Brush (electric)

A brush or carbon brush is a device which conducts current between stationary wires and moving parts, most commonly in a rotating shaft. Typical applications include electric motors, alternators and electric generators.

Carbon brushes
A pair of carbon brushes


For certain types of electric motors or generators to function, the coils of the rotor must be connected to complete an electrical circuit. Originally this was accomplished by affixing a copper or brass commutator or 'slip ring to the shaft, with springs pressing braided copper wire 'brushes' onto the rings which conduct the current. Such brushes provided poor commutation as they moved from one commutator segment to the next. The cure was the introduction of 'high resistance brushes' made from graphite (sometimes with added copper). Although the resistance was of the order of tens of milliohms, they were high resistance enough to provide a gradual shift of current from one commutator segment to the next. The term brush remains in use. Since the brushes wear out, they can be replaced in products intended to allow maintenance.

Metal fiber brushes are currently being developed. They may have advantages over current brush technology, but have not yet seen wide implementation.

Manufacturing process

Mixing components

Exact composition of the brush depends on the application. Graphite/carbon powder is commonly used. Copper is used for better conductance (rare for AC applications and not on automotive fuel pumps which run on carbon commutators). In order to maximize electrical conductivity and green strength, highly dendritic (electrolytic) copper powder is used.[1] Binders, mostly phenol or other resins or pitch, are mixed in so the powder holds its shape when compacted. Other additives include metal powders, and solid lubricants like MoS2, WS2. Much know-how and research is needed in order to define a brush grade mixture for each application or motor.

Compacting the mixture

The brush compound is compacted in a tool consisting of upper and lower punch and die, on mechanical or hydraulic presses. In this step, depending on later processing, the copper-wire (called shunt wire) can be inserted automatically through a hole in the upper punch and fixed into the pressed brush block by the powder pressed around. This operation, called "tamping", is usually performed using electrolytic copper powder, possibly with silver coating for some high performance applications.[2] After this process, the brush is still very fragile and in professional jargon called a 'green brush'.

Firing of green brushes

Next follows heat treatment of the "green brushes" under artificial atmosphere (usually hydrogen and nitrogen). Temperatures range up to 1200 °C. This process is called sintering or baking. During sintering, the binders either burn off or carbonize and form a crystalline structure between the carbon, copper and other additives. Baking is followed by graphitization (heat treatment). The heat treatment is transformed by a temperature curve exactly defined for each material mixture. Besides the mixture composition, the used temperature curve is the second big “secret” of each brush manufacturer. After the heat treatment, the brush structure is modified in a way which makes copying of the brush nearly impossible for competing companies.

Secondary operations

Sintering causes the brushes to shrink and to bend. They must be ground to net shape. Some companies use additional treatments in order to make the brush more durable by methods such as impregnation of the running surface by special oils, resins and grease.

Manufacturing of carbon brushes requires an in-depth knowledge of materials and experience in mixture compositions. Very small changes in brush contents by just a few percent of components by weight can significantly change the properties of brushes on their applications. There are just a handful of brush developing companies in the world, which are mostly specialized on certain types of brushes.

Carbon brushes are one of the least costly parts in an electric motor. On the other hand, they usually are the key part which delivers the durability (“life-time”) and performance to the motor they are used in. Their production requires very high attention to quality control and production process control throughout all steps of the production process.

Liquid metal brushes

From time to time the use of liquid metals to make contacts is researched. Drawbacks to this approach include the need to contain the liquid metal (as it is usually toxic or corrosive) and power losses from induction and turbulence.

See also


  1. ^ Zanon, Matteo; Rampin, Ilaria; Breda, Alessandro; Bortolotti, Francesco (2015-10-05). "The sintering behaviour of electrolytic and water-atomized copper powders".
  2. ^ Zanon, Matteo; Nassuato, Mirko; Rampin, Ilaria; Echeberria, Jon; Martinez, Ane Maite (2014-09-23). "The conductive behaviour of copper and silver-coated copper powders".
Arc lamp

An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, was the first practical electric light. It was widely used starting in the 1870s for street and large building lighting until it was superseded by the incandescent light in the early 20th century. It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II. The carbon arc lamp is now obsolete for most of these purposes, but it is still used as a source of high intensity ultraviolet light.

