Polishing and
buffing are finishing processes for smoothing a workpiece's surface using an abrasive and a work wheel. Technically
polishing refers to processes that use an abrasive that is glued to the work wheel, while
buffing uses a loose abrasive applied to the work wheel. Polishing is a more aggressive process while buffing is less harsh, which leads to a smoother, brighter finish. A common misconception is that a polished surface has a mirror bright finish, however most mirror bright finishes are actually buffed.
Polishing is often used to enhance the looks of an item, prevent contamination of medical instruments, remove oxidation, create a reflective surface, or prevent corrosion in pipes. In
metallographyMetallography is the study of the physical structure and components of metals, typically using microscopy.Ceramic and polymeric materials may also be prepared using metallographic techniques, hence the terms ceramography, plastography and, collectively, materialography.-Preparing metallographic...
and
metallurgyMetallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
, polishing is used to create a flat, defect-free surface for examination of a metal's
microstructureMicrostructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25X magnification . The microstructure of a material can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high /...
under a microscope. Silicon-based polishing pads or a diamond solution can be used in the polishing process.
The removal of oxidization (tarnish) from metal objects is accomplished using a metal polish or tarnish remover; this is also called polishing. To prevent further unwanted oxidization, polished metal surfaces may be coated with a wax, oil or lacquer. This is of particular concern for copper alloy products such as brass and bronze.
Process
Polishing is usually multistage process because the first stage starts with a rough abrasive and each subsequent stage uses a finer abrasive until the desired finish is achieved. The rough pass removes surface defects like pits, nicks, lines and scratches. The finer abrasives leave very thin lines that are not visible to the naked eye. Lubricants like wax and kerosene are used as lubricating and cooling media during these operations. Buffing may be done by hand with a stationary polisher or
die grinderA die grinder is a handheld tool which turns a burr or mounted abrasive stone at high speed. It is usually pneumatic , although electric die grinders are also common. The burr or stone is held in a collet and may be changed as required by the task at hand...
, or it may be automated using specialized equipment.
When buffing there are two types of buffing motions: the
cut motion and the
color motion. The cut motion is designed to give a uniform, smooth, semi-bright surface finish. This is achieved by moving the workpiece against the rotation of the buffing wheel, while using medium to hard pressure. The color motion gives a clean, bright, shiny surface finish. This is achieved by moving the workpiece with the rotation of the buffing wheel, while using medium to light pressure.
When polishing brass, there are often minute marks in the metal caused by impurities. To overcome this, the surface is polished with a very fine (600) grit,
copper platedCopper plating is the process in which a layer of copper is deposited on the item to be plated by using an electric current.Three basic types of processes are commercially available based upon the complexing system utilized:...
, then buffed to a mirror finish with an airflow mop.
Polishing operations for items such as chisels, hammers, screwdrivers, wrenches, etc., are given a fine finish but not plated. In order to achieve this finish four operations are required: roughing, dry fining, greasing, and coloring. Note that roughing is usually done on a solid grinding wheel and for an extra fine polish the greasing operation may be broken up into two operations: rough greasing and fine greasing. However, for inexpensive items money is saved by only performing the first two operations.
Polishing
knivesA knife is any cutting edge or blade, handheld or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools. Originally made of rock, flint, and obsidian; knives have evolved in construction as technology has with blades...
and
cutleryCutlery refers to any hand implement used in preparing, serving, and especially eating food in the Western world. It is more usually known as silverware or flatware in the United States, where cutlery can have the more specific meaning of knives and other cutting instruments. This is probably the...
is known as fine glazing or blue glazing. Sand buffing, when used on German silver,
white metalThe white metals are any of several light-colored alloys used as a base for plated silverware, ornaments or novelties, as well as any of several lead-base or tin-base alloys used for things like bearings, jewellery, miniature figures, fusible plugs, some medals and metal type.Some of the metals...
, etc., is technically a buffing operation because it uses a loose abrasive, but removes a significant amount of material, like polishing.
Equipment
Aluminium oxideAluminium oxide is an amphoteric oxide of aluminium with the chemical formula
23. It is also commonly referred to as alumina, corundum, sapphire, ruby or aloxite in the mining, ceramic and materials science communities. It is produced by the Bayer process from bauxite...
abrasives are used on high tensile strength metals, such as carbon and alloy steel, tough iron, and nonferrous alloys.
Silicon carbideSilicon carbide , also known as carborundum, is a compound of silicon and carbon with a chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
abrasives are used on hard and brittle substances, such as grey iron and
cemented carbideCemented carbide, also called tungsten-carbide cobalt or hardmetal or widia, is a hard material used in machining tough materials such as carbon steel or stainless steel, as well as in situations where other tools would wear away, such as high-quantity production runs. Most of the time, carbide...
, and low tensile strength metals, such as
brassBrass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. In comparison, bronze is principally an alloy of copper and tin. Despite this distinction, some types of brasses are called bronzes. Brass is a...
,
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
, and
copperCopper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable and a freshly-exposed surface has a pinkish or peachy color...
.
Polishing wheels come in a wide variety of types to fulfill a wide range of needs. The most common materials used for polishing wheels are wood, leather, canvas, cotton cloth, plastic, felt, paper, sheepskin, impregnated rubber, canvas composition, and wool; leather and canvas are the most common. Wooden wheels have emery or other abrasives glued onto them and are used to polish flat surfaces and maintained good edges. There are many types of cloth wheels. Cloth wheels that are cemented together are very hard and used for rough work, whereas other cloth wheels that are sewn and glued together are not as aggressive. There are cloth wheels that are not glued or cemented, instead these are sewed and have metal side plates for support. Solid felt wheels are popular for fine finishes. Hard roughing wheels can be made by cementing together strawboard paper disks. Softer paper wheels are made from felt paper. Most wheels are run at approximately 7500 surface feet per minute (SFM), however muslin, felt and leather wheels are usually run at 4000 SFM.
Buffing wheels, also known as mops, are either made from
cottonCotton is a soft, staple fiber that grows in a form known as a boll around the seeds of the cotton plant, a shrub native to tropical and subtropical regions around the world, including the Americas, India and Africa. The fiber most often is spun into yarn or thread and used to make a soft,...
or
woolWool is a fibrous protein derived from the specialized skin cells called follicles. The wool is taken from animals in the Caprinae family, principally sheep, but the hair of certain species of other mammals including: goats, llamas, and rabbits may also be called wool...
cloth and come bleached or unbleached. Specific types include: sisal, spiral sewn, loose cotton, canton flannel, domet flannel, denim, treated spiral sewn, cushion, treated vented, untreated vented, string buff, finger buff, finger buff, sisal rope, mushroom, facer, tampered, scrubbing mushroom, hourglass buff, rag, "B", climax, swansdown, airflow, coolair, and bullet.
The following chart will help in deciding which wheels and compounds to use when polishing different materials. This chart is a starting point and experienced polishers may vary the materials used to suit different applications.
Common buffing compound and wheel combinations
| | | Plastics | | Silver, gold & thin plates | | Nickel & chrome plating | | Copper, brass, aluminium, pot metal & soft metals | | Steel & iron | | Stainless steel |
|---|
| Buff type | Rough | Initial buff | Final buff | Rough | Initial buff | Final buff | Rough | Initial buff | Final buff | Rough | Initial buff | Final buff | Rough | Initial buff | Final buff | Rough | Initial buff | Final buff |
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| Sisal |
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X |
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X |
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X |
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| Spiral sewn |
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X |
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X |
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X |
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X |
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| Loose |
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X |
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X |
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X |
| Canton flannel |
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X |
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X |
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| String |
X |
X |
X |
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| Compound | | |
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| Black |
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X |
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X |
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X |
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| Brown |
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X |
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| White |
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X |
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X |
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X |
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| Blue |
X |
X |
X |
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X |
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X |
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X |
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| Green |
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X |
X |
| Red |
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X |
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X |
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X |
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- BLACK = Emery Compound, a coarse abrasive material for removal of scratches, pits, paint, rust etc.
- BROWN = Tripoli compound used for general purpose cut and color on most soft metals.
- WHITE = Blizzard compound, used for color and final finish of harder metals, has a cutting action.
- RED = Jeweller’s Rouge, designed to polish without any cutting action. Safe on thin plates. Use on its own wheel.
- BLUE = A dryer, almost greaseless wheel - designed to polish without any cutting action. Safe on thin plates. Use on its own wheel.
- GREEN = Used exclusively for Stainless Steel.
Applications
Polishing may be used to enhance the looks of certain parts on cars, motorbikes,
handrailA handrail is a rail that is designed to be grasped by the hand so as to provide stability or support. Handrails are commonly used while ascending or descending stairways and escalators in order to prevent injurious falls. Other applications include bathroom handrails—which help to prevent falls on...
s, cookware, kitchenware, and architectural metal applications. Pharmaceutical, dairy, and water pipes are buffed to maintain hygienic conditions and prevent corrosion. Buffing is used to manufacture of high-quality lighting reflectors.