Electromaganetic powder brakes/clutches
Release Date:19/04/2016
General description
The
electromagnetic powder brakes and clutches combines the resilience of a
fluid clutch with the locked-in stability of a friction clutch. Torque
is transmitted by a specially alloyed dry ferromagnetic powder.
The
clutchs can sustain continuous slip (within their empirically
established heat ratings)at a precise and stable torque value, which is
determined by excitation level.
Slip
between input and output level is not necessary in order to transmit
torque, and provided load torque does not exceed the torque for which a
unit excited to transmit locked-in synchronous operation will take
place. Conversely, if load torque exceeds the energised torque level,
slip will occur in an absolutely smooth manner at the predetermined
torque value.
For
all practical purpose, static and dynamic coefficients of friction are
sensibly equel also output torque is indepentent of speed, or slip
speed.
Powder
performance is unaffected by temperature rise at the working surface,
and clutchs will, at all times, have the characteristics that
transmitted torque is directly proportional to current. It should be
noted that use of dry powder rather than fluid- suspended powder medium
promotes consistency and accuracy of torque control.
Briefly,
the clutch comprises two concentric members, the body or input member
containing the field coil, and within it, and separated by a small
annular gap, an inner rotor, or output member. The annular gap contains a
ferromagnetic powder which is activated when the coil is energised.
The
resultant flux which is generated, passes through the powder, causing
it to align with the flux path, and thereby creates a driving bond
between input and output members, the strength of which is solely
determined by the value of d.c. current applied to the field coil.
technical data
Operating characteristics
The
torque transmitted by powder clutchs is proportional to field current,
and is infinitely variable from maximum design rating down to
practically zero in all models.
Torque/current characteristic
curves can vary by 5% dependent on whether current is increasing or
decreasing. This is due to magnetic hysteresis.
For all practical
purpose torque is independent of speed, either with or without the
presence of slip, and can be maintained within an accuracy of 5% for
speeds within the recommended operating range 50 to 3000 rpm.
Deenergised drag torque due to residual iron circuit magnetism, bearing
and seal friction, is less than 1% of design torque rating for any
clutch.
Response time to torque is determined by field coil
inductance to resistance ratio plus a magnetic delay due to eddy current
loss.
Note:
To ensure satisfactory operation clutchs and brakes must be mounted in horizontal attitude.
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