Apparent Density:
Measured in grams/cubic centimeter, this reading is used for quality control.

Resistivity:
Measured in micro-ohm-inches, indicates the resistance to current flow.

Shore Hardness:
Using a Shore Scleroscope tester, a diamond mandrel is dropped and the height to which it rebounds is measured. This is strictly a measurement to control the manufacturing of the materials, and has no effect on commutator wear. Softer brushes ride the commutator better than harder brushes, which have a tendency to bounce on out-of-round commutators.

Flexural Strength:
Measured in pounds/square inch, this is another reading that is used for quality control during manufacturing.

Contract Drop:
This is a measurement of the voltage drop between the positive and negative brush, under specific current, voltage, speed and temperature conditions. The higher rated materials reduce the effect of circulating currents and improve commutation. Even though the material may have a high contact drop, other factors must be considered to select the best grade for the application.

Friction:
A lot of factors influence friction, including ambient temperature, machine temperature, brush pressure, and humidity. To obtain optimum brush life and minimal commutator wear, the friction between the brush and the commutator must be low. In cases where the best brush grade for the application does not produce a low-friction, we can impregnate the brush with various resins. The resulting material is a very low friction grade that gives optimum performance.

Current Density:
This is a very general rating and is affected by voltage, amperage, temperature, and speed. The current density is calculated by dividing the total load by one-half of the brushes on the machine by the width and thickness of the brush:

C.D. = Load/(.5 x Number of Brushes x Width x Thickness) = amps/square inch.

Each brush grade has a range of current density in which it will give satisfactory operation.

Please consult our Engineering Department for this information.