Wednesday 22 March 2017

Stressing at Laverton

Today was the big day, when a maximum of volunteers was needed. Annoyingly, it was also a day of maximum rain, but we ploughed on regardless. Heavy squalls were forecast. We had four of them during the day, and one was already in progress at 08.30 when Haigh Rail started work on stressing the rail at Laverton bridge.

The pictures don't show you the falling rain, but rest assured, it came down OK. The faces tell their own story.

This then is the stressing unit, a pair of hydraulic rams operated by a pump and a small Honda motor. It's amazing what power can come out of such a small machine.
One rail is stressed at a time, and you can see the two gaps in question at the pulling point.

The first thing to do, after setting up the unit, is to measure the gap between the rails.

The actual gap required is determined on the day, and cut accordingly. You can get everything on-line these days, including the calculation to determine the gap required. Among the inputs are the length of the rails (500m each) their size, and the temperature of the rail. A colder rail is a shorter one, and this morning the air temperature was only 5 degrees.

Here Mick explains to our very own Bert Ferrule the finer details of the stressing process, and what the GWSR volunteers needed to do once it got under way.

Just to be quite sure, Mick then set off to measure the exact length of the rail to be stressed. It says 546m in the yellow patch below, but no doubt Mick has been stung before in his long experience of welding rail. Measure twice ! Weld once....

After returning from the southern anchor point, Mick retreated out of the rain into one of the vans to work out the distance required for the pull. It was 10 inches, so a bit needed to be cut off.

Among the debris of laying FB rail a number of analogue and digital thermometers were attached to the rail, to establish the exact temperature to be entered into the calculations. The rail here is on rollers, hence off the sleepers.

The hydraulic rams then came into play, the moment we had all wanted to see. The little generator was fired up, and imperceptibly the two ends of the rail began to edge closer to each other. We took a video of the process here:
...and you'd be hard pressed to see the rail move, but move it did. The process seemed quite silent, there was no scraping or 'twanging'. A small gauge was used to determine the correct gap for welding, and when this was reached, the process was halted, and preparations began for welding the two ends together.

In the picture, the stretched rail ends are manoeuvered together with bars and wedges, to be at the same height and parallel when they are welded.

While the two rails are held together under tension, the rail ends are heated up with gas burners and the now familiar 'Vee' shaped flames emerge from the moulds.

While this is going on, others are undertaking numerous small tasks to prepare the rail for clipping up. For example, once the rail is stretched, the rollers all have to be removed again, and every sleeper fitted with a rubber or plastic pad underneath, on which the rail will sit.

Also, once the rail is under tension, it has to be clipped up for at least 50m each side of the weld. The rest also has to be done of course, but the first 50m each side are the most important.

Today we were lucky enough to have some additional assistance from a team of NR employees, who came to help us, all the way from Nuneaton. Here we can see the NR team starting to clip up the southern side of the weld.

Clipping up involves fitting two plastic pads to the foot of the rail, and then hammering home an 'SHC' clip.

Frequently however, the plastic pads won't fit, because the sleeper is not perfectly central to the bottom of the rail. If the gap is there but not big enough, you can usually get away with some carefull hammering with a keying hammer, but if there is zero gap, you need a special wedge and a large crowbar. This is of course located in the back of the Landie, hundreds of yards away, if it isn't actually moving away in the opposite direction just when you need it! The site is one kilometre long, after all.

Another weld, another squall. But Haig Rail have seen it all before, so they are prepared. When this shower hit us, out came an enormous umbrella, so that the mould could be made 'watertight' (should that be 'steeltight'?) with clay, in the dry. Here the guys are at work on the Malvern side gap, the rail already having been stressed on this side as well.

The disposable crucible is fitted, and the combustion process launched. Within seconds the steel melts and flows into the mould. It's a violent chemical reaction in there, with a huge production of heat.

The combustion process has run its course, and here we see the molten steel emerging at the sides. A clipping up gang is at work in the distance on the northern section.

A further downpour helps us decide that it's lunch time. While Haigh Rail continue the welding and finishing (they were gone after lunch) the GWSR gang return to the mess coach at Winchcombe.
The atmosphere in the mess coach was thick with steam and the smell of garlic - Chicken Kiev today, from our gourmet chef, Monsieur Paul. The coach was full to bursting, with a good sized gang but also the volunteers from NR, who came to help today.

An hour later we returned, to find Haigh Rail all tidied up and returned to base.

This is all that is left of the first pulling point, a neat pair of welds, now ground down flat. You cannot tell that the rail is now under tension, except when you hit it with a hammer, as it gives a loud 'ping', even from 500m away!

After lunch, and with the first 50m all neatly clipped up, we set out to provide the two halves of 500m with all the fittings they need for the clipping up.

The NR gang made their way down the southern half, and removed all the rollers, and placed pads under the rail for every sleeper.

The next squall is also on its way, and this time it hailed - why not?

In the northern half, the GWSR volunteer gang did the same. The hail has passed overhead, and is now bothering Childswickham.

In the foreground, orange plastic pads (known in the parlance as 'biscuits', don't ask why) have been laid out, 4 to a sleeper.

In the southern half, two volunteers are sharing a basket to drop the biscuits on the sleepers, in pairs.

At the end of the day, all the pads under the rails were in, 75% of the materials laid out in the south and 100% in the north (or so the gang says, we suspect some exaggeration and rivalry here)

In any case, there is plenty of work for the Saturday gang, and the materials for them are now in place.

Finally, shock, horror, as two wartime bombs are discovered in the boot of a volunteer. For display only, he says. Yeah, right, and defused as well, you say?


  1. Up until the time this blog was started I had no idea that newly laid track required to be "stressed". Thank you very much for this splendid description and video.

  2. It's only CWR that has to be stressed.
    Thank you for your kind compliment.

  3. I must admit that I didn't know that there was so much to it. Working on engineering trains at night on a weekend, time goes quickly and I must say that I missed the nuences of the work involved. Regards, Paul.

  4. Jo, thanks for braving the lousy weather, along with the other volunteers, to bring us such an interesting post. I reckon you deserved your gourmet lunch!

  5. Another great report, you all deserved your gourmet lunch with the weather being so bad! Will there be a Saturday report as well?
    Paul & Marion.

  6. A,fascinating bit of video!.You can see the gap,between the rails,slowly narrowing!.Pity,about the lousy weather,though!.I,bet you really enjoyed your lunch!. Anthony.

    1. I was worried in case people found the video boring, what with the gap narrowing very very slowly. But it's got 4 'likes' already :-)

      My kit was still damp this morning....

      Maybe a short report on Saturday, it'll be 1 km to clip up.

  7. Jo, your blog continues to be a master class in explaining track laying on a heritage railway. Many thanks.One question.
    With the individual rails thermite welded together why is it necessary to stretch the rails? I have been told by a relation who is a director at British Steel that the steel used in modern rails is very different from those of old. Is it to do with rails not buckling in extremes of temperature, smoother ride, less wear?

    1. I think I'll quickly get myself into hot water if I try to explain this, so the best thing to do is Google 'CWR stressing' and read the papers you will find.
      It is certainly related to all three of the factors you mention.
      We weld our newly laid rail now to avoid having to use fishplates. These are high maintenance, we even find fishplates broken in half during our track inspections. 'Dipped' joints cause broken loco springs and wear on the carriages so CWR, although a bit more work intensive to install, saves a lot of work and money for all concerned.

  8. I arrived here totally by accident, while researching something unrelated. But now I've spent two hours, going back and forth via the links, and learning a lot. Thanks!