NSW 'B' class mogul

[David]

Thanks Barry. I do keep seeing that mod in the drag beam in your photos of the cab so I need to get onto it. I think I've made the blowdown valve so should be in a position to do it.

I'm looking at the curtain rails and it looks like more of the same but smaller (like the handrail brackets).

[David]

I took the diversion suggested above. I had made the blowdown valve body but not the spindle. That is made from a 38mm M5 stainless bolt. The thread is turned off towards the head I guess to give some extra room for steam, water, and crud to get past it.

I couldn't figure out how to turn the tapered seat so I used a file. Imagine the bolt being held in the chuck by its threads with the head sticking out. Then turn a taper on the thread side of the head - so towards the chuck. I hope it will seal well enough. I can't blow through it from the boiler side.

Then a 1/16" hole is drilled through the threaded end using a jig and a roll pin put in. Putting the roll pin in also had me stumped. I didn't want just just put the end of the pin against the hole and hammer it. I squeezed one end with pliers and forced that end into the hole, then tapped it in with a mallet.



Next I cut the necessary clearance in the drag box. The valve sits high enough on mine that only the roll pin needs clearance. The spindle is above the drag box. The roll pin might also interfere with the cab floor but I won't know until I try to make the floor.



The spanner is plain mild steel. The solder was blobbing rather than flowing so I thought "scratch rod". Sadly my next thought was to grab the stick of solder and use that! I'm usually a bit pre-occupied but that was particuIarly silly. I tried drowning the lot in flux and putting the heat back on but it didn't achieve much. It was a lot of work with the file and wire wheel to get it to what you see here. I'm not going to try to get it any better.

[David]

More of the same but smaller. The curtain rail brackets are exactly the same as the handrail ones but with a 10BA thread and a couple of mm smaller in all dimensions. It wasn't all smooth sailing and I have a double mistake to fix that I think will involve JB weld or soft solder due to an undersized thread having to go into a clearance sized hole in one case!

I'd convinced myself there must have been nuts on the threaded ends of the brackets due to not being able to get a 10BA thread all the way up to the shoulder, and not being able to cut a useful relief. I was wrong and luckily I decided to more closely check the instructions and photos after drilling one clearance hole when it was obvious the nut on the outside of the cab was unacceptable.

I still have to trim the 10BA threads sticking through the cab sides but I'm pleased to have these almost done.

The curtain rails themselves are 1/16" TIG filler wire. Seemed a bit harder than mild steel but a couple of hours fiddling with the die and running a tap through the nuts got things together.

I've bought some tobin bronze brazing rods having decided I'd have a go at the superheater elements after all.

[David]

I bought some 3/8" thick walled copper pipe at the last club running day. I did a test braze last night on thick copper scrap and today on 0.9m copper to see how the fluxed rods worked and it seemed to go well.So today was the day to try making superheater elements.

I have tried to make them overlong. One certainly is, the other should be long enough need some trimming.

I cut the length of pipe at an angle in the bandsaw then cleaned it up on the linisher. The second one, anyway! The first one I tried to do this but the angle was nothing like enough. I tried the grinder, and a file, and finally the linisher. The second one was much better and more easily made.



Held them in place with a big hammer and hanging off the bench to avoid setting it on fire.



First one.



Second one.



It's a tricky operation because you have to do some upside down brazing. I blew through them and couldn't detect a leak but 100 PSI might find one!

They're in the pickle before the next operation which is flatten them so they fit in the flue and fold and braze a shield over the end, while trying to not make a leak or a blockage. Might silver solder be sufficient for that job?

I soft soldered the two pieces of the firebox cladding together a few weeks ago, and then tried to fill the gaps with more soft solder which worked to a degree, but a lot of it went through the gaps or otherwise didn't fill out the lumps and bumps as I'd have liked. I started filing and sanding it back and probably gave myself a pretty bad dose of lead into the bargain.



Not wanting to use more solder I'm risking JB Weld to finish it up. The packet says it will withstand 287deg C when fully cured which should be enough.

I found some rust where I'd sanded the gal off and/or not washed the flux off sufficiently. I sanded off what I could, but I already started putting the JB Weld on so there's probably some under there.

I'll let that cure for a few days before I start sanding it back.

[Roger]

Good progress David, it's coming along nicely.

I'm curious to know what the melting point of the brazing rod is, I'm guessing you had to get it bright red to get it to melt? That's certainly an easier way to make them than adding a separate spear point to the tubes, I imagine it will bend easily now it's soft. Presumably the design shows how far they are away from the firebox. I'm sure you're already aware of the dangers, but in case you're not, don't be tempted to go any closer because they might melt.

[David]

Thanks Roger. Yes I had to get them bright red which is why I did some test pieces first - I was warned brazing was hi-temp and I might melt something. I was skeptical about the fluxed rod (more accurately my ability to use it) but the bronze seemed to flow ok even when the flux was a bit charred. I did start with a fresh end of a rod for each element.

They did bend easily BUT I can't get them closed up like Barry's photos show so they only just fit in the flue and it will be tight with the shielding piece on. I was squeezing them in the vise but was wary of cracking them. However, in the flue is the requirement so I think they're ok.

I was going to make them via a much more difficult means. Luckily I spoke to Barry about it at the running day and he set me straight. My plan was to cut a triangle out of the middle of the tube, anneal it, and bend it in half... not sure how I was going to accomplish that!

