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Post by alanstepney on Dec 22, 2014 19:13:17 GMT
I'm not against TIG welded boilers.
If I was still a boiler inspector I would happily accept them, but, and its a big "but", they must be done correctly, and it isnt just a matter of applying TIG to copper sheets. The actual process is quite complex, and, I suspect, that few amateurs could manage it without lots of practice and/or training.
Silver solder, on the other hand, can be used with fairly basic equipment, and by a novice, with the proviso that one needs fairly deep pockets to afford the materials.
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Post by ronhancock on Dec 22, 2014 20:19:02 GMT
Me i have trouble with Silver Soldering thats why i am tig welding one side silver solder the other. I am confident with my Tig welds as ex welder know when i have good penertration. Not so with silver solder even though i have seivert torch getting very hot and using oxyacetaline with number 8 nozle. And yes job is clean long soak in Citric Acid then hot water wire brush on angle grinder finaly wire wool. Get the place really red on oposite side to solder with plenty of Flux. And still not happy without the Tig. Also i have seen so many boilers with leaks worry me hence the Tig weld. As they say what suits one does not suit another. Next year as a practice going to build a stainless boiler so easy to weld just want to try and see the diffrence.
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Post by ronhancock on Dec 22, 2014 20:38:20 GMT
Thats probably where i am going wrong but can only get it to Run when i get high temp then not very well
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Post by mutley on Dec 22, 2014 21:05:01 GMT
You can rent a decent TIG set up if you do not have one available. Really..... 3mm copper sheet will need something around 200 -250 amps. I have a 50amp supply to my workshop, out of interest what is the supply current needed for a set rated at 60% duty cycle ,single phase of course. Most larger welders appear to be 3 phase. I think Alan has hit the nail on the head. Happy to accept TIG welded copper if done properly. Most model boilers are designed for silver solder and flanged plates to fit what is achievable within an amateurs workshop. I haven't seen an approved design for a TIG welded boiler yet so how do I assess the physical construction and its suitability and fit for purpose? As a club boiler inspector how do I assess the competence of an individual to TIG weld copper or even the weld strength? With Silver solder I can see the penetration and from experience judge the soundness of the joint. I have seen plenty of welds that look great but have zero penetration. Have any tests been carried out to understand how a copper welded boiler may fair over time? Are there any failure points that should be watched for? I'm not against using new technology but lets not run before we can walk.
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Dec 22, 2014 21:31:35 GMT
To me TIG welded boilers are the way to go, the big advantage of a welded boiler is that it is all copper. If you look up the coefficients of expansion for copper and silver solder they are significantly different meaning that the joints are stressed by temperature change. I guess this is probably the reason that copper boilers ultimately fail. A welded copper boiler being all the same material should not be stressed by a uniform temperature change.
The use of TIG kit with silver solder for me would be a worry, the heat is very concentrated and the temperature in the plasma stream can reach almost 3 times the temperature of an oxy acetylene flame, so the chances of boiling out the cadmium (in the old days) and zinc are fairly high.
Interestingly I have see a number of professional boilers fail with leaking tubes, especially superheater flues in the front tube plate. On one of them the silver solder came off one tube as a fillet and I managed to get it analyzed. The report came back that it was a silver solder, that there was no trace of Zinc or Cadmium (there should have been)the silver was widely dispersed and there were voids in the silver solder due to zinc and cadmium boiling out. The conclusion from the lab was overheating when it was soldered. It should be noted the boiler took about 20 years before it failed. There were also a couple of inclusions of FE of about 20 microns in size, probably from wire wool fragments.
I fail to see the sense in hybrid welded/silver solder joints If the welds are good what does the silver solder do? how does the silver solder penetrate a welded joint if it has proper penetration, or if you silver solder first and it penetrates how do you stop the silver solder A polluting the weld and B boiling out component parts of the solder.
