Eastern Railroad Discussion > flat wheels

Every railfan knows the sound of a freight car with a flat wheel.
Some questions:
-- What casues a flat wheel? A train going into emergency? But then wouldn't all the wheels in the train be "flattened?"
-- How flat does a wheel have to be before the car is taken out of service? Where is the wheel repair made...local yard RIP track?
-- Is there an equivalent to a hot box detector to flag a car that has a flat wheel?

Bill

While emergency brake applications indeed cause flat spots on wheels, they also can develop if a flaw in the metal causes an imperfection that is then amplified by the impact on the rail during each wheel revolution. Similarly, a flat spot from emergency braking may not be all that loud right after the breaking but it will get worse over time -- long after the cars in the train have been reclassified into many future generations of trains. Sticking brakes often are another cause of flat spots.

There are "impact detectors" that are used to detect flat spots on rail wheels. They are not as common as hot-bearing or dragging-equipment detectors, but many main lines have them.

I remember there was a discussion about flat spots before the server change, but I don't know if it was transfered.

A small pit on the wheel can cause a flat spot. Hand brake left on the car can cause sliding, which will cause a flat spot.

You need a crane of some sort of lifting device to lift the truck and car off of the wheel, then you can slide a replacement in.

There are detectors that detect excessive 'slamming'. If it is above a certain level, the detector will go off.

For example, there is a Wheel Impact Detector on the CSX Chicago Line at Mile post 109. It should be right next to the Springfield Detector.

Here's what the timetable says in reguard to the Springfield Detector.

"Trains will be notified by train dispatcher of an actuation of the wheel impact detector. When notified of an actuation, train speed must be reduced to not exceeding 30 mph, unless instructed by train dispatcher to stop and inspect the subject wheel(s)...After inspection the car(s) may be moved to the location specified by the train dispatcher at a speed not exceeding 30 mph. The conductor my further restrict the speed using discretionary judgement."

I imagine it takes a pretty hefty flat spot to set off the detector.

Take Care
be safe

Being a proponet of lower track speeds. If you see a flat spot, call it in!
Flat spot leads to car shake, car shake leads to a derailment at a grade crossing, call it in !!!!

What you are hearing is most likely not a simple wheel with a flat spot on it, but a shelled wheel. These are more common, and tend to make more noise.

A shell is like a divot out of the surface of the wheel. The cause is generally assumed to be the result of the intense heat generated between the wheel and the rail when a wheel slides, followed by quickly cooling the spot. The slide might be because of normal train braking, but is most likely caused by improper use of the handbrake. Crews spotting cars at ramps will often wind on the handbrake to get a more accurate stop, and locations that use car pullers will often not fully release the handbrake when they move the car. All will result in metal damage that might ultimately result in a wheel shell.

If you watch for cars that make the pounding sound as they pass, you will find a high proportion of them are tank cars, forwarder cars, covered hoppers and mill gons. These are cars that frequently see hand brake use. Further, the odds are pretty good that the thumper will be at the hand brake end of the car.

A shell doesn't develop immediately, but will pop out many miles after the damage was done. That means that you can't just inspect the wheel after it slides and know there will be no problem. You also wouldn't automatically change out the wheels, since a shell might not develop at all.

There are limits to the size of the shell that are acceptable. The wheel can remain in service, even with a wheel shell, as long as the limits are exceeded.

If you want to see a really severe flat spot, check out this site:

http://www.tsb.gc.ca/ENG/

Go to Reports, then Rail, then 1996, and then:

Report Number R96T0095

It gives a very detailed report on how a VIA LRC car was dragged for over 240 miles, with at least one wheel sliding the whole way. There's lots of other good stuff on this site, if your're into how RR accidents happen.

flat spot must be <2.5"long or <2" long (each) in adjoining spots. Thats when there are two flats next to each other with no curvature. Shelled out spots have the same requirements. See 49CFR229.75 (locomotive) and 49CFR215.103 (freight car) for other wheel and tire defects. CFR is the code of federal regulations. FRA website has a good link to them BTW.

Wow! Great responses. Thanks...

Bill