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 Problem | Cause | Treatment Method |
| The surface of the part has a loose black peeling or non-uniform appearance | heat treatment has a thicker oxide layer that is not removed completely | Sand blast or re-remove the oxide layer |
| Passivation film continuity and corrosion resistance test failed | Before passivation, oxide layer is not removed completely, Iron in the solution is overmuch, passivation liquid is super period | Sand blast or burnish and remove the oxide layer |
Common problems and treatment of electrolytic polishing
| Common Problems | Cause | Treatment Method |
| Local charred | The current is too large or the jig is not strong | Adjust and check |
| Corner corrosion | Overstand, overcurrent, excess Temperature | Adjust |
| Parts have Yin and Yang and local fogging phenomenon | The parts are not opposed to the electrodes or the parts are overlapped with each other | Check and adjust |
| The parts come from the same chemical tank, some are bright, some are not bright | Too many parts in the same tank, the jig is big resulting in large difference in current density at different area | Adjust the jig structure |
| Polished parts are fogging, not bright | Solution composition ratio imbalance, the use of time is too long | Adjust the content and proportion |
| Black spots in local | It has oxide layer on the suface | Remove the oxide layer |
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Post time: Jan-07-2021