|
Post by builder01 on Oct 9, 2016 18:19:56 GMT
What is the typical way of attaching super heater tubes to the return bends? My super heater tubes and return bends are stainless steel. The return bend is a block of stainless with two holes drilled for the tubes and a crossed drilled hole to connect the tube holes. The cross drilled hole will need to be closed with a plug.
Question, can these joints be silver soldered? Brazed, MIG or TIG? What method is typically used on these joints?
Thanks,
David
|
|
|
Post by vulcanbomber on Oct 9, 2016 18:26:24 GMT
I personally would TIG them.
|
|
|
Post by Roger on Oct 9, 2016 18:44:48 GMT
If they are Radiant types ie they protrude into the firebox then they have to be welded because they will melt.
|
|
|
Post by builder01 on Oct 9, 2016 19:17:48 GMT
Roger, I assume you are for TIG welding as well?
When you say "they will melt", you mean just the silver solder, not the super heater tubes, right?
David
|
|
|
Post by John Baguley on Oct 9, 2016 19:32:55 GMT
TIG welding would be best but I have used Silverflo24 on several sets with no problems. I run the superheaters right to the back of the firebox where the returns are possibly in a bit cooler area.
John
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Oct 9, 2016 21:27:17 GMT
Hi David,
I disagree with John. JM Silverflo24 has a melting range of 740 - 800 decrees celcius.
Jim Ewins showed that the firebox temperature was pretty much the same as fullsize in a miniature loco. This is hardly surprising given that coal of whatever size under a forced draught will burn at the same temperature - but it was a surprise to many in the late 1960s!
This is quite a bit above the melting point of Silverflo24 - especially of concern during the accumulation test for safety valves when the regulator is closed and the blower on to test the safety valves. With radiant type superheaters they get to the same red hot heat as if you left the shovel inside the firebox.
There are no cold pockets above the firebed due to radiant heat from the firebed.
Any radiant superheaters must be of stainless and the return bends or joints stainless welded.
For the LBSC type superheaters not of radiant type I have always brazed them up with sifbronze.
It is extremely annoying/inconvenient having to replace superheaters, and on some locos this requires quite a strip down job. Any cause of failure ought to be minimised, though the LBSC type of copper and non radiant type have perhaps a 10 year life span with decent use.
Cheers, Julian
|
|
|
Post by Roger on Oct 9, 2016 21:31:46 GMT
Roger, I assume you are for TIG welding as well? When you say "they will melt", you mean just the silver solder, not the super heater tubes, right? David Hi David, That's correct, the joints need to be TIG welded if they are in the firebox to make certain they don't melt. I presume you've got plenty of room to get the ends down the Superheater flues?
|
|
|
Post by Jim Scott on Oct 9, 2016 21:59:31 GMT
What is the typical way of attaching super heater tubes to the return bends? My super heater tubes and return bends are stainless steel. The return bend is a block of stainless with two holes drilled for the tubes and a crossed drilled hole to connect the tube holes. The cross drilled hole will need to be closed with a plug. Question, can these joints be silver soldered? Brazed, MIG or TIG? What method is typically used on these joints? Thanks, David Hi David The block return in your description is typical of Martin Evan's design of the mid 1960's and in truth has little to recommend it. As drawn it is very difficult even to TIG weld, the tubes being very close together seriously limits torch access at this point. The usual tried and tested method is to to produce TIG welded spearhead returns as described in several posts on this forum, but other designs of return bend are possible. There is not a great deal of info regarding the actual temperature achieved at the radiant end of the superheater elements but historic data from the late Jim Ewins suggests this could be in the region of 850 degrees C (cherry red). Whilst you might be able to silver solder or otherwise braze the 'hot' end, I concur with others here that TIG welding will give the best long term outcome. Jim S
|
|
|
Post by builder01 on Oct 10, 2016 1:22:17 GMT
Thank you Julian, Roger and Jim,
Yes, all of the tubes and return bends will be stainless steel. Also, yes, this is a Martin Evans design. It will be close, but, there is just enough room to get the return bends down the superheater flues. The majority of responses seem to go for TIG welding. I am not familiar with other types of return bends, so, I will do a little searching to see if there are better or different ways to make a return bend. In any case, looks like I will need to find someone that can do some TIG welding!
As for working in the smokebox, the front ring and door will be completely removable when the need arises. This should help a bit for initial plumbing and resolving issues afterward. Superheater tubes and headers should come straight out the front of the smokebox.
Any suggestions for finding out about the other type of return bends?
