The pressure used should be adequate to guarantee that the brush maintains continuous contact with the slip ring or commutator under all operating circumstances of the machine. Sparking under the brush is caused by contact loss between the brush and the slip ring or commutator. This can happen when the pressure applied by the handler is not high enough to keep the brush in constant contact with the device it drives.
Sparking under the brush can also be caused by excessive pressure, which may damage the brush or its housing. Excessive pressure can also cause problems with other parts of the handling system; for example, if the pressure is not relieved after the driver has stopped moving the handle, it will continue to drive the brush even after it has stopped. This can lead to overheating and failure of the motor.
Finally, sparking under the brush is indicated by black smoke from the motor's casing. This means that carbon particles have been released into the atmosphere where they can cause serious health problems over time.
Sparking under the brush is an important problem because it reduces the life of the brush and the motor it drives. Also, if left unattended, it can cause serious damage to these components. Therefore, brushing machines must be operated within their recommended pressures or they will not operate properly. If the pressure is too low, the brush will not make sufficient contact with the device it drives to transmit power efficiently.
Brushes capture the current generated by the armature coils' induced emf. When a brush is on a certain commutator segment, it shorts out that coil and drains current from the other coils. The other segments are now positive with respect to this negative-side coil, so they attract the brush away from them and pull it toward them. This action creates the pushing motion you feel when driving a mechanical pencil or rubber band gun.
The more coil pairs there are on the motor, the more brushes there should be to drain their current. A single-coil motor needs only one brush to short its coil out. A three-coil motor needs three brushes to short out its coils. A six-coil motor needs six brushes, and so on.
DC motors work on principles similar to those of AC motors, except that they use semiconductor devices instead of electromagnets to create magnetic fields when current is passed through them. These devices are known as switches because they connect or disconnect electrical circuits depending on whether they are on or off. In an AC motor, the position of the switch determines what part of the circuit is connected, so it can create a magnetic field that pulls or pushes against the rotor. In a DC motor, the position of the switch connects or disconnects two different parts of the circuit, so there is no magnetic field until current is passed through it.
Brush spring pressures ranging from 3 to 8 pounds per square inch result in long brush life and performance. Follow the manufacturer's spring pressure recommendations. The coefficient of friction between the brush and the commutator increases in a linear relationship with the commutator surface speed. Brush wear is related to friction coefficient. A low-copper or non-coated brush will last longer because less material is removed by each pass over the copper core.
The choice of brush force determines how much current can be carried by the motor. If the motor is to run at full capacity, then it must be able to carry as much current as possible under all conditions. This means that it must be able to stand up to heavy loading without failure, so a strong magnet is essential. Motors used for high-power applications usually require a stronger magnet than those used for low-power applications. Also, large motors need stronger magnets than small ones because more turns are placed in close proximity to one another. This increases the magnetic field strength across any given area, so more energy is required to overcome the resistance of the windings.
As mentioned earlier, the choice of brush force also determines how much current can be carried by the motor. If the motor is to run at its maximum capacity, then it must be able to withstand as much current as possible under all conditions.