drying out of flux / prefluxing of silver solder.

[julian atkinsParticipant @julianatkins58923]

hi phil,

keith never stated keep the flame away from the flux. the flux doesnt mind being in the flame. it does it no harm. what you must not do, as keith advises, is let the stick of silver solder melt in the flame. the silver solder must be melted by the metal being at a high enough temperature otherwise you get bad joints. in boiler work it is particularly important to have good joints.

keith has recently done a series of articles in EIM on silver soldering which i can thoroughly recommend.

it is not difficult in miniature loco boiler work letting the work get up to heat with propane and then applying the silver solder of correct grade with the correct grade of flux. i would agree that with some stages of boiler work very careful set ups are required and constant attention to the flame and where it is directed, but after the first few 'easy' joints on a boiler these things become intuitive. there are a few tricks for various awkward set ups in making boilers.

i am afraid i have no experience of oxy-acetylene silver soldering where quite different techniques and set ups are required, plus you have to be very careful on some designs to avoid localised heating and cracking of throatplate to boiler barrel joints previously done.

hi bill,

your Emma Victoria boiler is smaller than the Don Young Railmotor No.1 boiler i started when aged 18 with a 5 pint paraffin blowlamp. if you read Don Young's construction series for his Railmotor boilers in ME 1968 i think you will find it an excellent guide and one of the best, except the use of coke and easyflow flux. if you want all silver soldered stays i can give a bit of advice for doing this with propane.

always happy to help via PM or on here if you have any problems.

the cost of commercial boilers is very great and the savings by doing it yourself ought to encourage more to 'have a go'.

cheers,

julian

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Julian,

All very encouraging, I think I need to obtain a Sievert 2943; the largest I have at the moment is a 2942 at 26kw. Would you recommend a long neck tube?

It was Bill who mentioned keeping the flame off the flux. I was looking to obtain an informed response which you supplied, thank you. I have Keith's articles (from EIM) which are very informative.

Regards

Phil

[duncan webster 1Participant @duncanwebster1]

To echo CuP alloys comment, I once attended a talk given by them where he stated you don't need to clean before silver soldering. When I got home I found a bit of copper that had been buried in the garden for over a year, cut 2 bits, fluxed, heated, solder ran beautifully.Would I do this on a boiler, probably not, cleaning first might not be necessary, but it feels a lot better and you'd feel an awful twit if it didn't run.

[julian atkinsParticipant @julianatkins58923]

hi duncan,

i am not sure i understand the point you made, but i agree making miniature loco boilers requires a lot of 'know how' which to the best of my knowledge hasnt been thoroughly described in ME for very many years. those of us taught by old hands doesnt seem to have become accepted knowledge in many clubs especially with propane. and many mis-interpret LBSC's descriptions of 'braze' ie sifbronze the barrel to throatplate joints for which they were designed with often awful expensive results.

i am a great believer in silver soldered double flanged or single flanged throatplate to barrel joints silver soldered. you will never see such joints on LBSC's designs because he brazed them with sifbronze with his 'Alda' oxy-acetylene equipment which was well ahead of it's time and what most model engineers could not do with ordinary set ups in those days.

there have been many comments over many years that boiler designs supplied by the trade and ME ought to be updated. nothing has happened, leading to many tyros into a myriad of pitfalls and potential costly disasters none of their own making.

i know of at least 3 3.5"g Britannia LBSC boilers that have had cracked throatplate to barrel seams because the joint has been silver soldered as opposed to sifbronzed as per the original design. an extremely disheartening and costly experience for those involved.

cheers,

julian

[Bill DawesParticipant @billdawes]

Hi Julian, I have read many times in the past about the danger of overheating the flux so probably misunderstood that to mean not having the flame directly on it. Would I be correct though in saying it is best to heat up the job keeping the flame away from the flux in early stages where possible. I realise every job varies, in your photo example I guess it would be near impossible to do that with so many parts to be soldered close together. I have seen videos with the flame definitely on the rod but I suppose that is ok once the parent metal is up to temperature.

