Silver Soldering question

[prowess]

I've done a ton of welding, including a lot of Brazing, but I have only seen silver soldering done once at an O/A welding class I took about two years ago.

Here's the issue. I'm trying to build a small alcohol stove for camping (backpacking). I'm using .032 brass sheet (not super thin but not exactly hefty either), and making a round container (like a large cat food can) to hold the alcohol fuel. It must be leak proof and air tight, except for the fuel jets. We're talking a 4" round container here, 2" high so not much surface either. You basically fill the stove with denatured alcohol, light it, and when the alcohol comes to a boiling point, it vaporizes and jets out of holes you make in the top of the stove. Simple. But it will probably get around 280 or 300 degrees so you have to join the metal fairly well in order to prevent an accident. Keep in mind these stoves are made from soda cans, so the .032 brass is actually hefty compared to what most backpackers use. The issue is joining the brass, not wheter or not it's thick enough.

I've spent a whole day trying to braize the darn thing. Too thin to really get the material hot enough for the brass to flow well. You either get a a hole in your work, or you have a clump of brass sitting there. So I'm thinking Silver Solder.

I could try tigging it at a very low setting, but I think I'd rather join the brass via capillary action (a.k.a. brazing and/or soldering) rather than fusing the brass together.

Anyone ever done anything like this and have any ideas? Or can you confirm - YES, silver solder is the way to go.

Thanks!

[yorkiepap]

Hey prowess,
Yes, silver solder would be the proper method to use. Depending on the grade/composition(70/30, 60/40, 50/50), you will have to do some compensating with your flame intensity. I believe TIG would burn thru too much for the thickness you are going to use. That good 'ol O/A flame can really be controlled. I use Handi-Flux for my sil-sol applications, but your LWS can supply you good flux.
Your best results will be concentration on the heat you apply keeping in mind the thicker piece will need just a bit more heat. Be sure your metal is quite clean, gently warm the metal, and brush on the flux. As you start your heat to where the sil-sol starts to melt, you can control the puddle with the flame. Also, you gotta kinda feather the flame across the joint to allow the capillary action to take place. Then it's just adding filler as you progress & manipulating the puddle. Once you get the hang of it, it is a really superb process that will yield great results. Use a low pressure "soft" flame. I would strongly suggest some practice on some residual scrap to get the "feel" of the sil-sol. I've been doing sil-sol for many applications since '60 and never had a problem. Oh, BTW.... sil-sol is really excellent for cast iron/steel repairs. Anyway, hope this helps a bit..... If you need any more advice, just ask..... Denny

[moya034]

If I recall correctly, silver brazing alloy starts melting in the high 900's to the low 1000's F, so it should work fine for your application.

Just keep a few things in mind:

1. Cleanliness.
2. Good flux application.
3. Get the base metals hot enough.

The biggest issue people have is being impatient on the heating. That base metal has to be hot enough to melt the alloy without the flame. Always keep your flame moving. Concentrate your heat on the larger parts which will transfer their heat to the smaller parts.

Keep in mind when soldering and brazing, since these use capillary action, the molten alloy likes to follow the heat, so once your metal is at alloy melting temps, you want to move your heat to the "rear" of the joint in order to encourage an even flow of alloy.

FYI... there is a difference between silver brazing alloy and silver bearing solder. I'm assuming your question is referring to silver brazing. Any alloy that melts above 840F is brazing, and anything below is soldering. Calling silver brazing alloy silver solder is a bad habit that got started a very long time ago.

[Rocky D]

The strength in silver braze is reliant on how tight your joints are...sil braze is not strong by itself. It is also more leak prone than silicon bronze, and TIG. Tigging thin brass with sil bronze is accomplished much easier, no flux to mess with, and you can be more sure your welds won't leak. The trick is to use a large rod...3/32 or 1/8"...that way the rod takes the heat, and the bronze will melt sooner than the base metal.

[prowess]

Thanks Guys.
Really good information, as usual.

I've got enough material for some silver-braize trial. Then I'll also try Rocky's TIG suggestion. I don't use my Tigger machine often enough, so might as well give it a try. It's going to be tricky but nice practice. Leaks are key. I can't have leaking, so the Tigger may be the Ticket!

I'll keep you posted. I spent the morning trying to seal the leaks with regular flux rod brazing. Too much work for bad results. You get one leak sealed, you cause another from the heat transfer on that relatively thin brass.

More news when I finish the project. Won't be until Tuesday. Tractor Supply (at least my local T.S.C.) does not carry Silver Solder/Braze rods. Only Aluminum and Brass. My LWS won't open until Tuesday so the project is on hold till then.

Moya had a good FYI as well. We all speak of Silver Solder even when we mean silver brazing. It is a bad habit that even my LWS and Welding Instructors have fallen in to.