheres to the primer, and the primer adheres to the metal surface. However, primer will not adhere well to a smooth surface. In this case, the metal will be etched in an acid bath to rough up the surface just enough so that the primer will stick to it.
Electroplating is an electrochemical process. Any metal that will dissolve in acid can be electroplated. The metal object to be plated is dipped in an acid bath and attached to the negative terminal of a direct-current power supply. The metal which is to supply the plating material is dipped into the same bath and connected the positive terminal of the power supply.
When electrical power is applied, the plating material begins to dissolve in the acid. In doing so, it picks up a positive electrical charge. The dissolved and charged particles are attracted to the metal object on the negative terminal. When they reach the object, they begin plating onto it.
If the temperature and acidity of the bath, amount of current, and time during which the object is immersed are carefully controlled, the electroplating process is capable of producing consistent results.
Electroless and Immersion Plating
Electroless and immersion plating don’t make use of electrodes or electricity and are purely chemical processes. In electroless plating, the object to be plated is immersed in a solution containing the dissolved metal to be plated and reacting agents. A chemical reaction takes place that bonds the plating metal to the object. Copper and nickel are plated using this process. Immersion plating is similar to electroless plating except that reacting agents aren’t used because the metal substrate makes the necessary reaction possible. Zinc and silver are plated using this process.
In Cleveland, metal finishing can be accomplished using etching, priming, painting, and plating processes.