An Extra

Re: An Extra

I used to have model trains...same principle I think. Anyway I think the train wheels tend to stay on the middle of the rails when moving straight. The flange thingies on the insides of the wheels come into play when the train hits a curve. The wheels move off center and the flange thingies keep the wheels from derailing either right or left. When the wheels move to on side of the rails or the other the physics will allow the cars to take the curve. At least that's my recollection.

Tom

Partly

They do tend to stay centered, but why?

Also, in a curve, the flange is not the important part. It is a last ditch safety if all else fails. What allows the wheels to go around a corner and why do they stay centered? (they are related.

Re: An Extra

There is a particular curve and taper to the cross-section of the tire face - the part of the wheel that actually touches the rails. This taper allows the wheel-set to go around a curve without as much wear to wheel or rail as it would experience otherwise. The particular profile of the wheel has a specific name, something like "RP-25," that doesn't really give much explanation.

The profile has been in use on modern railroads since early in the Twentieth Century, but only made it onto model railroads in the 1960's.

Fred

Under clear skies, and no-where near a railroad, in Eastern Missouri

Re: An Extra

I thought it was the convexity of the rail not the tire. The roundedness of the top of the rail allows for the difference in speeds of the wheel but only to a point which is why designers use a set of railroad curves in laying out a bed. The curves provide a not to exceed turn radius dictated by speed of the train.

Re: An Extra

In a well-maintained railway, it is a combination of the rail-head and wheel profiles. The AAR and APTA set standards for rail-head and wheel geometries in this country, there are similar standards throughout the world.

In general, the conical profile of the main bearing surface of the wheel (generally a 1:20 to 1:40 taper) tend to keep the wheels centered on the rails. If the rail curve geometry is done right, the taper combined with centrifugal force creates a differential effect due to the larger effective rolling radius on the outside rail.

The flanges provide a safety factor for worn wheels & rails or for speed extremes.

;-)

Excellent. I thought that it was interesting that because of the taper, when the wheels are traveling straight down the track, if they start to go off, the differential action created by the taper steers the wheel back into alignment. In a corner, as you said, during the turn, the outer wheel travels up the taper and the other side down which creates a differential condition.

It is probably a similar condition that keeps bandsaw blades on the wheel of the machine.