Bullhead versus flat-bottom

In the Bluebell thread

The only response so far has been

It's great that bullhead can still be obtained if you need it, but a general discussion of the pros and cons would be interesting, particularly as applying to renewals on heritage railways but also why Britain stuck with bullhead for decades longer than most other countries. So I am starting this thread.

If there has been any extensive discussion previously, someone please link to it. I have found one relevant comment in the WSR thread:

 

Flat Bottom rail has been in regular use in the UK since the 1940's at least.
From 1950 onwards it became the standard choice of material. The only development changes to it since are to increase the physical size of the rail from 75lb / yard though 98, 109 110,113 (56kg/m) and now 60 kg / m

How far back do you want to go?

 

Certainly back to the Cowes and Newport Rly (1862). Gratuitous photo of the delightful Slaghter Gruning 2-2-2WT Pioneer submitted in evidence:


[Image courtesy Charlie Verrall flickr.com]

 

I believe London Underground still buy new bullhead rail quite regularly, which helps explain why it’s still available.

 

Bryan, what are the advantages of still using bullhead rail on parts of the modern network? As mentioned above, London Underground seem to still use it and it is still quite widely used on parts of the Mallaig line, presumably because flat bottom rail is not suitably. I've often wondered why this might be.

Peter

 

I read somewhere that the original idea behind bullhead rail was that it could be turned over and re-used when the top surface became worn.

 

They had not thought of the wear on bottom of the rail caused by the chairs.
That idea soon dropped.

 

It ultimately comes down to cost.

It has been known new bullhead is available for some time. TFL and NR have the budgets to get it. (Imported from china from memory).

Heritage railways can often rely on hand me downs from NR to get reuseable bullhead and flat bottom.
There is also the maintenance factor. Long section CWR has a lower maintenance requirement.

 

That was double headed rail, which was symmetrical so that the head and foot were the same size. The problem was that the chairs indented the bottom surface so that when the rail was turned over the "new" top surface was uneven. The head of bullhead rail is larger than the foot.

Sent from my SM-A105FN using Tapatalk

 

BH rail is still used all over the Network, not just on Rustic railways and is commonly available from Scunthorpe where it is produced on a batch basis as when required alongside the more usual rollings of FB113A and CEN60FB rails.
All depends on if it is cheaper to rerail or does it need a full relay.
What is the condition ofthe rest of the track components from the formation up.

I can think of no reason why FB cannot replace BH rail.

 

Back in tbe 1870s, the Isle of Wight (Newport Jnc) Rly originally constructed part of the Newport-Sandown line in upturned 2nd hand (ex-LSW) 'double headed' section. Unsurprisingly, the BoT inspector wasn't too impressed and the whole lot had to be relaid before the line was cleared to open.

 

On the Festiniog the older pway guys said that bullhead rail was both easier to curve and kept the alignment better. We can no longer get it in a suitable profile for narrow gauge though.

We still have double head rail in sidings. You definitely can't flip it over. Not only do the chairs leave marks in the bottom but it also gets heavily pitted.

Tim

 

It may just be that in some cases it's more economic to replace like with like.

 

I suspect that retention of bullhead largely depends on economics and practicality. If the rail is worn such that it requires replacing but the underlying sleepers, chairs and formation are in good condition then the rail will probably be replaced with like for like. This is one of the main reasons why LT still install a significnat amount of bullhead. On sub surface lines the sleepers, chairs and formation don't tend to deteriorate as quickly as when open to the elements. Underground lines do have relatively sharp curves which is easier with bullhead. Single track lines are also less likely to be totally renewed as this requires a full possession, possibly over several days. This is probably the reason why significant lengths of Scottish & Welsh single track lines retain bullhead rail. The same applies to single bore tube lines. Spot resleepering can be carried out between trains and rail replacement overnight without having to close a line for significant periods.

 

https://www.inyourarea.co.uk/news/first-class-arrival-keeps-south-devon-steam-services-on-the-rails/

 

Why and when did the two different designs evolve? What specific advantages do they have today? And would there be any point in using bullhead on a new or reinstated line?

 

If you go right back to the beginning, the rails were cast iron bars and they had to sit in something to keep them on the stone sleepers, e.g. the Cromford & High Peak rails still on the pit in the old shed at Cromford Wharf. The next step was wrought iron, and they kept the chair because it inclined the rail at 1 in 20 towards the middle, which matches the cones on the wheel tread. Bullhead in chairs was far superior to flatbottom rail simply spiked to the sleepers. Flatbottom was quicker and cheaper to lay, which was quite useful if you wanted to, for example, cross America and didn't worry too much about speed.

One problem with early FB track was the spike; the fixing depended on its strength on being hammered into the wood, once you draw the spike the grip is a lot less if you knock it back in, and if you drill new sets of holes eventually the sleeper breaks up. On BH track the the rail is keyed in the chair and the chair is screwed down, the screws make themselves a nice threaded hole; you can take the track to bits and re-assemble it whenever you like. On the whole, BH track is suitable for use by reasonably large gangs of semi skilled men with basic hand tools, and is very good at going round corners without fuss. FB on concrete sleepers requires much more in the way of heavy plant.

The critical thing for use of FB rail over bullhead was probably the development of more sophisticated fastening systems and concrete sleepers, especially the pandrol e-clip. Compared with that sort of system, bullhead needs a greater weight of material per mile, which costs more, but is not as strong and is far less suitable for modern plant and machinery.

So far as preservation is concerned, a lot of railways were able to pick up BH track by going to the owners of redundant industrial sidings and saying "you don't want that lot do you?" Quite often the sidings would be given away, sometimes miles at a time. There are a lot less derelict sidings than there used to be, particularly due to said salvage operations. Bullhead looks good, but you have to use what you can get, and out on the main line, good FB rail on concrete sleepers is a lot less effort to maintain once you have got it properly laid, compared with BH on wood. BH still has its place on a start-up scheme, e.g. the Yorkshire Wolds Railway, which seems to be buying cascaded track from the NYMR

 

I understand flexibility is the reason that bullhead rail is used on sections of the London Underground. Many of the curves are quite sharp, as can be felt when travelling on the trains. Flat bottom is used on straighter stretches. I would suspect that bullhead s used on the Mallaig line for the same reason.

 

95LB RBS BH is still rolled and is used on NR for replacement S&C where adjacent track is still BH and it is also used for check rails. It also has the advantage of being all to a common standard unlike FB which comes in different rail sections and uses different baseplates and components on S&C depending who manufactured it. FB is more stable, rigid, stronger and is cheaper because it does not require cast baseplates and it can be laid either as long welded rail or as continuous welded rail which allows tamping machines to be used which reduces maintenance costs. For a heritage/reinstated railway it really depends on the relaying method: if you have a large gang of 30+ strong men and you are relaying jointed track by hand and intend to maintain with MSP then BH would be better because it is slightly lighter and looks more in keeping with the steam age. If concrete sleepers are going to be used with CWR and you have access to heavy track laying machinery and you intend to use tampers for maintenance then FB would be better as you would be quicker to relay, gives a greater choice of sleeper types and it will work out cheaper in the long run with reduced maintenace costs and better ride quality.