Is the heat causing issues?

[WIMorrison]

The only thing I have found is that the expansion coefficient would give us an expansion of 0.12mm over 1000mm for 20 deg rise in temperature - say from 10 degress in the winter to 30 degrees at the moment. This means that the deflection is 6.7mm, still a lot though

[Trog]

The other option is to fix the rails to the sleepers and the sleepers to the formation such that the rails can not expand or contract along their length and are forced to go into tension or compression. Weak rail fixings encourage track distortion as they allow rail to be fed to a weak point, so that once the alignment starts to go the problem is concentrated at that point.

[Pete the Elaner]

The other option is to fix the rails to the sleepers and the sleepers to the formation such that the rails can not expand or contract along their length and are forced to go into tension or compression. Weak rail fixings encourage track distortion as they allow rail to be fed to a weak point, so that once the alignment starts to go the problem is concentrated at that point.

They would need to be very strong fixings.

[newbryford]

They would need to be very strong fixings.

 

 

 

I've seen unballasted flexitrack pinned every 6 sleepers or so start to kink, yet track glued down and ballasted with PVA is absolutely fine.

 

Cheers,

MIck

Edited July 9, 2018 by newbryford

[Pete the Elaner]

The only thing I have found is that the expansion coefficient would give us an expansion of 0.12mm over 1000mm for 20 deg rise in temperature - say from 10 degress in the winter to 30 degrees at the moment. This means that the deflection is 6.7mm, still a lot though

That is a different coefficient of expansion from what I found.

I have just re-checked & found something different again: 9.3 x 10^-6

Multiplied by 20 degrees is 0.186mm for 1 metre.

That was for Nickel Silver 770. Who knows what composition is used for rails & is the same composition used by Peco, C&L, SMP etc...?

[WIMorrison]

Whilst we found different co-efficiently they are substantially similar and produce a result that is muck lower than the 0.5mm per metre posited earlier which will still create a deflection that needs to be considered.

 

Some interesting suggestions and one that has plagued the real world since 1830 and they still haven’t found a 100% effective solution therefore I suggest we are unlikely to find a solution for our model world

 

I know that prestretching reduces the impact significantly and that is what is used on the prototype now - now sure if that would work with NS, might just mean we get a rail height that is nearer to the prototype- assuming there is a way to do the stretching!

[GoingUnderground]

Whilst we found different co-efficiently they are substantially similar and produce a result that is muck lower than the 0.5mm per metre posited earlier which will still create a deflection that needs to be considered.

 

Some interesting suggestions and one that has plagued the real world since 1830 and they still haven’t found a 100% effective solution therefore I suggest we are unlikely to find a solution for our model world

 

I know that prestretching reduces the impact significantly and that is what is used on the prototype now - now sure if that would work with NS, might just mean we get a rail height that is nearer to the prototype- assuming there is a way to do the stretching!

The thinning caused by putting the rail in tension before laying it will not be noticeable to the naked eye.

 

The risk in pre-tensioning the rail is that you exceed its natural elasticity, as measured by Young's Modulus, and you end up with a stretched piece of rail as opposed to a rail in tension. Another downside is that as the trmperature drops, the rail will still try to contact but being pre-tensioned, the tension will increase further.

[WIMorrison]

My reference to the deformation caused by stretching thus reducing the rail height was an acknowlement that the stretching had indeed exceeded Young's Modulus for the NS used in the model rail

[DCB]

The other option is to fix the rails to the sleepers and the sleepers to the formation such that the rails can not expand or contract along their length and are forced to go into tension or compression. Weak rail fixings encourage track distortion as they allow rail to be fed to a weak point, so that once the alignment starts to go the problem is concentrated at that point.

It works well if you lay the track in hot sunny weather. Mine is laid on cement as ballast so very very rigid.   If I lay it in cold weather without sufficient expansion gaps the rail pops out of Peco Code 100 sleepers rail fastenings as it flexes sideways.  When pinned the pinned sleepers break away from the rail and the track often moves sideways 2mm or more, I often put long pins against the side of the rails rather than against the sleepers on curves.

I find the 0.16 mm expansion in 1 metre for N/S rail with a 20 degree temperature change a bit misleading,

My 3ft 6'ish lifting section expands and contracts a lot more than that. Enough to break the solder at the alignment screws at the rail ends, the expansion was well over 1mm before I cut additional expansion gaps.

Outside the rails get almost too hot to touch at times and drop to well below freezing.

[WIMorrison]

There does seem to be a huge variation in the figures quoted on the web and without knowing which type of NS they use we are stuck. I have seen it from 19*10^-6 m/deg C which would mean 0.38mm per meter for 20 degrees rise all the way down to 8*10^-6 making it 0.16mm expansion.

 

I guess you can take your pick, but however we look at it the expansion isn't very much, though it does cause a surprisingly large deflection. 

[GoingUnderground]

My reference to the deformation caused by stretching thus reducing the rail height was an acknowlement that the stretching had indeed exceeded Young's Modulus for the NS used in the model rail

Pre-stretching, if done correctly simply puts the metal rail into tension, just like stretching a spring, and won't result in permanent deformation. If it does permanently deform, the whole purpose of pre-tensioning is lost as you end up with a permanently longer and thinner piece of rail which will expand with the heat, and you're back to where you started. Edited July 12, 2018 by GoingUnderground

[Alan Kettlewell]

I am finding several strange shirts and other control aspects happing on my layout and they are all down to the continued heat as seperation gaps between blocks close up which then confuses the feedback systems and shorts caused when points are set the wrong way.

 

Very frustrating as I know if I make the gaps large enough to cope with the current heat I will have large gaps in the winter

 

Any ideas on how to get around this - air conditioning isn’t an option

 

Hi Iain,

 

This may not be an option for you but might help others who have the opportunity to build a dedicated layout space - in my case, that's a big shed.

 

In my shed design I ensured two things -

 

1) I completely insulated all walls, ceiling and floor using 2 inch rockwool type slab material between the outer skin and the interior skin.  The interior skin is painted plasterboard.  So I have double skin all round.

 

2) Fitted an extractor fan in the eaves at one end which I can turn on in hot weather if necessary.

 

It's three years since I built it and so far so good.  It gets cool in winter of course so I put on electric heaters.  But on hot Summer days, as recently, it's the most pleasant place to be being lovely and cool.  There's been no evidence of damage or expanding track and I haven't needed to put the extractor fan on at all (damn, could have saved 80 quid there).

 

Anyway, I hope you solve it - can't be doing with having our fine modelling all messed up!

 

Cheers … Alan  

[WIMorrison]

Alan

 

when insulating mny 'shed' I thought about putting an extractor fan at the apex of the roof and decided not to as I thought OI have enough insulkation in the roof (6") and around the walls (3") and floor (2") to keep the heat out during the summer and heat in during the winter. It certainly kept the heat in during the winter making it a toasty warm environment, but I wasn't prepared for the summer we are having - I can see me cutting in a fan yet, unfortunately I wont be able to make the wood formers for it as easily as I could have due to a model railway being in the way, plus insulation and plasterboard

 

I will think about it, perhaps a 4" extractor (bathroom style) with an automatic shutter on the outside to keep rain and wind out may be an solution. It doesn't have to be big, all it has to do is take the accumulated hot air from the apex of the roof.

 

Iain