I am pro TIG welded boilers built by people who know what they are doing, I have no problem with silver soldered boilers built by people who know what they are doing. Call me an old dinosaur but I use a TIG welder for welding and that's it.
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Post by Deleted on Dec 22, 2014 21:45:48 GMT
Thanks for your input in this thread Paul, I have been keeping tabs on the arguments both ways...when I mentioned the possibility of going Tig i was talking purely on buying a professionally built boiler, not attempting one myself as my welding experience is purely Arc and that dates back many years. As I said I like the price of Tig, I also like the repair-ability of a Tig boiler and now that you have reminded all of us about the fact its all copper and thus taking away different expansion rates, I like this too....I still don't like the look around the tubes but could live with that and let's face it, it would never be seen after the first steam up. . I think the deciding factor would be to see a boiler built for Doncaster using Tig as per Don's drawing aside of any internal changes prudent for welding.
Pete
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Dec 22, 2014 21:46:23 GMT
from a purely cost point of view i reckon that most silver soldered copper boilers are almost equal in silver solder to copper, the cost of the silver solder perhaps being a bit more than the copper (i am rather over generous with my silver solder on boiler work). when i start to build a loco i start collecting things as i go along so that there is no sudden 'ive got to buy £200 worth of silverflo 55' in one go. as it takes a long time to build a loco the cost is spread over many years, and compared to other hobbies is quite cheap if you plan ahead.
there is good and bad silver soldering just as i imagine there is good and bad TIG welding.
cheers, julian
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Post by ronhancock on Dec 22, 2014 22:19:13 GMT
Suger i tig welded my boiler pipes my bronze bushes all with sifcopper 985 seems fine good penertration. I had to clean up a bit on the pipes did not look neat but passed by our boiler inpecters.
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pault
Elder Statesman
Posts: 1,497
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Post by pault on Dec 22, 2014 22:23:04 GMT
Hi Paul, I don't think anyone is suggesting silver solder is no good, or that different materials are no good its horses for courses. I have never seen a soldered bush weep or cause a problem, the joint is small/short and relatively lightly loaded so soldering is a sensible option. its the long joints that in my book benefit from welding A welded boiler needs to be designed as a welded boiler and no be a welded up silver solder design. I believe that no boiler should be built without the input of someone who knows what they are doing be it welded or soldered.
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Post by Deleted on Dec 22, 2014 22:24:00 GMT
Merry Christmas Paul. Whilst I agree with a lot of what you say about ungifted amateurs producing potentially dodgy boilers, I can't help feeling that you are letting your past experience interfere with your judgment on current and future developments within the hobby. I hope that you don't succumb to the 'Don't confuse me with facts, my mind is made up' syndrome! John
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bhk
Part of the e-furniture
Posts: 458
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Post by bhk on Dec 22, 2014 23:34:19 GMT
I'm going to leave the TIG argument behind and agree to disagree.
But in the interest of doing thing differently, what's people thoughts on MIG brazing a boiler, with a silicon bronze filler?
Cheers
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Post by ronhancock on Dec 22, 2014 23:51:46 GMT
Love to know more
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Post by Rob on Dec 22, 2014 23:56:37 GMT
You can rent a decent TIG set up if you do not have one available. Really..... 3mm copper sheet will need something around 200 -250 amps. I have a 50amp supply to my workshop, out of interest what is the supply current needed for a set rated at 60% duty cycle ,single phase of course. Most larger welders appear to be 3 phase. A 200 amp, 60% duty cylce tig welder I have looked at in the past requires a input supply of 18 amps, a similar model requires 22. When wiring my workshop, I based the requirements around what I thought would be the biggest draw - a welder and a compressor. I have 32 amp connections for both the compressor and a welder, and the workshop supply is also 50 amp. I think that should be sufficient for future expansion for the welder, though I think the inrush on the compressor is 30 amps or more as it stands now, so a new connection required if I want to go bigger on that!
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