×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

coefficient of friction

coefficient of friction

coefficient of friction

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

RE: coefficient of friction

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.

RE: coefficient of friction

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.

RE: coefficient of friction

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.

RE: coefficient of friction

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

RE: coefficient of friction

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

RE: coefficient of friction

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.

RE: coefficient of friction

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 :)

RE: coefficient of friction

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?

RE: coefficient of friction

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources