Rigid Wheel Axle vs Independant Freewheeeling Wheels

 
  prwise Locomotive Driver

Is there a specific engineering reason for rail rolling stock (and motive power) having a rigid wheel axle combination against something where the wheel revolves around a fixed axle. Sorry if this has been addressed before but could not find anything relevant on searches.

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  Gaz170 Junior Train Controller

Location: Gold Coast
You couldn't get traction motors to work on the alternative, otherwise I don't know.  May be an issue with bearings?
  raymond Deputy Commissioner

Location: Gladstone, Queensland
Talgo already do have inderpendent wheels on their locos and passenger coaches,guage changeing also.


  RAYMOND
  L1150 Assistant Commissioner

Location: Pakenham Vic.
Having the wheels fixed on the axle so they rotate together makes for better running around curves. If you roll a cone along a flat surface, it will roll in an arc. The tread on a railway wheel (that is the part which contacts the rail head) is not flat but tapers from where the flange is to the outer edge, which means that the diameter of the wheel is slightly larger closest to the flange and smaller at the outer edge. When a train enters a curve, natural forces will cause the wheel set to move over slightly with the wheel running on the outside rail of the curve moving to the larger diameter, ie closer to the flange, and correspondingly the wheel on the inside rail moving to the smaller diameter. If you draw imaginary lines between the larger and smaller diameters you will see that you have part of a cone shape, so the wheel set will naturally run around the curve without the flange necessarily contacting the rail side. Very Happy
  DBclass Chief Commissioner

Location: Western Australia
Having the wheels fixed on the axle so they rotate together makes for better running around curves. If you roll a cone along a flat surface, it will roll in an arc. The tread on a railway wheel (that is the part which contacts the rail head) is not flat but tapers from where the flange is to the outer edge, which means that the diameter of the wheel is slightly larger closest to the flange and smaller at the outer edge. When a train enters a curve, natural forces will cause the wheel set to move over slightly with the wheel running on the outside rail of the

curve moving to the larger diameter, ie closer to the flange, and correspondingly the wheel on the inside rail moving to the smaller diameter. If you draw imaginary lines between the larger and smaller diameters you will see that you have part of a cone shape, so the wheel set will naturally run around the curve without the flange necessarily contacting the rail side. Very Happy
L1150

Try and make the wheel and axle simpler, I dare you Twisted Evil. So simple, and it works, should be an engineering wonder.
  prwise Locomotive Driver

Having the wheels fixed on the axle so they rotate together makes for better running around curves. If you roll a cone along a flat surface, it will roll in an arc. The tread on a railway wheel (that is the part which contacts the rail head) is not flat but tapers from where the flange is to the outer edge, which means that the diameter of the wheel is slightly larger closest to the flange and smaller at the outer edge. When a train enters a curve, natural forces will cause the wheel set to move over slightly with the wheel running on the outside rail of the curve moving to the larger diameter, ie closer to the flange, and correspondingly the wheel on the inside rail moving to the smaller diameter. If you draw imaginary lines between the larger and smaller diameters you will see that you have part of a cone shape, so the wheel set will naturally run around the curve without the flange necessarily contacting the rail side. Very Happy
L1150
The taper on the wheel I get. Just trying to understand some history. With steam traction there was a need to fix both sides (valve gear synchronisation, keeping power strokes in synch ect). So at what point in history was the taper introduced. Without it there would have been continual shredding of wheels and rail I guess. Which then leads on to my question why have we kept it. Your response makes some sense although RAYMOND advises Talgo have done away with it and their web site claims independent is superior. (well they would say that wouldn't they). DBclass says that it is simple and therefore I guess cheap (guess we could debate that one too).  Does the taper really work that well that the flange does not rub on the rail. We still use flange lubricators (and the attendant mess up and down the track)  or are these just for curves tighter than the taper can compensate for.
  donttellmywife Chief Commissioner

Location: Antofagasta
The taper on the wheel I get. Just trying to understand some history. With steam traction there was a need to fix both sides (valve gear synchronisation, keeping power strokes in synch ect). So at what point in history was the taper introduced. Without it there would have been continual shredding of wheels and rail I guess. Which then leads on to my question why have we kept it. Your response makes some sense although RAYMOND advises Talgo have done away with it and their web site claims independent is superior. (well they would say that wouldn't they). DBclass says that it is simple and therefore I guess cheap (guess we could debate that one too).  Does the taper really work that well that the flange does not rub on the rail. We still use flange lubricators (and the attendant mess up and down the track)  or are these just for curves tighter than the taper can compensate for.
prwise
I suspect the taper was introduced shortly after the first train tried to go around a corner.

The Talgo design includes additional mechanical linkages between the bogie and car body to provide the equivalent steering.  This is additional complexity that is not warranted for normal rail service.
  DBclass Chief Commissioner

Location: Western Australia
The fitting of a steel wheel on a steel axle by interference is probably the simplest way I can think of to connect two parts.
It would be quite cheap I imagine. Nothing overly complicated. I read somewhere the bore is 1mm on circumference smaller then the shaft. In general intereference's are 1/1000 of the diameter. Or thou per inch. Same thing. Depending on the application.