What diameter rod would you suggest?, I am thinking of 1.5mm.

I propose to use HT5 flux everywhere, do you think that is ok?

Do you use two torches on boilers?

Regards

Bill

[julian atkinsParticipant @julianatkins58923]

hi bill,

CupAlloys HT5 flux is excellent for boiler work as identical to Thessco F or Tenacity 4A. different brand names, same product.

if you heat up the job within a reasonable timescale you have no worries about heating up the flux. that is what it is supposed to do with heat.

for the currently available non cadmium stuff ie J&M silverflo 55 or CupAlloys equivalent you would be better off with a larger diameter than 1.5mm for most boiler work ie plain joints. just my personal preference here, and others may disagree. 1.5mm is easily caught in the flame plus waves about too much with the sweat pouring and nerves on boiler work! i would use 1mm for rings around the tubes when silver soldering to the inner wrapper and tubeplate already done. i do however probably over do the silver solder – but this is better IMHO than being too mean. again just my personal opinion .

cheers,

julian

[Bill DawesParticipant @billdawes]

Hi Julian, thank you for response, I think I will go for 2mm then on joints, I have wondered if more than 1.5mm would be better as it does, as you say, wander about.

Interested you talk about sweat and nerves, I imagined someone that has done a lot of it would just calmly sail through the process, everything heating up quickly and solder running freely etc etc.Makes me feel a bit better about it.

Full up with a stinking cold at the moment so my new year resolution to get cracking on my build has already lost a few days. However now encouraged, I will make my first job soldering on the firebox extension, my confidence for the whole year ahead will depend on this being a success, I have high hopes of the right size burner and encouraging advice will see a new dawn in my silver soldering abilities!!!!.

(having had a lifetime in engineering from the age of 15 to now 74 years old I think it is about time I got this sorted)

Many thanks.

Bill

[CotswoldsPhilParticipant @cotswoldsphil]

i know of at least 3 3.5"g Britannia LBSC boilers that have had cracked throatplate to barrel seams because the joint has been silver soldered as opposed to sifbronzed as per the original design. an extremely disheartening and costly experience for those involved

Hi Julian,

This has become a very interesting thread…

The throat-plate to bottom-of-barrel joint on the Minnie TE boiler is just a silver-soldered butt joint as designed by Mr Mason. Could this be considered as a weak point especially as there will be some stress here in a TE boiler?

Regards

Phil

[julian atkinsParticipant @julianatkins58923]

hi phil,

i have just had a look at the Minnie boiler drawings in ME january 1969.

on a relatively small boiler i dont see a problem with the throatplate to barrel butt joint so long as you avoid localised heating on the later and final stages. as a precaution i would use J&M silverflo 24 on the above joint, and do the outer firebox wrapper to barrel and throatplate joint at the same time also using silverflo 24.

however silverflo 24 melts at 740 degrees C and it requires a lot of heat, and a bit of practice to use. the remainder of the boiler can be done with silverflo 55 which melts at 630 degrees C.

(L.C. Mason suggests C4 silver solder for the barrel to throatplate and outer wrapper joints, but this is no longer available)

if you are lucky enough to still have some easyflo silver solder or easyflo No.2 save it for the backhead to outer firebox and last bit of the foundation ring.

before you start, best in any event to discuss the matter with your club boiler inspector and show him the drawings.

cheers,

julian

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Julian,

The shell – barrel, throat-plate and wrapper were silver soldered with C4 the best part of 40 years ago, with some help at night-school. The shell has remained in the cupboard since then, having failed to get any farther with a firebox. I managed to buy a boiler from Reeves (in Moseley, remember them) at the time, to continue construction of my Minnie.

I hope with some new found knowledge to complete the boiler, so that I can say I built the complete engine. I will be joining the local club for moral and practical support. Not least of which is how to implement the requirement for two boiler feeds on this engine with just a single pump.

Regards

Phil

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