Finishing · Electrolytic polishing
Stainless Steel Electropolishing — a smooth, clean, corrosion-resistant part surface
Electropolishing, or electrolytic polishing, removes a thin, controlled layer of metal from the part, and with it micro-roughness, micro-burrs and light heat tint from welding. The surface of stainless and acid-resistant steel becomes smoother, easier to keep clean and better protected against corrosion. We can also laser cut, CNC machine, grind and inspect the part, all in a single order, with shipping across Poland.
01 · Scope of service
Electropolishing in Poznań — electrolytic polishing of stainless steel parts for companies across Poland
Do you need a part that is not only dimensionally accurate, but also smooth, clean and corrosion-resistant? Electropolishing finishes the surface of stainless steel where grinding and mechanical polishing fall short or cannot reach.
We offer electropolishing of stainless steel and acid-resistant steel: laser-cut blanks, milled and turned parts, bent and welded components. The process works wherever the current reaches, including edges and shallow recesses that a disc or belt cannot get to. In inside corners, deep holes and the insides of tubes, the effect is weaker (more on this below). This is why electropolishing works well for parts with complex geometry and for series in which every piece must look the same.
What you get with the electropolishing service
- Part assessment before the process: steel grade, surface condition, geometry, tolerances and the areas where a rack contact mark is acceptable.
- Surface preparation: grinding out scratches and welds before electropolishing, if the required result calls for it.
- Electropolishing with rinsing and drying: the part comes back clean and ready for assembly or packing.
- Post-process inspection: visual and dimensional; on request, measurement of critical dimensions on a CMM with a report.
Who is this service for?
For machine and equipment manufacturers, companies in the food, pharmaceutical and medical industries, and anyone with stainless steel parts after cutting, machining or welding who wants to deliver a smooth, uniform and durable component to their customer. Our facility is in Janikowo near Poznań, but we accept parts from companies across Poland, by courier or in person. You will find the full list of services in our offer, and you can read about the facility on the About us page.
02 · Technology
How does electropolishing work? Electrochemical polishing step by step
Electropolishing does not abrade metal; it dissolves it in a controlled way, fastest where the surface is roughest. Here is what happens to the part in the bath.
A part hung on a conductive rack becomes the anode, the positive pole of a low-voltage DC power source. Opposite it in the bath are the cathodes. The electrolyte is most often a mixture of phosphoric and sulfuric acid. Under the current, metal from the part's surface goes into solution, and hydrogen is released at the cathodes (and some oxygen at the part), which is where the gas bubbles in the bath come from. Current density, temperature and time are selected for the steel grade and the desired effect. The Euro Inox guide to electropolishing stainless steels gives typical values of 5–25 A/dm², 40–75 °C and 2–20 minutes.
Why do peaks disappear faster than valleys?
A thin, viscous layer of dissolution products forms at the surface of the part. It is thinnest over the peaks of the micro-roughness and the current density is highest there, so they dissolve fastest; the valleys are shielded and lose less. The surface profile smooths out, micro-burrs disappear, and sharp edges are slightly rounded. Iron and nickel go into solution more readily than chromium, so the passive layer that rebuilds after the process is richer in chromium. Because no tool presses against the surface, the process does not embed abrasive particles in it or leave a layer of deformed metal, and the hardness of the material itself does not hinder the process.
Process steps — from degreasing to drying
- Preparation: degreasing and removal of contaminants left from machining; grinding out scratches and welds if needed.
- Racking: mounting on a rack at points where a contact mark is acceptable.
- Electropolishing: a bath with parameters matched to the steel grade and the part.
- Rinsing, drying and inspection: removal of electrolyte residue from the surface and recesses, followed by evaluation of the result.
03 · Comparison of methods
Electropolishing vs. passivation and pickling of stainless steel, and mechanical polishing — which method should you choose?
All four methods improve the surface of stainless steel, but each does something different. The choice depends on whether appearance, micro-profile smoothness, removal of discoloration or corrosion resistance alone is what matters.
