Silver soldering

[Real silver solder (also called hard, or jeweler's solder) is difficult to use for copper joints. Everything must be really clean, and things have to fit exactly. This type of solder has very little ability to fill gaps. There are some solders that contain small amounts of silver ("silver bearing" solder -it might be called something else in the UK) which melt at lower temperatures and do a better job with gaps, but they aren't as strong. For most copper-to-copper joints, I prefer phos-copper rods. They are typically flattened rather than round in cross-section, and fill gaps well. Use them with an air-acetylene torch. This only requires one small acetylene cylinder (we call them "B-tanks" over here) and no oxygen - the torch entrains air by the Venturi principle. I'm not up on UK suppliers, but you should be able to find the torches and rod wherever plumbers go for supplies - this system is generally used for assembling copper pipes and fittings.]

Andrew Werby

Craig,

The best choice for Silver Soldering/Braising is a propane torch. Stay away from Oxy/Acet, you can do it with Oxy/Acet but it's MUCH easier with propane. The propane torchs burn cooler but generates plenty of BTU's to get the job done. There are 2 major players in the 'weed burner' market (slang for these types of torchs) Sievert and Goss. Sievert is a Swedish company with offices world wide, and is the big name in the game. Goss is a good-ole-'merican company.

--.- Dave

there's a bunch here:

Yep, they're in the UK Mike in BC

Obtain some so called "silver-bearing solder". It is usu. marked as 4 or 6 % silver and 96 or 94% tin. This solder is readily melted with ordinary propane tarches. Use acid flux (liquid) ordinarily sold as dilute hydrochloric acid. Joints made with this solder and flux are fairly strong, with tensile strengths usu. as good as the base metal (that is, copper, brass, etc). An advantage of silver bearing solder is the comparitivley low melting temperature. The temp. is low enough, around 1000 to 1300 deg., such that it is not apt to cause warping.

Another class of silver solder has much higher silver content, melts at a higher temperature and rquires a different flux, generally called "white flux". Various silver solders of this type are available - Harris EasyFlow

45 is one of the most popular. It flows freely (contains some Cadmium) and has 45% silver, thus it is expensive. Experienced model makers generally tend to recommend EasyFlow 45.

Do a Google and you will be inundated with information.

I've never had much luck with air/propane on anything other than tiny pieces. I would actually recomend O/A for anthing larger than about one cubic inch of material.

Jim

I use a propane torch for silver brazing. There are a few times when I use more than one of those hand held torches with the small attached tank, but usually using some insulating firebrick will confine the heat enough.

For copper try using what is referred to as Sil-phos. It is a copper alloy with some silver and phosphorus. I have the best results with the 15% silver. No flux is needed. It makes a strong joint and comes close to matching the copper in color.

You might google for info on a hi-heat torch. It is a propane compressed air and is suppose to be really good. I have not personally seen one. Runs about 40 to 50 USD.

I am currently contemplating building the smallest propane torch described in "Gas Burners for forges, furnaces and Kilns ' by M. Porter. Check Amazon for a longer description of the book. The torch might be exactly what you are looking for. Probably big enough for Jim to recommend for two or three cubic inches of material.

Dan

Oxy/propane works well. I've not used much acetylene since trying out propane. The lower heat is an inconvenience sometimes, but usually not too big a deal.

buckshot

Agreed, Jim! O/A is the way to go for silver soldering. You may have to "tailor" the flame a bit and keep it moving on small parts, but the technique is easily learned.

In compliment to Andrew Werby's good suggestions for heat, have a look at Harris Blockade.

lower temp than silversolder, good "build" on copper, excellent strength.

I think Harris products are available in the UK. Dang, I could have brought you a couple of sticks this trip. Next trip in August, let me know....

You can get a Sievert/Goss porpane/air torch that will make the biggest O/A rosebud you have look like a joke as far as BTU/s go. I've done silver braising work with both O/A and propane and I'd take the propane any day. Theses ain't some wimpy 'Bernz-o-matic' thingies on the end of a can you hold in your hand,. Were talking serious torch here, I've seen some of these 'weed burners' with 6 inch bell that will put out some serious heat. The trouble with O/A is it's way too hot but dosen't have the BTU's.

I certianly agree with Dan on the sil-phos approch to copper. I build copper boilers for 1/8 scale live steam. Were talking serious copper here, 6 or 8 inch Schedule 40, 4 or 5 feet long, with 20+ 3/4 inch flues and 10 pounds of copper bar in the mud ring, theres a LOT of mass to keep hot.. My local welding supply house has a Uniweld product UNI-1000 that I use. Same deal as Sil-phos, 0% silver, %7Phosphorus, %93 Copper.. The stuff is magic on Copper, no flux, runs like water at 1470 deg.. Works on close joints too (.001 inch). The nice thing is after the first hydro, when you find the leaks, you don't have to pickle and flux it, ya just heat it up again and go in with the rod. I've also done traditional Silver braising work building up 'weldmenst' out of brass or steal for things like cylinders etc using high content silver %65-%75.. stick with the Propane, you'll be happier in the long run.

Dave

The 45% stuff melts at 1200-1300 range, while the 4-6 percent stuff melts around 430F.

There's a solder paste called "solder-it" that comes in a syringe and is FAR stronger than any of the Radio Shack junk I've tried to use in the past. Can't comment on Lead content. Flux seems to work nicely on ferrous, copper, brass... /mark

Robert Sw> Obtain some so called "silver-bearing solder". It is usu. marked as 4 or 6

I have to disagree with you here. I've used air/propane, air/MAPP, air/acetylene and oxy/acetylene for silver brazing. Anything but oxy/acetylene takes far too long to heat up the work and creates heavy scale. Not want's wanted on finished surfaces like with guns(most of what I do). With O/A, it frequently takes more gas to purge the hoses than it does to get the job done. Last ramp I did took like about 5 seconds to fuse and join. I talked with a process engineer for one of the major A/C manufacturers, they use O/A for a lot of their silver brazing needs, if something cheaper would work, they'd be using it. They use a lot of furnace and induction brazing, too, but O/A is used for tubing joints, manifolds and the like. With O/A, you can use any of the brazing filler alloys, with propane, you're very limited. The good stuff all melts at a higher temperature than what can be achieved with air/propane or even air/MAPP. Look at a properties sheet from one of the major brazing alloy suppliers.

Stan

My experience with any torch that runs on air is that there's a lot of nitrogen along for the ride, and it winds up flowing a *lot* of gas to get the fuel/air mix right. And this tends to blow away the flux.

Leaks? What are those?

:)

you don't have to pickle and flux it, ya just heat it up again and go

Obviously you are doing *big* stuff - and have found the tool that works best for the job, namely getting a big part up to temperature. For small work that I hand-flux, I like the OA torch. No pickling required because once the borax flux comes off, it's pretty clean.

Jim

Mark sez:

" The 45% stuff melts at 1200-1300 range, while the 4-6 percent stuff melts around 430F."

Yep, 430F is the temperature usu. given in the charts for silver-bearing solder. O/A can be used on the 4-6% stuff, if you are careful. Example: My 20+ years old ring had shrunk on my finger. I opened it up the requisite amount and then silver-soldered in an appropriate piece of same gold content cut from junk jewelry. I used a #1 Victor tip for this because that was the smallest I had. The only trouble was lighting the small, low pressure, flame - open flame worked much better than sparky. It worked very well to illustrate using a tool well outside of design specs. Mainly, I wanted to see if I could do it.

Certainly, it would have been a lot easier to use one of the jeweler's sized tips - Harris Lil' Torch kit probably as recommended by Uncle Don Foreman.

Bob Swinney

I have managed to silver solder (45% silver) using a mapp turbo torch. I have also tried a Sievert and it was ok for very small items but my torch heads were on the small side.

A good reference is that you have to get the part to red color. If your torch can't do that in a reasonable time, you need more heat.

contrary to what someone else said, silver solder will fill small gaps but optimum gap is just a couple thousands of an inch. It depends greatly on how much heat you have. Very hot and its very thin. cool it down to just above melting and you can create fillets too.

chuck

Use a MAPP gas torch. It's just like a propane torch, but much hotter. They're available in just about every hardware store.

It's sold specifically for applications like you describe. I use mine to both silver solder and do light brazing. (I also own an oxy/acetylene outfit, but it's kind of an overkill for small jobs.)

Harry C.

I think people have different choices of fuel gasses because they are doing different sorts of work. Putting a ramp on a gun is different from making a boiler. For one you want to get a lot of heat in a small area quickly so the whole gun does not heat up. For a boiler you want to get a pretty big thing hot maybe with a particular area a bit hotter than the rest.

For the A/C manufacturer the speed of O/A saves time and therefore money. If it costs say $60 an hour to pay salary, benefits, shop overhead etc, you save money by spending a bit more on fuel and oxygen.

But I disagree that air/propane isn't hot enough for any silver brazing. According to the " Brazing Handbook " put out by the AWS, BAg23 has the highest brazing temp and it is 970 to 1038 C. That is possible with air/propane. Just not if the heat is escaping.

Dan

Good summary, Dan. Different tools and techniques for different jobs.