Magnetic particle/current brakes are unique in their design from other electromechanical brakes because of the wide operating torque range available. Like an electromechanical brake, torque to voltage is almost linear; however, in a magnetic particle brake, torque can be controlled very accurately (within the operating rpm range of the unit). This makes these units ideally suited for tension control applications, such as wire winding, foil and film tension control and tape tension control. Because of their fast response, they can also be used in high cycle applications, such as magnetic card readers, sorting machines and labeling equipment.
Fast response and accurate control: Voltage to torque is almost linear, so engagement is extremely fast, and controllability of magnetic particle units is very accurate.
Stable torque: Torque is independent of speed, but is proportional to the voltage/current applied to the field, allowing stable torque throughout the units operating rpm range.
Long life: Because the wear rate of magnetic particles is gradual instead of severe, the units have a very long life.
Excellent slip capacity: Because of the units' excellent heat dissipation, and because of their construction, they can operate in a constant slip mode (within max allowable wattage), which makes them ideal for tension controlling applications.
How It Works
Engagement: Magnetic particles (very similar to iron filings) are located in the powder cavity. Without any voltage/current, they sit in the cavity; however, when voltage/current is applied to the coil, the magnetic flux that is created, tries to bind the particles together, almost like a magnetic particle slush. As the voltage/current is increased, the binding of the particles becomes stronger. The brake rotor passes through these bound particles. The output of the housing is rigidly attached to some portion of the machine. As the particles start to bind together, a resistant force is created on the rotor, slowing, and eventually stopping the output shaft.
Disengagement: When current voltage is removed from the brake, the input is free to turn with the shaft. Since magnetic particle powder is in the cavity, all magnetic particle units have some type of minimum drag associated with them.
Cycling: Cycling is achieved by turning the voltage/current to the coil on and off.