Stainless steel electrolytic polishing and passivation

Stainless steel is widely used because of its high corrosion resistance and decorative properties, especially in medical equipment, food industry appliances, tableware, kitchen utensils and other aspects. Stainless steel appliances should be resistant to corrosion, the smooth and shiny appearance, clean, utensils surface should not be attached harmful substances. Therefore, it is necessary to completely remove the harmful substances of surface.

After hot processing or mechanical processing, the surface of stainless steel will form a black oxide layer, that will affect stainless steel appearance and performance, so taking appropriate measures to remove the black oxide layer is needed.

Here mainly describes two useful methods: the passivation and electrolytic polishing process

Passivation process:

Pretreatment – De-oiling – Cleaning – Deoxidation Layer – Cleaning – Passivation – Cleaning – Drying

Electrolytic polishing process:

Electrolytic polishing – cleaning – rinsing – air drying – passivation

Common problems and treatment methods of Passivation

Common ProblemCauseTreatment Method
The surface of the part has a loose black peeling or non-uniform appearanceheat treatment has a thicker oxide layer that is not removed completelySand blast or re-remove the oxide layer
Passivation film continuity and corrosion resistance test failedBefore passivation, oxide layer is not removed completely,  Iron in the solution is overmuch, passivation liquid is super periodSand blast or burnish and remove the oxide layer

Common problems and treatment of electrolytic polishing

Common ProblemsCauseTreatment Method
Local charredThe current is too large or the jig is not strongAdjust and check
Corner corrosionOverstand, overcurrent, excess TemperatureAdjust 
Parts have Yin and Yang and local fogging phenomenonThe parts are not opposed to the electrodes or the parts are overlapped with each otherCheck and adjust
The parts come from the same chemical tank, some are bright, some are not brightToo many parts in the same tank, the jig is big resulting in large difference in current density at different areaAdjust the jig structure
Polished parts are fogging, not brightSolution composition ratio imbalance, the use of time is too longAdjust the content and proportion
Black spots in localIt has oxide layer on the sufaceRemove the oxide layer

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polishing vs passivation


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