Silver Soldering with Oxy Acetylene

[heyfordian18]

I have been attempting to re-solder a couple of leaking stays on a copper boiler. Pickled to clean the joint, Easy Flow No.2 solder, tenacity flux, background heat from a Bullfinch Propane burner, and local heat from an Oxy Acetylene torch.
The problem is that the flux appears to be exhausted within a few seconds of starting the local heat with the Oxy Acetylene torch, developing small black deposits, and not going through the usual transition to liquid as the temperature is raised. The solder does not flow and looks porous under an eye glass.
Use the same batch of flux and heat only with the propane, either indirect or direct heat, and all is fine.
So I have concluded that I am doing something wrong with the torch settings and the flame.
Is the type of flame, neutral, oxidising, carburising, critical when working with this flux, or I am doing something else wrong?
Any advice and guidance on this will be most welcome as the beard is rapidly turning grey and the running season is upon us!

[Tel]

Neutral flame, but here's the trick - use the cutting torch with a small to medium tip, but just use the outer envelope of the flame - NOT the inner cone, and whatever you do, stay away from the oxy button.

[AndrewP]

It sounds as if you are overheating the flux and exhausting it.
Some numbers may shed light:-
Propane/air torch flame temp 1900 C
Oxy/Acetylene flame temp 3200 C
Easy-flo No2 melting temp 610 C
Tenacity flux nos 2, 6 and 14 up to 800 C
Tenacity flux nos 12 or 125 up to 1200 or 1300 C
Note that the higher temperature fluxes don't start working until 750 C so a mixture is necessary.
Normal recommendation for flame is fuel rich or reducing flame but with Acetylene this tends to give a "dirty" flame and I would suggest (and use) a neutral flame.

Suggestions?
If you can do it all with Propane or Oxy/Propane then fine.
If you need the Oxy/ Acetylene's heat then can you arrange to heat more remotely - not always possible with stays obviously.
Higher temperature flux - I'd probably try that first.

I'm with you on the beard but mine goes black again every time I singe it

[ianengr]

I'm wondering if you are using a new bottle of acetylene which has been overfilled with acetone and is being gradully pushed out of the system.

Is the boiler new or old ? Old boilers can be difficult to re-silver solder even when pickled and you will often find that you start more leaks than you fix.

Hope you have success.

Regards,

Ian.

[heyfordian18]

thanks all for the advice to date.
Tel:
thanks for the confirmation on the flame type. I'll also try a smaller tip this evening.

AndrewP:
to use just the propane burner on the firebox side worries me that I will disturb other joints. It' snot a very subtle tool! I'll do some research on higher temperature flux's. Anything come to mind? The really strange thing is that similar repairs I did on another boiler were completed without these problems.
Originally, I decided that oxy-propane equipment would be adequate, but could not source the equipment locally. Someone then offered me their oxy acetylene kit so I went with that.
Beard not singed yet, but nasty flash steam burn on left index finger through being in to much of a rush last night to cool the lump. At least it was only water and not the pickle tank.

ianengr:
the bottle is at about half full according to the gauge.
The boiler is 4 years old, and yes, the work has generated more leaky stays than I started with! Started with 2, and 3 later I still have 2 to do. If I can get the heat right I would re-solder the lot of them.

[brozier]

Heyfordian,

I'm reading Alec Farmer's Book "Model Locomotive Boilermaking" at the moment he mainly uses Oxy-Acetylene for Silver Soldering using propane to pre-heat. This book is difficult to get hold of but recommended.

Are you making up fresh batches of flux each time you start? He recommends adding a bit of washing up liquid when mixing it. This degreases as well as acting as a wetting agent. He uses quarter of a teaspoon to two heaped tablespoons of flux.

The tips he uses range from 10 to 18 (on a FN50 torch) he uses 18 for SIF bronze Brazing. 10 for joint strip to barrel, 11 for tubes to tube plate, 13 for tube plate to wrapper. I can't find a reference to what he is using when doing the stays.

When working in the fire box he always blocks up the tubes using with a fire brick at the smoke box end....

Hope this is of some use.

Cheers
Bryan

[brozier]

One thing I forgot to add. He preheats with propane before starting on the stays. And then does them all in one go.

Regards
Bryan

[Peter W.]

May 2, 2008 12:58:10 GMT brozier said:

Heyfordian,

I'm reading Alec Farmer's Book "Model Locomotive Boilermaking" at the moment he mainly uses Oxy-Acetylene for Silver Soldering using propane to pre-heat. This book is difficult to get hold of but recommended.
Cheers
Bryan

This is being serialised in "Engineering in Miniature" at the moment ( with colour photos ).
Cheers,
Peter

[heyfordian18]

Hi brozier,
thanks for the post.

I have kept up to date with Alec Farmers articles in EIM, and have tried his tips such as the washing up liquid. That is also included on the Johnson Matthey data sheet for the flux. Yes, and new flux mix each evening.

The EIM articles have not included all the details of nozzle size, so your notes are helpful. I have been using a No.10 in my Butbro torch, and I will try a smaller size this evening, but not sure that is going to give me the temperature I need.

AndrewP's list of temperatures has got me thinking flame "too hot", but if Alec can do it........?

Next flux is Tenacity 20 with working range of 750 - 1000 which seems too high to me.

[brozier]

Looking at the CuP Alloys site, The Johnson-Mathey site and the Alec Farmer book - they all recomend EasyFlo flux for use with Easy Flo No2 solder NOT Tenacity.


See JM EasyFlo2 here www.jm-metaljoining.com/products-pages.asp?pageid=61§ionid=3

and JM EasyFlo and Tenacity Flux here

www.jm-metaljoining.com/products-pages.asp?pageid=63§ionid=3

Maybe that is the issue....

Regards
Bryan

[heyfordian18]

Bryan,
good point, always sensible to follow advise from those who have the experience.

I have been using tenacity No.5 as the data sheet states

"It is particularly recommended for brazing stainless steel at temperatures above 700¢ªC and also for brazing large assemblies in steel or copper wherever prolonged heating is necessary."

and heating up a boiler does take some time.

As EF No.2 is only 608 - 617 C melting range, EF flux may be more active at those temperatures.

I'm off to the workshop now to experiment with flux's and nozzle sizes.

[chris vine]

Hi Heyfordian,

I have found that easyflo flux is much easier than tenacity, however your and others point that tenacity lasts longer is valid on a large item like a boiler.

I use propane air whenever possible and have an oxy propane torch for extras. It is only an oxy acetylene torch but connected to a propane cylinder. The nozzle I use is like a little pepper pot and has 6 little nozzles. This gives a slightly gentler (if gentle is appropriate here) flame.

I think a useful trick (which you probably already have tried) is to keep the oxy flame completely away from the joint in question and keep it between stays or even a little further away. This will protect the flux and the solder and will prevent you from forcing things.

Theory says you should not melt neighbouring joints because the second melting will be at a higher temp.

For all joints I try to have the solder pre positioned, immersed in flux. The only thing you have to be careful of is when the water boils out, the solder can be moved away from the joint. However if you warm very gently at the beginning just to dry the flux out, this won't happen. (and the flux is not working or being exhausted at this point)

The advantage of putting the solder in place is that when the metal is hot enough the solder runs and you know you are hot enough. This is important when there are other joints nearby!!

Chris. (not a boiler maker)

[heyfordian18]

Chris,
thanks Chris, for sharing your experience. I think I will try the fluxed solder ring on the stay. I have used that technique on a front tubeplate, and it worked very well with a big propane burner on working on the outside of the barrel.

I did a few experiments and test pieces yesterday, and had more success with Easy Flow flux than with tenacity. Indirect heat is always OK, but the tenacity does appear to burn very quickly when the oxy acetylene flame gets near it.

Next attempt on the boiler to get the 2 stays re-soldered will be with a No.7 nozzle and a gentle flame.

I'll report back!

[PH]

Since I know absolutely nothing about the chemistry involved, this might be a daft question, but it is possible to get the best of both worlds by making a mix of Easyflo and Tenacity?

[AndrewP]

That is what I do PH for assemblies that require prolonged heating and I believe it helps.
I always use a mixture of boric acid and borax which work at different temperatures as a background flux/scale preventative and I know that works but that is on precious metals I admit.

Andy

[Shawki Shlemon]

Hi
Old boilers are not easy to silver solder because it is almost impossible to clean them no matter what you try .
How bad is the leak ? if not very bad try to support the other side with some dolly and give the stay a bash ,this may fix the leak.
Talk to your boiler inspector and ask if you can seal the leak with
soft solder ( this is allowed in the OZ code provided the the soft solder is not structural .

[petercolman]

Gentlemen calm down, the purpose of the flux is to clean the surface, the torch heats the JOB the solder is melted when the joint is ready, if the flame is running at the elevated tempreature of oxy acet and the solder is already in place, you run the risk of boiling off the extra elements in the solder before the solder can flow.
I can remember seeing a guy silver soldering jewelry rings in silver with oxy acet, he put about 100 of them on a carbon block, gave each one some heat and than applied the solder, a good on each time.
The vasrt ammount of concentrated head is a risk with this metod and requires some skill.
take care
Peter

[ausdan]

Shawki,
Reading this thread, was wondering what is you take on Flux brands in Australia, I see the following mentioned, but don't believe they are readably available here

Easy-flo No2 melting temp 610 C
Tenacity flux nos 2, 6 and 14 up to 800 C
Tenacity flux nos 12 or 125 up to 1200 or 1300 C

I have some comweld No2 , but have not got started on the boiler as yet...what do you use ? For 45% s/solder with Cadmium

cheers

[heyfordian18]

Shawki,
I did contemplate using Comsol at one stage. I know my club permits that for repairs.

Peter C,
this sort of repair certainly requires considerable skill, and at a much higher level than mine!

I feel that I have mastered the heating technique so as not to burn off the flux. EasyFlow flux is giving a better result than the Tenacity, but each re-heat and repair generates further problems with joints. Some of them well away from the heat source. Something else is not right with either the existing solder or the metal. I think that the boiler is dying and will soon be beyond (my skills) repair.
2 thoughts - any known problem with mixing EasyFlow and SilverFlow brands of solder?
- Anyone attempted to dismantle a boiler to salvage the plates and reassemble with new stays and joints or is it easier to start afresh?
Yes, I am getting desperate!

[baggo]

It sounds as though you are fighting a losing battle with this one

If heating the boiler is causing the existing joints to fail then there's definitely something wrong somewhere. Perhaps some of the joints were originally done with something other than silver solder e.g. brazing or were not sound to begin with?

I think it would be a very difficult, if not impossible, task to strip the boiler and start again. IMHO best to bite the bullet and build a new boiler from scratch.

John