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Carbon Brushes (May 2010): Making The Grade

May 20, 2010
Making The Grade

The grade of a brush is usually found stamped on the face of the carbon. The grade indicates the material composition of the carbon. It represents one of the more technical challenges in carbon brush applications.

Brush grades are usually classified according to the manufacturing processes and the types of materials used. The different grades in use today are derived through a variation of raw materials, molding pressures, temperature and duration of the baking process and after-treatments. These elements produce varied resistivity, hardness, and strength that in turn affect contact drop, friction and commutator filming. All grades fall within the four major categories of carbon graphite, electrographitic, graphite and metal graphite. The major characteristics of each category are as follows.


  • Used on older machines
  • High strength and hardness
  • Low resistance & poor commutation
  • For machines requiring polishing
  • Generally slower-speed machines: cranes, hoists, elevators & welders


  • Good commutation ability
  • Adequate strength with low abrasion
  • Good friction characteristics
  • Versatile
  • Resistance, strength, hardness and density can be controlled through material composition of raw materials
  • Widely used in all types of motors & generators for: steel and paper mills, excavation, cement, transportation and aerospace


  • Good for current densities
  • Low contact drop
  • Polishing action
  • Metal content application:
    50% - material handling, battery charging & welding generators.
    60% - plating generators & rings.
    75% & up - rings and grounding brushes.


  • Good filming characteristics
  • Smooth riding
  • Reduces threading
  • Thermally limited
  • Generally used on: slip rings and FHP motors
For answers to any questions you may have about grades or applications, call Scott Tussey, Manager of Carbon Brush Sales at 800-822-9190.

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