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Post by cplmickey on Feb 4, 2011 12:52:46 GMT
Just wondered what thoughts others had on the make up of the boiler barrel joint. I have seen many butt joints with internal strip but I also have one made with a castellated joint (a tapered barrel I bought from Reeves I think). I'm about to make a parallel barrel and a butt joint is obviously easiest but is it the best?
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Post by Deleted on Feb 4, 2011 13:10:43 GMT
I'm about to make a parallel barrel and a butt joint is obviously easiest but is it the best? Not good! See the 'Boiler plates' thread for the evidence...... JB |
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redmog
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Post by redmog on Feb 4, 2011 15:50:46 GMT
I'm about to make a parallel barrel and a butt joint is obviously easiest but is it the best? No it's not the best. Although correctly done it will be within the safety factor required. If it's parallel, then a length of seamless drawn copper tube of the correct wall thickness would be my choice. Chris |
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Post by jgb7573 on Feb 4, 2011 15:55:47 GMT
Correct me if I'm wrong, but although a butt joint on it's own is not permitted, a butt joint with a strap either inside or out, riveted in place and then silver soldered is entirely satisfatory.
John
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redmog
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Post by redmog on Feb 4, 2011 16:17:16 GMT
a butt joint with a strap either inside or out, riveted in place and then silver soldered is entirely satisfatory. John Yes, a butt joint with a strap is permitted and satisfactory, and it's always good to get it checked out by an authorised boiler inspector. Out of interest, am I right in thinking that the minimum overlap should be x 3 the thickness? Chris |
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Post by cplmickey on Feb 4, 2011 21:40:00 GMT
I would happily buy a piece of seamless drawn copper tube but have absolutely no idea where to get it from. I need 6 1/8 inch OD of 4mm thick copper. Any pointers for that please.
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Post by Deleted on Feb 4, 2011 22:11:13 GMT
I would happily buy a piece of seamless drawn copper tube but have absolutely no idea where to get it from. I need 6 1/8 inch OD of 4mm thick copper. Any pointers for that please. Try here: they have 6" & 6 1/4" tube so may well have what you need. www.livesteammodels.co.uk/pdf/MES2011b.pdfJB BTW When I talked about butt joints earlier I was referring to the throatplate end. Sorry for any confusion caused! |
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Post by Shawki Shlemon on Feb 5, 2011 8:02:23 GMT
If you are happy to use slightly over/under size ( the difference in performance will be negligible ) , then a seamless tube is the best option but it will involve a lot of modification to joining parts . Otherwise a butt joint using a strap of the same thickness as for barrel , the width of the strap 10 T and rivets spaced at 10T and silver soldered , the strap can be inside or outside . Of course check with your boiler inspector .
.
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Post by mutley on Feb 5, 2011 11:30:12 GMT
I think the Uk regs call for the butt strap to be on the outside. I need to check the regs when I get home.
Andy
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chiptim
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Post by chiptim on Feb 6, 2011 17:09:27 GMT
I recommend PLHILLSales for copper supplies.
Tim
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Post by cplmickey on Feb 6, 2011 21:27:07 GMT
Thanks for all your replies on this and for letting me know of a supplier (livesteammodels) only a couple of miles from work. I'll also check out PLHillsales for similar items.
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Post by GWRdriver on Feb 10, 2011 13:37:41 GMT
mickey,
FYI, US standard Type "K" copper tube is 6.125" OD x .142" (3,6mm) wall thickeness.
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chiptim
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Post by chiptim on Feb 10, 2011 15:16:48 GMT
Not knowing anything about your design 4mm seems very thick for the barrel? I'm comparing it to my boiler that has a 5" barrel at 10SWG for 100PSI working pressure.
A 6" barrel that's 4mm thick will take a huge amount of heat to solder.
Does the design call for that?
Tim
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Post by ettingtonliam on Feb 10, 2011 15:40:52 GMT
Tim
10SWG is 3.251mm. Pro rata, if 10SWG is right for a 5" barrel, then a 6" barrel will need 3.9mm for 100 psi, so 4mm is about right.
Richard
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chiptim
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Post by chiptim on Feb 10, 2011 15:59:35 GMT
Sorry my mistake its specified as 12 or 13 SWG so approx 2.5mm.
Tim
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redmog
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Post by redmog on Feb 10, 2011 17:02:30 GMT
Tim 10SWG is 3.251mm. Pro rata, if 10SWG is right for a 5" barrel, then a 6" barrel will need 3.9mm for 100 psi, so 4mm is about right. Richard A 10g x 6" dia. drawn copper tube has a Calculated Safety Factor of 8.5 at 100psi, which is more than adequate, and is used by many published 5" gauge locomotive designs. Chris |
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chiptim
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Post by chiptim on Feb 10, 2011 21:02:12 GMT
OK so if 10g 6" diameter is good to 100PSI with a safety factor of 8.5 either 4mm has a greater safety factor or it can be used at a higher pressure. I thought I had read that copper boilers aren't generally designed for use above 100PSI because the strength of the copper decreases rapidly with rising temperature, the temperature in a boiler proportional to the pressure. Hence my question whether the design called for that. Now there's nothing wrong with increased saftey factor but a valid concern regarding the ability to solder it. Of course we don't know what heating equipment the author has available but am I correct in thinking that the butt strap doesn't generally take the heat well from the main piece of copper and often requires a separate flame?
Sorry, I don't want to divert the attention away from the original question which is very intreresting.
I think in the other thread (or somewhere on this forum) it says that regular rivets help transfer the heat to the strap but in my (limited) experience they wouldn't transfer enough heat and are more there to hold the assembly together and maintain a suitably small clearance.
I would have thought that there's a greater chance of messing up the fabrication of a castellated joint such that you have voids to fill larger than the ideal gap!
Much harder to mess up a butt strap joint but slightly harder to reach melting temperature.
Tim
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Post by alanstepney on Feb 10, 2011 21:51:30 GMT
The "secret" to any silver soldering (or one of them) is to have plenty of heat.
So, if adding a butt strap absorbs some of the heat, then one needs to have more or greater sources of heat.
You can run copper boilers at higher temperatures, but there are rarely any advantages, and the FOS is, as you imply, reduced.
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redmog
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Post by redmog on Feb 10, 2011 21:54:49 GMT
OK so if 10g 6" diameter is good to 100PSI with a safety factor of 8.5 either 4mm has a greater safety factor or it can be used at a higher pressure. I thought I had read that copper boilers aren't generally designed for use above 100PSI because the strength of the copper decreases rapidly with rising temperature, the temperature in a boiler proportional to the pressure. Hence my question whether the design called for that. Now there's nothing wrong with increased saftey factor but a valid concern regarding the ability to solder it. Tim Tim, I agree, I wouldn't like to silver solder 4mm copper tube with my heat source. It just wouldn't do it successfully, but we don't need to on our boilers. If your Jesse barrel is 2.5mm x 5" dia it has a Calculated Safety Factor of 8 at 100psi. More than adequate, so why increase the CFS to make construction more difficult. I find it challenging enough with the thickness of copper we use. That's one of the reasons why I like parallel barrels, drawn copper tube makes an easier start. Still following your boiler with interest. Chris |
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Post by cplmickey on Feb 10, 2011 22:37:33 GMT
The loco I'm building is Martin Evan's GWR Dart and it specifically says 5/32" (4mm) on the drawing so who am I to argue?
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