Plastic Deformation of Large Wheel on Rail 3

[JJ8th-e]

I have encountered an issue with an industrial application involving a 28"-diameter, 2-1/2" wide, flat-tread hardened medium carbon steel wheels on a standard 104# crane rail in a low speed application of heavy load (about 85,000 pounds per wheel). The wheels were hardened to what was deemed sufficient at 315-325 HBN but, after about five months of regular use, some of the wheels have deformed permanently to match the crown of the rail. My gut reaction says that a small amount of deformation is not a cause for alarm for once the contact area grows to match the rail crown it should reach an equilibrium and cease to further deform plastically but I am unsure how to back up this beyond intuition.

In the original analysis, it seems there was no focus beyond a prescribed hardness of wheel and complete disregard for the rail crown. Upon review of baseline Hertzian contact stress analysis in the cylinder-plane condition, the maximum Hertzian contact pressure is very close, if not possibly exceeding, the yield strength of the hardened wheel and this does not even take into account the reduced line of contact due to the rail's crown. So, this provides part of the explanation of the exhibited concavity of the wheel, mushrooming as much as 3/16" and causing some annoying interference on some guarding sheet metal, but I am not sure how to further prove that there should not be any further deformation of the wheels without some rather daring assumptions. FEA seems like a suitable route but I do not have that at my disposal in this case.

I would greatly appreciate any insight or suggestions in addressing this issue. Thank you!

 

[3DDave]

Grind off the mushroom to remove the interference and see if it comes back. If it doesn't then great. If it does come back then the wheel needs re-working or replacement which is what you'll do if the analysis shows it is insufficient. At the best case you need to turn down the wheel and shrink fit a much harder rim onto it. Worst case, time for a new, harder wheel.

I'd grind off the mushroom and mark a spot with a center punch as paint can get removed. Check the width next to that punch mark with a caliper and come back in a month and measure again.

 

[FacEngrPE]

The choice is to either use wheels that are soft enough to turn - like yours are, and periodically machine the wheels, or to use wheels with a thick hard case (4mm of 58 rockwell c). These very hard wheels can not be machined, but are resistant to spalling, if the suppliers process is good. Wheels with a thin hardened case somtimes spall and peal.

I would expect to see the top of the crane rail work harden and flatten if use with the very hard wheels. If you do not have welded rail joints, with loads this high I expect to see joint bar problems.

 

[MintJulep]

85,000 pounds per wheel is an enormous load.

For comparison, a fully loaded freight rail car weighs on the order of 263,000 pounds, spread over 8 wheels is 32,875 pounds per wheel.

 

[FacEngrPE]

The largest Goliath cranes use A 150 section rails.
DIN 15 070 / FEM 1.001 provide some guidance for application,

http://www.harmersteel.com/v2/wp-content/themes/kayjayone/catalog/33.pdf

This series rail section and the matching wheels might work out better than what you are using.

Gantrex has published an easier to read document based on the European standards that allows calculation of rail head width from load and wheel diameter. This document makes a point that railroad rail in crane service may experience web crushing.

https://files.engineering.com/getfi...38&file=TGN_08-Crane-rail-selection-09-12.pdf

 

[racookpe1978]

Are all 8 wheels uniformly deforming? Are you sure that the axles (bearing cases, bearing pads and frames 1 (or 2) wheels are not "mis-aligned" so they are receiving much higher than design loads?

 

[IFRs]

Seems to me that the OP's question is: has the deformed wheel stopped deforming since it is now experiencing a larger contact area having changed from flat wheel on rounded rail (in setion view) to a concave wheel on a convex rail. Their issue is having postulated this, how to prove it? I can think of two options: use it and monitor closely to see if the rate of change of the effective wheel radius slows down, or find some way to do a rolling load test on a sample.

 

[TugboatEng]

I would think that any metallic wheel that plastically deforms to carry it's load would fail by fatigue within very few revolutions.