Winch drum wrapping pressure

[heddichead]

thread404-332009

Hello all,

This might be the unsolved problem in the industry.

Came across the problem of solving the stresses in the winch drum subjected to multi-layers of wire rope. I am using FEA to model the scenario and requires the compression pressure when it is subjected to wire rope tension at different layers.

I have read a lot of materials and forum and the radial pressure on the core is based 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.

The textbook Design of Weldment by Omer W Blodgett suggests to consider summation of compression pressure in the outer 2 layers using the formula above.

The stresses is very high in FEA and by hand calculations (thin wall theory). Any one knows any other way to approximate the compression pressure......

Many thnksssssssssssss

 

[GregLocock]

FEA is going to be of little help. In my experience, with one type of cable, the important factors were friction and the ratio of axial to radial stiffness of the cable. A 2 layer approximation may be appropriate for steel cable in dry conditions, but is non conservative for plastic wrapped cables in seawater.

Cheers

Greg Locock


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[EngineerTex]

I am using FEA to model the scenario and requires the compression pressure when it is subjected to wire rope tension at different layers

I agree with Greg about FEA not really being a lot of help. One of the issues with wire rope on a winch drum is that modeling it as compression pressure on the OD of the drum is the exact opposite of what you would get in the real world when you look at stability/wall buckling. The FEA program will assume that the pressure remains constant as any slight deformation (inward) occurs. When, in fact, the wire rope causes an increased stability. If you imagine the cross section becoming distorted into a somewhat elliptical shape, the wire rope would exert less force on the flatter* side and more force on the pointier* ends, returning it to a stable shape. This is the opposite of what happens if you subject a cylinder to significant pressures on the OD as when in a pressurized fluid on the OD and not on the ID, which is what I think you are trying to model in FEA.

With some hand calculations to which you (on the minimum end) and Greg (on the most conservative end) referred, you might be able simply to get the compressive pressure of the wire rope on the drum, but if you're not looking for stability/buckling, I assume that you wouldn't be using FEA.

*with all due respect to the mathematicians reading this, I do know that an ellipse doesn't actually contain flatter or pointier parts.

Engineering is not the science behind building. It is the science behind not building.

 

[3DDave]

EngineerTex - what you were getting at is that areas of higher curvature get higher pressures and areas of lower curvatures get lower pressures. A uniform pressure distribution won't represent that condition.

heddichead - I would say that -yes- the loads are high. It's been discussed here before (thank Google)

http://www.eng-tips.com/viewthread.cfm?qid=316932

There are two problems to the analysis - crushing of the drum and destroying the side plates. I do like this observation:

"In practice in a real life case with a cable with a high ratio of axial to radial stiffness we measured no increase in drum pressure after the first seven layers at constant tension, whereas when we lubricated the cable we did not find a practical limit."

There is also a paper attached at the end of the old post.

 

[heddichead]

Hello all,

Many thanks for replies.

EngineerTex (Mechanical)---
We are actually doing the FEA to check the stress in the existing winch design (heavy winch 250t at 1st layer and 140t at 8th layer). Will not go to buckling and stability check yet. So we just simply apply the wrapping pressure due the wire rope tension. The drum is designed to 15 layers of wire rope tension and the layer 1 ( innest to the drum surface) has highest wire rope pull tension and decreases proportionally to the torque.

"Design of weldment" suggest to consider the wrapping pressure by summing the outer 2 layers using P=2T/Dd. If calculating in this way, the wrapping pressure is the highest at 2nd and 3 rd layers and will decrease as it goes to 15th layer. However, even applying the wrapping pressure of first layer ONLY, the stress is still very high, close to yield.

Van ZYL 2000 approach is even conservative. He suggests to sum all the wrapping pressure of each layer.

Instead of using the formula of P=2T/Dd to relate wire rope pull tension to wrapping/ compression pressure...any other formulae/ways of estimating the wrapping pressure? Thanks.

3D Dave---
The wire rope is actually coiled along the drum in a very flattened manner. So it can be assumed the areas are equally pressurized by the wire rope. I went to the forum thread before and also read the paper attached. The paper does not show after 7th layer at constant tension there is no increase in drum pressure? Do you have any reference for that?

Thank you all a lot.

 

[heddichead]

Hi GregLocock (Automotive),

In another forum thread, i saw you mentioned you built a spreadsheet model to estimate the wrapping pressure based on the axial and tangential stiffness, without using the formulae? How did you come out with that? Please can you advise...thank you.

 

[3DDave]

It was clearly stated in the thread - read it again. The paper was a bonus.

 

[GregLocock]

No I built the model based on the winching tests, where my partner in crime built a strain gage load cell and we spent a happy day messing about with a full size drum and winch assembly. We'd already measured the stiffness of the cable radially and axially, and I spent a rather soggy afternoon establishing the coefficient of friction for various lubrication conditions.

So, in order to build an accurate model I already had a lot of test work done.





Cheers

Greg Locock


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

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[heddichead]

Hello all,

3DDAVE
Yes. If using the formulae to calculate the wrapping pressure accumulated up to 15 layers, it can be seen that the there is less effects as it goes outer layer...However, the wrapping pressure is high at 2nd and 3rd layers when we sum up....and this results in very high hoop stresses, same outcome in FEA.


GregLocock
oh. understand. so it is a experimental relationship and outcome to determine the wrapping pressure rather than using theoretical formulae... that must be a lot of works.

So, are 2nd and 3rd layers of wire rope pull generating higher pressure than only 1 layer of wire rope tension? is there any experimental relationship that can be derived? Thanks.

 

[heddichead]

Recently found the latest study on wrapping pressure on winch drum subjected to multi-layers wire rope tension.

http://www.ktf.no/fileadmin/Dokumen...erienced_by_winch_drums_and_reels_systems.pdf

Instead of directly summing the wrapping pressure calculated at outer 2 layers (per esign of Weldments" textbook) the derived formulae by taking account of friction coefficient and configuration geometry of wire rope is shown in the link.

The wrapping pressure at 1st layer remains the same as using the P=2T/Dd. but when accumulating to 2nd, 3rd, 4th layers and above, it is multiplying a summation of the factor which is almost 1 at each outer layers.

So this keeps the wrapping pressure much smaller compared to directly summing the outer 2 layers.

Any comments??? THanks a lot.