Rope tension 2

[dimisora]

Hi,

If I wind a rope on a reel with a certain force, producing a tension in the rope, is there a way to calculate what the resulting pressure or force is acting on the central tube of the reel?

I thought about using the analogy of a pressure vessel but this results in very high pressures on this tube which are not realistic.

Any pointers?

Thanks,

Dimitri.

 

[itsmoked]

Yes the FORCE is the tension on the reel. The TORQUE is that same tension times the distance between the surface of the rope touching the reel and the central axis or radius of the reel.

This is why winch makers all specify the winch's pulling power as the first wrap on the drum. Subsequent wraps will result in less force available.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[GregLocock]

Very complex analysis. The crucial relationship is the ratio of the radial stiffness of the cable to its axial stiffness, and the coefficient of friction.

The high pressures you calculate aren't, necessarily, unrealistic.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[WmacG]

In Blodgett's "Design of Weldments", there is an example of calculating the pressure on the drum of a winch. In his example, he uses only the pressure from the first two layers of cable around the drum. The subsequent layers tend to force the preceding layers into a smaller diameter and reduce the pressure that they apply to the drum. This was on page 5.3-7.

 

[pauljohn]

The companies that make winches for yachts, (Harken, Lewmar etc) would certainly be able to help you as this question is an important part of their design process.

 

[Compositepro]

I once wrote an artcle on using stretch wrapping to generate pressure while curing composite tubes. The basic equations are simple but if you get into high modulus steel there can be added factors that be com significant. It helps to imagine the drum in two "D" shaped halves held together by rope tension. The force holding the two halves together is two times the rope tension on each section of drum that is equal to the rope diameter. This force acts on an area between the two drum halves that is equal to the rope diameter times the drum diameter. That is the theoretical "hydrostatic pressure" between the drum halves. Since fluid pressure is the same everywhere in the fluid (disregarding gravity), this is also the pressure at the surface of the drum. It is important to remember the distinction between pressure in a fluid and stress in solids. The actual contact pressure of the rope with the drum will be even larger because only a fraction of the drum area is actually in contact with the rope.