Magnetic particle clutch

A magnetic particle clutch is a special type of electromagnetic clutch which does not use friction plates. Instead, it uses a fine powder of magnetically susceptible material (typically stainless steel) to mechanically link an otherwise free wheeling disc attached to one shaft, to a rotor attached to the other shaft.

This clutch is a form of powder clutch. Torque is transmitted mechanically, through a metal powder filling. In the magnetically controlled version, an applied magnetic field is used to lock the particles in place. Unlike a pure magnetic coupling though, this field takes no part in transmitting torque magnetically.

When a magnetic field is applied to the powder, it forms chains connecting the disc and rotor. The strength of the chains depends on the strength of the magnetic field.

In the late 1970s and early 80s, these were used in high-speed line-printers to stop a spinning drum stamped with 96 or more colums, and 40 or more rows containg the alphabet. The drum was stopped momentarily by the clutch while hammers struck ink and paper in the approprite column. Each revolution of the drum, produced a full line of text and symbols. These drums spun at 300 to 1200 RPM.

Some advantages over a friction plate clutch include:

  • it doesn't exhibit stick-slip phenomenon or stiction
  • the torque may be easily and quickly controlled
  • it is more resistant to wear
  • it may be used for continuous slip applications
  • it has a very fast response time

References


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