Pacer wheel screech question at Cardiff

[truckman060473]

ok so everyone knows the pacers screech on bends but why is the noise so bad going out of Cardiff towards Queen St? the curve just out of Central station is not sharp at all, yet the noise made here is so loud. And there appears to be grease on the line if you look down. it looks as if the gauge is wrong or something, causing the flanges to rub, coz I've been on sharper bends on the pacers where there was little or no noise

 

[142094]

I have no local knowledge but it may be that the speed of the Pacer is causing the louder than normal noises - from experience up here especially just over the High Level Bridge on the Gateshead side, Pacers go slow around the curve and squeal quite a lot.

 

[9K43]

Have a ride through Brockholes Tunnel on the Penistone Line out of Huddersfield, there more banging an clattering that would waken the most tired on secondmen on the engine.

 

[sprinterguy]

I have no local knowledge but it may be that the speed of the Pacer is causing the louder than normal noises - from experience up here especially just over the High Level Bridge on the Gateshead side, Pacers go slow around the curve and squeal quite a lot.

Memories of Pacers screaming round that curve are engrained into my mind! The curve to the south of the High Level Bridge is quite a tight one, but I have sometimes wondered why the Pacers screech so much more rounding that bend than any other. Given that the wheelsets of a Pacer are completely fixed in direction in relation to the frame, it's not surprising that the flanges rub against the rail on curves such as these. Why it causes so much noise at low speed is a mystery for me as well.

I wonder if the track camber/cant has got anything to do with it?

 

[142094]

Might well be, although I do know there is a grease trap there taht had little effect for years. Have to say they sound a lot less squeaky than they used to so someone at Heaton must be doing something right!

 

[Old Timer]

The distance of the wheelsets under the Pacer frame, and the radius of the curve will dictate whether or not there will be an "screech" as the train passes through a curve.

There is a minimum curve radius within which the Pacer will always bear against the outside rails but I cannot remember what it is.

Curves are designed so that trains passing through at the relevant line speed do not bear against either rail. Unfortunately where there is a wide variation in speed, vehicles outside of the "norm" will either bear on the outside or the inside rails which leads to sidewear on the inside of the railhead. Rail flange lubricators are installed where sidewear is a particular problem.

Some years back a train operated water-based lubrication system was installed at Barnt Green on the Redditch branch. I am not sure if it is still operational.

 

[DaveNewcastle]

Good track geometry design will reduce the "screech" to almost zero.
But that design involves some assumptions, Start with the basics of the track gauge, the cant on the track, the cone-profile of the wheel, the speed of the wheel, the weight on the wheel and the axle spacing between the 2 axles on a bogie.
With all that knowledge, you can design a curve that won't "squeal" or "screech".
A difficult job, but its possible.

But what are you supposed to do if one of these variables can't be relied on?
Weights differ. Speeds differ. Wheel profiles differ. But the worst case for the designer might be the differences in axle spacing. Its going to be tough designing a curve which works over a range of speeds with bogies AND with the wide wheelbase of a Pacer. Maybe impossible. Which is why the designers have to give up and install grease dispensers.

More technical info here: http://www.rtu.mmu.ac.uk/pubs/Evans%20Iwnicki%20-%20vehicle%20dynamics%20and%20the%20wheel%20rail%20interface.pdfI recommend this read.

 

[Old Timer]

Good track geometry design will reduce the "screech" to almost zero.
But that design involves some assumptions, Start with the basics of the track gauge, the cant on the track, the cone-profile of the wheel, the speed of the wheel, the weight on the wheel and the axle spacing between the 2 axles on a bogie.
With all that knowledge, you can design a curve that won't "squeal" or "screech".
A difficult job, but its possible.......

That is quite true in theory and principle. The design of a "perfect" curve is something that can be designed in a matter of minutes. That however misses the principal factors which lead to sidewear.

If a vehicle travels at a specific speed through a curve then sidewear will not exist provided that the track geometry is maintained within the tolerances. I can show you mixed traffic railways where there is a narrow speed band and no sidewear, and I can show you dedicated high speed and freight only lines where there is no sidewear. What I cannot do however is to show you a mixed traffic railway where there is no sidewear.

The issue however as I pointed out earlier is one of having a broad range of vehicle wheelbase and vehicle speeds, this in itself makes it impossible to produce a track geometry design which is suitable for all operating conditions where mixed traffic operates

The reference, whilst interesting to those not deeply involved, is however more concerned with the prevention and control of RCF, still a subject not fully understood in its entirety. The article offers the choice of RCF control or sidewear.

 

[Adam_Harrison]

If you have ever been in Hartlepool, the curves just before and after the station are very tight! Very loud screech in she station aswell as that is on a tight curve

 

[DaveNewcastle]

The issue however as I pointed out earlier is one of having a broad range of vehicle wheelbase and vehicle speeds, this in itself makes it impossible to produce a track geometry design which is suitable for all operating conditions where mixed traffic operates

Actually, I think you are agreeing with me, its maybe the convoluted way in which I reached my conclusion : "Maybe impossible" that led you to think I dissent !

But OT, although I was responding to a post by you, I wasn't aiming my reference document at you, but rather hoping to use this topic to present the subject of rail design and the underlying theories to those on here who are less familiar with some of the basic principles of railway design. For example, anyone who doesn't already understand what happens to the 2 conical wheels on a fixed axle when it enters a curve of a railway track might be pleasantly surprised by an article such as the document I quoted. I hope so.
(I wouldn't presume to tell YOU anything you don't already know!)