What Is A Mill Finish?
Mill Finish refers to the surface appearance and texture originally imparted to the brass, bronze or nickel silver extrusion to the product by the mill. For architectural extrusions mill finish is also refer to as “As Fabricated,” As Extruded,” “Hot Extruded” and “As Manufactured.” All of these terms refer to the condition of the raw extrusion as shipped from the mill.
Extruded products “mill finish” are slightly oxidized due to the hot extrusion process and are usually clean of dark staining but may have fine lines or die marks running down the parts. The general appearance is duller than the sanded or polished final product. The surface is smooth, but lacks reflectivity. Additional marking or discoloration may result where the product is subjected to fabricating processes such as roll straightening. This finish may not be suitable for end use applications without mechanical or chemical surface treatments.
Surface finishes of 125 to 250 mu in. can be expected for an architectural extrusion in brass, bronze or nickel silver. Since there are many applications where a mill finish is suitable for end uses we recommend that when in doubt, request a sample of your required alloy in its mill finish state. Any mill will gladly provide samples for your review.
The samples in the photograph above show architectural bronze and commercial redd metal in a mill finish and a quick polish without any other preparation. In many applications, a mill finish is suitable for a satin or polished surface without other secondary processes.
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