What is Zinc Electroplating?
To protect metals such as iron and steel from rusting, one of the processes known as zinc electroplating is used. Zinc electroplating has to do with the electro-deposition of a thin layer of zinc metal on the surface of another metal which is known as substrate. The zinc coating serves as physical protection which prevents rust from affecting the underlying metal surface. The reason why zinc is chosen is its ability to fight corrosion.
Zinc Electroplating at Metaloft
Cleaning the Substrate
The first step is to clean the substrate (the metal for zinc plating); any contamination on the surface of the metal will prevent the zinc electroplating coating from properly adhering to the substrate. Typically, an alkaline detergent is used to clean the surface, soaking the metal in an alkaline bath for 5 –10 minutes at 150 F is generally enough to rid most of the surface of soil and dirt. After the initial bath, further cleaning is completed via an electro-cleaner. At the cathode or anode end of the metal, an electric charge is applied, producing the release of oxygen or hydrogen from the solution that cleans the substrate surface at a microscopic level.
To finish the preparation of the substrate, products are put through a process called activation, or pickling, which consists of submerging the metal into various acid solutions to remove oxides and scales which were formed on the metal during manufacturing, storage, and handling. Activation often uses acids, such as sulfuric acid or hydrochloric acid, and the type of metal and thickness of scale present will determine the dipping time, the acid type, and temperature required for the zinc electroplating process.
Preparation of the Plating Solution
The zinc electroplating process requires a specialized electrolyte solution for the substrate to be immersed into. This plating bath consists of a zinc metal ionic solution as well as various chemicals to assist in the plating process. The proper solution helps produce the required chemical and physical properties of the finishing plating and is often categorized into two types of baths. Acid Zinc baths are an efficient method of plating; they are fast and superior in covering, but they also provide poor throwing power and thickness distribution. Alkaline Zinc baths are less efficient and slower, but they produce a better thickness distribution and ductility.
Once ready for plating, the metal can be introduced to two methods of plating: either rack plating or barrel plating. Rack plating is designed for larger parts, and they are affixed to metal racks which are then submerged into a tank containing the plating bath. Barrel plating is designed for smaller parts, and instead of a tank, the parts are put into a barrel and rotated to provide a uniform finish. While in the bath, an electrical DC current is applied to a node for a set duration of time, which results in the zinc ions depositing onto the cathode (the substrate.) The flow of electricity has to be uniform, or else you’ll end up with an uneven zinc electroplating coating.
Rinsing and Drying
After the Zinc electroplating is completed, the now zinc coating substrate must be rinsed with water and then dried. If there is extra contamination, then it may be rinsed multiple times to ensure a clean surface. If additional protection is required, passivates and sealers can be applied after the rinsing.