Frictional Losses around Sheaves 1

[Ussuri]

I have a simple question (I Hope) which is outside the extent of my knowledge. I have a 64mm diameter wire rope passing over and then under two 1.1m diameter sheave blocks. The sheaves are mounted on a trunnion/axle type bearing. I assume they will be in good condition and properly lubricated.

The wire rope is connected to a winch and needs to pull 650 kN at the leading end. I am aware I will get frictional losses around each of the sheaves that will mean the winch has to pull greater than the 650 kN. My question is by how much? Can someone direct me to any useful publications which might be able to give me this type of information?

Regards



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"The world keeps turning, it keeps me in my place; where I stand is only three miles from space"
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[CanuckMiner]

Ussuri,

I have a paper that gives a method for estimating the friction loss of sheaves with plain bearings (8% loss). The paper references a document by MacWhyte ropes (now under "new ownership"). My google search for the original reference proved fruitless.

I'm not sure what a trunnion/axle type bearing is, nor how it compares with a plain bearing.

The paper I have can be found at

http://www.ppipella.com/download/WireRopeSheaveFrictionTU2.pdf

Cheers,
CanuckMiner

 

[Ussuri]

Thank you. Thats very helpful, have a star.

 

[CanuckMiner]

Ussuri,

Thank you for the star.

I actually went back and checked my library and came across "efficiency" factors from Wire Rope Industries. They list the same 8% loss for plain bearings as noted in the paper I linked you to, and also provide a recommendation to use 4% loss for roller bearings.

I didn't pay too close attention to your particular sizes the first time, but an 1100mm dia. sheave for a 64mm dia. rope might be a bit on the small side (i.e. 17:1 diameter ratio). Depending on the construction of the rope, the number of cycles the rope will see, etc. you may want to consider increasing the sheave size. If you haven't already done so, I suggest that you review the minimum diameter ratios recommended by the wire rope manufacturer.


Cheers,
CanuckMiner

 

[Barry1961]

You will also have the force to bend the cable which will depend on the type of cable. This can be very significant if you are bending at the minimum radius.

Barry1961

 

[Ussuri]

Thanks for the responses. I have checked the bridon wire rope product data which advises a minimum D:d ratio of 16:1. But I will suggest possibly increasing the sheave size to reduce the risk of bend fatigue.

The operation is only supposed to take a few hours and there should not be very much spooling in and out, hence reducing wear on the wire.