Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R39/00—Rotary current collectors, distributors or interrupters
  • H01R39/02—Details for dynamo electric machines
  • H01R39/18—Contacts for co-operation with commutator or slip-ring, e.g. contact brush
  • H01R39/20—Contacts for co-operation with commutator or slip-ring, e.g. contact brush characterised by the material thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R39/00—Rotary current collectors, distributors or interrupters
  • H01R39/02—Details for dynamo electric machines
  • H01R39/18—Contacts for co-operation with commutator or slip-ring, e.g. contact brush
  • H01R39/20—Contacts for co-operation with commutator or slip-ring, e.g. contact brush characterised by the material thereof
  • H01R39/22—Contacts for co-operation with commutator or slip-ring, e.g. contact brush characterised by the material thereof incorporating lubricating or polishing ingredient

Definitions

• This invention relates to brushes for the supply of electric current, and more particularly concerns long wearing commutator brushes.
• Metal graphite brushes such as the conventional copper-graphite brushes containing about 30 percent to 75 percent copper, and 25 percent to 70 percent graphite have several desirable properties. At low current densities and rubbing speeds, that is, about 60 amperes per square inch and 2500 feet per minute, respectively, the copper graphite brush generally operates satisfactorily with a low contact voltage drop and a low temperature. When used under these conditions, the copper-graphite brush is free from dusting and can render service for a relatively long time. But when more stringent conditions are imposed on the. brush, the operating life is considerably impaired. Increasing either the current density or the rubbing speed can cause a rapid increase in brush wear.
• the performance of the conventional brush is hampered by the elfects of ring wear, high coefficient of friction and dusting.
• the brush is also sensitive to commutator or ring eccentricity. Often the combination of these factors will intensify sparking, burn portions of the ring surface, and even cause the release of small streamers at the trailing edges.
• a brush embodying the principles of my invention may be readily formed by introducing as additive material into a conventional metal graphite brush composition of approximately 30 percent to 75 percent copper and 25 percent to 70 percent graphite, small quantities of lead and boron nitride. present in the brush composition in amounts between 1.1 percent and 15 percent by weight of the copper graphite mixture.
• EXAMPLE I The composition of a copper graphite mixture containing approximately percent copper, 50 percent grahite and suitable binder material was modified by adding to it about 5 percent lead powder and 1 percent boron nitride powder. The said ingredients were then well mixed and molded at a pressure of 15 tons per square inch to a block of suitable size for making a commutator brush. The block was then baked at 900 C. by suitable heating means for a period sufiicient to impart known and inherent brush characteristics.
• Table II sets forth the' conditions and results of a number of typical tests wherein the brush was tested at sea level conditions.
• the brushes were subjected to current densities of amperes per square inch and amperes per square inch.
• the procedure used for testing the brushes consisted in applying the brush to a machine having an operating speed of about 6500 revolutions per minute, giving a rubbing speed of 5100 feet per minute.
• a brush spring pressure between 7.1 p. s. i. and 7.3 p. s. i. was used.
• the current flow through the brush was adjusted to between 20 and 40 amperes at .a current density between 60 amperes per square inch and 120 amperes per square inch.
• Tests were conducted in room air for a total of 20 hours or more. During that time readings were taken of contact drop voltage, brush temperature, and coeflicient of friction. At the end of the tests brush length was measured and brush life in hours per inch of wear was calculated.
• the improved performance manifests itself in longer brush life, smaller ring wear, low coefficient of friction, low operating temperatures, and greater current load capacity.
• An electrical contact brush consisting of about 30% to 75 copper, 25% to 70% graphite, 0.1% to 5% boron nitride and 1% to 10% lead, said boron nitride and lead rendering said brush substantially resistant to dusting conditions and imparting longer wear life thereto.

Landscapes

• Motor Or Generator Current Collectors (AREA)
• Conductive Materials (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=76328925

Family Applications (1)

Country Status (4)

Cited By (3)

Citations (3)

Family Cites Families (1)

• 0
  • CA CA580791A patent/CA580791A/en not_active Expired
• 1952
  • 1952-02-29 JP JP491956A patent/JPS326919B1/ja active Pending
• 1955
  • 1955-03-08 US US493069A patent/US2844544A/en not_active Expired - Lifetime
• 1956
  • 1956-03-07 DE DEU3782A patent/DE1041147B/de active Pending

Patent Citations (3)

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