By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Silver soldering problems

All Topics | Latest Posts

Search for:  in Thread Title in  
Mark B16/11/2013 16:54:34
71 forum posts
36 photos

I've never silver soldered before and my aim is to make a boiler for a 1" Minnie traction engine...

I've done lots of plumbing soldering before without any issues, so I thought I'd practice on a few bits of copper. The idea was to silver solder with some SF24 and then add to it with some SF55.

Starting with the SF24 soldering, I cleaned everything up, mixed up some Tenacity 5 with clean water and a spot of washing up liquid.

I then liberally applied flux over the point with plenty of overlap. Heated it up and tried to apply solder... it melts, but doesn't really flow very well... continue heating still doesn't flow...continue heating everyone goes black!

So I cleaned it up in sulphuric acid and the results are not that good!

Next I thought I'd try adding to the copper by adding on some more with SF55. Went through the same process and I achieved what looks to me like a good mint with flowing solder as I'd expect.

I've tried on some more scrap copper, but I just cannot get my SF24 to flow to make a good point. It melts, but doesn't flow...

Can anyone point out what I'm doing wrong? There is no way I'm going to make a decent boiler.

Here are my results:

SF55 end (I think this is okay)

SF24 end (what a disaster!)

 

 

Edited By Mark B on 16/11/2013 16:56:29

JasonB16/11/2013 16:57:36
avatar
Moderator
21632 forum posts
2493 photos
1 articles

What are you using to heat the parts, if the torch does not have the power to heat the base metal you will end up just melting blobs of solder onto the surface.

J

Mark B16/11/2013 17:07:49
71 forum posts
36 photos

I'm using a Sievert 3941 burner. It's only a small bit of copper. The photographs are of 28mm copper tube which I'm practicing with.

Gary Wooding16/11/2013 17:20:46
909 forum posts
233 photos

To solder (braze) successfully it helps to understand how it works.
Soldering refers to the process whereby pieces of metal are joined by melting another metal (the solder) so that it wets the joint and holds it securely when it freezes. That's basically it, but there are a few "gotcha's".

The important word is "wets". It's just like water. Put a nice clean pipe in water and freeze it; it's then difficult to get the pipe out, but use an oily pipe and it's much easier. The difference is that the water wetted the clean pipe, but couldn't wet the oily one. If the pipe wasn't oily but dirty, the effect would be the same. Solder works in exactly the same way. So all you have to do is make sure the joint is nice and clean and you'll get a good joint, right? Well, no, it's a little more complicated than that, but not a lot.

To melt the solder you have to heat it up. The trouble is that the very act of heating it also makes it dirty. The oxygen in the air is only too eager to oxidise everything it touches, and, as far as solder is concerned, metal oxide is dirt. Most metals oxidise rather slowly at room temperature, but heat them up and the effect is very rapid - so rapid as to make soldering impossible, unless you prevent the oxygen from reaching the hot joint.
There are only three ways to do this: solder in a vacuum, solder in an atmosphere devoid of oxygen, or coat the joint with an oxygen barrier that can withstand the heat. The first two options are rather impractical, but the third is fine; the barrier is called a flux. The job of the flux is to cover the joint with a barrier to stop the oxygen from oxidising it. Resin is a good flux for soft solders, and borax for hard solders or brazing. If the joint and the solder are nice and clean then these fluxes work rather well, but that's all they do; they are known as inactive fluxes. If the joint is a little dirty these simple fluxes do nothing except act as a barrier, but there are others that can do a small amount of cleaning too. Baker's Fluid is one such active flux for soft solder and EasyFlo is one for hard solder. The active fluxes are certainly better than the inactive ones, but they are not magic, you shouldn't rely on them to do the cleaning for you. Active fluxes usually contain some rather toxic and dangerous additives (potassium biflouride?) which do the cleaning bit.

So, now you have a nice clean joint and a flux, so it's plain sailing, yes? Well almost. Most problems are caused by heating the solder rather than the joint. All that happens is that the solder melts, goes into a ball, and refuses to flow into the joint because it freezes before it can wet it. The secret is to heat the joint, not the solder. When the joint gets hot enough it will melt the solder which will then flow nicely into the clean, fluxed joint. The final thing that can go wrong is to burn the flux. If you heat the flux for too long, longer than a minute or so, it will lose its properties and allow the oxygen to pass. This is normally the result of insufficient heat, so if it happens, remove the heat, clean the joint, and start over, perhaps with a better source of heat, or better insulation to prevent the heat from leaking away. If you can't get the joint up to temperature with adequate insulation then you need a greater quantity of heat - ie. a bigger flame. Your photos show that you aren't using enough heat to get the boiler hot enough to melt the solder.

