Contact - Free Overrun Clutches

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These are basically similar to conventional sprag clutches, but the sprags have their centre of gravity offset to the pivot point such that in the overrun mode the sprag elements are thrown out of contact with the stationary race by centrifugal force These clutches are for applications involving long periods of high speed freewheeling, when no wear occurs, such as barring motors, starter drives, pump and motor backstops. Three basic

Types RSBI and RBI Types RSBI and RBI backstop clutches consist of cylindrical inner and outer races between which are located individually spring loaded, special shape sprag elements contained in a cage. The cage is flexibly connected to the inner race to allow the sprags to engage easily during torque application. When the inner race rotates at high speed the off-centre weight of the elements causes them to rotate within the cage to produce a gap with outer race. These clutches are designed for backstop applications on the high speed shafts of motors, gearboxes, compressors and pumps. They can also be used within slow speed barring drive. Although basically these clutches require no lubrication, their sprag design does permit the use of E.E or H.E additives. Type RSBI is dimensionally equivalent to many competitor units; type RBI offers higher torque capacity.

Types RAZ and RIZ Types RAZ and RIZ freewheel clutches combine an RSBI sprag cage unit with cylindrical inner and outer races dimensionally equivalent to same reference AGF roller ramp freewheel. The outer race is supported on two 60 series ZZ sealed bearings. A range of flanges of same dimensions as AGF series enables fitting of gears, sprockets or pulleys, and units with keyseated outer race can also be provided. Type RAZ clutches have sprag clutch cage connected to outer race to enable high speed overrunning of the outer race. This series mainly used for overrun applications such as starter drives and barring motors. Type RIZ clutches have sprag clutch cage flexibly connected to the inner race to enable high speed operation of the inner race. Whilst also suitable for overrun applications, more often this series is used as backstop. Both RAZ and RIZ clutches are available with elastomeric coupling as used with AGF series, with RIZ being preferable as these allow whole unit to be stationary during overrun.

Types CR and RS/BF Both types CR and RS/BF can only be used as backstops, and are normal1y mounted on rear of electric motor, or on shaft extension of gearbox. Special shaped sprags are mounted in a cage connected to the outer race, which is of top hat shape to enable connection to rotating shaft. The inner race is flanged to enable connection to machine frame. The two series were originally produced by two different companies, and both have remained in production as they are dimensionally different. The units were the only selection for contact-free backstops, but now the RSBI and RBI series are preferred for new applications. The CR series units offer the highest torque capacity with 300mm bore units capable of 75,000 Nm torque. Special clutches have been supplied with torques in excess of 150,000 Nm. Both series have covers available to provide a fully sealed unit.