Silver soldering question

[benchmark]

Til now i have always used tin solder to do my small boiler work.
As my boiler projects get bigger i decided to get some silver solder and use that instead. After watching numerous instructional videos on youtube and reading DIY guides on the net i tried it a couple of times yesterday with poor results.

The flux just gets brown then burns away into a crust without liquifying. From what i have read the flux should liquify to clear flowing fluid indication its time to apply the silver solder. this does not happen i my case .
I have tried on both copper and brass with same disappointing results, could it be that the surfaces need to be cleaned more thoroughly?


I am using this flux and solder (it is specified for model making)
http://cgi.ebay.co.uk/Silver-Solder-1-5mm-Flux-Kit-Brazing-Model-engineer-/360334888469?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item53e5a20e15

and i use a handheld propane/buthane torch

[Gerhard Olivier]

Sorry can help, but is very interested in the answer as I have a fair bit of silver soldering that I need to do and dont want to buy the wrong stuff.

Any help here would be appreciated by me also.

Gerhard

[PTsideshow]

Can't help with the solder or flux as, I'm on the other side of the pond. I will say that the material to be joined has to be CLEAN, CLEAN, CLEAN. Yes really clean and at the proper temperature for it to flow.

The other thing is it isn't soldering, it is  silver brazing at these temps. So soldering techniques don't work well.

You can use a pickle to clean the parts, rinsing and then dry before soldering,  pool reducer Ph down works good and is cheaper than the Sparex brand. Citrus acid also works, keep finger/skin oils off the parts.

The proper temperature is a must along with keeping the flame tip ahead of the solder. Heating the materials and drawing the solder to the joint. And not overheating the solder or joint.
The 5 most common jewelry alloys have a flow point from 618'C to 809'C  1145'F to 1490'F

With flux at times less is more. The speed at which you move the torch and the distance the tip is away from the join are things that come with practice. the type of metal, the size and thickness all will play a role. The solder also must be clean.

For jewelry/art metal work the paste fluxes which are a lighter weight, and start out either as a petroleum jelly based with borax added, it also can be a mixture of boric acid and gum tragacanth with a little water to form a paste.

And the solders are different in their alloys and flow temperatures, in jewelry the use of easy, medium, and hard solders. Which refer to the melting and flow temps, so complex constructions can be assembled with out previous solder joints coming apart.

The nice thing about the jewelry silver solder is the sheet version can be cut and placed at the join to minimize the excess and to control flow. It is available at any jewelry supply house locally or on the net.

For small scale work it does a great job.

You will have to check on the gas you are using in your torch, for the general temp it hits you will want it to be above the flow point of your solder.

The other thing to remember is that copper and brass are heat sinks and require more input of heat to do the job.

They have a new generation of torches that will raise the temp with propane to high enough temps to silver solder. EZ torch brand is an in house jewelry supply brand here in the states.


This is one, it is sold under the brand of Shark,


This is the other common use torch for silver soldering, whether AC & heating, or silversmithing.
This is an air/acetylene version generically called a prest-o-lite torch

Here is one of the largest producers of brazing wire etc. this is their knowledge base, section be sure to read the brazing book

Hope this helps

[Bernd]

Sounds like you aiming the flame right at the flux. Try heating the metal around the flux to a dull red. The flux should start to turn on you and get clear. Apply silver solder and remove heat. Try that on a couple of prcatice pieces. Remember heat the metal not the flux. Let the metal heat the flux.

Hope this helped some.

Bernd

[sorveltaja]

Benchmark, it sounds like you have used wrong kind of flux, despite the product's description.

What you described about that flux, how it gets brown and burns away, reminds me of soft soldering flux.

I have used two different brands of silver soldering flux, one works really well, but with another I just can't get good results. Don't know why .

So there seems to be differences even between silver soldering flux brands.

One, that has worked for me is Felder's "CUFE Nr. 1".