So, the four main points for a good soldered joint are:

1. Make sure the joint and solder are both clean.
2. Use a good appropriate flux.
3. Heat the joint not the solder.
4. Complete the joint quickly.

I hope this helps.

Gary

Keith Hale16/11/2013 17:59:30
avatar
329 forum posts
1 photos

Hiya Mark

Try this **LINK**

This will more than point you in the right direction.

regards

keith

Edited By CuP Alloys 1 on 16/11/2013 18:02:02

Stub Mandrel16/11/2013 18:44:04
avatar
4311 forum posts
291 photos
1 articles

And doesn't just liberally apply flux over the joint, try to get some IN the joint, ideally before assembly.

Neil

julian atkins16/11/2013 23:02:14
avatar
1244 forum posts
353 photos

hi mark,

if you have a look at my albums you can see the first few stages of a boiler ive brazed up with silverflo 24. you need to get the copper very very hot for silverflo 24! sort of glowing bright pink as it melts at 740 degrees celcius. silverflo 55 is only 630 degrees celsius. tenacity 5 is the wrong flux - you should use tenacity 4A or thescco F flux.

my personal view is that until you have mastered silversoldering you are better off doing the whole boiler in silverflo 55. as long as you flux up previously done joints there shouldnt be a problem given careful thought to how various stages are heated up. my first loco boiler was done throughout in easyflo 2 many many years ago.

cheers,

julian

John McNamara16/11/2013 23:15:40
avatar
1328 forum posts
122 photos

Well put Gary wooding

A good explanation, I have never built a boiler, and my silver soldering is rather basic. Your explanation will improve my work.

Regards
John

Edited By John McNamara on 16/11/2013 23:16:14

julian atkins16/11/2013 23:38:37
avatar
1244 forum posts
353 photos

if i may add a few words to gary's advice, easflo flux is really working at it's optimum limit for silverflo 55 and for boiler work a more active and longer lasting flux is required. easyflo flux is ok for very quick heat ups in non ferrous stuff with easyflo 2 and easyflo (neither of which are now obtainable for the amateur in the UK). gary didnt mention gap between work. for silverflo 55 this should be 2 to 4 thou max. i run a 2 thou feeler gauge round all joints. for silverflo 24 a different technique is required as it forms a fillet and the heat required makes application of the silver solder somewhat difficult and uncomfortable if there is heat throw back from the brazing furnace. i wouldnt advise a tyro or beginner to use silverflo 24. i was advised many years ago by alec farmer of Reeves fame to use thessco F for boiler work which is what ive used eversince. it is ok and active for silverflo 24 but you do need to really whack the propane heat up to try and do the job without the heat up taking too long. 15 mins start to finish is quite ok.

cheers,

julian

Edited By julian atkins on 16/11/2013 23:40:01

Edited By julian atkins on 17/11/2013 00:10:12

Keith Hale17/11/2013 07:08:33
avatar
329 forum posts
1 photos
Posted by CuP Alloys 1 on 16/11/2013 17:59:30:

Hiya Mark

Try this **LINK**

Successful silver soldering explained. It covers joint design, fluxing, heating techniques and alloy application. It includes a video clip.

This will more than point you in the right direction.

regards

keith

Edited By CuP Alloys 1 on 16/11/2013 18:02:02

FMES17/11/2013 12:32:05
607 forum posts
2 photos

Personal view only, it doesn't look clean enough to me, and I guess the heat has been applied to the rod rather than the copper.

If the flux goes black, you have either burnt it or the job just isn't clean enough.

I will normally pickle in Sulphuric Acid after first gently warming the components, not too hot or the fumes get a bit overpowering, and then wash off under water.

I'll repeat this until the copper is a peachy colour all over, and then apply the flux mixed with water and a little meths which helps to further degrease the surface without leaving a residue when you heat it.

The heat is initially applied away from the area to be soldered using some good firebricks to give some reflected heat on to the job.

The flux should dry, and then form a clear liquid, at this point it is just about time to apply the ss rod, if its hot enough and clean enough the solder will readily run into the joint and flash into any gaps.

If the flux goes black, stop, and repeat the pickling process.

The hotter you can get the job before pickling helps to clean it better but watch the fumes.

When the soldering is completed, allow to cool and pickle and wash again. If further soldering operations are required apply more flux straight away, but this is only for protection and should be washed off, repickled and reapplied so that its fresh.

Hope this helps.

Mark B17/11/2013 21:06:23
71 forum posts
36 photos

Thanks all for you advise so far - this is all most helpful. I had another go this afternoon with more heat. I used a bigger burner and the copper got cherry red, but the results were not that much better. I think this is only part of my problem. From what I've picked up so far I think I also need to consider:

- The consistency of my flux mix. I might be a bit thin and hence I've not got enough flux applied.

