In this guide, we will tackle a more complex method—electropolishing.
While it is more technical, and often requires specialized hardware to perform, it offers many of the benefits of both of the prior methods in a single treatment.
“Electropolishing offers many of the benefits of passivation and pickling methods in a single treatment.”
Also unlike other methods, this method is nearly universal, allowing treatment of most types of stainless with good results.
While some grades work better with electropolishing than others, there’s little risk of damage when completed properly and most grades will still achieve good results.
So how does electropolishing work? Let’s dig into the details…
The Basics of Electropolishing
Electropolishing works much the same as electroplating—but in reverse.
Instead of placing a layer of a new metal evenly across the surface of a piece of metal, electropolishing uniformly removes a layer of metal—often a chromium-depleted layer—leaving a fresh layer at the surface ready to withstand corrosion and environmental exposure.
Essentially, electropolishing is performed by creating an electrolytic cell involving a stainless steel object immersed in an acidic bath.
This removes inconsistencies and contaminants on the metal’s surface ion by ion—leaving a smooth, shiny surface when the process is complete.
Blending both the smoothing and cleaning benefits of pickling with the corrosion boosting benefits of passivation, electropolishing offers benefits few treatments can match.
Electropolishing: A Complex Solution for Corrosion Concerns
Of course, performing the electropolishing process isn’t as simple as other methods….
Requirements will vary based on the method you use and the parts you plan to treat. However, in most cases you’ll need:
- A pool to perform the process
- An electrolytic acid solution
- A strong, clean DC electricity source
- Protective gear and safety equipment
- A way to dispose of electropolishing waste
Note: While tanks may be used for electropolishing, the process creates gases. If not properly vented, this can lead to hazards such as ruptures and, in extreme cases, explosions.
In most cases, the electrolyte solution used is both acidic and highly viscous—with common options including mixtures of sulphuric and phosphoric acids.
Much like with passivation or pickling treatments, consulting MSDS information for all chemicals and following all recommended safety protocols is essential to reducing risk to both the stainless steel and personnel.
Thorough rinsing is also required after treatment to ensure no solution remains in welds, seams or cavities.
On top of this, monitoring the electrolyte pool throughout the process is essential.
Agitation is required to prevent streaks due to gassing or the creation of flow marks on the surface of the steel.
The temperature must remain stable in a concise range.
On top of this, the specific gravity of the mixture must also stay within a specific range depending on the solution used.
Where the electrodes connect to the metal is also critical to maximizing results.
While fairly straight-forward on simple shapes, fabricated parts and other complex shapes often require complex electrode setups to ensure that current flows evenly throughout the metal and creates a uniform passivation layer.
Benefits of Electropolishing and Typical Applications for Electropolished Stainless
Electropolishing is one of the more complicated methods of treating steel available.
However, in exchange, you get a lustrous finish, exceptional passivation, and long-lasting results.
It also brings a level of precision you can’t find with pickling, allowing you to remove a layer of metal as thin as 0.0001 inches from the surface of the steel.
Other benefits of electropolishing include:
- Works on complex shapes that are incompatible with physical polishing
- Single-step treatment that both cleans and passivates surfaces
- Removes minor burring for easier cleaning in operation
- Improves cleanability compared to most mechanically applied finishes
- Reduces bacterial growth in hygiene-sensitive environments
- Reduces surface stress on machined parts such as springs
- Improves reflectivity
- No risk of flash attack or hydrogen embrittlement
- More affordable than plating
These benefits make electropolished stainless steel popular across a wide range of industries, including:
- Textiles: Dye vats
- Pharmaceuticals & Food and Beverages: Processing tanks, brewing vessels, pipework, valves, powder hoppers, food mixing blades, water tanks, molds, and cutters
- Medical: Surgical instruments, surgical implants, vein stents, surfaces, and storage
- Architectural: Floor plating, handrails, sculptures, door fixtures, light fixtures, gates, and accents
Numerous specifications provide guidance on both performing electropolishing and assessing results.
Popular standards to consult include:
- ASME BPE Standards for Electropolishing Bioprocessing Equipment
- ASTM B912, Passivation of Stainless Steels Using Electropolishing
- SEMI F19, Electropolishing Specifications for Semiconductor Applications
- ISO 15730:2000 Metallic and Other Inorganic Coatings–Electropolishing as a Means of Smoothing and Passivating Stainless Steel
Due to the technical nature of electropolishing and equipment requirements, you may choose to outsource polishing or order fabricated parts pre-polished to reduce expenses and risk.
Choosing a qualified service provider is essential to getting the most out of your investment.
If you’re in need of advice on stainless steel purchasing or have a question about how stainless steel might help your business or industrial endeavors, Unified Alloys has more than 40 years of experience assisting operations across North America. Call today to discuss solutions to your needs.