winch drum thickness 1

[milus]

Hello,

I'm starting the design of a drum for a winch with three rope layers.
I have read some normatives (UNI 9466, DNV “Offshore Standard DNV-OS-D101,”...) but they lead to an oversized thickness of the drum.
The main problem is to correclty evaluate the rope pressure on the drum, do you have any suggestion? Also some book or documents to consult.

Greetings,
Milus

 

[MikeHalloran]

If you don't know how to evaluate the rope pressure, how can you conclude that drums designed per standards are too thick?



Mike Halloran
Pembroke Pines, FL, USA

 

[kingnero]

I am sure this has been discussed before on here, I remember reading it through as it's certainly an interesting, non-trivial problem, and if memory serves me correct, there wasn't a definite answer back the neither...

Find that thread, maybe you'll find some pointers there.

 

[TD2K]

http://www.eng-tips.com/search.cfm?q=winch&action=search

 

[milus]

The normes propose a calculation of the rope pressure that isn't realistic because they suppose to have an uniform distribuition of the pressure along all the drum, pressure=2*Rope pull/(pitch*rope diameter).
I have read that Ernst and Dietz have studied this problem but I can't find anything about them.
I have also read the other thread but I haven't find anything.
An example: an old winch as a thickness of 35 mm and worked for a lot without problems, if you use the normes you should have a thickness of 60 mm!

 

[GregLocock]

Important real world parameters

ratio of axial to radial stiffness of cable

number of wraps

friction coefficient of cable on cable

We ended up measuring it.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[milus]

@GregLocock

in the design phase I can suppose these parameters.
Is there a formula to apply to calculate the pressure on the drum?
I have found some papers of Dietz, Mupende, ecc... but these papers are in German.

 

[GregLocock]

I built a spreadsheet model rather than using a formula. Long gone to the bit bucket.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[chicopee]

Assuming that a drum thickness is overdesigned, did you consider wear and tear as well as regrooving the drum?

 

[chicopee]

I did not study the whole example as I download it a few minutes ago, however take a look at it:
publications.usace.army.mil/publications/eng-manuals/EM_1110
Appendix C - Publications, US Army Corps of Engineers
This example provides typical calculations for determining a sector ... Assume
design load to be split 70/30* between hoist drums .... to the difference between
the drum windings of each hoist drive one drum will .... t = Thickness Under Rope ...
Drum thickness may also be dependend on wire rope anchorage, shock loading and accelerative loading(inertia).

 

[milus]

@chicopee

I have visited the link but it isn't correct.
I have found this: [URL unfurl="true"]http://publications.usace.army.mil/publications/eng-manuals/index.html[/url]
which is the file that you suggest to read?

thanks

 

[chicopee]

My approch to drum thickness would be based on torsional stress and related angular deflection between the driven gear and the furthest point of the line load,allowances for drum grooving and possibly regrooving due to wear and tear, inertial and impact loading, and pehaps the influence of the bending stress when the line load is in between the bearing supports. I would discount the influence of the drum flanges.

 

[chicopee]

One more item to influence drum thickness is the line load anchorage to the drum unless anchorage is on the drum flange.

 

[Cockroach]

I have not have had much success designing wireline drums for use in oilfield applications. Infact, I've crushed the cores on several designs.

I know you can approximate the radial pressure on the core in accordance to the very simple equation P=2T/Dd. "T" is line tension, "D" is the diameter of the drum and "d" is the wire rope diameter. The equation is layer sensitive; the next successive layer would change the diameter of the drum core by D'=D+2d. In other words, laying a layer of wire rope of diameter "d" on the nude drum core of diameter "D" would increase the second layer pressure to P'=2T/[(D+2d)d]. And so on, the model is therefore iterative in nature.

One of the problems I've encountered and solved, the next successive layer of wire rope laid on that below fits inbetween adjacent coils. This is typically referred to the Kepler Cannon Ball Packing Problem. Drawing a line between centre points of two adjacent coils in a layer, then to the centre of a coil laid above it, forms an equilateral triangle whose sides are 2d. So you need to account for the geometry somewhat, it is not exactly D+2d to the outer surface of a drum with "n" wire rope layers. I solved this by physically metering length onto the drum and noting the spiral equation spooling the rope.

There is not a lot of literature out there, but there exists a welding specification which is dedicated towards wire drum fabrication. I can't find that paper right now, maybe someone in the forum has come across it. Something about "Lincoln Welding" as the publisher. Anyways, the paper discusses in detail the ends of the wire rope layers and how they impart side load to the flanges of the drum. I firmly believe this is my problem, crushing the drum core was preceeded always by watching the flanges begin to wobble. Kind of kookie, but I noticed that spooling on the wireline had a bearing load dependent on the fleet angle of the rope to the centre line of the drum. This was governed by 2Tsin(theta/2) were "T" is rope tension, "theta/2" is the half angle subtended by the sheave to immediate contact point of wire on the drum. So this too changes, for an increasing diameter drum with successive wire rope layers changes this fleet angle.

Jarring, that is the tendency to intermediately change the rope line tension has been my greatest nemisis. The lads in the field really like to jar on wireline rope, typical tensile loads of 1000 lbf running can double, so a guy needs to carry a hefty factor of safety for this uncertainty. This greatly influences the stress imparted to the drum, particularly at the ends of the layers and to the flanges. The flanges in turn give the drum core a bending moment which increases the radial pressure. The core therefore becomes lobed, contributing to an uneven stress and contributing to an increased collapse probability.

I must admit, my work on drums has been entertaining. It remains one of the more elusive problems I've encountered in mechanical engineering design. I stopped kicking out design work on drums, but occassionally entertain reviewing the phenonema, especially when a forum such as this reminds me of the application.

Best of luck, the problem is a beast. I was spooling slick line and braided five strand wire rope to a single drum for wireline applications, remember noting lengths of the different ropes was a problem. Continue to reply to this forum, I would be most interested with your experiences and methodology in overcoming design failures.

Regards,
Cockroach

 

[chicopee]

Core crushing is one reason to limit the number of wire rope layers on winch drums.