The term is now used for gas discharge lamps, which produce light by an arc between metal electrodes through an inert gas in a glass bulb. The common fluorescent lamp is a low-pressure mercury arc lamp. The xenon arc lamp, which produces a high intensity white light, is now used in many of the applications which formerly used the carbon arc, such as movie projectors and searchlights.

Boulton Carbon Company

The Boulton Carbon Company was a manufacturing company located in Cleveland, Ohio, USA, from 1881 to 1886. It was devoted to the manufacture of carbon points (or carbons) used for arc lighting. The company was organized in 1881 by W. H. Boulton and Willis U. Masters and formally incorporated in 1883. A controlling interest in the company was acquired in 1886 by a group of investors led by Washington H. Lawrence. In 1886, Lawrence reorganized the Boulton Carbon Company as the National Carbon Company. Under the leadership of Lawrence, the National Carbon Company became the dominate carbon company in the United States and was one of the founding members of the Union Carbide & Carbon Company in 1917.


A brush is a common tool with bristles, wire or other filaments. It generally consists of a handle or block to which filaments are affixed in either a parallel or perpendicular orientation, depending on the way the brush is to be gripped during use. The material of both the block and bristles or filaments is chosen to withstand hazards of its intended use, such as corrosive chemicals, heat or abrasion. It is used for cleaning, grooming hair, make up, painting, surface finishing and for many other purposes. It is one of the most basic and versatile tools in use today, and the average household may contain several dozen varieties.

Brush Electric Illuminating Company

Brush Electric Illuminating Company was a Manhattan, New York business of the late 19th century. In April 1881 it made a bid to the New York City gas commissioners to provide lighting to the district encompassing Broadway and Fifth Avenue, from 14th to 34th Streets. It included the cross streets in between as well as Union Square and Madison Square.The New York City Board of Aldermen granted Brush the lighting contract by voting over the veto of New York City Mayor William Russell Grace. The system of lighting required two electrical circuits. One of the circuits was for lighting the squares with two large lamps. The other was for lamps located at intervals along the streets of the city. Each square was to contain a light elevated 208 feet above the ground. It was to be mounted upon an ornamental pole or tower.

Brush Electrical Machines

Brush Electrical Machines is a manufacturer of electrical generators typically for gas turbine and steam turbine driven applications. The main office is based at Loughborough in Leicestershire, UK.

Brush Traction

Brush Traction is a manufacturer and maintainer of railway locomotives, part of Wabtec Corporation, based at Loughborough in Leicestershire, UK, and situated alongside the Midland Main railway line.

Charles F. Brush

Charles Francis Brush (March 17, 1849 – June 15, 1929) was an American engineer, inventor, entrepreneur, and philanthropist.

De Saisset Museum

The de Saisset Museum at Santa Clara University opened in the early 1950s after Isabel de Saisset, the last member of a French pioneer family bequeathed her estate to the University of Santa Clara. The museum owns nearly 10,000 art pieces and historical artifacts, including the work of early Californian artist and university alumnus Ernest de Saisset and a considerable collection of California mission artifacts. The de Saisset recently completed a major renovation of its storage facilities and is open to the public free of charge.

John W. Lieb

John William Lieb (February 12, 1860 in Newark, New Jersey – November 1, 1929 in New Rochelle, New York) was an American electrical engineer for the Edison Electric Light Company. Lieb was president of the American Institute of Electrical Engineers from 1904 to 1905. He received the IEEE Edison Medal for "the development and operation of electric central stations for illumination and power."

Lytham St. Annes Corporation Tramways

The Lytham St. Annes Corporation Tramways and its predecessor companies operated an electric tramway service in Lytham St Annes between 1903 and 1937.

National Carbon Company

The National Carbon Company was founded in 1886 by the former Brush Electric Company executive W. H. Lawrence, in association with Myron T. Herrick, James Parmelee, and Webb Hayes, son of U.S. President Rutherford B. Hayes, in Cleveland, Ohio. In 1890, National Carbon merged with Thomson-Houston, Standard Carbon, and Faraday Carbon.

