How much force to wrap spring around pipe? 1

[doctorsundar]

I am trying to compute the surface stress on a steel tube when a spring (made of steel wire) is wrapped around the outside of this tube. The steel wire wraps itself around this tube as the tube spins at about 50 rpm.

I suppose that I first need to compute the tension in the steel wire. When an initially straight steel wire gets bent permanently into a circular shape of radius R, I suppose that it has undergone plastic deformation. How can I compute the force needed to plastically bend a wire into a circle of radius R?

This force will compress the circumference of the pipe, i.e., impose an external pressure on the pipe. To compute this pressure, should I consider local deformation, i.e., compute the Hertz contact stresses at the contact area between the pipe and the spring? How can I do this?

Any help will be appreciated. Thanks.

Sundar

 

[olixus]

Hello,

There are many factors that can come into play.

1) Section Area

Is it a circular or rectangular wire? Also, the bigger the wire, higher will be the force required to bend and also its desire to go back to its initial shape. You mentionned contact force and the cross section hsape will definitely make a difference in the surface contact between the spring and the tube.

2) Tube Diameter

It will make a big difference is you have a big diameter vs a small one.

3) Material

You mentioned steel wire, but most often, springs are made of Music Wire (ASTM 228) of Chrome-Vanadium steel wire (ASTM 231

4) Application

I'm not sure I understand exactly what kind of application you want and if you desire to obtain the storage effect of a spring, or just a compression force around the pipe. If you squeeze the spring around the tube/pipe, you will not have the spring effect because of the friction and therefore the concept of spring is useless here. Whereas if you desire to have a compression spring, you cant expect to have a tightening force as when the spring will be compressed, the coil diameter will expand and will be looser around the pipe.

IF all you want is to wrap a wire around a pipe to act as some sort of retainer so the pipe doesnt expand, it will depend on how tight you want it to be and I believe the method by which you will achieve this configuration will have an impact too!

Good luck!

 

[dgallup]

Don't forget the spring back. Unless both ends are restrained some way the spring will relax and become bigger than the pipe OD.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[IRstuff]

You don't say how dense the windings are, nor what the relative dimensions of the tube and wire are. Both are important factors in even bothering to do any calculations at all.

TTFN
faq731-376

 

[zekeman]

This is the kind of problem that is best done empirically,owing to its complexity.

Accordingly, any attempt at analysis will be fruitless, since there are curvature, deformation, spring-back, and frictional force issues that are impossible to formulate.

That said, your best bet is try the literature or spring manufacturers, or do the experiments yourself.

 

[mfgenggear]

maybe form the wire while stretching "yielding the material" to help remove springback.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[rb1957]

think that axial force is tensioning the spring, but transverse force is required to bend it.

i think you could bend a spring around a drum by pushing normal to the cable, at say two points pi*R apart (or more). these forces are reacted by the drum, yes?
i think the work done by one force is P*pi*R.

but i don't think the real world will work this way ... i think you need to put some tension on the spring, to make it conform to drum.

now the drum is turning (at 50 rpm) ... that'll be different again, 'cause i guess you'll restrain the end of the cable on the drum. now tensioning the spring as the drum winds up will wrap the spring around the drum ...

like zeke says ... too many variables to feel anything like confident !

like someone says ... ask someone who does this for a living, with practical experience.