Polishing (metalworking)

Polishing and buffing are finishing processes for smoothing a workpiece's surface using an abrasive and a work wheel or a leather strop. Technically, polishing refers to processes that uses 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.^[1] 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 appearance of an item, prevent contamination of instruments, remove oxidation, create a reflective surface, or prevent corrosion in pipes. In metallography and metallurgy, polishing is used to create a flat, defect-free surface for examination of a metal's microstructure under a microscope. Silicon-based polishing pads or a diamond solution can be used in the polishing process. Polishing stainless steel can also increase its sanitary benefits.

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 wax, oil, or lacquer. This is of particular concern for copper alloy products such as brass and bronze.^[2]

While used less extensively than traditional mechanical polishing, electropolishing is an alternative form of polishing that uses the principles of electrochemistry to remove microscopic layers of metal from a base surface.^[3] This method of polishing can be fine-tuned to give a wide range of finishes, from matte to mirror-bright. Electropolishing also has an advantage over traditional manual polishing in that the finished product will not experience the compression and deformation traditionally associated with the polishing process.

The condition of the material at hand determines what type of abrasive will be applied. The first stage, if the material is unfinished, starts with a rough abrasive (perhaps 60 or 80 grit) and each subsequent stage uses a finer abrasive, such as 120, 180, 220/240, 320, 400 and higher grit abrasives, until the desired finish is achieved. The rough (i.e. large grit) passes remove imperfections within the metal surface like pits, nicks, lines and scratches. The finer abrasives leave progressively finer lines that are not visible to the naked eye. A no. 8 ("mirror") finish requires polishing and buffing compounds, and polishing wheels attached to high speed polishing machines or electric drills. Lubricants like wax and kerosene^[4] may be used as lubricating and cooling media during these operations, although some polishing materials are specifically designed to be used "dry." Buffing may be done by hand with a stationary polisher or die grinder, 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 (a softer metal) there are often minute marks in the metal caused by impurities.

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.^[1]

Polishing knives and cutlery is known as fine glazing or blue glazing. Sand buffing, when used on German silver, white metal, etc., is technically a buffing operation because it uses a loose abrasive, but removes a significant amount of material, like polishing.^[1]

El pulido se puede utilizar para realzar y restaurar el aspecto de ciertas piezas u objetos metálicos en automóviles y otros vehículos, pasamanos , utensilios de cocina y elementos arquitectónicos metálicos. En otras aplicaciones, como en la industria farmacéutica, láctea y en fontanería especializada, las tuberías se pulen para prevenir la corrosión y eliminar los lugares donde pueden proliferar bacterias u moho. El pulido también se utiliza en la fabricación de reflectores de luz.

La tiourea tiene afinidad por ciertos iones de metales pesados, formando complejos de coordinación solubles . ^{[ 6 ]} Una consecuencia práctica de su afinidad por los metales es que la tiourea es un componente del abrillantador de plata . ^{[ 7 ]} Según la etiqueta de los productos de consumo TarnX ^{[ 8 ]} y Silver Dip , ^{[ 9 ]} los productos líquidos para limpiar plata contienen tiourea junto con una advertencia de que la tiourea es una sustancia química incluida en la lista de carcinógenos de California . ^{[ 10 ]}

• Mecanizado por flujo abrasivo
• Electropulido
• Afilado de cuchillos
• Acabado de superficies