In order to provide the best user experience, we had to abandon support for Internet Explorer versions prior to IE9. Upgrade your browser.

Carbon Brushes (July 2012): Spring Pressure

July 27, 2012

Carbon Brush Spring Pressure

The force applied to a brush to hold it in contact with the commutator or slip ring is one of the most critical variables in brush performance. Brushholder spring pressure is the most common mis-rigged item in motors and generators, causing erratic performance, higher maintenance costs and expensive repair bills.
Brushes must be held firmly against the commutator to work properly. One might think that longer brush life is possible if the spring pressure is purposely set at a lighter pressure. Actually, the opposite is true. If the pressure is too light, imperfect contact and commutator threading may result. As springs weaken with age (rapidly if overheated), low spring pressure is a common problem. Brushes may momentarily separate from the rotating surface when struck by the irregularity. This ‘brush bounce’ interrupts current flow, leading to sparking and damage to the brushholder and commutator.
Brush wear increases when the pressure falls below the recommended lower limit. This wear is more severe than that caused by high pressures. Please note, however, that pressures that are too high or too low should not be tolerated. Excessive brush pressure can also result in higher frictional losses and needless wear.
Brush pressure is given in pounds per square inch (f/a) of brush cross-section. While it is often impossible to give the best pressure for any grade under all conditions of service, some limits of pressure can be recommended. Each grade has a limited range of pressure within which performance is considered optimum. The following is a basic guide for classes of applications:
Class of Application Brush Pressure
General Industrial 2 to 4 lb/in2 (13.8 to 27.6 kPa)
Mill-type Motors 3 to 5 lb./in2 (20.7 to 34.5 kPa)
Railway Service 3.5 to 9 lb/in2 (24.1 to 62.1 kPa)
Where vibration is severe, such as crane motors, truck motors and similar machines, the brush spring pressure should be about the same as for railway motors. When using metal-graphite brushes, the spring force must be adjusted to compensate for the heavier weight, depending upon whether the brushes are in the top or bottom holders of the machine.
In all cases, the manufacturer’s recommended brush pressure range is the surest way to the best results. Please contact Scott Tussey, manager of Carbon Brush Sales, at 800-822-9190, with any questions about recommended spring pressures for specific grades and applications or for more information about measurement instrumentation.

« Return To Articles
Quick Contact

Newsletter Signup

Join our email list and we will keep you informed of sales and promotions and other great deals!

Email Subscribe

Request Literature

Request our Electrical Contact, Carbon Brush, or Control Coil catalogs (via Mail).

Request Now
International: 856-762-0172
Domestic: 800-822-9190

Repco Quick Contact

If you do not see what you need, please let us know what it is and we''ll do our best to help you.

First name required.
Last name required.
Company required.
Valid email required.
Phone number required.
If you are looking for a quote, please include model & quantity in your comments!
Comment required.
Send your inquiry now and we will respond promptly.
Interest is in general information for pagename=articles/Carbon_Brushes__July_2012___Spring_Pressure.
Please check the recaptcha box.

Site Search

OEM, Product, Repco ID #s or Terms