Mill finish is the

surface texture Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a surface from the perf ...

(or finish) of

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

after it exits a

rolling mill In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...

extrusion Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...

die, or

drawing Drawing is a form of visual art in which an artist uses instruments to mark paper or other two-dimensional surface. Drawing instruments include graphite pencils, pen and ink, various kinds of paints, inked brushes, colored pencils, crayons, ...

processes, including sheet,

bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar * Chocolate bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a layer of cloud * Bar (u ...

, plate, or

structural shapes Structural steel is a category of steel used for making construction materials in a variety of shapes. Many structural steel shapes take the form of an elongated beam having a Profile (engineering), profile of a specific cross section (geometry ...

. This texture is usually rough and lacks lustre; it may have spots of

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

or contamination with mill oil. Most mill finish surfaces are

machined Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

or treated with

polishing Polishing is the process of creating a smooth and shiny surface by rubbing it or by applying a chemical treatment, leaving a clean surface with a significant specular reflection (still limited by the index of refraction of the material accordin ...

industrial etching Chemical milling or industrial etching is the subtractive manufacturing process of using baths of temperature-regulated etching chemicals to remove material to create an object with the desired shape. Other names for chemical etching inclu ...

, or some other

surface finishing Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. Finishing processes may be employed to: improve appearance, adhesion or wettability, solderability, corrosion re ...

process before they are considered complete. The quality and characteristics of mill finish can vary widely from one mill to another, and even from one lot (set of similar parts all processed consecutively or in a short time) to another.

Hot rolled In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...

parts are usually dark and dull, their surface oxidized from being hot worked. Extruded products may have die marks running the length of the stock. Other mill finishes are surprisingly smooth and uniform. It is possible for a mill to influence the finish of produced stock. Carefully maintained and polished rollers can increase the smoothness and

lustre Lustre or Luster may refer to: Places * Luster, Norway, a municipality in Vestlandet, Norway ** Luster (village), a village in the municipality of Luster * Lustre, Montana, an unincorporated community in the United States Entertainment * '' ...

of their product, and some rolling mills will follow rolling with an annealling process to give the stock a matte finish.

Sources

* * Metalworking {{metalworking-stub