Brush ( electric ) - wikipedia Brush ( electric ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( October 2016 ) A pair of carbon brushes A 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. Contents 1 Etymology 2 Manufacturing process 2.1 Mixing components 2.2 Compacting the mixture 2.3 Firing of green brushes 2.4 Secondary operations 3 Liquid metal brushes 4 See also 5 References Etymology 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. 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 MoS, WS. 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. 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 Commutator ( electric ) Slip ring Electric motors AC - Alternating current DC - Direct current PM - Permanent magnet SC - Self - commutated Fundamental types AC motor DC motor DC motors Homopolar Electrically - excited field or PM field brushed DC Unipolar AC SC mechanical commutator Repulsion Universal AC SC electronic commutator Brushless DC ( BLDC ) Switched reluctance ( SRM ) AC asynchronous ( induction ( IM ) ) Shaded - pole ( single - phase ) Dahlander pole changing motor Squirrel - cage rotor ( SCIM ) Wound - rotor ( WRIM ) Linear induction AC synchronous ( SM ) Hysteresis Interior / Surface PM ( IPMSM / SPMSM ) Reluctance ( SyRM ) Wound - rotor ( WRSM ) Special magnetic machines Doubly - fed Linear Servomotor Stepper Traction Non-magnetic Electrostatic Piezoelectric Ultrasonic Enclosure Type Hermetic TEFC Components and accessories Armature Braking chopper Brush Commutator DC injection braking Field coil Rotor Slip ring Stator Winding Motor controllers AC / AC converter Amplidyne Adjustable - speed drive ( ASD ) Cycloconverter Direct torque control ( DTC ) Metadyne Motor controller Motor soft starter Motor starter ( engine ) Power inverter Thyristor drive Variable - frequency drive ( VFD ) Vector control Voltage controller Ward Leonard control History, education, recreational use Timeline of the electric motor Ball bearing motor Barlow 's wheel Lynch motor Mendocino motor Mouse mill motor Experimental, futuristic Coilgun Railgun Superconducting machine Related topics Blocked - rotor test Circle diagram Closed - loop control Electromagnetism Open - circuit test Open - loop controller Power - to - weight ratio Torque and speed of a DC motor Two - phase system People Arago Baily Barlow Botto Cook Davenport Davidson Dolivo - Dobrovolsky Faraday Ferraris Froment Gramme Henry Jacobi Jedlik Lenz Maxwell Ørsted Park Pixii Saxton Siemens Sprague Steinmetz Stimpson Sturgeon Tesla See also Alternator Electric generator Inchworm motor SI electromagnetism units C - Capacitance ( F ) Q - Charge ( C ) G, B, Y - Conductance, susceptance, admittance ( S ) κ, γ, σ - Conductivity ( S / m ) I - Current ( A ) D - Electric displacement field ( C / m ) E - Electric field ( V / m ) Φ - Electric flux ( V m ) χ - Electric susceptibility U, ΔV, Δφ ; E - Emf ( V ) L, M - Inductance ( H ) H - Magnetic field ( A / m ) strength Φ - Magnetic flux ( Wb ) B - Magnetic flux density ( T ) χ - Magnetic susceptibility μ - Permeability ( H / m ) ε - Permittivity ( F / m ) P - Power ( W ) R, X, Z - Resistance, reactance, impedance ( Ω ) ρ - Resistivity ( Ω m ) References Jump up ^ Zanon, Matteo ; Rampin, Ilaria ; Breda, Alessandro ; Bortolotti, Francesco ( 2015 - 10 - 05 ). `` The sintering behaviour of electrolytic and water - atomized copper powders ''. Jump up ^ Zanon, Matteo ; Nassuato, Mirko ; Rampin, Ilaria ; Echeberria, Jon ; Martinez, Ane Maite ( 2014 - 09 - 23 ). `` The conductive behaviour of copper and silver - coated copper powders ''. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Brush_(electric)&oldid=842066077 '' Categories : Electrical power connectors Electric motors Scottish inventions Hidden categories : Articles needing additional references from October 2016 All articles needing additional references All articles with unsourced statements Articles with unsourced statements from February 2018 Talk Contents About Wikipedia Deutsch Español Euskara فارسی Galego Italiano Nederlands Polski Português Slovenčina Svenska 中文 5 more Edit links This page was last edited on 20 May 2018, at 00 : 33. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. 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Question: explain the function of the brush ring in electric generator
Answer: conducts current between stationary wires and moving parts