Carbon Brushes

The brush is cut on a slant on the top or bottom and it is the angle other than a right angle on the top or bottom of the brush. Bevels generally range from 0° – 45°

The surface of the brush which touches the commutator or slip ring. The condition of the brush face can be a good indicator of brush performance.

The metal top of a brush connected to the block of carbon with a wire or spring. The cap provides the stationary electrical contact. Used primarily in small fractional horsepower motors.

The curved bottom surface of the brush designed to meet the curvature of the contact surface.
Also referred to as a concave radius.

The final composition of the raw material. Manufacturers give each unique composition a designation called a brush “grade”  See Helwig Grades

Descriptions of the types of brush grades:

Graphite:

• Graphites are for use in special applications requiring the low friction characteristics of this material. When brushes must operate at very low current densities or very high peripheral speeds, a graphite grade should be used.

Carbon Graphite:

• Carbon Graphites offer cleaning action for use at slow speeds, low current densities and medium to low voltages. These grades were developed early in the history of motors and generators and are therefore found most often on older equipment, particularly with flush mica commutators.

Electro Graphite:

• Electrographites are the most common grades used on modern equipment with good performance at high voltages, high current densities and high speeds. There is a wide range of characteristics within this category. Most electrographite grades are capable of handling overloads well.

Silver Graphite:

• Silver graphites have material contents of 15–95% silver. The added conductivity and lower voltage drop of the metals allow metal graphite brushes to perform well
  at very high current densities and low voltages.

Copper Graphite:

• Copper graphites have material contents of 15-95% copper or copper alloy. The added conductivity and lower voltage drop of the metals allow metal graphite brushes to perform well at very high current densities and low voltages.

For more information about materials and brush grades, please visit our Grade Information page.

The upper part of the carbon shaped to hold the end of the spring in place. Commonly used on brushes with springs and caps.

Also known as a Helwig Quick Disconnect terminal, is an electrical connection that doesn’t require nut and bolt to hold the terminal in place.

A series of letters and numbers that delineate a specific brush from another.

Multi-section brush where two or more wafers come together to form the whole brush. The wires from the various wafers generally meet in one terminal. These brushes are often held together with a Red Top pad.

Combination of hard plastic and rubber square glued to the top of the carbon brush. Pads hold the multiple brush sections together, insulate spring from carrying current and absorb excess vibration. The spring or spring finger will make contact with the brush on the pad surface.

The wire is attached mechanically to the carbon with a rivet. The wire is generally wound around the rivet and up through holes in the carbon material for an extra secure connection.

A wire or wires that connect the brush to the terminal.

Where the wire enters the brush. These locations are numbered in relation to viewing the front of the brush.

Insulation over the shunt wires. Some have a painted cloth appearance and others resemble a soft flexible rubber tubing.

Groove on the top of the brush often used to stabilize the spring. Face slot – cuts in the brush face.

A coiled spring that surrounds the shunt of a brush, connected with a cap. Typically only seen on fractional horsepower brushes.

The wire is embedded directly into the brush.

A device at the end of the wire of a brush that makes a convenient stationary electrical connection.

Helwig’s electrical brushes are made from low friction, conductive carbon materials that include natural graphite, carbon graphite, silver graphite, copper graphite, and electro graphite.

Graphite:

• Graphites are for use in special applications requiring the low friction characteristics of this material. When brushes must operate at very low current densities or very high peripheral speeds, a graphite grade should be used.

Carbon Graphite:

• Carbon Graphites offer cleaning action for use at slow speeds, low current densities and medium to low voltages. These grades were developed early in the history of motors and generators and are therefore found most often on older equipment, particularly with flush mica commutators.

Electro Graphite:

• Electrographites are the most common grades used on modern equipment with good performance at high voltages, high current densities and high speeds. There is a wide range of characteristics within this category. Most electrographite grades are capable of handling overloads well.

Silver Graphite:

• Silver graphites have material contents of 15–95% silver. The added conductivity and lower voltage drop of the metals allow metal graphite brushes to perform well
  at very high current densities and low voltages.

Copper Graphite:

• Copper graphites have material contents of 15-95% copper or copper alloy. The added conductivity and lower voltage drop of the metals allows metal graphite brushes to perform well at very high current densities and low voltages.

For more information about materials and brush grades, please visit our Grade Information page.

The proper way to install a brush in a DC electric motor is:

1. Start by disconnecting the power of the machine with the approved lockout procedures.
2. Remove the old brushes and inspect (take note of unusual conditions of the brush or brush holders).
3. Inspect the commutator for any unusual conditions as described in the Helwig Carbon Commutator Condition Guide.  Download here.
4. Check the inside of the holder cavity for dust, dirt, carbon build-up or burned areas. Clean if necessary.
5. Check the terminal connections. Clean if necessary.
6. Now, secure holders to the mount by checking for tightness, proper alignment.
7. Check the spring force of current springs with a Helwig Digi-Scale and make sure they are within the recommended range.
8. If the replacement brushes are made from a different grade of material, you will need to remove any old film from the brush tracks. Use a dry untreated canvas or rubber abrasive.
9. Install new brushes into the holders, paying attention to the orientation of angle holder designs.
10. Apply the constant force spring. After applying the spring, pull up on the brush and release gently. This makes sure the brush moves freely in the holder.
11. Connect the terminals, make sure your connections are tight and secure.
12. Now, seat the brush with commutator garnet paper.
13. Lastly, for final wear in operate the DC machine at no load.

Brush sizes are designated as: Thickness x Width x Length of the carbon. If the brush design includes a Red Top, the length measurement should include the pad. On brushes with bevels, the length is measured on the long side. Brushes with a head-on top include the length of the head.

The much-maligned brush is not responsible for most of the machine malfunctions attributed to it. Sparking at the brush face is usually the first symptom of trouble elsewhere.

Common Reasons for Sparking:

• Brush holders are
  • not evenly spaced
  • off electrical neutral
  • damaged or dirty
  • too far from the commutator surface
• Wrong interpole strength
• Overloads
• Defective armature windings
• Incorrect spring pressure
• Poor undercutting of commutator
• Foreign material on commutator surface
• Black commutator film
• Brushes binding in holder
• Restricted brush motion
• Out-of-round commutator
• High bars or flat spots
• Machine vibration

For more details and solutions on brush sparking download our FREE version of Brushes, Sparking and Machine Maintenance wrote by M.S. May – Speer Carbon (a Helwig Carbon Products company)

1. Place commutator garnet paper of sufficient width to contact all brushes with abrasive side out and secure with masking tape the full circumference of the commutator.
2. Rotate by hand in the direction of rotation until the brushes have taken on 75% of the radius. Eighty grit paper does the primary shaping and should be followed by 220 grit for a fine finish.

To view Helwig’s garnet paper listing click here.                4% discount on orders of 10 or more rolls!

The numbers on your brushes display vital information about the brush.

Commonly these numbers include:

• Grade Information
• Helwig Carbon Part Number
• OEM Part Number
• Customer Part Number

For specifics to your application, please contact Helwig Engineering to diagnose your brush wear problem.

Call (800) -962-4851 or Contact Us

Rapid brush wear is a problem that can be caused by a multitude of factors. There isn’t one easy answer to this question, as each situation can be different. A natural answer to this question that many will quickly jump to is the carbon brush grade. However, we’ve seen that, more often than not, the brush grade is not the culprit.

The NUMBER ONE reason for increased brush wear that we see is from low spring pressure! Inadequate spring pressure can cause rapid electrical brush wear. Clock and fingerstyle springs tend to lose force as the brush wears, and all springs will fatigue over the course of time. This will reduce the effective force at the brush face and increase the rate of brush wear.  Reference our Recommended Spring Pressure Chart for more.

To find out other common reasons for rapid brush wear for generator, slip ring and motor brushes, read our blog: 3 Reasons for Rapid Brush Wear

As a general rule of thumb, if the brush wears below a usable length, it is time to replace the brush.  Often, signs of cracking, disintegrating, or burning, the brush should be replaced.

When motor brushes wear out, the electric motor will arc & spark, and the electrical circuit may be incomplete. This situation can be dangerous and should be dealt with immediately.  Usually, the problem can be solved by replacing the brushes.

For more details and solutions on brush sparking download our FREE version of Brushes, Sparking and Machine Maintenance wrote by M.S. May – Speer Carbon (a Helwig Carbon Products company)

Brush grades are typically found stamped or marked on the front side of the brush. The grade designates the material composition of the brush.

Brush grades are regularly organized according to the manufacturing processes and the types of materials used. Today’s grades are determined through a variety of raw materials, molding pressures, temperatures, duration of the baking process, and post-process treatments. Material elements provide different levels of resistivity, hardness, and strength that directly affect friction, contact-drop, and surface film.