David
|
|
|
Post by yorkshireman on Oct 10, 2016 6:09:08 GMT
"Any suggestions for finding out about the other type of return bends?"
here David:
Series in Model Engineer starting 18 December 2009
Johannes
|
|
|
Post by fostergp6nhp on Oct 10, 2016 16:40:28 GMT
What about the Doug Hewson super heaters, bent out of 1 length of tube with only needing jointing into the headers.
|
|
miken
Part of the e-furniture
Posts: 480
|
Post by miken on Oct 11, 2016 7:18:21 GMT
Question, can these joints be silver soldered? Brazed, MIG or TIG? What method is typically used on these joints Thanks, David If you tig weld them or get someone to weld them for you it is very important that they fill the inside of the joint with argon during welding to ensure a full penetration joint without any "coking" which is the horrible black mess that will occur on the other side of the weld if you don't (im not exactly sure what the coke is but it is no longer stainless steel and it reduces the thickness of the steel in that area).
Mike
|
|
|
Post by Deleted on Oct 11, 2016 8:26:12 GMT
What about the Doug Hewson super heaters, bent out of 1 length of tube with only needing jointing into the headers. I have heard talk of Doug's superheaters before, not heard of anyone who's used them though...I do like the idea if they are efficient...anything that's closer to scale floats my boat..... Pete
|
|
|
Post by builder01 on Oct 11, 2016 9:39:38 GMT
Okay, so I need someone that can TIG weld and has argon gas to fill the tubes while being welded. I hope this is a typical setup for a welder. Otherwise, this is becoming complicated.
Still not much of a description of the Doug Hewson super heaters. I wonder what they are?
David
|
|
|
Post by Deleted on Oct 11, 2016 9:52:45 GMT
From what I understand David they are more like the prototype, so there is no join, the tube is simply bent around at the firebox end, like a long 'U' bend, one continous tube from the header and back, they are smaller in diameter than the usual model setup. So the same as the prototype although scale wise they are bigger. What I don't know and would want to find out before going this route is are they as efficient?
cheers
Pete
|
|
|
Post by John Baguley on Oct 11, 2016 11:09:44 GMT
The Hewson ones are bent from 1 length of 5/32" x 24swg tube. They are also a 'double bend' - they go into the firebox, return, and then bend back towards the firebox again to form a double U shape. As Pete says, they are like the full size elements.
I would imagine that they are very efficient as they have a large surface area compared to the bore. I read somewhere that the Hewson Class 4 has something like 60 feet of tubing in the superheaters! They have 8? elements or something like that. Not sure that all the elements extend into the firebox - some may finish at the ends of the tubes.
The catalogue advertises elements bent from 1mtr to 4mtr lengths of tube. I suspect that you should sit down when asking for a price though!
John
|
|
|
Post by Roger on Oct 11, 2016 11:27:17 GMT
I imagine the 'double bend' superheaters are thick walled tube, else I imagine they would collapse on bending. Maybe they use Wood's Metal to prevent that from happening though. I'd be interested to see how that's done.
|
|
|
Post by Deleted on Oct 11, 2016 11:31:40 GMT
Thank's John...that very interesting...some things may be worth paying for. I've just checked the drawing for Doncaster, she has three 1 1/4 OD 16swg superheater flues at 20 1/2" long, I would assume that if one wished they could fit a number of these 5/32 tubes down each flue. I don't know enough about this subject yet, to be fair I haven't even begun to look at it but I guess there is a formula for what space you need around the superheaters for them to work correctly, you can't just stuff as many tubes down the flue as will fit. I'll have to take a look at this some time soon....great...I love learning new things.... Kind Regards Pete
|
|
|
Post by RGR 60130 on Oct 11, 2016 12:25:09 GMT
I've a feeling that Doug has spoken recently in one of the magazines about making his superheaters. Does that ring a bell with anyone? As regards efficiency, did Ballan Baker not have some fitted when he won IMLEC?
Reg
|
|
miken
Part of the e-furniture
Posts: 480
|
Post by miken on Oct 11, 2016 12:42:17 GMT
Okay, so I need someone that can TIG weld and has argon gas to fill the tubes while being welded. I hope this is a typical setup for a welder. Otherwise, this is becoming complicated. David
Yes this is a common set-up for a tig welder when welding pressure vessels. The tig process typically uses argon anyway. Your man will probably refer to it as "backing up" the weld. On the argon regulator for the welding machine he should have a second outlet with a flow meter. He will simply take a length of flexible plastic hose from this outlet and connect it to the end of the superheater. So filling the tubes with inert gas.
Here is a horrible picture of a stainless joint that hasn't been backed up. It seems that Americans call it "sugaring" . Which I haven't heard of before.
www.mig-welding.co.uk/forum/threads/weld-sugaring.46697/
Just interested, but what size tubes do you require?
|
|