One problem I can see with having a bearing in the wheel itself running on the axle, apart from the lack of steering, is the design would probably require a more substantial bearing then is already being used. When two roller bearings are fitted to a railway axle their alignment is in the shaft itself, so only vertical loaded from the wagon is taken and some axial load from steering. With a bearing in the wheel bore on the axle the bearing would be taking the same vertical load but a lot more axial load from the wheel.


I believe flange greasers are to help in sharper curves then normal, and when wheel profiles are not quite correct. As they wear they go out of shape and dont perform as well.
  BDA Chief Commissioner

Location: Sydney
There are pros and cons to a single rotating assembly vs fixed (non rotating) axles . Fixed is the simple cheap solution but the disadvantage is a crude "differential" action if you like . Crude because it won't suit all curve radiuses and you will be dragging wheel tyres around often enough . Actually the wider the rail gauge the worse this gets .
Also the "tapered" wheel profile helps rail vehicle to track well on straight rails and if you get hollow wheels they can hunt badly at speed .
The advantages of non fixed wheels is they can turn at different speeds and the rotational inertia is just the wheels not the fixed axle .
In this day and age bearings are not an issue but those that could reliably stand up to the radial and axial loads would not be cheap . Obviously with them you don't need axle box bearings so the number remains the same .
I think a problem with driven independent wheels could be the in bogie forces if one side stopped being driven under high load and low speeds .  Another would be control of braking forces to avoid skidding wheels .
I think it's hard to see a real advantage beyond fixed axles because they are tried proven and cost effective .
  prwise Locomotive Driver

Thanks for the responses. Seems to be simplicity coupled with some sound engineering principles in terms of bearing loadings wins out in this case.
  BDA Chief Commissioner

Location: Sydney
Mostly a case of it it ain't broke don't fix it .
  lustychant Chief Commissioner

Queensland had no taper on the NG ie vertical rails and wheel treads/tyres that were parallel both left and right up until the 1970's I'm led to believe. The first use of tapered rails and wheel treads/tyres on the QR was introduced on the new/rebuilt coal roads in the 1960's
  DrSmith Train Controller

Queensland had no taper on the NG ie vertical rails and wheel treads/tyres that were parallel both left and right up until the 1970's I'm led to believe. The first use of tapered rails and wheel treads/tyres on the QR was introduced on the new/rebuilt coal roads in the 1960's
lustychant

QR were a bit behind the times. How-ever, free rotating wheel-sets were tried back in the 70's on an ore road in North America. They were "pushed" by a Paul Giesking but did not last. Lack of the ability to find a central position and negotiate curves does not bode well. Modern trams get away with independent wheels but the use of ac motors can "lock" them like being on an axle.
  bengt Station Master

Location: Stockholm, Sweden




An unusual way to design axles.
  DBclass Chief Commissioner

Location: Western Australia
I couldnt read that so I googled it and found a readable size here :

http://www.railroad.net/forums/viewtopic.php?f=91&t=152712


How common were roller bearings in 1930? According to the Timken website, their bearings were used in a railway wagon application for the first time in 1925. http://www.timken.com/en-us/about/Pages/Timeline.aspx

This wagon was built 5 years later. I wonder what their idea was? It will fit a standard wagon so maybe that was their idea?

I wonder how much roller bearings cost back then compared to plain bearings. They (roller bearings) are madly cheap now. I have a Timken Railway Bearing Manual that has case studies comparing plain bearings to roller bearings for rolling resistance and failures. I suppose it was to get railways keen on the idea. Kind of funny now that a roller bearing is 'the' last word in reliability. Plain bearings have their place still.
  bengt Station Master

Location: Stockholm, Sweden
I couldnt read that so I googled it and found a readable size here :

http://www.railroad.net/forums/viewtopic.php?f=91&t=152712


How common were roller bearings in 1930? According to the Timken website, their bearings were used in a railway wagon application for the first time in 1925. http://www.timken.com/en-us/about/Pages/Timeline.aspx

DBclass
You can read the picks by right clicking on the pics.

I Sweden the state railway SJ had most of the coches in the fast trains Stockholm - Göteborg fitted with SKF or NKA roller bearings when electric traction was introduced in 1926. However roller bearings were first fitted about 1920 and onwards.
Already from 1912  several cars were fitted with ball bearings but in the long run the ball bearings were not up to the hard pounding.

By 1930 more than half of cars in long distance passenger cars were fitted with rollerbearings.
  DBclass Chief Commissioner

Location: Western Australia
You can read the picks by right clicking on the pics.

I Sweden the state railway SJ had most of the coches in the fast trains Stockholm - Göteborg fitted with SKF or NKA roller bearings when electric traction was introduced in 1926. However roller bearings were first fitted about 1920 and onwards.
Already from 1912  several cars were fitted with ball bearings but in the long run the ball bearings were not up to the hard pounding.

By 1930 more than half of cars in long distance passenger cars were fitted with rollerbearings.
bengt

Right clicking doesnt seem to work. Anyway.

I wondered about the hammering on the bearings. Until welded rail come into use I imagine the rolling bearings would have faired worse then plain bearings. Ball bearings is interesting though. I wonder how they made them? rollers is a fairly straight forward process but making round balls would take some developing. I think now they roll them between two plates, or something to that effect.

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