In 1894 the company began marketing Leclanché wet cells. At the same time, E. M. Jewett, was working in the company's Lakewood plant on the west side of Cleveland, under the direction of George Little. Jewett became interested in dry cells and, in his free time, conducted experiments in the laboratory. He developed a paper-lined, 1.5 volt cylindrical dry cell which he showed to Lawrence, who gave Jewett and Little a green light to begin manufacturing commercial dry cells. The trademark "Columbia" was proposed by Nelson C. Cotabish, a sales manager at NCC. In 1896 the company marketed the very first battery intended for widespread consumer use: the sealed, six-inch, 1.5 volt Columbia. NCC was the first company to successfully manufacture and distribute sealed dry cell batteries on a large scale.The company introduced the first D cell battery in 1898.

The existing National Carbon Company grew significantly in 1899. The firm "incorporated under New Jersey laws January 16, 1899 as a consolidation of the following companies engaged in the manufacture of lighting carbons, carbon brushes for generators and motors, carbon batteries, carbon diaphragms and back plates for telephones, carbons for electrolytic purposes and kindred products.

American Carbon Co Noblesville Ind

Brush Carbon Works Cleveland Ohio

Faraday Carbon Co Jeannette, Pennsylvania

Globe Carbon Co Ravana Ohio

National Carbon Co Cleveland Ohio

Partridge Carbon Co Sandusky Ohio

Phoenix Carbon & Mfg Co St. Louis Mo

Solar Carbon & Mfg Co Pittsburgh

The Standard Carbon Co Cleveland Ohio

Thomson Houston Carbon Co Fremont, Ohio

The Washington Carbon Co Pittsburgh

The company supplied approximately 75% of the US carbon market in the world.In 1906, National Carbon Company, which had been supplying Conrad Hubert's American Electrical Novelty & Manufacturing Company (maker of Ever Ready flashlights and batteries) with materials for batteries, bought half interest in the company for $200,000. The name was changed to The American Ever Ready Company and the trademark was shortened to one word - Eveready. In 1914, The American Ever Ready Company became part of National Carbon Company now forming a manufacturer making both batteries and lighting products.

In 1917, Union Carbide acquired National Carbon Company.

From 1917 until 1921 Eveready used the trademark "DAYLO" for their flashlights and on their batteries.

The American Chemical Society designated the development of the Columbia dry cell battery as a National Historic Chemical Landmark on September 27, 2005. The commemorative plaques at Energizer in Cleveland and at Energizer headquarters in St. Louis read:

In 1896 the National Carbon Company (corporate predecessor of Energizer) developed the six-inch, 1.5 volt Columbia battery, the first sealed dry cell successfully manufactured for the mass market. The Columbia, a carbon-zinc battery with an acidic electrolyte, was a significant improvement over previous batteries, meeting consumer demand for a maintenance-free, durable, no-spill, inexpensive electrochemical power source. Finding immediate use in the rapidly expanding telephone and automobile industries, the Columbia launched the modern battery industry by serving as the basis for all dry cells for the next sixty years.

St. George Lane Fox-Pitt

St. George William Lane Fox-Pitt (born 14 September 1856 in Malta, died 6 April 1932 in South Eaton Place) was a British electrical engineer and student of psychic phenomena.

His parents were Lieutenant General Augustus Henry Lane-Fox (1827–1900) and Alice Margaret (1828–1910, née Stanley). When his father's cousin Horace Pitt, 6th Baron Rivers, died, the family took the name Fox Pitt-Rivers on May 25, 1880.

In 1878, Fox-Pitt was granted a patent on a light bulb with a platinum-iridium filament. The patent also describes a system for power distribution using incandescent lamps in parallel.On 12 December 1879, Charles Francis Brush founded the Anglo American Electric Light Company Ltd. in the UK and then acquired the patent rights to produce the Lane-Fox incandescent lamp in the same year. On 24 March 1880, he founded a new company, Anglo-American Brush Electric Light Corporation, which took over the previous one.

About 1880, Fox-Pitt is said to have successfully experimented with charred plant fibers as the filament material. That was about the same time as the development of the light bulb with carbon filament by Edison in the United States. By 1883, Fox-Pitt had obtained further patents.

Fox-Pitt wrote books on the philosophy of science, education, and social problems. He was temporarily Vice President of the Moral Education League and organized the International Moral Education Congress. He was also one of the first active members of the Society for Psychical Research.In 1891, he repurchased the patent rights of the Anglo-American Brush Electric Light Corporation and built himself a small lamp factory.

In 1898, he participated in a railway concession in Ecuador.In 1899, he married Lady Edith Gertrude Douglas (1874–1963, the daughter of John Sholto Douglas, 9th Marquess of Queensberry).

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