Sprag Geometry
The design of sprag geometry is central to the performance of any sprag freewheel / clutch. At Tru-Sprag, we bring decades of expertise and proficiency in designing any type of sprag, namely,
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Centrifugally Disengaging Sprag: In this design, centrifugal force induces a moment on the sprag, which tends to lift (disengage) it from contact with the inner race and only the spring force keeps the sprag in contact with the inner race.
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Centrifugally Engaging Sprag: This design operates oppositely. Centrifugal force tends to increase (engage) the contact force between the sprag and the inner race.
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Neutral Sprag: Although most of the sprag freewheel applications use either an engaging or a disengaging sprag design, there is a third alternative in which the effect of centrifugal force tends to neither engage nor disengage (neutral) the sprag from the inner race.
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These three designs offer a degree of flexibility when designing the sprag freewheel for a specific application. Each application is unique and must be closely examined to determine which sprag type is most appropriate. E.g. disengaging sprag to reduce sprag wear, where freewheel is not expected to engage at a high speed. But, engaging sprag to increase engagement reliability, where freewheel is expected to engage at high speed.
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A detailed analysis of the operating conditions that impact sprag performance needs to be conducted before finalising the selection of one of the three sprag types.
Torque Capacity:
We have proprietary software programs to compute theoretical toque carrying capacity of a specific sprag freewheel by analysing its designed sprag geometry and incorporating critical boundary conditions such as contact stress, friction angle etc.
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We also have multiple test benches with torque capacity up to 60000 Nm to validate computed capacity and also to verify smooth loading and unloading of freewheel without any slippage during all stages of the test.
Freewheeling Wear:
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Excessive wear causes gripping angle of freewheel to increase to the point where, eventually, the freewheel will not operate properly.
Due to the multitude of factors influencing wear, its behaviour is predominantly an empirical matter of study. Our test benches are capable of achieving speeds up to 4000 rpm to closely observe effects of wear on sprag freewheels.
Furthermore, to enhance the freewheeling wear life under high speeds, we offer units equipped with wear resistant sprags. These sprags undergo a specialised surface hardening treatment in which the alloy metal body is integrally bonded to an external chromised case, resulting in a surface hardness of 1300–1600 Hv.
