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Surface Finishes of Stainless Steel Sheets
The surface finishes of stainless steels used in several industrial ambits not always assume a value of exclusively aesthetic type. There is, in fact, an intimate relationship between the finish type and the suitability for withstanding determinate aggressive environments. In general, we can anyway state that the smoother and more compact will be the sheet metal surface, with low roughness values, the higher will be its resistance to corrosion.
No.1 Finish is produced by rolling stainless steel that has been heated prior to rolling (hot-rolling). Since this finish is seldom used in fabricating, there is no way to duplicate it by hand without removing the “scale” and altering the finish appearance.
No.2B Finish is a bright, cold-rolled finish commonly produced in the same manner as No.2D, except that the final light-cold rolling pass is done using polished rolls. This produces a more reflective finish that resembles a cloudy mirror. Duplicating the bright, cold-rolled finish can be difficult because of the variation in finish from one manufacturer to another.
No.2D Finish is a uniform, dull silver-gray finish that is applied to thinner coils whose thickness has been reduced by cold rolling. The 2D finish is most often used in the manufacture of auto industry exhaust systems, trays, pans and items used in petro/chemical plants and roofing drain systems.
No.3 Finish is characterized by short, relatively coarse, parallel polishing lines, which extend uniformly along the length of the coil. This moderately reflective finish is used in the manufacturing of food processing equipment not having direct contact with food, plus brewery and restaurant equipment.
No.4 Finish is characterized by short, parallel polishing lines extending uniformly along the length of the coil. It is obtained by mechanically polishing a No.3 finish with gradually finer abrasives. This finish is the most popular finish for appliances, the food and beverage industry, elevators, escalators, hospitals and any work area where there is food contact. It is the favorite finish of architects and is often classified as a sanitary finish.
No.6 Finish is a dull, silver-white finish with relatively short linear polishing lines. It has a lower reflectivity than No.4 finish. This finish has ceased to exist in the marketplace as a traditional No.6 finish, though a satin finish is prevalent and sometimes mistakenly identified as a No.6 finish.
No.7 Finish has a high degree of reflectivity and a mirror-like appearance. A No.4 finish that has been polished to 320 grit is buffed for up to 10 minutes, but existing grit lines are not removed. The remnants of fine polishing lines can be seen by an observer standing several feet from a panel.
No.8 Finish is the most reflective polished finish that is covered by the ASTM standards. In comparison to a No.7 finish, the grit lines are much less visible, but they can be seen if the finish is examined closely. The resulting finish is mirror-like but not a perfect mirror.