Problem with silver brazing

It sounds like the heat from the first joint is oxidizing the metal of the second joint. Try these things: 1) less heat on the first joint. Play the torch carefully, heating just long and hard enough to make a good joint.

Fred Splittgerber wrote: (clip) when I heat the second site and apply my L-Ag40Cd, is that the silver forms a little ball and does not want to flow into the gap. I'd appreciate any ideas and/or suggestions. (clip) ^^^^^^^^^^^^ I can think of two possible causes. 1.) While you are completing the first joint, the heat causes some oxidation at the second joint, which you are not cleaning away completely. 2. You may be afraid of using too much heat, which could cause you to lose the first joint, while completing the second one.

I suggest that you clean and flux both joints at the same time, and play the torch over the pair at the same time. When you reach the flow temperature of the silver solder at both joints they should both flow by capillary action. Sometimes it helps to hammer the solder flat (if it is round) and place a little coupon of solder in the joint, along with the flux, prior to heating.

Because of the high thermal conductivity of the copper, you could probably run both joints at the same time. I am unfamiliar with the flux part number, but I would simply use a borax type flux, fluxing both joints at the same time.

You say that you clean off the second joint before brazing it, does it become very oxidized during the first one? If so then that's probably your trouble. Find a way to fixture your copper horseshoe to the longer piece, flux and run both joints in the same operation.

For small pieces like this it is vital to not blow the flux off the metal by overheating it, or using too large a flame velocity. Better to use a larger tip and a softer flame. But key is to keep the film of molten flux continous over the entire part at all times.

Jim

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Thanks, Jim and Leo. I just tried making the second joint with a bigger torch ("turbo torch"), and everything worked fine. The only problem is that that torch has way too big a flame; guess I will have to find a more suitable compromise. It appears that the whole contrapture (after completing the first joint) dissipates too much heat for the sesond site to get up to proper temperature. Thanks again for your suggestions. Fred

Oftimes with small stuff you really want to jig it up and do the whole job at one shot. There are several alternatives to doing a job like this. I've been there with small parts and soldering - imagine a part that is no more than

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

Thanks, Bob and Jim.

"jim rozen" wrote in news: snipped-for-privacy@drn.newsguy.com

It sure does.

Currently, I am using a custom contrapture of alligator clips to secure the pieces in place. Any better suggestions?

All the best, Fred

I'm not sure of your setup. I use a Little Torch with Mapp and Oxygen and a #5 tip. I use Harris Stay-Silv5 which contains 5% silver, and about 94% Copper and 1 % phosphorus in small size rod(1/6"). The phosphorus acts in lieu of flux. I braze copper wire, tubing and sheet in about the size you are using with no real problems and I'm no pro by any stretch. See some of my piddlin' at:

"Lawrence L'Hote" wrote in news:VBQXb.320887$xy6.1553625@attbi_s02

Hi Larry, Pretty neat toy to have - my brazing setup consists of a simple propane/butane (no extra oxygen) torch (2 tip sizes). The small tip simply does not deliver enough energy for the job, the big one delivers too much. Well, an in-between may be available (I live in Germany, and it may take a trip to a welding supply place to find just the right size).

What a nice website! Fred

That probably works pretty well. Another way I would consider doing it is to clamp the pieces down to a stainless sheet, with small screws and a strap of stainless to hold down the horseshoe.

If you set it up so there's a gap or a cutaway under the region where you want the joints to occur, this will give you a solid fixturing. The stainless is nice because with its low thermal conductivity it won't pull the heat away from your copper wire.

Be sure to keep plenty of flux on the joints - I typically view jobs like this as a) flux the hell out of it, b) flow the flux gently with the torch to get it to wet, c) repeat a) above, and then finally bring it up to temp to actually run the joint.

Jim

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Fred Splittgerber wrote: (clip)The small tip simply does not deliver enough energy for the job, the big one delivers too much.(clip) ^^^^^^^^^^^ I suggest you try preparing both joints, and then apply the heat using the "too large" tip--keep it moving across both joints, and back the torch away as much as necessary to keep the temperature under control. Silver soldering likes the heat to be spread out--different from welding. That's why oven soldering and brazing work so well.

I would second using Sil-phos when brazing copper, but I prefer using the stuff with 15% silver. It cost a bit more, but I like the results better.

I agree with all the folks that say to apply flux to both of the joints before you start. Even if you do the joints one at a time, the flux on the second joint will protect it from oxidizing while you do the first. You shouldn't need the flux with the sil-phos, but it doesn't hurt.

Everything will work easier if you can get an insulating firebrick or two to rest the work on, so the heat stays around. Actually using about four bricks is even better. Two bricks flat and the other two on edge on top to from a corner to work in.

Dan

"Dan Caster" wrote in news: snipped-for-privacy@posting.google.com

I appreciate all the suggestion made in this thread. I tried brazing on a firebrick - it is quite amazing that even my small torch does the trick in this setting.

Regards, Fred