One of the greatest challenges in manufacturing carbon brushes is supplying a grade that will maximize performance for the manner in which the motor or generator is operating. Consideration must be given to the actual running loads, duty cycle, voltage, peripheral speeds and the environment.
Helwig Carbon’s technical staff is experienced in selecting the proper grade for your application. Choosing the wrong material could cause considerable damage to your equipment. However, overall, grades have been held more accountable for brush performance than is warranted. While selecting the proper grade is crucial, other factors often have a greater effect on brush performance.
Many of the grades used today are derived through variations in raw materials, molding pressure, temperature, duration of the baking process and after-treatments. All brush grades fall into five categories:
- Carbon Graphite
- Copper Graphite
- Silver Graphite
Each material is designed and developed to perform under certain operating conditions. A best grade for each application is offered, although, several grades with similar characteristics may offer satisfactory performance.
Carbon graphite grades were developed early in the history of motors and generators. These grades, therefore, are found most often on older equipment, particularly those with flush mica commutators. Carbon graphite offers cleaning action for use at slow speeds, low current densities and medium to low voltages.
Electrographite is the most common grade used on modern equipment. With excellent performance at high voltages, high current densities and high speeds, wide ranges of characteristics exist within this category. Most electrographite grades are capable of handling overloads.
Graphite grades are used in special applications requiring low friction characteristics. When brushes must operate at very low current densities or very high peripheral speeds, a graphite grade should be used.
Copper graphite has a material content of 15 - 95% copper or copper alloy. The added conductivity and lower voltage drop, allows metal graphite brushes to operate at very high current densities and low voltages.
Silver graphite has a material content of 15 - 95% silver. The added conductivity and lower voltage drop, allows metal graphite brushes to operate at very high current densities and low voltages.