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Does taper or flange handle train curves, Or both?

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Faulty

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1. The flange rarely ever touches the rail and curves are mostly handled by the taper on the wheels and are rarely ever handled by the flange..

2. The flange DOES touch the rail on curves and the taper is only there to help centre the wheelset on straight tracks and is not enough to act as a differential.

3. The flange touches the rail on curves, and the taper is there to help centre the wheelsets and to allow the wheels to spin independently on curves a bit like number 1 except the flange always touches except for straight tracks and GIANT curves.

What is correct?
 
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snowball

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There are others on here who know better than me but I think 1 is correct. Flange contact only occurs on the tightest curves or if curves are taken at excessive speed. When it does you can hear the squealing.
 

Faulty

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Thank you, But the spacing between the flange and rail seems so small it just wouldn't be that. I know that railway curves are generally very large but I'm still not sure what's the definite answer.

Also the same with the taper, It seems too small.
 

Highlandspring

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Number 1 is more or less correct, and the terminology is ‘coning’ rather than ‘taper’ in the UK at least.
 

Faulty

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I've been looking for videos to see this, Although most of them are at the wrong angles.
 

Wilts Wanderer

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The relationship between wheel and rail is very complicated but you must remember that there are two rails and two wheels working effectively against each other in any curve. Also the forces are immense, especially given the contact area is smaller than a 5p piece. It’s effectively a system of balanced forces which is continually adjusting itself.
 

philthetube

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ideally all taper, but on mixed stock lines, with different speeds or when trains are running at below line speed flange has to come into play,
 

billio

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ideally all taper, but on mixed stock lines, with different speeds or when trains are running at below line speed flange has to come into play,
Does this mean contact is also affected by the cant of the track in a curve ?
 

edwin_m

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The simple theory is that the wheelset will move sideways until the ratio of the diameters of the two wheelsets at the contact points is the same as the ratio of the curve radii of the two rails. When this happens the outer wheel travels the slightly further distance of the outer rail in one rotation with neither wheel slipping and flange contact is not necessary to keep the train on the track. As the rail radii differ by about 1.5m and the actual radii are in the hundreds or thousands of metres, the amount of coning doesn't need to be very much to allow running without flange contact on most curves.

This is complicated by the presence of lateral forces, which cant may reduce, cancel out, or even overcompensate for if the train is going more slowly than the equilibrium speed. The suspension components also affect the ride - in particular dampers can make the bogie stiffer in rotation (the big shock absorbers some trains have mounted horizontally outside the bogie). These reduce the tendency to hunting (above a certain speed the centreing forces over-compensate and the bogie effectively zigzags along the track) but make it more difficult for the bogie to align itself on curves and hence may make flange contact more likely.

All wheelsets on British trains are rigidly connected by the axle so the wheels cannot rotate independently. The above mechanism doesn't work on independent wheels, such as on many low-floor trams and a few train types such as the Talgo.
 

philthetube

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ideally all taper, but on mixed stock lines, with different speeds or when trains are running at below line speed flange has to come into play,

Does this mean contact is also affected by the cant of the track in a curve ?

Yes, but the cant should match the train speed so that there is no flange contact, only a problem when train speed varies.
 

coppercapped

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If you really want to know about rail vehicle stability I can recommend this book. The author was one of the leading lights in BR's groundbreaking research into the wheel-rail interface in the 1960s.
 

Flying Phil

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Yes, but the cant should match the train speed so that there is no flange contact, only a problem when train speed varies.
Interestingly I noticed at Market Harborough station what appears to be a flange greasing system which was inside the outer rail on the curved canted track. I assume because some trains stop and others are on the 60 limit, the grease is to reduce the squeal/wear going round the curve?
 

Flying Phil

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If you really want to know about rail vehicle stability I can recommend this book. The author was one of the leading lights in BR's groundbreaking research into the wheel-rail interface in the 1960s.
That research lead directly onto the APT-E and APT-P project.
 

Bedpan

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I remember seeing a "hands on" display at the science museum many years ago which dealt with this. There was a curved and inclined track which you could roll an axle with flangeless wheels down, and the coning/tapering always kept the wheels on track (excuse the pun) however much the track was curved.

One thing I'm not sure about is what causes the squealing. I assume that it's due to wheels on a fixed axle travelling different distances on sharp curves rather than the flanges touching the inside of the rails, but does anybody know for sure?
 

