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7.5 gauge derailment issues

Geochurchi

Registered
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
 

FWurth

One Millionth Post
Last Subscription Date
07/29/2019
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
 

pegasuspinto

Registered
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?)
 

pegasuspinto

Registered
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
 

Geochurchi

Registered
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
 

Geochurchi

Registered
Hi All, after taking many measurements and comparing old with new we believe the problem is the flange height, IBLS spec’s. NLT .0187 ours were .0115, vendor admits there was an error in machining and is replacing the wheels.
Let’s hope that was the problem.
Geo
 

dkamp

eMail NOT Working
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.
 

b7100

Subscriber
Last Subscription Date
07/10/2019
(Not a train person) and above explaination is excellent but as far as getting things square can the assembly be set up on a milling machine table and checked with a dial indicator? Also I assume all 4 corners have to have the weight somewhat evenly distributed. If there is no suspension??? Then a flat surface (like a surface plate) and maybe some feeler gauges might be a way to check that. Then as mentioned check the flange angle. So feel free to correct me on any of this. That is what this forum is about - to learn.
 

Geochurchi

Registered
After much time and effort an all-volunteer squad found many problems with the track, roadbed and have corrected most everything, we have picked up a volunteer who is quite familiar with this stuff.
Geo
 
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