Zinc Electroplating Process

The zinc plating process provides a physical barrier that will stop the rusting process from starting.

There are ways to use zinc when it comes to plating, which includes:

• chloride zinc plating,
• alkaline non-cyanide zinc,
• alkaline cyanide zinc, and
• zinc alloy plating.
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• This said, the selection of any process will depend on the substrate, the coating, and the costs.

To achieve the best results in the zinc electroplating process, you must complete the right plating line with suitable equipment. These equipment include Industrial Tanks that can either be made of Polypropylene and SSTL, Filtration systems, Rectifiers, Heaters, Air Agitation lines, Cranes, Load Bars, Fume hoods, Copper Cathodes, Racks, Anode Baskets and Zinc Anodes.

Different Zinc Plating Processes

Since the zinc plating process has been available for many years, and as such, many procedures have been developed to apply zinc coatings depending on the type of substrates, the cost and the coating requirements.

There are some crucial factors you have to consider. You must check the processes available and their advantages and disadvantage. Therefore, before you chose any method of applying zinc to your products, consider the following:

1. What does the specification for the substrate require?
2. Is it a zinc deposit or zinc alloy deposit?
3. The corrosion protection requirement
4. The uniformity of the deposit thickness required.

After you have determined these factors, there are other secondary factors you have to consider like:

1. Deposit characteristics
2. Make-up and the cost of operation
3. Operating factors (pre-plate, corrosiveness, efficiency, etc.)
4. Environmental restrictions like heavy metal removal, air quality, ammonia, etc.

When you have evaluated these factors and compared them to your circumstances, you can narrow down the best choice for plating that will work for you.

Cyanide Zinc Electroplating

This process of electroplating was formally prevalent in the industry, but as a result of the regulations attached to using cyanide in zinc electroplating, the popularity dwindled gradually.

One good reason for choosing this plating method is that it can use a low current density to parts. However, one major setback to cyanide plating is the hydrogen embrittlement problem which disturbs the process.

Acid Chloride Electroplating

This process is newer than other methods. It brought a vast change in the industry and right now many people are using the process for all their zinc plating baths especially in developed countries.

One main advantage of this process is that is has a high cathode efficiency which makes the plating faster with fewer side reactions. Also, it requires minimal treatment of waste depending on the process you select.

However, it still has an advantage in that, the chemical used in the process is highly corrosive, and this nature cause’s solution is laying in recesses thereby posing a danger to the final coating if you fail to rinse it thoroughly.

Alkaline Non-Cyanide electroplating

In the industry today, people are still using this process because it is cost-efficient and reliable like chloride zinc process.

One setback to using this process is that the solution usually contains high-levels of carbonates which causes a reduction in the solution conductivity that hinders the depositing process.

Due to its complexity, zinc plating requires a high level of technical knowledge, expertise, special machinery and electroplating equipment, a rectifier, ancillary tank where the zinc anode will pass through a proper dissolution, plating station and the required reservoir are needed.

Typical Zinc Application Process

1. Preparation and cleansing of the surface.

The substrate’s surface should be adequately cleaned before plating so that any contaminants remaining on the surface will not prevent adequate adhesion of the zinc coating. Surface cleaning is done using alkaline detergent solution after which acid treatment is applied to wipe off surface rust.

2. The preparation process of the electroplating solution.

In other to prepare the solution needed, you will have to immerse the substrate into a specially formulated electrolyte solution otherwise known as the plating bath which consists of the zinc metal ionic solution and other chemicals that facilitates or catalyzes the plating processes. The ionic solution, as well as the compounds, also enhance the production of the desired chemical and physical properties of the finished product.

Acid zinc and alkaline zinc are the particular types of zinc used in this process.

Acid zinc is a popularly used plating technology. Its popularity base on its high efficiency, fast deposition, and superior covering power, although its demerit comes from its ability to provide low throwing power and thickness distribution.
Alkaline zinc offers less plating efficiency and a slower electro-deposition rate, though its degree of thickness distribution and flexibility is more pronounced than that of zinc.

3. Choose the best plating procedure

After the preparation of the solution, the parts involved are ready for plating. One might choose rack plating, in which larger particles are firmly fixed to the metal racks that are placed within the tank with the plating bath, and these parts remain stable during the plating process. Or barrel plating in which the components are kept in the barrel plating equipment and then rotated to provide smoother finishing. It is usually used in cases involving too smaller pieces for plating tank.

4. Electrical current

Electroplating is otherwise known as electrodeposition because electric current is used to deposit metals on metals or the surface of the substrate. The substrate serves as the cathode in zinc plating. There is an introduction of a direct current [DC] that originates from the anode into the bath. This current flows to the substrate and the zinc ions are deposited onto the surface. The circuit is then completed by the current flowing back to the anode from the cathode.

5. After production treatment procedure [post-treatment activities]

The parts are ready for post-treatment which involves rinsing the components in the water to remove any left-over contaminates and remnants of the plating bath at the finished or final stage of the electroplating process. The parts are expected to pass through thorough rinsing if heavy contamination is detected or suspected to ensure absolute dryness of the zinc plated parts. The application of passivates and sealers is necessary in the post-treatment process in cases where additional corrosion protection is highly needed.

Conclusion

Zinc plating has many benefits, but it does not work for every condition. When you expose the steel parts are at a temperature level of 500 degrees Fahrenheit or more, you should avoid using zinc.

Also, avoid using zinc electroplating for seawater or marine applications or in any tropical environment because they can contribute to forming heavy corrosion. Finally, don’t use zinc plating on equipment or products that you can ordinarily keep in closed areas where there is heavy moisture condensation.