Carbon Brushes (May 2010): Making The Grade

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.

Carbon-Graphite

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

Electrographitic

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

Metal-Graphite

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.

Graphite

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.