The tubes in my boiler are bent about 3/4 of the way back which limits how far I can get the elements towards the firebox anyway. There was too much upward angle on them when they were soldered into the firebox. I did assume you could put the elements as far back as you liked as long as they were in the flue... I can imagine they might melt in the firebox although given how red they were before the braze melted I reckon it would take some doing from the fire.

How do you clean superheater flues? I can see how you'd get a brush in there.

[Roger]

Hi David,
Maybe you can get them to a dull red heat and then try bending them closer, that might just work. The melting point of the braze will be even higher now it's been alloyed with the Copper, so you shouldn't have any fear of melting it.

I reckon that as long as the tubes aren't in the line of sight of any of the fire, you'll be fine, but others might know better.

I imagine cleaning the tubes is tricky, a small brush ought to fit, at least that's what I'm hoping.

[David]

I soldered the shields on tonight with 15% silver solder. The elements don't fit in the flues now but after they're cleaned up I'll try and tap the shields down closer to the pipes and file them down if that's not enough.

I did try squashing one in the vise given it had just been annealed again but it made no difference and I heard an ominous 'crick' and something (hopefully flux crystal) popped off. I guess even if I just caused a leak I can fill it with more solder or braze like we do boiler leaks. I think the braze in the V is the immovable object meaning they won't squash any tighter.



In the next picture there are lengths of solder under the flux.

[Roger]

I'm not sure why the shields are there, I can't see the point in them really. If you do need protection, you might just consider flowing some 15% Silver Solder over the surface of the point. I would have thought that they would need protecing all of the way along if it was a problem.

[David]

It seems reasonable to me that the bits facing the firebox will get the most abrasion and the shields should take the brunt of the damage from that until they wear away.

I've spent many hours this afternoon and evening on my 3rd go at the clack valve model in an attempt to design something castable. The bores are bigger and the curves are smoother and there are no sharp corners in the bores. There was a mismatch between the sketch I'd used to do the outsides of the pipes and the one I used to make the core, so I deleted one sketch and redid everything from the other. I also had to redo the placement of the studs/nuts on the flange because they were not concentric with the flange itself, again due to those two sketches. Basically the whole model was redone aside from the initial 'bulb' shape of the body.

[Roger]

Surely if abrasion was that big an issue, the corners of the tubes would all get worn away? How do you know that wear is an issue as all?

[steamer5]

Hi Roger,
I had my copper superheaters ware out....or abraded out...which ever! The loco was approx. 30 years old by the time that happened! Ive replaced them with stainless so they should see me out! I cant remember were they failed but it wasn't far from the end.

David keep up the good work!

Cheers Kerrin

[mugbuilder]

The curved ends will abrade away in time and an engine that is used frequently needs the superheater reinforced to ensure long life. I have seen many that have worn  paper thin prior to leaking. Engines that dont work hard wont really need reinforcing as the abrasive particles dont move so fast. The copper is very soft and should crush to fit in the flue. The ends can be streamlined a bit to assist in the gas flow. It doesn't matter much if it is a bit untidy.  

[David]

I know at least 2 people who've had their superheater elements get worn through so it seems common enough. I'm wondering if it will become more common with the Welsh coal we burn now. My smolebox has a lot more grit in it after a run than it used to and the grit is a lot bigger in size.

[Roger]

That's very interesting and somewhat surprising. It does make me wonder if coating the ends with 55% Silver Solder, in a similar manner to how you would Tin with Soft Solder, would make a big difference. The surface would be a lot harder and it would alloy with the Copper so that it wouldn't come off.

[gwr14xx]

Sept 28, 2019 6:59:37 GMT Roger said:

 The surface would be a lot harder and it would alloy with the Copper so that it wouldn't come off.

A harder surface may not be better - the action of the grit is akin to shot blasting, and it is usually the case that a harder surface is more easily eroded than a soft one. The grit just tends to bounce off a soft surface! The idea of a replaceable, sacrificial shield would be better.

  Eddie.

[Roger]

Sept 28, 2019 7:48:32 GMT gwr14xx said:

Sept 28, 2019 6:59:37 GMT Roger said:

 The surface would be a lot harder and it would alloy with the Copper so that it wouldn't come off.

A harder surface may not be better - the action of the grit is akin to shot blasting, and it is usually the case that a harder surface is more easily eroded than a soft one. The grit just tends to bounce off a soft surface! The idea of a replaceable, sacrificial shield would be better.

  Eddie.

We did find something similar with erosion on a vacuum foot that used to get eaten away by fibre glass dust. The solution was to add silicone rubber top the surfaces for the same reason.

[Deleted]

Hey guys...am I missing something here...are we talking wear from abrasion on the inside or outside of the superheater tubes. It's just that the discussion seems to be centering on sheilds on the outside whereas I would have thought that any abrasion would be caused by gases passing on the confined space inside?

Pete

[uuu]

The steam within the superheater tubes is not the problem. It's the combustion products (including ash, unburned coal, and any mineral contaminants) passing down the flue that is the issue - particularly when they first meet the nose of the superheater.

Wilf

[Deleted]

Thank's Wilf, I understand now, I mistakenly thought that the discussion was around the superheater tubes rather than the flue tubes they sit in. Rather than fit sheilds would more not be gained from fitting a fire arch, bearing in mind all the extra benefits that this gives?

Pete