Better yet, if you can find silver soldering rods, that are coated with flux. Those, that I have used, are yellow coloured, and look quite thick, but inside the flux coat is 1.5mm rod. Works like a treat. There is some specific name/brand for flux coated soldering rods, but I can't remember what it was .

Unfortunately it takes sometimes trial and error to find a working combination, when beginning that silver soldering thing.
But when found, silver soldering could be even easier, than soft soldering.

[Bluechip]

Hi Benchmark

Some info here, see topics, down left hand side


http://www.cupalloys.co.uk/

Dave BC

[HS93]

Hopw big is the Boiler , it sounds like you are taking to long getting it hot with to small a flame, I would only use that torch on a mamod sized boiler and then I would proberley want a bit more heat to get it flowing.

peter

[andyf]

Hi Benchmark,

I tried silver soldering some steel items with a butane/propane torch like yours. I had to put my items on the gas kitchen stove and heat them with that from below and with the torch from above top to get things hot enough. So I took advice: http://madmodder.net/index.php?topic=3904.0 and now have one of the propane sets which John Bogstandard recommended. This works much better, and the trigger on the side of the torch is very convenient - releasing it drops the flame to a pilot light.

Andy

[benchmark]

Thanks for the responses guys,

Sounds like you aiming the flame right at the flux. Try heating the metal around the flux to a dull red. The flux should start to turn on you and get clear. Apply silver solder and remove heat. Try that on a couple of prcatice pieces. Remember heat the metal not the flux. Let the metal heat the flux.

Hope this helped some.

Bernd

I did exactly that and when it didnt work i tried with the flame directly on the flux, that didnt work either 

it sounds like you have used wrong kind of flux, despite the product's description.

What you described about that flux, how it gets brown and burns away, reminds me of soft soldering flux.

i thought of that too and have now ordered new flux and silver solder rods in a kit from Germany this time but i would have assumed that the one i bought from the UK should have been good stuff since it too came as a kit and from a renown model engineering shop who had it on sale on ebay.

Some info here, see topics, down left hand side


http://www.cupalloys.co.uk/

Thanks, i will read that too .

Hopw big is the Boiler , it sounds like you are taking to long getting it hot with to small a flame, I would only use that torch on a mamod sized boiler and then I would proberley want a bit more heat to get it flowing.

The boiler is a Tubal cain size, much smaller than a mamod TE boiler.

I tried silver soldering some steel items with a butane/propane torch like yours. I had to put my items on the gas kitchen stove and heat them with that from below and with the torch from above top to get things hot enough. So I took advice: http://madmodder.net/index.php?topic=3904.0 and now have one of the propane sets which John Bogstandard recommended. This works much better, and the trigger on the side of the torch is very convenient - releasing it drops the flame to a pilot light.

i may just buy myself a new torch like the pictures above but just for fun i tried heating the silver solder directly and it melts so this should be a sign that my torch it hot enough, correct?

[Jasonb]

If you have been supplied the easyflow flux shown in the e-bay page then its the right flux. Did you mix the powder with water? it needs making into a stiff past and applying to a well cleaned surface.

Its more than likely the blow lamp you have is not getting the heat into the matal fast enough and you are eventually exhausting the flux. You really want a separate propane cylinder of at least 3.9kg size with a torch that has a 25mm burner, something like this

The stick of solder will melt long before the work reaches a suitable temp for the solder to actually flow, try heating in a room that is not too brightly lit, the work should be glowing dark red, if its not you are not getting it hot enough

Jason

[benchmark]

I will give it a second shot in a darker room, thanks.

[Dean W]

Hopw big is the Boiler , it sounds like you are taking to long getting it hot with to small a flame, I would only use that torch on a mamod sized boiler and then I would proberley want a bit more heat to get it flowing.
peter

Hi Kenneth;
I think Peter may be on the right track.  The flux description in the ebay sale looks right for a proper brazing flux, which is what you need.  I don't know for sure though, since we don't have that brand here.  If Bogs or Stew come in, they can tell you the exact name of the flux you need, just so you can be sure of having the right thing.

