Indexing applications are when an oscillating motion is converted to a unidirectional rotation. One direction will drive the clutch and the opposite direction will cause the clutch to freewheel.
An easy application to grasp the concept is a socket wrench. The wrench will turn the bolt in one direction but if the wrench needs to be turned back to regain leverage, it ratchets instead of turning the bolt the opposite direction.
It can also be used in production lines where a product moves a step, it stops, an action is performed, and then it moves again. This start-stop action can be accomplished by an indexing clutch timed with the oscillating motion of an input device like a piston.
In industrial or automation applications, this can happen really fast. That means a sprag clutch needs to be able to keep up with the indexing operation.
For a sprag clutch, the indexing frequency is the number of times the sprags are able to go from being disengaged to fully engaged and back to fully disengaged per second, in other words to make one full cycle.
It is measured in cycles per second, or Hertz. If the application indexing frequency is above the maximum value for the clutch, there will not be enough time for the sprags to fully engage and transmit torque before disengaging again.
When transitioning from engaged to freewheeling, the inertia (the resistance to change in motion) of the sprags disengaging causes them to want to lose contact with the mating surfaces because they want to continue to lay down.
To minimize this effect, GMN-designed sprags have the lowest possible inertia. Additionally, springs are used to resist the inertia and keep the sprags in contact with the surfaces.
GMN Products for Optimal Indexing Frequency
The FE 400 M series insert elements have a meander spring that weaves in and out of each sprag. This spring pushes between the cage and the toe of each sprag creating independent spring forces for each individual sprag. This is ideal for high indexing frequency applications. It is rated for 60 Hz, but tests have been successful up to 120 Hz.
The FE 400 Z, FE 400 Z2, and FE 8000 Z insert elements use a tension spring that goes around the outside of all the sprags. This produces a slightly lower spring force than the M series. The resultant maximum indexing frequency for these insert elements is 10 Hz for the FE 400 sprag and 5 Hz for the FE 8000 sprag.
Interested in GMN Sprag Clutches?
Check out our Sprag Clutch Guide resources below for more information.
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