Faulty

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I remember seeing a "hands on" display at the science museum many years ago which dealt with this. There was a curved and inclined track which you could roll an axle with flangeless wheels down, and the coning/tapering always kept the wheels on track (excuse the pun) however much the track was curved.

One thing I'm not sure about is what causes the squealing. I assume that it's due to wheels on a fixed axle travelling different distances on sharp curves rather than the flanges touching the inside of the rails, but does anybody know for sure?

I was going to say, I think the squealing on sharp curves is simply the tread sliding and not the flange rubbing, Or at least most of it.

Also is the museum you are talking about the one in tokyo?
 

Taunton

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The worst flange squeal on the network is from the viaducts at Borough Market Junction. It always has been. The continual noise that penetrates to Southwark Cathedral, the market, etc is a considerable and longstanding blight on the area. Is there any reason why it cannot have been engineered out?
 

coppercapped

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That research lead directly onto the APT-E and APT-P project.
And to all subsequent designs of rolling stock including the various High Speed Freight Vehicle (HSFV) suspensions which led to the single axle bogies used under the Pacers, both the power and trailer cars of the High Speed Diesel Train (aka the HST), the Series 3 bogies used under suburban stock for many years and much else.
The key factor is the positive location and control of the yaw stiffnesses of the axles and the yaw stiffness of the bogies while allowing the suspension to behave as a mechanical filter. The filter function is intended to limit the pass through of the excitations of the wheelsets, caused by irregularities in the alignment and stiffnesses of the track, to the passengers.

After a few journeys in Class 800s I'm not sure that the book has yet been translated into Japanese...
 

Lucan

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The flanges do not touch the rails on straight track, nor on curves up to a limit. Ideally anyway. As someone said, if the train speed/curvature is not balanced by cant then the wheelset can move outwards (or inwards) to compensate, and if the imbalance is too much the flanges will touch. This is probably more noticable inwardly at slow speed on maximum canted track.

On the tightest curves there is not enough conicity to compensate for the difference in rail length between inner and outer rails, so flange contact is inevitable. That is the squealing.

All this is complicated by wheel tread profile wear which causes departure from the cone; in fact I have seen wheel profiles where the working part of the tread had negative conicity. Last I heard there was an aim to design suspensions to allow for a worn profile and to discover a stable "worn profile" to which wheels would be actually be made new and would hopefully go for longer between re-turning on the lathe. I have been on trains with such worn wheel profiles that the wheelsets are hammering from side-to-side between the flanges on straight track.

On those sharper curves where flange contact is inevitable greasers can be used, but the grease pots require frequent re-filling. The grease (perhaps suprisingly) is as much to reduce the tendency to derail by flange-climbing as it is to reduce wear. Even so rails on some London Underground curves (with which I am more familiar) need replacing every few months, and the flanges of 67 Tube Stock on the Victoria Line wore more on one side than the other, the line having a general curvature.
 

furnessvale

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The flanges do not touch the rails on straight track, nor on curves up to a limit. Ideally anyway. As someone said, if the train speed/curvature is not balanced by cant then the wheelset can move outwards (or inwards) to compensate, and if the imbalance is too much the flanges will touch. This is probably more noticable inwardly at slow speed on maximum canted track.

On the tightest curves there is not enough conicity to compensate for the difference in rail length between inner and outer rails, so flange contact is inevitable. That is the squealing.

All this is complicated by wheel tread profile wear which causes departure from the cone; in fact I have seen wheel profiles where the working part of the tread had negative conicity. Last I heard there was an aim to design suspensions to allow for a worn profile and to discover a stable "worn profile" to which wheels would be actually be made new and would hopefully go for longer between re-turning on the lathe. I have been on trains with such worn wheel profiles that the wheelsets are hammering from side-to-side between the flanges on straight track.

On those sharper curves where flange contact is inevitable greasers can be used, but the grease pots require frequent re-filling. The grease (perhaps suprisingly) is as much to reduce the tendency to derail by flange-climbing as it is to reduce wear. Even so rails on some London Underground curves (with which I am more familiar) need replacing every few months, and the flanges of 67 Tube Stock on the Victoria Line wore more on one side than the other, the line having a general curvature.
As done by professor Heumann many, many years ago. The trouble was that the new worn profile, side cut rails on curves at 27 degrees, which was the angle at which rails had to be changed or transposed to avoid wheels climbing out.

Some internet research could discover whether this problem was adequately solved.
 

philthetube

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The flanges do not touch the rails on straight track, nor on curves up to a limit. Ideally anyway. As someone said, if the train speed/curvature is not balanced by cant then the wheelset can move outwards (or inwards) to compensate, and if the imbalance is too much the flanges will touch. This is probably more noticable inwardly at slow speed on maximum canted track.

On the tightest curves there is not enough conicity to compensate for the difference in rail length between inner and outer rails, so flange contact is inevitable. That is the squealing.

All this is complicated by wheel tread profile wear which causes departure from the cone; in fact I have seen wheel profiles where the working part of the tread had negative conicity. Last I heard there was an aim to design suspensions to allow for a worn profile and to discover a stable "worn profile" to which wheels would be actually be made new and would hopefully go for longer between re-turning on the lathe. I have been on trains with such worn wheel profiles that the wheelsets are hammering from side-to-side between the flanges on straight track.

On those sharper curves where flange contact is inevitable greasers can be used, but the grease pots require frequent re-filling. The grease (perhaps suprisingly) is as much to reduce the tendency to derail by flange-climbing as it is to reduce wear. Even so rails on some London Underground curves (with which I am more familiar) need replacing every few months, and the flanges of 67 Tube Stock on the Victoria Line wore more on one side than the other, the line having a general curvature.
Wow, great post, you put that so much better than I could.
 

Bedpan

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I was going to say, I think the squealing on sharp curves is simply the tread sliding and not the flange rubbing, Or at least most of it.

Also is the museum you are talking about the one in tokyo?

It was the Science Museum in London probably about 25 years ago, but the demonstration was exactly the same as the Youtube videos you have posted.
 

ac6000cw

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All this is complicated by wheel tread profile wear which causes departure from the cone; in fact I have seen wheel profiles where the working part of the tread had negative conicity. Last I heard there was an aim to design suspensions to allow for a worn profile and to discover a stable "worn profile" to which wheels would be actually be made new and would hopefully go for longer between re-turning on the lathe. I have been on trains with such worn wheel profiles that the wheelsets are hammering from side-to-side between the flanges on straight track.

On the UK mainline network, my understanding is that various 'worn wheel' profiles have been in use ever since BR Research developed them in the 1960s (50 years ago) - the P8 profile appears to be the commonest one in use today. There are some wheel profile gauges here, which illustrate the different shapes - https://www.comech.co.uk/shop/c/gauges/wheel-gauges.html?limit=52

But wheel profiles have to be matched to the railhead shape and inward inclination of the rails to work correctly, so one of the problems that had to be solved for the Sheffield Tram-Train trials was to produce a wheel profile that worked OK on both NR track and the existing tram system track (which has a different railhead profile) - see https://www.railengineer.uk/2013/12/06/making-the-wheel-rail-interface-work/
 

RSimons

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I volunteer at a small rail museum in Dauphin, Manitoba and made a model to illustrate this method of steering railway vehicles down the tracks (much cruder than the ones shown!). A visitor commented that this method is not used in Canada so I searched the internet for confirmation without success. I then contacted CN and two manufacturers of railway vehicles. Both manufacturers had clearly not heard of the concept but CN provided detailed confirmation.

The model is popular with preteens who delight in showing it to their parents.
 

edwin_m

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BART in California, which could be described as a metro developed by aerospace engineers, adopted a cylindrical rather than coned wheel profile and suffered the consequences in wheel/rail wear. According to Wikipedia they have now decided to change it.
 

ac6000cw

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Perhaps to complete the picture we should mention 'check rails', fitted on the inside of the inner rail of tight curves, which stop the wheelset moving too far laterally (which would allow the outer wheel flange to climb up the outer rail and hence derail). I think the squealing you get in this situation is a combination of contact between the inner wheel flange and check rail, and wheel slip because the necessary speed differential between the wheels can't be accommodated by the conicity (if it could you wouldn't need the check rail anyway, in theory).

(Image below from http://www.rail.co.uk )

3-check-rails-by-Phil-Marsh.jpg
 

edwin_m

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Manchester Piccadilly platform 14 appears to have acquired a check rail on the outer rail???
 
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