Wrap spring on rod - axial force calculation

[Mechv5]

Hello everybody,

I want to use a wrap spring, pretensioned mounted on a rod, as a brake (to lock the sliding of the rod in axial direction. What should be the calculation approach for the capable axial locking force, depending on the interference between spring and rod, number or spring's coils, etc.? Any documentation I could use (idealy downloadable pdf file(s))?

Thank you in advance.

 

[israelkk]

I have no knowledge of such use of helical spring for brakes or clutches. The wrap spring brake/clutch is ussually working for rotational braking because the friction between the coils and the shaft tends to decrease the inner diameter of the spring thereby increasing the gripping torque on the the rotating shaft.

When you will push the shaft linearily the spring inside coil diameter will increase (compressed spring diameter grows when loaded).

 

[OHSpringGuy]

One consideration will be friction. Another consideration is once the spring is torqued around the rod and grip force is applied, you can quickly overstress the moment arm and exceed the yeild strength of the material. Since you are dealing in Bending stresses the % stress before yeild is quite higher. This solution may take some trial and error. Feel free to send me a drawing of our problem and I can possible help with your solution.