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Post by circlip on Apr 12, 2008 15:59:08 GMT
Thanks for clarification Andy, for a minute I thought good boiler practice had disappeared with the cadmium ;D
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Post by AndrewP on Apr 12, 2008 16:25:39 GMT
It's allright Ian. Would you, like me, then question the oft seen advice to leave a clearance between boiler components 'for the solder to flow into'. I'm thinking particularly of tube to throatplate joints where it seems I have seen the need for this to be a loose fit stressed.
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Post by baggo on Apr 12, 2008 17:48:34 GMT
Cup Alloys also recommend gaps in joints of between 0.075 and 0.15mm 'for the solder to flow into'
LBSC used to recommend making tubes a good tight fit in the tubeplates and bushes etc a 'drive' fit into their holes. Even Martin Evans followed this philosophy but altered it slightly by suggesting filing little nicks on the inside of the holes for the solder to flow through to the other side. Either practice could mean no solder between the tubes or bushes and the sides of the hole possibly leading to a weak joint. Martin's 'nicks' would at least mean you got a fillet on both sides.
It is accepted practice now that a slight gap is needed for a sound joint. The problem as I see it with making tubes etc tight to begin with is that the tubes may expand more than the tubeplate and make the joint an even tighter fit with zero gap.
One problem area I've found is the fire hole ring where it is peened over onto the plates. The joint closes up and the solder does not penetrate through the plate to the other side. It's easy to solder both sides on the firebox backplate but not so easy on the backhead. Mind you, peening over the ends of the fire hole ring does add to the strength of the joint.
John
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Post by alanstepney on Apr 12, 2008 18:03:07 GMT
The gap required, and gap filling properties of silver solder vary according to the type.
See:http://www.jm-metaljoining.com/ for data on various grades.
The one sure thing is that there MUST be a gap for the solder to flow into. Hence I have always ignored the LBSC & Martin Evans way of fitting tubes, and left a gap between them and the tubeplates.
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Post by circlip on Apr 12, 2008 19:58:40 GMT
Salways going to be a contentious issue in't it? In defense of my outlook I can only point to full size examples that have also been used in models at times, throatplate end - tubes upset, tubeplate end - tubes expanded, don't forget that the access faces were recommended to have countersink ends to allow the solder to "caulk" and fillet the tube ends. What would a boiler inspector/insurer say? The trouble is that the witchunt to ensure boilers have to be ultra safe has been fueled by the blame /claim culture that we are now cursed with. I'm not saying that safety should not be paramount and that some peoples "efforts" at boiler making in the past shouldn't have been confined to the bin, but a lot of personal preferences still make interesting reading. Posted WITHOUT trying to raise controversy Ian.
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abby
Statesman
Posts: 927
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Post by abby on Apr 12, 2008 20:26:07 GMT
Gap or no gap , haven't we been here quite recently ? I think we should all do a test piece to put this one to bed ! P.S post pics of course
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Post by baggo on Apr 12, 2008 22:48:18 GMT
Here's one I prepared earlier ;D Backhead with bushes for 2½" A1. Soldered from other side with Cup Alloys 424 (the equivalent of Silverflo 24). Tenacity 4A flux. Bushes 'easy' fit in holes. No problem with penetration there!
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Post by circlip on Apr 13, 2008 5:00:41 GMT
Sorry, I didn't see that thread abby, but then again I don't read every posting in every section. I did say it was a contentious subject so if thine eye offends thee, cut it out. General chat seems to be the obvious place that most beginners would pick up on. Baggo, you have hit the nail on the head. What constitutes "Easy fit"? ? ? Give three people a micrometer and a piece to measure and get them in isolation to measure and write down the size? Trouble is when the word "Gap" is used it has a different meaning to different folks. Apart from that, your example of plate flanging should be a prime example for beginners to aspire to. Ian Ps. Not only beginners.
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Post by baggo on Apr 13, 2008 9:07:21 GMT
The 'gap' would be about 3 thou ( 0.075mm), certainly not a 'rattle' fit. Although not apparent from the photo, all the bushes are actually at an angle to the backhead so that the faces are vertical when the sloping backhead is fitted. The holes were reamed at the required angle so that the bushes would hold themselves at the correct angle when soldered.
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Post by circlip on Apr 13, 2008 12:02:09 GMT
Think the posting you referred to was on the Gauge 1 site abby and I make no apologies for posting the following here. The suitability of using plumbing pipe materials for boiler construction was mooted, - take care. I did all the plumbing work in my house using all new materials a few years ago. The carpet in the bathroom became decidedly wet around the toilet (no we hadn't) and after checking ALL connections, porcelain/copper/threaded and finding them all water tight, it was a bit of a mystery. I then noticed the condensation on the cold water inlet pipe to the flush box and wiped it dry for it only to "condense" again. There was a mucky black line about two inches long (sorry, 50MM) down the pipe that was condensing and no we don't polish the pipes in there. This took about twenty years to show itself and given that the local water pressure is quite high is rather surprising. So check VERY carefully before you Solder your superheater tubes in, you might have to change them. Ian.
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jamespetts
Hi-poster
Closet eccentric. Also bakes cakes.
Posts: 185
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Post by jamespetts on Apr 13, 2008 14:45:07 GMT
We are all, of course, soldering with adequate, preferably forced, ventilation aren't we? I do all my silver soldering in the garden :-D
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abby
Statesman
Posts: 927
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Post by abby on Apr 13, 2008 15:20:29 GMT
I can't remember where the thread was to be truthful Circlip , but the point I was trying to make is that between us we could prove or disprove - bit like mythbusters - whether or not any gap is desirable and if so how much. John's very clear picture shows that 3 thou is not too little and I will try a really tight rivetted joint - if I can find some rivets , I got some somewhere - and see the results . I worked for a time in an aero-space lab preparing and evaluating weld test-pieces so it should come back to me. As for the plumbing , does any one polish the pipes ? LOL ! but I can't see the point , if any , that you are making , apart from gauge and size is plumbing copper different from any other copper ? I suspect it is not but I don't know for sure , is there a different BS ?and my superheater tubes are 5/32" dia , hardly a plumbing size!
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Post by circlip on Apr 13, 2008 16:07:25 GMT
In the better class of Pubs, the "Pipe work" is usually polished. The point I was trying to make abby was that although the copper plumbing pipes are usable to us and are to BS whatever, a stress fracture which must have been in the pipe from manufacture took twenty years to appear and could have been part of a model boiler construction.When I said superheater tubes I should have qualified by saying flue tubes, the ones that the superheaters (another questionable feature in our sizes) slide into. Regards Ian.
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Post by alanstepney on Apr 13, 2008 17:43:52 GMT
Rather than do our own tests to see what gap is correct / best, surely the easiest approach is to take note of what the makers of silver solder say.
People like Johnson Mathey have the expertise, and they suggest certain gaps, fluxes, cleaning methods, etc, based upon many years experience, and laboratory tests.
Given that most silver solders are to a standard specification (BSI, ISO, etc) what JM say can be applied to other makes.
I'm all for checking things out, but see little point in re-inventing the wheel.
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Post by havoc on Apr 13, 2008 17:45:27 GMT
If you look careful at the boilers that are tested to destruction in the new-zealand paper then you will notice that most failures are at marks caused by production process of seamless drawn copper tube. (gauge 1 boilers)
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