Discussion in 'Locomotive M.I.C.' started by ADB968008, Nov 4, 2008.
Tyre turning is an every day feature of railways, but what exactly is it / does it involve ?
Basically, making sure the tyre profile is a circle and that the flange height correctly meets the specification.
Dont forget about old tyres been removed and new ones been placed on the wheel as well.
That is pretty basic, Lil Bear! The profile of a wheel tyre is quite important in keeping the vehicle on the rails. The basic tyre tread is coned at (without looking it up, I think) 1 in 20. This gives the wheelset (two wheels and an axle) a self steering property. As this wears, it becomes hollow and starts to loose this self steering. Again, without checking, I think the maximum allowable hollow wear is 2mm. Equally as important is the radius where the flange meets the tread and the angle of the glange. If this is allowed to wear there is a danger that the wheel will climb over the rail on curves, again leading to a derailment. Flange wear is much harder to correct that tread wear as, to restore the correct profile, it may be necessary to remove a substantial amount of the tyre metal. Another important factor to consider is that both wheels on an axle are the same diameter to within a very close tolerance. With steam locos, all driving/coupled wheels need to be of essentially the same diameter and there are limits to the variation allowed with such as bogie and tender wheels as, having different diameter wheelsets affects the springing. Thus, you might have a wheel tyre that is unworn and as good as new but the tyre has to be turned because an associated tyre is worn beyond its allowable limits.
Tyre turning use to involve removing the wheelsets from a loco and mounting them in a large specially designed wheel lathe. It often still does although, nowadays, many depots/workshops have computer controlled ground lathes which can turn the correct wheel profile without removing the wheelset.
I have been told that this can only be done a small number of times before the wheelset has to be turned in a lathe - is there any truth in this??
There is a limit for the number of times a wheel can be turned if that is what you mean?
Everytime you 'turn' a wheel you reduce the radius as you take some material off to return the wheelset to a true circle. There obviously is a limit as to how small the radius can become. Once this limit is reached a new tyre is needed for the axle/wheelset.
All the foregoing is essentially true but a question sometimes asked is "how often tyres need to be turned?". This is not only influenced by the mileage in a given period but also the nature of the road the trains operate over.
Not just for the photographers, but one of the major benefits a heritage line can have is a turntable or a wye as locomotives and rolling stock can be turned periodically to even out tyre wear. E.g. A quick glance at the SVR reveals a route that is essentially a clock-wise curve from Kidderminster to Bridgnorth. I've no doubt several other lines are not dis-similar.
Ask Heathrow Express or Merseyrail about tyre turning...
Good point; although I was thinking about heritage lines. I guess LUL's Circle line and Glasgow's Clockwork Orange could suffer similarly.
I am lead to believe that you can only turn tyres on a ground lathe once, the next time they require turning they have to be turned between centre's!
Ian would be best person to ask.
That is what I meant - thanks
Some ground lathes have centres which they turn between which is fine to use as many times as you can till you run out of tyre/wheel. Other ground lathes are just profiling machines that basically return the profile to that specified for the vehicle. They have no centres and therefore no fixed reference point. Therefore the wheel can have a perfect profile but not be a true circle. Hence it is only allowed to turn a set of wheels on this type of machine once before they have to be turned on centres again.
Exactly. Its all about ensuring the tyre surface is a true radius about a single centre. Other constant diameter polygon shapes exist. Think about the rotor in a Wankel engine. That's a multi-centre shape.
The Circles turn occasionally, rather than going through Aldgate they are routed to Aldgate East where they reverse and go back out the way they came. So although the service is still going in the same direction (ie anti-clockwise) the train is the other way round.
Don't post very often, but as I run a wheel lathe for a living.......
There are a number of differant wheel profiles used, dependant on speed and type of stock. the basic profile is a P1, this is what your MK1's and loco wheel sets would normally have. On a steam loco or 08 shunter the middle driving wheels have a P9, this gives a thinner flange which helps when going aroung corners.
Most modern passenger stock (and some loco's) use P8, this is a P1 with around 20000 miles of wear. They found slightly worn P1's rode better than freshly turned. Frieght wagons use vairous differant profiles, it is normally written on the sole bar. The wheel turning and examination Group standard is GM/GN2479, effectivly our bible.
Modern ground wheel lathe do not normally use centres, if the wheel set has roller bearings a clamping method is employed that use's the axles own bearings. The wheel does not come off the lathe eccentric, therefore you can turn as many times as you require until the final turn size is reached. We turn for hollow wear (up to 6.5mm is allowable) and wheel damage. flats, cavities and Rolling contact fatigue.
This time of year we are flat out turning for wheel slide damage. Leaves on the line or 'poor rail head condition' as NR call it.
Our lathe is a double headed lathe, we turn two wheel sets at once. We can turn a bogie complete in around 50 minutes. Just to make it clear, the coach/loco/wagon is driven on to the lathe and nothing requires removing from the vehicle.
Have a look at this website:http://www.hegenscheidtmfd.com/gb/home_frm.htm
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