Super Heater return bends

I'm getting the materials together to fabricate the super heater for my 5" gauge "Speedy". Does anybody know a supplier for return end castings for the 1/4" heater tubes.

In the book building "Speedy". LBSC stated the tubes should be brazed and not silver soldered. What is the difference between both methods ?

I saw an article in ME ?? where the tube ends were mitred and brazed together to form a 'V' return without end castings. The principal difference between Silver solder and Brazing would be the melting temperature of the joint, brazing being higher. What tube material will you be using as this may help others to help you.

BobH

hi peter,

LBSC was a bit vague if you didnt know what his equipment was. he specified all superheater return bends to be sifbronzed to the copper element pipe. this is something ive done for 30 years on numerous locos. when he referred to 'spelter' and 'brazing' he was referring to sifbronzing joints.

i would make the return bends out of solid copper as LBSC did. you cut off a slice of bar, drill the angles meeting, then in my case end mill out for the fit of the elements with a generous chamfer added.

no one makes these parts unless you want radiant superheaters extending into the firebox when they need making out of stainless and welded and quite expensive.

old fashioned sifbronze 'brazing' seems to be a bit of a lost art these days, having been surplanted in industry by MIG and TIG welding. ive still got loads of sifbronze brazing rod and flux.

cheers,

julian

Bill Steer wrote a series of excellent (IM not very HO) articles in Model Engineer (ME) about superheaters.

This index will let you find the references, if you search Bill Steer

The very thorough crucial articles for practical construction techniques are in three consecutive issues of ME, Volume 104, published 2010.

Issue Number 4368, 31 December - 14 January 2010, page 24 covers solid return bends manufacture.

Issue Number 4369, 15 - 28 Janury 2010, page 85 continues solid return bends & brazing, and starts arrowhead return bends.

Issue Number 4370, 29 January - 11 February 2010, page 160 continues arrowhead returns, and brazing of same.

I used the methods Mr Steer advocated to make arrowhead return bends in copper superheater tube with great success. I used hollow oblong section tube to make the tool to hold the tubes for brazing rather than using solid material as he advocated, but otherwise followed his method exactly. I used the tube simply because I had some to hand and 'it would do the job'.

Regards,

Phil.

Edited By Weary on 27/03/2014 22:49:39

Julian,

I searched the web and found loads of sifbronze for sale. Would my Yellow MAP gas torch develop sufficient heat to carry out the brazing. I intend to fabricate the super heater return ends as directed by LBSC using machined blocks of copper and 1/4" copper tubes.

hi peter,

i am not familiar with your make of torch. you need to get the copper to about 900 degrees ie hotter than red more like glowing pink. with the firebricks arranged like a furnace this isnt difficult. i form the sifbronze rod into rings to fit the copper tube against the return bend. it helps if the bulk of the return bend is shaped and reduced in size beforehand so the copper tube doesnt overheat. mix the red flux powder into a stiff paste but only add it on the outside of the joint. i make the holes in the return bend a tight fit for the copper tube further in, but then a generous clearance and then a chamfer. dont cut the copper tube to length till you have finished the return bends!

cheers,

julian

Brazing is preferred to silver solder for radiant (i.e. in the firebox) superheaters as they can get red hot when the steam isn't flowing.

Some time ago I tried brazing with brass rod and borax as a flux. It needed a fair bit more heat than silver solder, but I was able to make the joint OK.

Neil

hi neil,

the late jim ewins found that the temperature of the firebed was same as fullsize ie 1160 to 1600 degrees celcius, and hence also other temperatures in the extensive tests he did on one of his 5"g locos.

you should never silver solder return bends for the above reason hence why LBSC always advocated sifbronzing same. you might get away with using silverflo 24 instead of sifbronze but personally i wouldnt chance it.

i can categorically state that silver soldered return bends (of the LBSC non-radiant type superheaters) will quickly fail! don young silver soldered his and i had to remake them and braze up with sifbronze!

cheers,

julian

Edited By julian atkins on 28/03/2014 21:38:45