Chemical passivation (e.g., in nitric or citric acid, per ASTM A967) removes free iron and contaminants from the surface and speeds up the rebuilding of the passive layer, but it does not change the appearance or roughness and does not remove pronounced heat tint from welding. Pickling in a bath or with pickling paste (per ASTM A380) removes scale, weld discoloration and the chromium-depleted layer, but the surface becomes matte. Mechanical polishing gives a finish up to a mirror shine and removes scratches, but only where the tool reaches, and the microprofile may retain micro-scratches, a layer of deformed metal and embedded abrasive particles.
Electropolishing combines several of these effects: it removes a thin layer of metal, smooths the microprofile, removes light discoloration and passivates. The ASTM B912 standard describes it explicitly as a method of passivating stainless steels. It cannot replace grinding for deep scratches, though. That is why, when the requirement is "mirror finish and corrosion resistance," we first grind and polish the part, and electropolishing is the final step.
When to choose electropolishing, and when is passivation enough?
If the part only needs to regain full corrosion resistance after machining and appearance does not matter, passivation is often enough. If it needs to be smooth, easy to clean, free of micro-burrs and have a uniform shine, including on edges and in places a disc cannot reach, choose electropolishing. For welds with dark tint or scale, you usually start with pickling or grinding. Not sure which to choose? Describe the part and its operating conditions in the quote form and we will advise you.
Comparison of stainless steel surface finishing methods
| Method | Removes material | Appearance and roughness | Weld discoloration | Passive layer |
|---|---|---|---|---|
| Electropolishing | yes · typically 5–10 µm per side, more on edges | bright, smooth surface without micro-burrs; Ra usually reduced by tens of percent, at most by about half | removes light heat tint together with the chromium-depleted layer; for dark heat tint, pickling or grinding first | chromium-enriched — passivation method described in ASTM B912 |
| Chemical passivation | no (negligible) | unchanged — appearance and roughness as before the process | does not remove pronounced heat tint | restored after removal of free iron (e.g., ASTM A967) |
| Pickling (bath or paste) | yes · thin layer | matte surface | removes heat tint, scale and the chromium-depleted layer | restores itself after pickling; often combined with passivation (ASTM A380) |
| Mechanical polishing | yes · where the tool works | from matte to mirror finish; removes scratches, but micro-scratches, a layer of deformed metal and embedded abrasive particles may remain in the micro-profile | removes it mechanically — by grinding the discolored zone | does not strengthen it — passivation or electropolishing recommended after polishing |
04 · Welds and edges
Removing weld discoloration and deburring — electropolishing of welds, laser-cut parts and CNC parts
Rainbow heat tint at a weld and micro-burrs after cutting or milling are not just a matter of appearance. These are the spots where stainless steel is most susceptible to corrosion.
During welding, stainless steel heats up and oxidizes, and discoloration (heat tint) forms near the weld, in colors from straw through brown to blue. Beneath the oxides remains a thin layer of metal depleted in chromium, so corrosion resistance drops at that spot even if the material is acid-resistant. This is why discoloration near welds on stainless steel is often where rust blooms begin. Electropolishing dissolves light tint together with this layer and passivates the exposed surface, so it also serves as passivation of stainless steel after welding. Dark tint and scale must first be removed by pickling or grinding; the weld face remains visible, and the process does not remove welding defects. We assess the condition of the welds before quoting, based on photos or a sample.
Deburring of cut parts and components after CNC machining
Edges and peaks dissolve fastest, so electropolishing removes micro-burrs left after laser cutting, milling and turning, and slightly rounds sharp edges. This matters for parts that are handled by hand, for sealing surfaces, and anywhere a burr could break off while the machine is running. We remove larger burrs mechanically beforehand: electropolishing finishes the edge but does not replace deburring.
