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....
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 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.
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.
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 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.
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.