Electropolishing

A smoother, cleaner, more corrosion resistant stainless surface than mechanical polishing can reach.

How it works

The part is immersed in an electrolyte bath, an acidic solution such as sulfuric or phosphoric acid, and connected to the positive terminal of a power supply so the part becomes the anode. Current concentrates on the microscopic peaks of the surface, which release metal ions toward the negatively charged cathode first. The peaks come down faster than the valleys. On stainless steel the process typically removes 20 to 40 micrometers (0.0008 to 0.0016 in) of material, leaving a smooth, bright, sanitary finish.

Advantages over mechanical polishing

• No heat, no embedded abrasive. Mechanical polishing can be aggressive enough to overheat the surface, deform thin parts or embed abrasive particles.
• Reaches irregular shapes where abrasives are impractical, and removes the fine directional lines mechanical polishing leaves behind. It also deburrs small imperfections.
• More sanitary. A microscopically smooth surface gives bacteria less to hold on to.
• More corrosion resistant. The process removes surface iron, leaving the surface richer in nickel and chromium.

Mechanical preparation is still needed on surfaces coarser than about 220 grit before electropolishing.

Welds have to be right first

Electropolishing exposes what is underneath. A weld with hidden voids or poor penetration becomes a problem in the bath. Sound, full penetration welds electropolish without issue. Every N.B. Oler solvent tank is welded before it is electropolished, so the weld has to be right before it ever sees the bath.

Where it is used

Electropolished stainless is the norm wherever the finished product is consumed: cannabis extraction, pharmaceutical, medical and dental, and food and beverage. It is also used where improved corrosion resistance matters, such as aerospace and automotive components.

Sources. Cutchin, J. H., Electropolishing Applications and Techniques, The Fabricator (2015); Delstar Metal Finishing, Electropolishing vs Mechanical Polishing (2015); New England Electropolishing, Electropolishing Basics (2020); Electro-Glo Distribution, 7 Industries That Depend on Electropolishing (2019).