If it takes the torch a very long time to heat your boiler, the flux may be pooping out before it gets a chance to flow the silver.  It takes more heat than you would think, since copper alloys draw the heat away so fast.  You don't always need so much of a higher temperature flame, but a larger volume of heat.  In other words, a larger burner.

Good luck with this, and hope you get it sorted out!

Dean

[Jasonb]

Dean I have already said that the Easyflow flux shown will be fine provided that is what has been supplied, I use it myself

J

[Stilldrillin]

Kenneth.
I too have the Maccmodels pack. 

First time ever was a (just) failure. 

Cleaned up. Tried again. With more heat....... Perfect! 

Not needed silver solder/ brazing since. 



 "Good `ere, innit!" 

David D

[cidrontmg]

Having done some silver soldering, I noticed some points that don't seem right.
First, that blow lamp seems far too small to do what you are attempting (soldering a boiler). It will be good for very small things, jewelry size.
Lack of heat is the most likely cause why your flux won't turn watery. If you are used to soft soldering, silver needs a completely different "attitude" to heating the workpiece(s). The workpiece(s) must be glowing dull, otherwise no go. And if they are copper, brass, bronze, they must be glowing at least some 1-2 cm away from the intended seam also. To get enough heat to even a small boiler will need a huge torch, if you donīt build yourself some sort of a brazing hearth. It doesnīt need to be anything fancy, one of mine is here. It's just 3 1/2 fire bricks. I have a bigger one, but it is seldom used. The hearth should not be bigger than needed to keep the workpieces "inside". It is rather essential for everything except very small things - so small that the flame is big enough to completely engulf the workpiece. Anything bigger will need the heat to be constrained somehow, or else you will need an enormous torch (maybe even two or three), and you'll risk setting the whole shop afire...


Thereīs also a drill press vise in the hearth to keep the workpiece in place (if needed). The vise is not used for anything else. For a pillar drill, it was rather ridiculous, but here it serves all OK.
For heat, I have a 14 kg gas bottle, with a Sievert burner, with various sizes of nozzles. And I also have a blow lamp similar to yours, for very small jobs  
When you are silver soldering, the idea is to heat the clean workpieces quickly, so they won't have time to oxidize. First, warm it slowly until the (possible) water in the flux has evaporated, and then let go full blast. The workpiece should begin to glow in far less than 5 minutes, if it doesn't, there's not enough heat capacity in the burner. Point the flame to the biggest piece, the rest also gets heated on the side. Do not point the flame to the joint itself. When the workpiece is hot enough, the joint will also be.
Use as little solder as possible to get a completely sound joint. If you are feeding with a stick, you usually end up using way too much. If possible, put small pieces (or a loose ring, or small pallions) near the joint, and you can see when they melt, and get sucked in the joint by capillary force. When that happens, extinguish the flame, and let it cool. Do not heat it any longer than is needed.
The idea behind the "as little solder as possible" is not the price, although silver solder is far from cheap. But it is a real PITA to remove any excess solder. And if you don't remove it, it will look ugly... So if thereīs no excess to start with, will save a lot of time and swearing...
There's all sorts of tricks to make neat silver joints, and to keep it from spreading all over. Also the flux will tarnish the workpieces, so don't spread it all around the place. Liberally to just where it is needed, no more. But you will learn best by doing. It's not difficult at all, IMHO it's a lot easier than soft soldering, which I've also done quite a bit.
 

[Ned Ludd]

Hi Guys,
If the burner is too small, could it be that the flux is exhausted (time thing not a heat one) before it has had a chance to do its job. If so perhaps a change to Tenacity flux instead of Easiflo might help, once a bigger burner is obtained.
As another guide to the right heat, if the rod does not melt and "flash" as soon as you put it to the joint, it is not hot enough. As has been said, it takes an awful lot of heat to solder a boiler, even a small one.
Ned

[benchmark]

I will be going shopping for burners and will look for a good propane burner or i may even get an oxy acetylene burner that oozes over 1000 degrees centigrade of heat.

