The main offenders with regards to wheel squeal is the SCT trains. Why would this be?
I have always thought that their wagon length could be a major factor, what's their shortest length rolling stock 62' with their longest I think is 78'.
i am scratching my head as to why that might come into it.
wagons of whatever length have bogies at the end, which swivel, so doesn't that take the actual length of the wagon out of the equation, provided the bogie is free to swivel across a sufficiently wide arc?
i would have thought a long rigid wheelbase 4 wheel wagon would have more chance of wheel squeal, but then again i have not seen any evidence that they were worse than bogie stock.
i wonder if it is something to do with concrete sleepers, long sections of welded track, both resulting in track that just hasn't got enough 'give', or poor track cant on the curves?
i have not noticed much wheel squeal on UK freight wagons at all .
As an observation of the SCT train there are two aspects that come to mind that may contribute to the observation of that particular train being worse than others:
1. The train is certainly set up for long distance high speed running, in that the bogies I expect will be set up to provide maximum stability for running at speed and not allowing hunting at speed and knocking the payload around. The down side of this set up is that the bogies take a lot of energy to get them to steer and conform to the curve. The result is that the bogie has to lozenge a fair amount to get the bolsters to steer and the angle of attack while the bogie is doing this is higher. While not every vehicle will be like this the probability of having contact pressures high enough to displace the lubrication is also higher and it basically dries the rail out from lube (that's the short version, there is more than this to discuss but that’s enough for now)
2. The train is hauled by AC traction. The result is that a greater load can be hauled at lower speeds for the given HP. Basically the train I would expect to be a comparatively slow runner. This relates to the track by there being less centrifugal force created in the vehicle to force them to the outside of the curve. When there is not enough centrifugal force to overcome the effect of the superelevation and gravity, not all the wheels of the bogie are against the high rail where their best steering action is achieved. The leading axle is against the high rail but in a condition with a higher angle of attack and higher contact pressure (same as what happens as described in point 1). The trailing axle hangs down toward the low leg and operates in a condition of 'negative steering' where the contact on the cones of the wheels is not assisting the curving action. This condition is best described as 'under speeding for the curve' or 'operating in the range of cant excess'
In short the observation I expect is the train is operating too slow for the curves geometry (superelevation) applied and the vehicle set up is not optimal for performance of the trains for that terrain.
Knowing that the Adelaide Hills makes up for a short part of the trains actual journey and ideal solution just for the Adelaide Hills is not going to happen in a practical sense. Freeing the bogie set up up to allow for better steering for example would limit the trains speed due to stability which would limit its overall performance given its coast to coast requirement where it spends most its time at speed. Any set up of this train would be a compromise and no perfect solution is possible.
Can anyone advise what speed the SCT train actually achieves climbing hills? For that matter, what it does going down too? 30km/hr? 40km/hr? 20km/hr? The slowest typical speed being the driver for any set of calculations.
From a track Owners perspective the noise while a public nuisance is also representing wear and tear. There are gains to be had by setting the track up. These being:
- set the cant so that the slowest train can operate with some level of cant deficiency (allow force in the vehicle to make the bogies conform and steer to the curve by forcing them out centrifugally)
- set the maximum speeds up by the allowable transition change and maximum cant deficiency
- lubricate and lubricate well, not too much, never too little
- grind the high leg with a suitable high leg profile that allows some 'grease relief' on the gauge corner (don’t do this and you will spall out the gauge corner given that there is grease about.
- grind the low leg of the rail to suit the effective gauge of the track at that point in time. By this I mean placing the contact band of the low leg rail relative to the wear on the high leg. The actual profile is to suit the typical wear allowance on the wheel sets so the contact is at the smallest diameter of the wheel.
As a closing comment, I did see a current curve list for the Adelaide Hills, I noted that it was the same as the curve lists we once used rail grinding there 12 years ago. Is there anyone from ARTC land that cares to comment that the curve geometry has been ruled out as a factor?