By polishing the cold rolled steel sheet with an abrasive belt of a certain grain size (grit), a surface is obtained which has a silver-like metallic shine, which improves the decorative effect.
The finer the grain of the abrasive belt, the brighter and more even the finish. However, polishing can results in a surface finish that is poorer than that of the original finish. Polishing with a coarse grinding belt of grit P80 may for example give an Ra value of 1.0-2.0 µm. The roughness of the surface in this case is still not up to that of finish 2B. Using successively finer grit belts, an almost mirror-like surface can be produced. The mirror-finish has an Ra value of 0.02-0.05 µm.
Surface roughness and structure can also be affected by different polishing techniques, even if no differences are detectable with the naked eye. Wet polishing, for example, produces a finer surface than dry polishing. The grain size (grit) of the abrasive belt and the resultant surface roughness of the sheet do therefore necessarily not have a fixed relation. Wet polishing also produces a cleaner surface with less microscopic defects than dry polishing, this means that dirt, bacteria and corrosive substances generally do not attach as easily to wet polished surfaces. However, the dry polished surface has a more matte lustre that is often sought after in aesthetic applications.
The ground or polished surface has more or less clearly visible scoring, which also makes scratches from daily wear and tear less visible. A polished surface is also easy to re-create, for example after repairs or welding work, compared with a 2B or 2R surface.
Polished sheet is used for purposes where quality of appearance and hygiene are very important, such as:
- Commercial kitchens (work surfaces, cooking utensils, dishwashers, freezers)
- Households (cooking vessels)
- Public places (sanitary facilities, hospital equipment, kick-plates)
The use of brushing (with Scotch Brite®, for example), usually on a 2B surface, provides a silky-matt finish without clear grinding scores. A brushed surface also has the advantage that it can easily be re-created. The Ra value for brushed sheet can be around 0.1-0.4 µm. Brushed stainless steel sheet is used in situations where appearance is an important factor, such as:
- Buildings (sheet metal cladding and lift interiors)
- Vehicles (car hub caps, wall panels for express trains)
- Households (sink units)