[Jasonb]

Be carful with oxy acetylene it is a very localised heat and you may not get good penitration also its easy to burn through the copper.

Jason

[Bogstandard]

Benchmark,

The silver solder you have is ok, but lay it down as pallions or circles around the joint rather than trying to feed by hand.

Your main stumbling block is your flux. The latest, Tenacity 5, designed for prolonged heating times, is what you really require, and don't use too much, just enough to cover both joint faces is plenty. Other fluxes will exhaust their cleaning properties well before you have the job up to solder flowing temperature, just like the one you are using now.

Two points about the heat source, don't use oxy/acet unless you can control it like a real professional, get a good sized propane burner, around 3/4" to 1" will be fine for smallish boilers. We made Stews boiler for his 3.5" loco with two burners, one at 3/4" and the larger background one was somewhere around 1.25".
NEVER point the heat source directly at the flux or solder. Play it onto the metal around or under the joint, when the job gets up to temperature, the solder will flow by itself towards the point of highest heat, it is then you can come in with your hand fed rod and fill in any gaps that are left.

Once you have mastered the technique, you should never have any more problems.


Bogs

[cidrontmg]

There's maybe some confusion about heat capacity and temperature. They are not the same thing. A lit match will have quite a high temperature at its "sweet spot", certainly far over 1.000 ^oC. It will actually melt iron - if the iron "lump" is  small enough. Test with a strand of 000# steel wool and see for yourself. But the heat capacity of a match flame is not much to write home about. It will not raise the temperature of one litre of water very rapidly.
The flames of small and large propane burners will attain +/- the same temperatures, but heating a litre of water to boiling will take a lot less time with a big burner. The two burners have different heat capacities.
In making a good silver solder joint, itīs not so much about temperature than about heat capacity. Most of the time the workpieces are very good heat conductors (copper, brass, bronze), that have to be constantly supplied with quite a lot of heat to keep them at a proper temperature. That is why a hearth would be needed. You will need a lot less heat capacity in the burner (meaning a lot less gas also, it's not free after all...) if you prevent the heat from escaping freely.
It is not enough to have a small spot at the tip of the flame over the melting point. That's a sure recipe for a failed silver solder joint. Itīs all OK when actually "gas welding" pieces together, or even brass brazing them. Silver solder behaves differently. It will be sucked into the (well prepared) small cavity of the joint by capillary force (yes, even somewhat "uphill"), but only if 1). the surface is clean (=well fluxed), 2). the cavity is small enough to create that capillary force, and 3). it is hot enough also farther off from the flame tip, so it will not begin to solidify. It's often said that silver solder will "follow the heat". That's very true, it does.
Using an oxy-acetylene flame for silver soldering is asking for trouble if you don't do it daily, or train a lot how to control and manipulate the small but hot flame. And it is hot, it will reach 3.500 °C (6.330 °F). It's not so much the ultimate attainable temperature that interests, as long as it is well above the solder melting point. The important thing is the heat capacity. It has to be in relation to what you are trying to solder. With oxy-acetylene, you are very likely to heat just a small spot, not the whole workpiece (and there is always more than one workpiece to heat), and that spot to far too high a temperature.
Yes, you can overheat when silver soldering, and make the joint (or even the whole attempt to do it) fail because of that. If you go over the top with the temperature, several bad things will happen. First, the oxidizing of the workpiece will be greatly accelerated, second, the flux will not work well or at all way beyond over its intended temperature range, and third, the solder, being an alloy, not pure silver, will start burning and evaporating some of its constituent metals, causing a change in its designed properties, and in 99.99% of cases for the worse. The metals in silver solder materials are rather low melting and even have low(ish) vapourizing temperatures, so blasting at silver solder with 3.500 °C, thereīs a real danger of creating some metal vapour by overheating the material(s). Zinc (in brass) will evaporate at 907 °C, even silver starts evaporating at 2.162 °C. Metal vapours are not a good thing to breathe even in small quantities.
Oxy-acetylene is certainly nice to have in a shop. But it's not my first (or even second) choice for doing silver soldering