coefficient of friction

[proejuan]

What is the coefficient of friction for calculate the pull force in a rail car?

 

[GBor]

You have two: Static friction (prior to the start of it rolling) and Rolling friction (after you overcome static friction). Generally, you can use dry steel on dry steel, which, if I recall correctly, is about 0.3. After it starts rolling, I think it drops off to around 0.1. There is a railway engineering forum on eng-tips, I think. You may way to find it.

 

[MintJulep]

The rail forum here isn't very active.

What exactly are you trying to calculate? The resistance of a rail car to rolling is made up of many things.

 

[arto]

Way back when, there were articles in the ASME transactions on the "hunting" of railcars [bopping side-to-side]I seem to recall that empty cars had more friction because the wheel flanges rubbed more.

 

[proejuan]

MintJulep:
I need to calculate the resisting force for design the counter weight to haul the rail car.

 

[MintJulep]

Under steady state conditions, train resistance can be approximated by the modified Davis equation, listed below.

I don't understand what you mean by using a counter-weight to haul a car, but if it is what I picture in my mind, then you have a constant force, which means acceleration. Note that most of the terms of the equation have a speed component.

Train Resistance:

TR = 1.3W + 29n + 0.045WV + [0.0024 + 0.00034(Q-1)]AV^2 pounds force where:
TR = Total train resistance in pounds force
W = Total train weight in tons
V = Train speed in miles per hour
A = Frontal area in square feet
Q = Number of cars in the train
n = Number of axles in the train

or TR = 6.4M + 130n + 0.14MS + [0.046 + 0.0065(Q-1)]AmS^2
Newtons where:
TR = Total train resistance in Newtons
M = Total train mass in metric tonnes
S = Train speed in kilometers per hour
Am = Frontal area in square meters
Q = Number of cars in the train
n = Number of axles in the train

 

[GregLocock]

Gbor, actually wheels don't work like that. Your calculation would be fine if the brakes were on!

For those of us who think in terms of rolling resistance, then a steel tire rolling on a steel rail has a coefficient of .001 to .002 according to the blue book, but MintJulep's equation is better.

The implied coefficient there is 6.4/(1000 * 9.81), 0.00065







Cheers

Greg Locock

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

 

[GBor]

Chalk up another poor response. My father worked for the railroad for 30+ years...guess I'm remembering the wrong information.

Thanks for straightening me out

 

[dimjim]

I think the greatest resistance will come from the type of bearings installed. I have seen box cars being pulled by a strong man when wheel bearings were equipped. Are all box car wheels now bearing equipped?

 

[GregLocock]

Gbor, not often I catch you out!



Cheers

Greg Locock

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