Glossary

Carbon brush is being used to transfer electrical current from a moving (usually rotating) to a stationary point within an electric circuit.

Carbon brush types include electro-graphite, pitch bonded, silver impregnated, copper impregnated and resin bonded. There are many industrial applications for these products. They include traction, earthing, aerospace and within generators.

Carbon brush is used for outstanding motor performance. The right carbon brush is important for long commutator life, maximum brush life. The correct brush grade is the key to meeting the unique operating requirements of such diverse applications as mining, transportation, aerospace and power Generation to name just a few.

CARBON-GRAPHITE BRUSHES made their entrance early in the brush industry. Their properties of high hardness, material strength and pronounced cleaning action usually give long brush life under severe operating conditions, although they may not commutate as well as those with softer grades. These grades are limited to lower current densities and are used on slower machines, particularly those with flush mica commutators. The high friction generated with this type of material also makes it unattractive for some modern day applications.

ELECTROGRAPHITIC BRUSHES are baked at temperatures in excess of 2400 C. This process physically gives the material more of a graphitic structure. They generally have good commutating characteristics, but may not always be used because of high currents, or severe mechanical or atmospheric conditions. This material is fairly porous which permits treatment with organic resins. The treatments increase strength and lubricating ability which in turn helps increase brush life. These brushes are generally free from abrasive ash.

METAL GRAPHITE BRUSHES are generally made from natural graphite and finely divided metal powders. Copper is the most common metallic constituent, but tin, silver and lead are also used. This material is ideal for a variety of applications because of its low resistivity. Metal graphites are used on commutators of plating generators and wound rotor induction motors where low voltage and high brush current densities are encountered. They are also used for grounding brushes because of their low contact drop. These brushes exhibit a definite polishing action.

GRAPHITE BRUSHES are composed of natural or artificial graphite bonded with resin or pitch to form a soft brush material. Natural graphite usually contains ash, which gives the brush an abrasive, cleaning action. The fast filming properties of these brushes is beneficial in protecting the commutator or slip ring during operation in contaminated atmospheres. Their low porosity is also valuable in reducing commutator threading. They are not capable, however, of sustained operation at higher currents, like electrographic materials.

CARBON-GRAPHITE

Used on older machines
High strength and hardness
Low resistance & poor commutation
For machines that require some polishing action
Generally, slower speed machines
GRAPHITE

Good film characteristics
Smooth ride
Reduces threading
Thermally limited
Generally used on slip rings & FHP motors
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 & grounding brushes
ELECTROGRAPHITIC

Good commutating ability
Adequate strength with low abrasiveness
Good friction characteristics
Versatile
Resistance, strength, hardness and density can be controlled through raw material combinations
Very widely used today in all types of motors & generators for:
steel and paper mills, excavation,
cement, transportation & aerospace

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