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Rail expansion

brianmason

Joined: 23-08-02

Topics: 7

Replies: 11

Posted: Wed 23rd Nov 2011, 10:19am
Rail expansion

Does anyone know how to'calculate' how much 19mm (3/4") aluminium bullhead rail in 10 ' lengths will expand(to allow sufficient gaps between rail joints?)

Thanks
Brian M Secretary ALRC
 

Replies To This Post

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Wed 23rd Nov 2011, 3:40pm

A slightly tricky one Brian as you really need to know the temp range required to calculate it accurately. Therefore do you need to be that accurate? Not really. However 1m of rail will grow 0.23mm for every 10 degrees C.

The section will actually make no difference to your problem, only the length. On the very hotest day the rail ends may be allowed to almost touch, but on the coldest day the gap will open considerably. You will undoubtedly get some "creep" on bends, just make sure you allow enough space for it to happen.

 

nomis

Joined: 1-01-70

Topics: 2

Replies: 17

Posted: Thu 24th Nov 2011, 1:15pm

You could always cut a short length that will fit inside your oven / freezer and start experimenting.

If you use a kitchen thermometer, you should be able to get pretty accurate values for extreme UK weather conditions!



Alternatively, install rail with a tight gap in summer, and a loose one in winter, then adjust as needed.
 

brianmason

Joined: 23-08-02

Topics: 7

Replies: 11

Posted: Wed 30th Nov 2011, 7:18pm

Thanks for those replies Folks, I will pass 'em on !
Brian M
 

johnnicholson

Joined: 1-01-77

Topics: 12

Replies: 69

Posted: Thu 1st Dec 2011, 12:42pm

At Ruswarp Miniature railway I was told that a rail joint had been lined up with the end of the platform flag. The trains always ran the same way round and by the end of the season the rail joint had moved about 750 mm from the end of the flag in the direction of running. This 0.5 mile track used aluminium rail and it is thought that the whole circuit had crept round a bit. It is suprising how with expansion and running the track will move without you noticing the effects.

Sorry slightly off topic but still interesting

John
 

brianmason

Joined: 23-08-02

Topics: 7

Replies: 11

Posted: Sun 4th Dec 2011, 1:59pm

Thanks John, yep, we have noticed how our track 'creeps', keeps the track Boys busy!
Brian M
 

Nathan

Joined: 1-01-70

Topics: 1

Replies: 3

Posted: Sun 11th Mar 2012, 10:48am

Another option could be to install an expansion joint (or two) as we did at swanley. it doesn't look the worlds best, but works well, this will allow the rail to expand and contract as necessary without too much hassle, i don't remember having any serious 'kinks' in the track since its been installed.

Nathan
 

brianremnant

Joined: 6-08-07

Topics: 0

Replies: 2

Posted: Sun 22nd Apr 2012, 10:44am

The expantion for aluminum is quoted as 0.000023mm/degrees C therefore with a temperature range of say 0 drgrees to plus 25 will give you a increase in lenght of 1.752mm per 3M-10FT,hope this helps.
 

HauteSaoneFrance

Joined: 2-01-14

Topics: 27

Replies: 91

Posted: Mon 20th Jan 2014, 10:48pm

Gosh mind boggling stuff to someone new like me ! I'm planning steel rail in modules of 6 m lengths, the temp range in my parts (France Haute Saone) is approx -15 c to + 45 c so a 60 c difference but as I have no intention of running in -15 would it be ok to gap each section to allow for an expansion of say 45c C divided by 10 X 0,23mm X 6 m = 6.21 mm gap, this would be assuming that the rails were laid on a day when the temp was 0c. I'm using Xz's figure of 0.23 mm per 10c per I m of rail length though I know this is for alloy rail , presumably the expansion of steel is marginally less?
 

Mick

Joined: 1-01-89

Topics: 7

Replies: 114

Posted: Tue 21st Jan 2014, 8:33am

When we used welded bar rail at Sheffield we had to put expansion joints at about thirty foot intervals. These were overlapping scarf joints, well greased. However, with flat bottom rail and slotted fishplates (greased)and correct bolts/nyloc nuts tightened to a torque that allows some slight movement but keeps the rail aligned, we simply allow a gap of around 3mm between rail ends. As stated by others above the track creeps about anyway so it's no use being very exact, no need to worry about calculating coefficients of expansion. Leaving too great a gap leads to wheel wear and the track dipping down at the joints - the latter especially on aluminium rail. I've posted a photo of a typical joint at Sheffield - steel rail of course.
When we used welded bar rail at Sheffield we had to put expansion joints at about thirty foot intervals. These were overlapping scarf joints, well greased. However, with flat bottom rail and slotted fishplates (greased)and correct bolts/nyloc nuts tightened to a torque that allows some slight movement but keeps the rail aligned, we simply allow a gap of around 3mm between rail ends. As stated by others above the track creeps about anyway so it's no use being very exact, no need to worry about calculating coefficients of expansion. Leaving too great a gap leads to wheel wear and the track dipping down at the joints - the latter especially on aluminium rail. I've posted a photo of a typical joint at Sheffield - steel rail of course.
 

George

Joined: 27-01-10

Topics: 0

Replies: 20

Posted: Tue 21st Jan 2014, 1:44pm

Hautesaone,
As an extra. Rail temperature is not necessarily equal to ambient temperature. As a matter of fact rail laying in the sun can become quite literaly to hot to handle.
If you build in fair weather with small gaps you may end up with big gaps in winter. If you build an oval you might see gaps between the sleepers and the soil in the curves at the temperature extremes. No exact science needed for us modelers. 2 to 3 mm normaly should be plenty.
Best of luck
George
 

HauteSaoneFrance

Joined: 2-01-14

Topics: 27

Replies: 91

Posted: Tue 21st Jan 2014, 7:31pm

Thanks Mick and George, I get both your points and George I'm in total agreement that anything steel in temps of 40c + would indeed be too hot to handle? I've got a scheme for my initial track layout and I'm going to put a post up on this soon so comment and advice from everyone will be greatly appreciated
 

JeffJF

Joined: 1-01-96

Topics: 0

Replies: 1

Posted: Sun 2nd Mar 2014, 4:09pm

This is what happens if you get it wrong!! Actually, it’s not quite what it seems. I had just laid the track, and I left the fishplates tight to help alignment. The weather warmed up before I loosened them, and this was the outcome. Beware!!
This is what happens if you get it wrong!! Actually, it’s not quite what it seems. I had just laid the track, and I left the fishplates tight to help alignment. The weather warmed up before I loosened them, and this was the outcome. Beware!!
 
 
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