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flat strip spring in wave format for drag spring in annulus.

flat strip spring in wave format for drag spring in annulus.

flat strip spring in wave format for drag spring in annulus.

I am looking for design info for an annulus spring to act as a friction drag between the inner and outer shell. Radius is 21mm, torque wanted is 0.7 N-m initially.
width is 3.5 mm , annulus height is 2mm.
By initial fit estimates cof as 0.05, grease packed. Net force = 700 N, drag force = 35 N.
by dividing into wave-to-wave pitch, 1mm compression, 60 degrees pitch, I get thickness
of 0.5mm, using the leaf spring formula, L = 1/4 pitch (cantilever)
I now have to deal with end conditions.

I estimate circumferential expansion as around 5 %
3 "points" of the leaf springs are missing or ineffective, and the outer "points"
have one long arm and one short arm, plus transfer some end effects further into the spring.
1) What pitch and number of points do I need to restore the net force to 700 N ?
I could crowd the end points closer together to compensate for end effects.
non-centered thrust is not a problem.
2) What surface speed can I run up to, assuming bearing grade and finish rings, spring grade
steel for the "flat" spring.-probably simple carbon steel, grease packed.
The intended rpm is about 60 rpm at present.
The application is a "packaged" self-activating spooling clutch, as opposed to a one-way bearing.

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