Electropolishing

Electropolishing combines a chemical bath with an electrical current that precisely removes a uniform layer of surface material from the part. It works to remove contaminants and microscopic imperfections such as cracks, burrs, jagged edges and more — for improved roughness average (Ra) up to 50%.

Electropolishing is the Swiss army knife of metal finishing in that it can eliminate the need for additional metal finishing processes like hand deburring, tumbling, sanding and other mechanical processes.

Passivation

During passivation, stainless steel parts are placed into a basket and submerged into a nitric or citric acid bath. Depending on the alloy, acid concentration, temperature and time can be adjusted to effectively remove free iron and other contaminants on the part’s surface.

By creating a chromium-rich, passive layer on the part surface, passivation improves corrosion resistance while also removing surface contamination. Parts are typically passivated in a bulk process.

Which is better for parts?

While passivation is useful for removing free iron and contaminants from metal parts, electropolishing offers a wider range of benefits:

  • Electropolishing is 30 times more effective than passivation in preventing corrosion (see salt spray test below)
  • Electropolishing improves pathogen resistance and cleanability for food and medical parts by removing microcracks and surface defects that create issues with effectively cleaning
  • Electropolishing can be used on far more metal alloys than passivation even when there are low levels of chromium and nickel — this includes aluminum, Nitinol and titanium
  • Electropolishing provides a bright, clean and uniform appearance

Side-by-side comparison

Figure 1: A side by side comparison. Source: Able ElectropolishingFigure 1: A side by side comparison. Source: Able Electropolishing

Corrosion protection

Below are results from an independent lab’s testing of eight stainless steel alloys after 24 and 888 hours of ASTM B-117 salt spray testing. The test was performed on unpolished and passivated coupons, passivated coupons and electropolished coupons. See the results below.

Figure 2: Results from an independent lab’s testing of eight stainless steel alloys after 24 and 888 hours of ASTM B-117 salt spray testing. Source: Able ElectropolishingFigure 2: Results from an independent lab’s testing of eight stainless steel alloys after 24 and 888 hours of ASTM B-117 salt spray testing. Source: Able Electropolishing

More stainless steel corrosion examples

A set of parts was submitted to ASTM B-117 salt spray testing at an independent testing facility. The test parts included a wire weldment fabricated from 304 stainless steel. The testing was performed for 144 hours on each part in the raw, passivated and electropolished state.

What materials can I passivate?

Figure 3: What materials can be passivated. Source: Able ElectropolishingFigure 3: What materials can be passivated. Source: Able Electropolishing

See it in action

Watch the video on electropolishing versus passivation to see the metal finishing processes in action.

Electropolishing for precise, consistent and effective metal finishing

Passivation and electropolishing are chemical processes for improving the surface finish of metal parts, but only electropolishing can consistently and precisely remove surface imperfections and improve Ra by up to 50% for a wide variety of metal alloys including stainless steel, aluminum, titanium, Nitinol and many other metal alloys. Don’t trust critical parts to anything less.

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