Electropolish vs. Passivation: Choosing a Stainless Steel Finish

January 7, 2021 | Custom Wire Baskets

marlin steel wire basketChoosing the right finish for your custom wire basket is just as important as choosing the right base material.

A well-chosen finish can help improve the functionality of the basket, improving chemical resistance, handling characteristics, and other important operational aspects of the basket.

Two examples of popular finishes are electropolishing and passivation.

 Let's discuss which finish is best for your application.

What Is Passivation?

Passivation is a metal finishing process that is widely used to prevent corrosion. For stainless steel, the passivation process involves using citric acid or nitric acid to remove free iron from the metal surface. 

The chemical treatment provides a thick protective oxide layer on the product, making it resistant to chemical reactions with the air that corrode the stainless steel. Passivation does not typically change the appearance of the material being passivated.

3 Benefits of Passivation

Here are three benefits of passivation:

1. Reduced Maintenance

The corrosion resistance that passivation provides helps to protect even the smallest parts of your stainless steel applications. This means you don't have to perform extra maintenance to ensure that rust doesn't weaken the bolts and small parts of your product that would cause your application to malfunction or fall apart. 

2. Removes Contamination

The passivation process removes all grease, oils, and dirt from the surface of the stainless steel, providing a uniform, smooth appearance and finish.

No matter what you use your finished custom stainless steel basket for, you can ensure it resists contamination and is easy to clean to maintain sanitation standards. 

3. Increases Corrosion Resistance

Stainless steel already has corrosion resistant properties, but the process of passivation strengthens these properties. It unipotentializes the surface of the stainless steel with the oxygen it absorbs, creating an oxide film. This results in a desired low corrosion rate of the metal.

What Is Electropolishing?

Electropolishing is a process that uses a temperature-controlled bath of electrolytes and an electric current to dissolve the surface layer of material. This process leaves only a smooth, featureless surface.

Electropolishing leaves steel with a clean, featureless surface

Electropolishing is commonly used for applications in the food and pharmaceutical industries, as well as in the manufacture of semi-conductors.

The smoothness of this finish leaves the material almost perfectly nonstick, as almost all of the microscopic flaws that debris would normally stick to are removed.

3 Benefits of Electropolishing Stainless Steel

Here are three benefits of electropolishing stainless steel.

1. Enhanced Surface Appearance

Electropolishing stainless steel gives a clean and shiny look to the surface of the metal. This makes it easy to tell if the stainless steel tool, basket, or part is sterile or not.

It also increases weldability without affecting the hardness of the surface or introducing peeling or abrading. 

2. Better Corrosion Resistance

Electropolishing produces the maximum resistance to tarnishing and corrosion in various metals and alloys. With Marlin's electropolished steel baskets, you can use them in a variety of harsh environments and be sure that they won't tarnish or corrode easily. 

3. Improved Sanitation Control

Electropolishing provides a smooth surface that eliminates microscopic pits for contaminants to hide.

Medical or pharmaceutical stainless steel applications need to be easy to sanitize to stop the spread of germs and viruses. Medical tools that have uneven or rough surfaces contain spots where microbes can hide. This increases the risk of contamination and bacteria, viruses, and other microbes may spread.

What Is Natural Finish?

Natural finish stainless steel refers to the natural appearance of the sheet. This means that no processing has been done to improve or protect the surface. The appearance is dull grey and has a minimally reflective surface. 

It is best for any application that is not visible, or applications where the appearance isn't important.

Why Finish Stainless Steel?

Here are some reasons why it's best to surface finish stainless steel rather than leaving a natural finish:

  • To withstand environmental conditions such as dust, harsh chemicals, solvents, and dust.
  • To get a smooth polished appearance. This is especially important when you use stainless steel applications for medical, manufacturing, or lab purposes.
  • To make sure the surface is easy to clean. This is necessary when using stainless steel in food production since polished stainless steel is easier to clean than natural finish stainless steel.
  • To become more resistant to impact, abrasion, corrosion, and scratches. 

Choosing the Right Finish For Your Custom Metal Basket Applications

In most cases, electropolishing is faster, easier to control, and can be applied to a number of different stainless steel alloys with ease. Plus, it provides a superior finish and removes discoloration that passivation would leave behind.

However, electropolishing isn’t always the better option. One of the key advantages of passivation is that it can alter the composition of the oxide layer that protects stainless steel from rusting. In some cases, altering the composition of the oxide layer can be useful for enhancing the steel’s resistance to corrosion.

Your choice of whether to electropolish or passivate your stainless steel should be based on the application that the steel will be used for.

If you need to have a smooth, easy to clean surface that’s free of defects, then electropolishing will be your best option. On the other hand, if you need a good way to remove surface contaminants while altering the corrosion resistance properties of the metal, then passivation might be the better option for you.

Custom Order Your Stainless Steel Products From Marlin

Order one of Marlin Steel's custom baskets and get advice from the experts about which stainless steel finish is best for your needs. 

These baskets and other stainless steel products are assembled by Marlin's engineers and highly-precise robots that provide fast production, so they can be shipped to you in no time. 

Contact the engineers at Marlin today to start your order.

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