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7.5 gauge derailment issues


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  #1  
Old 04-27-2019, 01:48:34 PM
Geochurchi Geochurchi is offline
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Default 7.5 gauge derailment issues

Hi All, we just installed new wheels,axles,bearing on a powered truck, problem is we are having derailment issues at various locations along the track, curves or straight section, never had the problem before, any thoughts would be greatly appreciated
Geo
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Old 04-27-2019, 02:52:28 PM
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FWurth FWurth is offline
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Default Re: 7.5 gauge derailment issues

Could be any number of things. Only happening since wheel change points to it was something just changed. Not enough flange height? Maybe the truck suspension is now too stiff to allow wheels to keep in contact with the rail? New wheel sets less tolerant of old flaws in track, OK, maybe just address those track issues? Good Luck
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Old 04-28-2019, 05:19:07 AM
pegasuspinto pegasuspinto is offline
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Default Re: 7.5 gauge derailment issues

Are the wheels in gauge? Is the truck 'out of square'? Is one driver slipping on the axle causing asymmetrical loading? Does the truck derail the same way every time? (Example, the trailing fireman's side wheel is always jumps over the rail?)
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Old 04-28-2019, 09:20:00 AM
Geochurchi Geochurchi is offline
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Default Re: 7.5 gauge derailment issues

Hi, always derails on Fireman side, I doubt there is slippage on the axle, not sure how to check that or where to check to see if truck is out of Sq. We will double check the gauge.
Here is a pic of what we are dealing with.
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Old 04-28-2019, 09:36:56 AM
pegasuspinto pegasuspinto is offline
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Default Re: 7.5 gauge derailment issues

Roll the truck over, put a drop of paint on the flange on all 4 wheels, flip it and set it gently down on a flat surface so all 4 wheels hit at the same time and leave paint, and then pick it back up again and move it aside. Measure the paint front to back side to side and in an X, all the measurements should be in pairs and pretty much identical.

You might could just flip the truck end for end and reverse the motor wires, maybe it would never give you trouble if it goes the other way
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Old 04-28-2019, 10:00:37 AM
Geochurchi Geochurchi is offline
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Default Re: 7.5 gauge derailment issues

Hi, unfortunately we can’t flip the trucks easily because it is hydrostatic drive and the hoses won’t permit that, we will try and check for squareness at some point.
Geo
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Old 04-28-2019, 10:50:32 AM
CharlieB CharlieB is offline
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Default Re: 7.5 gauge derailment issues

Check the bevel angle on the new wheel tread?
Looks pretty flat in the picture.

Last edited by CharlieB; 04-28-2019 at 11:11:48 AM.
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Old 04-28-2019, 11:56:40 AM
Big Bird Big Bird is offline
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Default Re: 7.5 gauge derailment issues

Here's a screenshot of the ibls web page for 7 1/4 gauge track.
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Old 04-29-2019, 05:45:13 PM
Geochurchi Geochurchi is offline
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Default Re: 7.5 gauge derailment issues

Hi All, after taking many measurements and comparing old with new we believe the problem is the flange height, IBLS specís. NLT .0187 ours were .0115, vendor admits there was an error in machining and is replacing the wheels.
Letís hope that was the problem.
Geo
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Old 05-04-2019, 03:23:03 AM
dkamp dkamp is offline
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Default Re: 7.5 gauge derailment issues

The photo of gauge posted above, is incorrect... it illustrates the rails being close to the flanges, which is NOT the way the arrangement actually works. In trackway layout, the wheel/rail contact point in straight running places the rail contact point in the MIDDLE of the wheel. In a curve, one side will be CLOSER to the flange, the other will be CLOSER to the outer edge of the wheel. In a curve, the distance between rails is slightly greater. If it is NOT built this way, you WILL have flange contact, and derailment. Furthermore, the radius of the curve MUST be calculated, limited, and controlled.

When I was teaching classes on passenger train braking systems, I always included a half-hour segment on wheel/rail interface. Here's a condensed version:

Locomotives and railcars have a "steering wheel". Where is it?

It is at EVERY PLACE where the locomotive or railcar TOUCHES the rail. EVERY WHEEL is a 'STEERING WHEEL'.

What keeps the train ON the track? Invariably, students would answer "The flange".

No. The flange contacts the rail when wheel/rail interface geometry is incorrect. The wheel TAPER keeps the train ON the track.

Place a common Dixie cup on the desk, and give it a push. It doesn't roll straight... it rolls in a circle. Why? Because the top of the cup is substantially larger in diameter than the bottom.

Imagine two cups, with wide edges forward, stuck on a shaft, and sitting on two rails. Roll the cups down the rails, and it will stay centered. Simpletons would say it stays centered because it's weight draws it to center, and while there's some truth to that concept, it is NOT the reason why the axle/wheel assembly stays centered- it stays centered because it STEERS towards center.

Place the axle off-center, and one cup will attempt to roll on a large circumference, while the other will be forced to roll on the SMALL circumference. Since they're on a common shaft, it is the equivalent of the cup rolling all on it's own- it will 'steer' itself until the wheels are rolling on EXACTLY THE SAME CIRCUMFERENCE.

That means, if you want the axle to be able to negotiate a tighter turn, the taper of the wheel (from flange to outer) MUST be steeper.

A steeper wheel face profile equates to a 'quicker' steering action of a railcar axle because the difference of circumference between the right and left wheel is higher, with LESSER deflection than a 'flatter' profile. The 'gotcha' is that A wheelset with totally flat profile will bang flanges and derail. A wheelset with TOO AGGRESSIVE of a wheel face profile will tend to 'hunt' at certain speeds relative to the railcar's center of gravity, and distance between axles on a bogey.

While they may identify that there's an issue with the flange height, the REAL problem is that your trackway geometry is not compatible with your wheelset taper and flange spacing.
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Old 05-04-2019, 07:22:03 AM
Geochurchi Geochurchi is offline
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Default Re: 7.5 gauge derailment issues

Thanks for that post, the more info the better.
Geo
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