60007 (4498) Sir Nigel Gresley Overhaul

Quite right about 6201, 71000 and D213. I wasn't sure what other arragements had been set up.

 

Here is a photo for you which I took earlier this afternoon showing the flue tubes ready to be expanded. I don't think that we will be needing that new tube plate though.

Bob.

 

Not sure how you could set up a chop saw in the smokebox.

 

Perhaps there is some confusion with the method being used here? It looks a bit as if a cutting torch is being used, whereas I assume they are being cut with a grinder, which is quite accurate enough and leaves a tidy edge, if done by a trained worker!

 

You are joking I presume.

I said trestle. So obviously they would be out of the box.

If that’s a grinder that’s in my eyes almost worse!

Is it such a hassle to measure the tubes and cut them to the correct length?!

 

Cutting off the flue tubes in situ is an acceptable practise ( see attached file)

Also the picture was taken by a senior member of the SNG's engineering team, and the work is being overseen/ carried out by one of the industry's most experienced boilersmiths, so I think everything is just fine.

 

Thanks for the info.

 

I was expecting Estwdjhn to come galloping in on his white charger to give good reasons but, as he must be too busy bashing boilers, I'll have a go. Boilers are usually built and repaired by boilersmiths. They are 'smiths', who, like blacksmiths, coppersmiths and tinsmiths generally bash bits of metal around. That's where the name comes from (to smite.) Boilersmiths don't generally work to the nearest thou, only the nearest boiler. They also tend to use a BBH (bloody big hammer) and that BBH isn't a precision piece of kit. Whilst tubeplates are, in theory, flat bits of metal, once they have been talked to with a BBH and other brutal bits of kit they aren't that flat or indeed parallel to each other and the distance between them can vary by quite a bit, even on the same boiler. I've known tube lengths differ by as much as 1" over the width of the boiler.
As I generally play with industrial loco boilers I don't really have any personal experience of installing superheater flue tubes but have watched it done on several occasions. First job is to tap a thread in the copper tubeplate and cut a 45 degree chamfer on the water side. You do this with a tap on the end of a long mandrill. If you are lucky you will have a machine to do the job. See:

There will be a chap in the firebox keeping an eye on things and shouting instructions to the operator at the smokebox end so it isn't a precision machining job. When you then come to install the tubes you might have a fancy tube driver to screw the flue in as in this next video:,

In which case you could measure each tube and cut to length, taking a good guess as to exactly how long it will need to be to stick out the requisite amount when screwed fully home. Expensive if you make a mistake, though! However, I've never seen one of these tube drivers and whenever I've seen it done the practice has been to weld a suitable driver onto the end of the tube and screw it in with an air driven tool or a big ratchet. You don't have a driver for each flue to you have one and weld it to a tube. When the tube is installed, you cut it off and weld it to the next tube. It goes without saying that the tube has to be over long. You then trim the tube to the correct length, ready for expanding. Doing it this way, even if you have a posh driver, reduces the risk of mistakes. As I said, writing off a flue tube that it too short is an expensive mistake.
The above is just my take on the subject.

 

Do you mean a mandrel?

 

Do you mean as a technical term for posh driver? Not exactly, although I guess it incorporates one although I wouldn't really consider it as such, more a wedge. The 'posh driver' is a piece of kit(another technical term!) which is inserted in the tube end and a hexagonal mandrel/wedge pushes out jaws which grip the tube when it is rotated. Have a look at page 9 of https://static1.squarespace.com/sta...B9001-Is02+-+Tubing+of+Locomotive+Boilers.pdf for a sketch of one. They obviously exist but I've never seen one.

 

I was wondering what a "mandrill" was.

 

Mandrill.

 

I thought it was a big drill turned by hand!

 

I wondered if it was a disrespectful term to those wielding the big hammers.

Visions of Arny ripping the business end off a pillar drill and wielding it on the tube plate.

 

Oops. Missed that one! I can't even think of an excuse.

 

I'm wondering whether this discussion (the one about boilers, not the one about monkeys) should be moved to the Boiler design & construction ex Patriot thread. While it's here, I have a question. If the flue tube is screwed into the tube plate at one end, what is the equivalent means of fixing at the other end?

 

Tube expanders in the same way that the small tubes are fitted.

 

I'm not sure myself but is it when the other end of the tube is expanded by inserting a expanding driver inside on a drill to push out the ends of tube making it a tight fit in the tubeplate? Then it is bottlecapped over using a pneumatic drill with a specially shaped tool on it like a hook shape. As you hammer away round the end of the tube you move it round the full circumference end of the tube and it flattens it out over the tube plate making it water tight, so only heat goes through the tube. This last process is called capping or rimming

 

The process is called beading - rimming is something completely different!
Ray.

 

So beading then is sealing the ends of the tubes. Beforehand to that is that process called tube rolling when the tubes are expanded around the tubeplate hole is that, been drive expanded?