Tag Archives: yarrow

Tube Expanding and Economiser Headers

Just an update on progress with the boiler and other (interrupting) activities.

Tube Expanding

Nigel was good enough to make the trip north and assist with the tubing of the first boiler.

This was actually a simple, if repetitive, job.

Fitting the tubes

We firstly supported the three drums in the casing end plates, which were temporarily joined with lengths of timber. When fitting the tubes the game plan is to first locate the “centre” row of straight tubes, then fit the outer rows.

In practice there is not enough clearance to insert the first end of the tube with the drums in their correct orientation, so one firstly turns one of the drums in the casing to allow one end of each of the first row of tubes to be slid into this drum, and then the drum can be rotated back to its correct orientation and the free end of the tube inserted into the other drum.   (Hint: Insert them into the mud drum first, we actually started by inserting them into the steam drum first, but they fall out as you rotate this drum).

Once the straight tubes are in place then the outer rows can be inserted by inserting the tube into one drum and pushing it in as far as the first bend, this then provides the clearance to allow the  tub to be swung into place and then you can slide the free end back into the other drum.

Once the tubes are in place you can commence expanding (in fact we expanded the straight tubes into place before inserting the bent ones. Drilling all the holes with a 12.1mm drill actually worked well and provided just enough clearance to allow assembly – any tighter and it would have been a real struggle.

How much expansion?

Before expanding we did the maths on how much expansion was needed. The idea is that firstly you expand the tube to take up the slack between the tube and the hole (12mm OD, 12.15mm hole) so this was 0.15mm on diameter, then you expand the tube by 5% of its wall thickness. So given a wall thickness of 0.7mm this meant expanding the tubes a further 0.07mm. So the resulting ID of the tube was 10.82mm.  We did this by test expanding one tube in stages and checking the diameter, and when it was right we measured the free-length of the mandrel still showing. This proved to be about 20mm, so we then made a 20mm collar for the mandrel which stopped the expanding at the right point.

This worked very well, the load on the drill driving the expander could be heard to change as the expander reached the collar, thus making it simple to know when each tube was tight, without a lot of squinting down the drums. It’s really a two man job, as one needs to hold the tube so that the required 3mm+ of the tube is extended into the drum, while the other drives the expander and “contraption”. A video of the process in action:

We actually fitted about three-quarters of the tubes that we could reach from one end and then turned the boiler around and did the tubes at the other end. It might have been better to work from both ends, as by the time we had finished the mud drums had been pushed out sideways in the casing by about 1mm – no big issue, but information we will use when expanding the other boilers.

One other issue was that the “contraption” and expander proved too long to be assembled inside the smaller mud drums. We solved this by shortening the “chuck” on the “contraption” and by shortening and regrinding the square drive on the expander.

Here are some pictures showing the process. About 14hrs work to expand the tubes for one boiler.

Interruptions

The next part of the job was to turn up the ends for the drum, and also the economiser and superheater ends.

I decided to start with the economiser and superheater ends. Having first drilled another 12.1mm hole in the centre of the blanks for the inner headers (to take one of the super heater tubes), this was initially a simple turning job with the blanks held on a mandrel pre-turned in a 3-jaw chuck – this lead to Interruption 1, the clutch on the Harrison started slipping when confronted with the loads of highspeed turning with the insert tooling I was using. So an hour of so cleaning and refilling the parts washer followed by getting all the oil off  the clutch plates solved the problem.

Then we needed to cut 70mm diameter 12mm deep recesses in the centre of each part – I started by boring one of these, but it was slow work, so I decided to change over to milling these – here two more interruptions intervened in progress. Firstly the Mill started a rather worrying clicking noise from the gearbox – trying to ignore it didn’t seem to work, so I concluded I needed to strip it and investigate, as any major failure would be catastrophic as there very few parts available if anything broke.

Rambaudi Mill Gearbox Servicing

Rambaudi Mill Gearbox Servicing

This was simple to do, but hard on the nerves  – more parts washing, lots of inspecting and new grease restored the machine to full (quiet) operation. I think small bits of dirt and swarf had migrated into the gears and spindle bearings, and the cleaning sorted things.

 

Lastly, I spent a while trying to resharpen a bunch of broken and worn milling cutters with pretty limited success – so I bit-the-bullet and purchased some new cutters, including a 16mm “ripping” cutter designed to rough out at higher speed – a good choice.

Recess Milling and PCD drilling

I decided to mount the header blanks on a rotary table and then mill the 70mm recesses with the ripping cutter, then remount the blanks on the table with a stud through the centre hole, located between a set of stops to drill the 12 M8 tapping holes using the DRO’s PCD program – nice and simple and accurate. More pics.

A boiler making “Contraption”

More Progress on the Boilers – and a “Contraption”

We now have all the components to commence the “real construction” of the boilers.

Boilerplate and Steel

As you will recall from earlier posts we have drilled the holes in the steam and mud drums, and ordered the plasma cut 3mm plates for the housings from Ashby Welding in Church Crookham, and (after a lot of searching) ordered the 20mm Boiler Plate for the drum ends – which was eventually sourced from Brown MacFarlane in Stoke on Trent with the very capable assistance of  their Account Manager Alan Taylor. So the Landy made another round trip to Hampshire with a good load of steel in the back!

Boiler Plate and Casing Steel

Boiler Plate and Casing Steel

A First Set of Tubes

While in Hampshire Nigel Thomson and I spent a few hours in is workshop making a first set of 5 boiler tubes, so that I could test fit them in the boilers. They all fitted, as the pictures below indicate. So now he and Mark have only 600 or so more to do! (and you can see the plasma-cut end plates from the CAD drawings in an earlier post).

Boiler Drums in Casing

Boiler Drums in Casing

First Tube set in place

First Tube set in place

A Contraption

In order to finally fit the tubes a “tube expander” is fitted into the end of each tube and this is wound into the tube to expand it into the drum, and this secures it in place. This requires that we have a mechanism to reach inside the steam and mud drums to screw the expanders into and out of each tube, and also to drive a countersink bit to clean and de-burr the inside of each of the 1,200 tube holes in the drums. We thought of using a right-angle air ratchet wrench to do this, but having tried this out I decided to opt for a more “traditional” chain-driven tool, that Louise immediately  christened “A Contraption”….

Here are some pictures and a video of The Contraption with some old bloke demonstrating its use, and showing how well it cleaned up the holes in one half of one of the steam drums.

The pictures below show the effectiveness of de-burring the holes on the right-side of this steam drum (and it was quick too)…

Deburred Tube Holes in Steam Drum

Deburred Tube Holes in Steam Drum

Boiler Begins!

Sorry for the long silence, we have been working hard to relocate to Cumbria and convert the garage into a workshop – with that approximately complete it allows me to get started on the boiler for Befur. So this post concerns itself with this topic. Continue reading