A process known as zinc plating is frequently used to protect metals such as iron and steel against corrosion. Rust, being the biggest threat to any metal, has corrosive effects that can be devastating when serving larger applications within the automotive, military, and industrial fields. According to NACE, The global cost of corrosion is estimated to be US$2.5 trillion, which is equivalent to 3.4% of the worldwide GDP.
Zinc plating involves electroplating a thin coating of zinc metal onto the surface of another metal object – a substrate. The zinc coating creates a physical barrier that prevents rust from reaching the underlying metal surface. Zinc is chosen because of its ability to fight corrosion. Great Lakes Metal Finishing has been performing high-quality zinc and zinc-nickel plating for over 25 years to provide customers with products to protect against rust.
The Zinc Plating Process
Zinc plating is a relatively complex process that requires a high level of expertise. When preparing to plate, it’s essential to clean the surface of the substrate before plating thoroughly. Any contaminants remaining on the surface could prevent proper adhesion of the zinc coating. After preparing the surface and the plating solution with either acid zinc or alkaline zinc, the parts are ready for plating. Engineers must decide between rack plating and barrel plating, which often depends on how large the piece being plated is. After choosing between rack and barrel plating, the actual act of electroplating is performed.
Finally, the post-treatment procedure is performed. Upon completion of the electroplating process –zinc plating–the parts are rinsed off in water to remove any remaining contaminants. In cases of heavy contamination, the components may need to be rinsed several times before being dried thoroughly. In situations where additional corrosion protection is required, the application of chrome-free passivates or hexavalent chromates along with optional topcoats or torque modifiers can be applied at this time.
Factors that Impact the Results of Zinc Finishing
There are a variety of factors that can influence the outcome of a zinc plating project, most of which can be effectively managed and controlled by an experienced metal finishing solutions provider. Some factors include the temperature of the plating bath and the level of zinc concentration in the plating solution. Higher bath temperatures tend to reduce hydrogen diffusion and increase the consumption of brighteners and other additives, whereas the level of zinc concentration will affect the brightness and texture of the plated product. Higher concentrations will produce a rougher surface, while lower concentrations will result in a brighter finish with elegant crystals.
Other controllable factors that affect the result when plating with zinc include:
- Substrate surface condition
- Use of additives such as surfactants and brighteners
- The concentration of hydrogen ions
- Duration of actual plating time along with amps per sq. ft of surface area
- Degree of filtration of the zinc plating bath
- The efficiency of the rinsing operation
While there are plenty of benefits to zinc plating, the process is not ideal for every situation. The applied zinc coating will generally be dull-gray in color, although post-treatment chromates are available in a wide range of colors, including yellow, black, clear, and olive drab. Many are available as chrome-free passivates or hexavalent chromates.
How Does a Zinc Coating Prevent Corrosion?
One of the most important benefits of zinc plating is that it will significantly increase the corrosion resistance of the underlying substrate. But how does this happen? Zinc coating is a sacrificial coating, meaning the finish will corrode before of the metal substrate that it protects. Additionally, zinc creates zinc hydroxide, which bonds with carbon dioxide to produce a thin layer of zinc carbonate. The zinc carbonate adheres to the zinc on the coated metal to provide even more corrosion protection.
Frequently, zinc is alloyed with other metals, which can result in improved performance than when plating with zinc alone. A zinc-nickel alloy, which can consist of a nickel component of anywhere from 6% to 20%, can dramatically increase corrosion protection. Zinc-nickel is now widely used in automotive industry applications and is available in both rack and barrel applications.
Zinc Plating for Military, Automotive, & Industrial Applications
Zinc plating is used for many industrial applications. Zinc can provide a corrosion-resistant coating on smaller metal parts such as nuts, bolts, screws, and fasteners. In general, most hardware parts are coated with zinc. Zinc plating has also gained widespread use in the automotive industry as a means of protecting parts such as brake pads, brake calipers, and power steering components. Additionally, zinc plating is used in the production of tanks, armored personnel carriers, and other heavy military vehicles, in addition to military weaponry.
Other Benefits to Zinc Plating | Why Choose Zinc Finishing?
Besides zinc’s capability to tolerate temperatures of up to 650°F with a melting temperature of 787°F-– which can help lower cooling costs -– zinc offers excellent protection against corrosion. Other key reasons to choose zinc plating include:
- Cost-effective plating
- Flexibility & Ductility
- Environmentally friendly
Because zinc can be found very easily, it is viewed as a more cost-effective plating process. When using metals such as gold or palladium, they tend to be more expensive because they are harder to obtain. This makes zinc plating a preferred choice for any company that is keeping a close eye on expenditures.
Flexibility & Ductility
Zinc is compatible for use in a wide range of bath chemistries, providing greater flexibility for customizing the plating outcome. Zinc is also amenable to both rack and barrel plating processes. Zinc is an extremely ductile metal, meaning it can be stretched into long, thin strands without breaking. This makes zinc easy to contour to the shape of the underlying substrate.
Before zinc plating, cadmium was the preferred metal for electroplating in applications where maximum protection against corrosion was required. However, cadmium is a highly toxic substance that can have a cumulative poisoning effect over an extended period. Zinc plating is considered to be a relatively eco-friendly process, especially when compared to its cadmium counterpart. Zinc also offers the advantage of recyclability.
Zinc plating can improve the appearance of an iron or steel part or component. The introduction of colors during post-treatment can also help you customize the look of the finished product. GLMF offers a wide range of colors, including yellow, black, clear, and olive drab plating services, both trivalent and hexavalent, along with various dye colors.
Measuring the Effectiveness of Plating With Zinc
There are a variety of factors that contribute to how long a zinc coating will provide reliable protection against corrosion. An excellent way to assess the effectiveness of a zinc finish is through the application of a procedure known as salt spray testing. Frequently used by the automotive industry, salt spray testing consists of spraying the parts with a 5% salt solution dissolved in water in a closed cabinet at a constant temperature. The testers record how long it takes for the appearance of “white” rust, a powdery substance that often forms on the zinc-coated steel, as well as the more destructive “red” rust. This indicates whether or not the zinc plating process needs to be adjusted to comply with the desired manufacturing tolerances.
The quality of the coating is vital, which is why you should carefully evaluate the company you choose to provide your zinc plating services. Thicker coatings and the use of the right post-treatment products can also increase protective capabilities. The surrounding environment also plays a critical role in the formation of corrosion.
Great Lakes Metal Finishing Company Offers Comprehensive Zinc Plating Services
GLMF is your source for cost-effective zinc plating solutions that can be customized to the needs of your industrial, automotive, or manufacturing operations. We offer zinc plating that can provide a protective coating for nuts, bolts, screws, metal brackets, and other essential parts. During salt spray testing, our zinc-nickel plated parts were able to withstand the formation of white rust exceeding 400 hours and red rust to exceeding 1,200 hours. Our zinc-nickel plating process has also become a preferred choice in the automotive industry due to its excellent corrosion protection. Contact us today to learn more about the many benefits of zinc plating to find the best fit for your application.