Brushed metal is metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 that has been abraded

Abrasive machining

Abrasive machining is a machining process where material is removed from a workpiece using a multitude of small abrasive particles. Common examples include grinding, honing, and polishing...

 ("brushed"), usually with a fine grit sandpaper

Sandpaper

Sandpaper, also known as glasspaper, is a heavy paper with abrasive material attached to its surface.Sandpaper is part of the "coated abrasives" family of abrasive products. It is used to remove small amounts of material from surfaces, either to make them smoother , to remove a layer of material...

. The brushing gives the metal a distinctive look, as it retains some but not all of its metallic lustre

Lustre (mineralogy)

Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....

 and is given a pattern of very fine lines. It can be compared to metal with several small scratches all running in the same direction. Commonly used metals for brushing include stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

, aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 and nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

.

Stainless steel

Brushed stainless steel comes in various finishes. No. 3 and No. 4 are typical. These finishes are hard to repair when scratches appear. Another brush finish is the HairLine finish. The advantage of this finish is that the grain is continuous and runs the length of the sheet. The importance of continuous long grain HairLine finish is to allow for repair of minor scratches. One can easily repair scratches using the proper 80–120 grit abrasive pads or sandpaper and sand the length of the grain until the scratches are removed.

The surface of stainless steel is actually an extremely thin but stable and passive chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

-rich oxide film, on which stainless steel relies for its excellent corrosion resistance. The surface finish on stainless steel should therefore be developed and maintained to ensure this vital property, and also for the secondary reason of the pleasing aesthetic appearance of stainless steel.

Specifications

The Standard Mill Surface Finishes are laid down in Specifications (BS

British Standards

British Standards are the standards produced by BSI Group which is incorporated under a Royal Charter...

 1449, Part 4, and the Committee of Stainless Steel Producers, American Iron and Steel Institute

American Iron and Steel Institute

The American Iron and Steel Institute is an association of North American steel producers. Its predecessor organizations date back to 1855 making it one of the oldest trade associations in the United States. AISI assumed its present form in 1908, with Elbert H...

).

The finished are designated by a system of numbers, and these are broadly described hereunder relative to the finishing operations employed. It should be remembered that different grades of stainless steel can result in a variation of visual appearance for the same finishing operation. The thickness can also have an effect, generally the thinner the material the smoother the surface finish.

Preparation

The thicker gauge sizes of stainless steel are hot rolled. This is done at high temperatures and will always result in a scaled surface. Stainless steel flat product is supplied in the annealed

Annealing (metallurgy)

Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...

—i.e. fully softened—condition. This is also a high temperature operation and unless carried out in a very closely controlled inert

Inert gas

An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...

 atmosphere, will result in oxidation (scaling) of the surface. The scale is usually removed by a pickling

Pickling (metal)

Tarnision is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper, and aluminum alloys. A solution called Tarnision liquor, which contains strong acids, is used to remove the surface impurities...

 process, that is the removal of the scale by use of suitable acids, and then passivated

Passivation

Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...

 by the use of nitric acid

Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

.

No. 0 Finish

Also referred to as hot rolled annealed (HRA). The plate is hot rolled to required thickness, and then annealed. No pickling or passivation operations are affected, resulting in a scaled black finish.

This does not develop the fully corrosion resistant film on the stainless steel, and except for certain high temperature heat resisting applications, this finish is unsuitable for general end uses.

No. 1 Finish

Plate is hot rolled, annealed, pickled and passivated. This results in a dull, slightly rough surface; quite suitable for industrial applications which generally involve the range of plate thicknesses. Grinding marks may be visible in isolated areas.

Some of the thinner thicknesses within the plate range are cold rolled; but sheet, coil and strip gauges are produced by cold rolling, i.e. rolled without any heating of the material. Cold rolling hardens the material, and the thinner sizes may have to be subjected to an intermediate anneal and pickle, or bright annealed, during the reduction of thickness to final gauge.