Stainless steel laser-cut parts straight from the laser
We cut stainless sheet on a fiber laser up to 20 mm, and we mill and turn parts in our CNC machining department. The striations on the edge after cutting thicker sheet will remain; electropolishing only softens them. The process itself can be the next step of the same order, with no need to look for another supplier and no second set of documentation.
05 · Part preparation
How to prepare a part for electropolishing: steel grade, geometry, contact mark and tolerances
The result of electropolishing depends largely on what happens to the part beforehand, from the choice of grade to the notes on the drawing. A few decisions at the design stage save rework.
Steel grade and surface condition
Unstabilized austenitic grades such as 1.4301 (AISI 304) or 1.4404 (AISI 316L) electropolish best. Titanium-stabilized grades, e.g., 1.4541 and 1.4571, are usually not electropolished, and in free-machining grades containing sulfur, e.g., 1.4305, sulfide inclusions can leave matte spots. The process also will not remove deep scratches, pores or pitting; it softens their edges, but they remain visible.
Geometry, holes and the rack contact mark
- Contact mark: a small mark is left where the part is mounted on the rack; indicate on the drawing the surfaces where it is acceptable.
- Holes and pockets: in deep blind holes and narrow gaps the effect is weaker, and gas collects in holes, so the position of the part on the rack matters.
- Closed profiles and tubes: these need vent and drain holes; the inside of a tube requires an internal cathode, otherwise the effect inside will be negligible.
- Edges and corners — outer edges lose more material than flat surfaces, inner corners less; specify functional sharp edges on the drawing.
- Cleanliness — no paint, marker, stickers or silicone greases, which interfere with the process.
Tolerances, fits and threads
The layer removed is typically 5–10 µm per side, so the shaft diameter decreases and the hole diameter increases by twice that amount — this matters for fits, threads and tight-tolerance dimensions. We account for the allowance already during milling and turning, and after the process we can verify critical dimensions as part of measurement and inspection of finished parts.
If the drawing calls out a standard (e.g. ISO 15730 or ASTM B912) or a roughness requirement Ra, include it in your inquiry. We will agree on the scope of inspection and documentation before quoting.
06 · Applications
Electropolishing for the food industry, pharmaceuticals and medicine — where a smooth surface matters
Electropolishing is used wherever a stainless steel surface needs to be easy to clean, corrosion-resistant and free of micro-burrs, from process piping to fittings and fixtures in public spaces.
Industries where electropolishing is used most often
The common denominator: for cleanability, Ra is not the only factor; the absence of micro-scratches, a deformed metal layer and embedded particles matters as well. That is why an electropolished surface is usually easier to clean than a mechanically polished one with the same Ra, and it keeps its corrosion resistance longer. If additional requirements apply, such as a finish class (e.g. ASME BPE), Ra for food-contact surfaces (EN 1672-2 and EHEDG guidelines, usually Ra ≤ 0.8 µm) or process validation for medical devices, include them in your inquiry. The Ra after the process depends on the initial Ra, so we will agree on surface preparation and the scope of inspection before quoting.
- Food and beverage industry — machine components, perforated screens and baskets, fittings and accessories where a smooth surface reduces buildup of deposits.
- Pharmaceutical and biotechnology — parts of agitators, tanks and process piping where cleanliness and repeatable washing matter.
- Medical and laboratory — components of equipment and instruments where burrs or micro-crevices are unacceptable.
- Chemical and energy — parts operating in aggressive environments where corrosion resistance matters.
- Automation and machine building — parts with holes and edges that cannot be polished evenly by mechanical means.
- Architecture and design — stainless steel elements in public spaces: uniform gloss and easier cleaning.
Why order electropolishing from ADJATECH?
Because a part doesn't have to arrive at our shop finished. We can cut, machine, grind, electropolish and measure it within a single order — with one point of contact and one party responsible for the result. We serve companies from Poznań, Greater Poland and all of Poland; you can find project examples in the our projects section, and you can send your questions via the contact page.
