Finishing Your Steel: Electropolishing vs. Passivating Stainless Steel

In Custom Wire Baskets, Wire Forms

Marlin Steel on June 9, 2015

Wire Basket 1045001For some custom metal basket applications, choosing the right finish for the basket can be 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, or other important operational aspects of the basket.

Two examples of popular finishes would be electropolishing and passivating. Both of these finishing processes involve removing contaminants from the surface of metal rather than adding material to it, leading some to confuse the two.

However, these are two very different processes, with different benefits and limitations.

Which one is best for your application? To answer this question, here’s a comparison of these two finishes:

Electropolishing

Electropolishing leaves steel with a clean, featureless surface 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.

This process 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. Some manufacturers use the process to smooth out threads of material to prevent galling and seizing.

Electropolished materials are also typically easy to clean because of the non-stick nature of the finished surface. The process can even remove the heat discoloration caused by spot welds.

Key advantages of this process include its ability to be used on very complicated shapes with ease and the speed with which it can be performed, providing a cost savings.

Passivation

As a process, passivation shares a few similarities with electropolishing. Like electropolishing, passivation involves using a chemical bath. However, unlike electropolishing, passivation does not involve the use of electrical currents to strip the top layer of material.

Passivation is primarily used to remove contaminants from the surface of stainless steel. Such contaminants are usually accrued during the manufacturing process.

Another key difference between passivation and electropolishing is that passivation does not typically change the appearance of the material being passivated.

Passivation is not necessary to form the oxide layer that protects stainless steel, but specific passivation treatments may thicken or change the composition of stainless steel’s protective oxide layer.

One major disadvantage of passivation is that the processor must know the specific alloy of stainless steel being treated before the process can be set up. Using the wrong passivation solution could cause damage to a metal form rather than simply stripping contamination from it.

Which Process is Better?

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.

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Author: Marlin Steel
Marlin Steel
Marlin Steel is a leading manufacturer of custom‐engineered products from steel wire and sheet metal. Its industrial material handling containers serve many industries including aerospace, defense, medical and automotive.

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