The starting material for cold rolling always has a No. 1 finish. Cold rolled material is supplied with the following standard mill finishes.

No. 2D Finish

A no. 1 Finish after being cold rolled, annealed, pickled and passivated. This results in a uniform dull matte finish, superior to a No. 1 Finish.

Suitable for industrial application, and eminently suitable for severe deep drawing

Drawing (manufacturing)

Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis...

 as the dull surface, (which may be polished after fabrication) retains the lubricant

Lubricant

A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...

 during the drawing operation.

No. 2B Finish

A 2B Finish is given a subsequent light skin pass cold rolling operation between polished rolls.

This is the most common finish produced and called for on sheet material. It is brighter than 2D and is semi-reflective. It is commonly used for most deep drawing operations, and is more easily polished to the final finished required than is a 2D finish.

No. 2BA Finish

This is more commonly referred to as a bright annealed (BA) finish. Material with a No. 1 finish is cold rolled using highly polished rolls in contact with the steel surface. This smooths and brightens the surface.

The smoothness and reflectiveness of the surface improves as the material is rolled to thinner and thinner sizes. Any annealing which needs to be done in order to effect the required reduction in gauge, and the final anneal, is effected in a very closely controlled inert atmosphere. No oxidation or scaling of the surface therefore occurs and there is no need for additional pickling and passivating.

The final surface developed can have "mirror" type finish similar in appearance to the highly polished No. 7 and No. 8 Finishes.

Note: Much of the 2B Finish sheet imported is not a true 2B Finish. Mills which operate bright annealing facilities will often carry out all the annealing operations of cold rolled material in such facilities. This leads to a superior "2B" finish as no oxidation or scaling takes place during the annealing operation, even though the actual rolling may be effected on polished rolls as for normal 2B Finish, but not highly polished as would be needed to produce a BA finish.

The following finishes are all mechanically produced polished finishes. As well as being standard mill finishes, they are also applied to stainless steel articles and components to meet the required aesthetic criteria. It should be appreciated that factors such as hand polishing vs. mechanical polishing; polishing a flat product as against a component of complex shape; thickness and composition of material can affect the visual appearance of the final surface.

No. 3 Finish

This is a ground unidirectional uniform finish obtained with 80–100 grit abrasive.

It is a good intermediate or starting surface finish for use in such instances where the surface will require further polishing operations to a finer finish after subsequent fabrication or forming.

No. 4 Finish

This is a ground unidirectional finish obtained with 150 grit abrasive. It is not highly reflective, but is a good general purpose finish on components which will suffer from fairly rough handling in service (e.g. restaurant equipment).

No. 6 Finish

These finishes are produced using rotating cloth mops (Tampico fibre, muslin

Muslin

Muslin |sewing patterns]], such as for clothing, curtains, or upholstery. Because air moves easily through muslin, muslin clothing is suitable for hot, dry climates.- Etymology and history :...

 or linen

Linen

Linen is a textile made from the fibers of the flax plant, Linum usitatissimum. Linen is labor-intensive to manufacture, but when it is made into garments, it is valued for its exceptional coolness and freshness in hot weather....

) which are loaded with abrasive paste. The finish depends on how fine an abrasive is used, the uniformity and finish of the original surface. The finish has a non-directional texture of varying reflectiveness. "Satin Blend" is an example of such a finish.

No. 7 Finish

This is a buffed finish having a high degree of reflectiveness. It is produced by progressively using finer and finer abrasives and finishing with buffing compounds. Some fine scratches (grit lines) may remain from the original starting surface.

No. 8 Finish

This is produced in an equivalent manner to a No. 7 Finish, the final operations being done with extremely fine buffing compounds. The final surface is blemish free with a high degree of image clarity, and is the true mirror finish.

Faces

The finer polished finishes (No. 4, No. 6, No. 7 and No. 8) are generally only produced one side of the sheet, the reverse side being either a 2B or No. 3 Finish.