Pole face clutches happy in wet or dry conditionsThe Mönninghoff 450 series of pole face clutches featuring a 'double flux crossed' design achieves high torques and operates even in conditions where oil or water are present. Covering torques from 400 to 2000Nm, the 450 clutches are well-suited to mobile applications. Clutches are available in three sizes giving backlash-free torque transmission with either static or dynamic engagement.
Available in the UK from Techdrives, the 450 series clutches are engaged by applying a DC voltage to a stationary coil. This generates magnetic flux which travels into the rotor, a rotating plate that forms one of the two friction surfaces. The flux then crosses an air gap and pulls another plate, the armature, into contact with the rotor generating the torque by friction. In fact the clutch is designed so that the magnetic flux crosses the air gap twice, hence the description 'double flux crossed'. This doubles the attractive force, increases the torque and leads to compact dimensions. The double flux crossing is achieved by using a two part armature with inner and outer rings, and a rotor where non-magnetic material blocks the flux from travelling radially.
Friction is achieved through steel-to-steel rubbing surfaces without friction material. The rubbing surfaces, which are the magnetic poles, are gas nitrided. Wear is virtually zero provided the operating conditions meet the limits for engagement speed, energy and frequency of operation. Generally this means slip times of less than one second. Use of steel rubbing surfaces makes the clutches unaffected by minor contamination of oil or water - this will quickly be burnt off. They can be used even in continuous splash conditions with a suitable torque derating.
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