- Maybe my cleaning isn't good enough. I've been cleaning up with wet and dry paper and pre-cleaning in washing up liquid - and rinsing off in hot water. However sounds like I should dip in acid too.

I'm really glad I've not started on my boiler, but only practiced on old copper pipe first. SF24 soldering is most unforgiving (SF55 just worked).

I'll report back on what happens.

julian atkins17/11/2013 22:22:05
avatar
1244 forum posts
353 photos

hi mark,

cherry red isnt hot enough for silverflo 24 plus you need to use the right flux. tenacity 5 is for stainless steel. you need tenacity 4A

cheers,

julian

Mark B18/11/2013 08:53:00
71 forum posts
36 photos

I guess the wrong flux isn't going to help matters! I really hope this is the issue as silver soldering can't be that difficult.

I'm going to talk to my "knowledgeable" supplier who sold me the Tenacity 5.

So to be correct for SF24 I should use Tenacity 4a, and for SF55 will 4a be okay?

For the time being I'll think I'll hold off with my experiments as all I'm doing is wasting expensive materials.

Thanks

Mark

julian atkins18/11/2013 10:20:26
avatar
1244 forum posts
353 photos

hi mark,

yes, plus keep the silverfo 24 in stock for when you have really mastered silver soldering, as it takes a lot of heat (far more than silverflo 55) and skill to use. use silverflo 55 instead.

cheers,

julian

Speedy Builder518/11/2013 12:30:49
2447 forum posts
195 photos

Hi Mark, I have been using silver solder since I was an apprentice some um..... years ago, when easyFlo came my way for free. It was not until last year that I started to have any problems as it was the first time I was s/soldering heavy gauge copper. Copper (unlike steel, s/steel or brass) EATS HEAT like nothing else - Its a good conductor of heat and so it is essential to heat either side of the joint first and then start to concentrate on the joint itself. Use plenty of hearth bricks to both retain and reflect the heat back onto the component. Just for an experiment, silver solder a fitting onto some 15mm copper pipe and see just how your SF55 flows. You will only need a dab of solder. If you have the right flux and temperature I am sure you will see a nice fillet being formed. Good luck.

Bob H

JasonB18/11/2013 12:53:43
avatar
Moderator
21632 forum posts
2493 photos
1 articles

Your Tenacity 5 should be fine for copper, I use it for any jobs where I will have longer heating time. JM say its OK for copper.

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

 

Flux should be a thick paste

Don't clean with emery or wet & dry, pickle and wire brush is better

Edited By JasonB on 18/11/2013 12:54:50

shaun meakin 118/11/2013 16:19:38
avatar
58 forum posts
1 photos

HI Mark, some really good advice here. The guys are right, your problems seem to be twofold, using the wrong flux and not enough heat. Tenacity5 (or as I prefer HT5!!) is fine for the high temperature alloys and indeed will work with the low temperature but as the residues are quite corrosive please ensure you clean as much off after brazing. Do not use wet and dry as this can leave residues that the flux cannot remove. The joint area doesn't have to be really, really bright and clean, as long as there is no oil or grease the flux will sort out the rest. Ensure you have plenty of flux all around the joint area. if you are mixing a paste as it seems it should have the consistency of a thick yogurt. The 3941 burner isn't producing enough heat especially for the sf24 (or, again as I prefer 424 - sorry guys for the plugs!!). Try a 2941. The rest is as per the excellent advice given above, particularly from Gary but also the links to CuP Alloys' hints and tips as posted by keith. Especially, as we always say, 'heat the joint, not the rod'!

fizzy20/11/2013 18:48:51
avatar
1825 forum posts
120 photos

I know ive posted this before but the HT5 flux doesnt seem to allow the SS to flow anywhere near as well as SF. I use this to my advantage!

oldvelo21/11/2013 04:32:36
277 forum posts
54 photos

Here Goes I'll stick my Totally Biased Opinion on good Brazing-Silver Soldering technique.

All advice offered so far is good practice.
The bit that I would like to add is that you use the flame and hot gas stream to protect the area of molten metal at all times by NOT flicking the flame sideways on and off the area to be Joined!!!
Move the Torch closer or further away from the joint keeping the flame on the area you are working on this will allow you to control the temprature of the molten puddle from liquid to solid.
The Enemy of molten Silver Solder is AIR.
Whatever source of heating is used it is the hot and almost inert gas that is the flame and hot gas stream that will protect the puddle.

Eric


All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Warco
cowells
emcomachinetools
Eccentric July 5 2018
rapid Direct
JD Metals
walker midge
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest