Most metals that contain high iron content will corrode and rust when not stored properly. Rust occurs when iron reacts with oxygen and water. The presence of these products of unwanted oxidation on parts affects aesthetics and can lead to catastrophic failure. Additionally, rusted parts are weak and deteriorate faster.
When using zinc plating for surface finishing, it is common to wonder if zinc plating can remove existing rust. While zinc plated results in a protective barrier that inhibits rust formation, it cannot amend an already corroded part. The presence of rust on a workpiece will interfere with the zinc plating process and lead to detrimental consequences. Read on to learn about zinc plating and the best methods for rust removal.
What is Zinc Plating
Zinc plating is an electrochemical process that uses zinc to coat the surfaces of other metals such as iron and steel. This additional layer of zinc improves the aesthetics and performance of the final part. To carry out zinc plating, you have to first prepare the surface of the workpiece by cleaning off all forms of contaminants. You then immerse the workpiece into an electrolyte solution containing zinc ions and pass a direct electric current. The ions flow continuously and become deposited on the workpiece surface as a solid layer.
Thereafter, clean and dry the final part and apply suitable post-treatment such as passivation to reinforce the zinc layer. When carrying out zinc plating, it is important to include additives such as brightness and surfactants. These additives ease the process and improve the quality of the coating.
Pros and Cons of Zinc Plating
Using zinc plating when finishing a part offers many benefits. It allows the part to perform maximally without breaking down. Let’s look at some advantages of the zinc plating process.
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Corrosion Resistance
Zinc plating offers sacrificial protection. When the parts are exposed to corrosive environments, the coating takes the fall to protect the substrate. Because the harsh chemicals will not get to the underlying metal in time, you can be sure of part durability and longevity. This ultimately saves costs as you do not have to replace the components frequently.
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Aesthetics
Parts coated with zinc metal are more visually appealing when compared to bare ones. The good thing about zinc plating is that you can further process it to improve its appearance and for customization purposes. This feature is important in jewelry and decorative applications. With zinc plating, you can boast of more sales. Components with a polished and matte look are more attractive to end users.
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Cost-effectiveness
Using zinc plating as the finishing technique in product development helps to reduce manufacturing costs. The equipment and consumables used in zinc plating are relatively affordable and accessible. Additionally, it is easy to carry out which reduces the cost of labor. Note that the unit cost of zinc plating decreases as the production volume increases.
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Electrical Conductivity
Zinc is a good conductor of electric current. It allows the free flow of electricity from one point to another. This makes zinc plating an excellent choice in applications where electrical conductivity is needed. Using zinc-plated components for electrical connectors, terminal, and wiring systems ensures performance over time.
While zinc plating has unparalleled advantages, it also comes with some shortcomings. The following are important limitations of zinc plating you should be aware of.
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Environmental Concerns
Zinc plating comes with some environmental issues because of the chemicals used. The process produces harmful wastes that can affect human health when released into the environment. Because of the potential damage zinc plating can cause, some regulations have been put in place for check and balance. Compliance with these laws will inevitably increase operating costs.
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Limited Thickness
The coating of zinc plating is usually between 10 to 20 micrometers thick depending on the dipping time and concentration of the solution. This limit can be a limitation for applications requiring thicker coatings such as places heavy duty protection is needed. Furthermore, you can experience cases of inconsistency in coating which can lead to part failure.
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Susceptibility to Damage
While zinc plating coatings are durable, they are susceptible to mechanical damage. They are soft and prone to scratching, flaking, and chipping. When this happens the underlying metal becomes exposed to attack from external sources. Furthermore, the process of repairing a previously plated part is challenging. You need to completely remove the old coating before applying a new one.
Does Zinc Plating Remove Existing Rust
No, the zinc plating process does not remove existing rust on a workpiece. Rather than remove, zinc plating protects the metal and prevents it from rusting. Note that the state of the workpiece determines how well the plating operation goes. The presence of rust can interfere with the electrochemical reaction. Additionally, rust prevents proper adherence of the zinc coating to the workpiece.
How to Remove Rust Before Zinc Plating
There are various ways one can remove rust before zinc plating. They are grouped under two broad categories namely mechanical and chemical.
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Mechanical Methods
This involves the use of physical tools to scrape away the rust particles from the surface of the workpiece. These methods are cheap and they do not require special skills to carry them out. The following are some common ways you can mechanically remove rust
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Abrasive Blasting
Abrasive blasting describes the process of propelling abrasives such as silica sand and glass beads at a high speed against the workpiece. Abrasive blasting is fast and the particles can reach all areas and contours. Additionally, the surface of the parts has a uniform appearance.
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Grinding
You can also grind the surface of the part to remove existing rust. The tool here is a grinding wheel made up of abrasive particles that rotate at a high speed to give very fine finishes. Grinding does not result in burrs and is suitable for heavy rust.
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Manual Tools
There are manual tools such as scrapers, chisels, and wire brushes you can use to scrape off rust. This method is cost-effective as you do not need special tools and high power to carry it out. However, the use of manual tools requires significant physical effort and can be time-consuming.
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Chemical Methods
Another way to remove rust is to use chemicals. Let’s discuss the various chemical methods for rust removal
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Acid Pickling
Acid picking is a chemical cleaning technique that entails immersing the part in an acidic bath. The acid which can be hydrochloric or sulfuric dissolves the rust and other contaminants. The time spent on acid pickling depends on the initial state of the workpiece.
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Electrolytic Process
You can also use electrochemical reactions to remove the rust particles. What you do here is to immerse the part into an electrically conducting solution made of water and sodium carbonate. This process converts the rust to iron.
Conclusion
Zinc plating is a common process used to coat parts in many manufacturing industries. It protects these components and gives them a beautiful look. However, zinc plating cannot remove an existing rust. Rather, you have to clean off the rust chemically, mechanically, or a combination of both techniques. When removing rust and other products of corrosion, you should assess the metal surface for the rust extent. With this, you can determine the most appropriate removal method. Do you have further questions and clarifications? Reach out to an industry-recognized zinc plating service provider today.