brazing/ soldering 304SS to 303SS

[yantra3d]

I have a .1 thick 304 SS pipe (3/4" OD) that I would like to braze/solder to a 7/32" rod of type 303 ASTM-A582 stainless. Is there any reason why these two types cannot be joined together or should it not be a problem?

The joint doesn't require a lot of strength so would it actually be possible to solder these two together or will they require brazing? Also, what temp would you recommend?

I'm new to this so any advice or tips would be greatly appreciated! Thanks.

[keebler303]

I've silver soldered stainless using acid flux, worked quite well, just use plenty of flux to keep the oxides cleaned off. They don't recommend welding 303 but I'm not sure about brazing or soldering. I have welded 303 without too much trouble before. Its probably not a real strong joint but for non structural applications I'm sure its fine.

Matt

[Geof]

Silver solder will work quite well. The correct temperature for silver soldering is just on the edge of red hot; if you can see it glowing red you have overshot. Actually the best indicator is the flux because when it melts and flows over the surface then the temperature is just about correct to melt the silver solder.

[yantra3d]

Thanks a lot for the info guys... I really appreciate that.

I was originally planning on buying an oxy-acetaline rig to braze with but I came across those smaller and less expensive benzomatic rigs that use propane or maap gas, do you guys have any experience with those? Would it be worth considering and if so which would you recommend, propane or maap? I guess I should do some more research on silver soldering and see which one would work best for the stainless.

[Geof]

Propane is really not adequate for silver soldering, at least the higher temperature versions such as Braze 450 which are also the strongest. Even maap is marginal although on small thin sections it is workable. It may be okay for stainless because you have the advantage of low thermal conductivity so the heat does not get dissipated as quickly.

[yantra3d]

Thanks a ton Geof... this is very helpful info. So it sounds like acetylene gas would be the best way to go then, is that right?

While I have your attention, which gas rig would you recommend for brazing copper? I will be joining a .040 rod to a .040 thick pipe made of c10100. Can this be done with acetylene as well? Thanks again for all your help... very much appreciated.

[Geof]

Brazing copper????? I hope you mean silver soldering, or silver brazing. Which is also called low temperature brazing.

Normally the term 'brazing' means the high temperature version also know as bronze welding. High temperature being up around 900 degrees C, low temperature brazing is down around 450, hence the term Braze 450 which is actually the name of a type of silver solder.

Silver soldering copper is fairly easy and yes an acetylene flame is best, a nice soft flame which you keep moving to avoid overheating any particular area.

But I have to qualify my comments: 0.040" rod to 0.04" wall thickness pipe????? Hoo boy, my first response is that you are crazy, but please don't be offended; that diameter rod is smaller than your silver solder wire. If you have never done silver soldering before you are biting off a big mouthful; those sizes are down in the jewellery work region. You are in a totally different league than your stainless stuff mentioned in your first post.

I have never worked this small but I have seen it done and the technique is quite different, at least what I have observed. The acetylene torch is set up with a very soft acetylene rich flame not quite rich enough to create soot but certainly rich enough to have a large yellow cone, and there is a small air nozzle just beside the flame with a tube that you blow through. The result when you blow is a little hot flame going sideways from the soft flame, this hot flame comes from the extra oxygen in the air you are blowing. The little hot flame is what you play on your work and because you are blowing you control the intensity of this flame very carefully; stop blowing and it does not exist. This allows you to control the heat applied to your tiny work pieces to avoid overheating. You also use much thinner than normal silver solder.

I have to say this is what I have seen years ago, maybe there are different techniques in use now. You need to start searching out silver-smithing techniques because that is the realm you are in I think.

An alternative is oven brazing where you fixture everything up with a little foil of silver solder between the parts to be joined and then heat them up in an oven but that is a whole different ball game.

[keebler303]

I have drilled holes in a copper pipe and silver soldered SS thermocouples into the holes. The thermocouples were .062 OD and fairly thin wall and I did not have any trouble soldering it with a propane torch and standard size silver solder. If your pipe is only .040" ID then it will be much tougher, but if its a fairly large pipe and you are joining a small rod to it, you shouldn't have too much trouble. Just keep most of the heat on the larger piece and move the flame over the small rod just a second before adding the flux/solder. Also, I generally use solid solder (no flux) and use separate liquid acid flux in an eyedropper. I drop a few drops of flux on the joint and then follow up with the solder as quickly as possible, keeping the heat on it the whole time.

Matt

[yantra3d]

This is great info guys.. Thanks a ton! I can do some research from here now that I know what I'm dealing with.

The copper parts consist of a small .040 diameter "wire" (like what you'd find wrapped in standard 120VAC domestic power line) and a 1/2 diameter "pipe" with a .040" thick wall. My plan was to drill a small hole in the side of the pipe to fit the wire into and then join them together using some form of brazing/soldering, etc...

If you can recommend a better method for joining the wire to the side of the pipe then that would be great. The wire will need to be joined on the interior wall of the pipe. He pipe will be only 1/2" in length but I was thinking that it would be easier to drill a hole through the side wall and feed the solder from the outside.

The oven/foil method sounds appealing. I will try to research that and see what I can come up with.

Thanks again for all the help guys!

[keebler303]

Here is a pretty good video of the brazing method known as "furnace brazing". They are using torches instead but if you put it in a furnace, it would do the same thing.

"http://www.youtube.com/watch?v=7ZPS_iwoeJg"]YouTube- How It's Made Bicycle

Matt

[Geof]

Putting the wire in a hole in the tube makes it easier, now you can primarily heat the tube and don't really have to play the flame on the wire. Because the wire will be surrounded by hot tube it will heat okay.

An alternate way I have heated thin sections, such as switch contacts, for silver soldering is to put them in contact with a piece of stainless sheet about 3/32" or 1/8" and heat this sheet from the back; the sheet gets red hot and heats the delicate parts by radiation.

Before doing this thoroughly heat the sheet bright red to oxidize the surface as much as possible so it will not take the silver solder otherwise you run the risk of silver soldering everything together.

[yantra3d]

That video was very interesting... thanks keebler. I've never seen that welding method used and I would have assumed that it was done with a welding rod... pretty cool!

Well, I jumped on this ebay auction for this Smith Jeweler's kit:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=150409931798

I don't normally buy something without doing a lot of research first so hopefully I didn't make a mistake with this. It seemed like a good deal and I didn't want to pass it up so I bit the bullet.

This rig uses "atmospheric air" instead of oxygen but can produce a flame of 4770' F... do you think this will work for soldering the copper parts I mentioned?

I probably should have held off and went with a oxy-acetylene rig that could tackle both the copper and stainless parts but wasn't sure if I could use the larger rig required for SS to work with the smaller copper parts.

All the parts are still new and in original packaging so I guess I could always relist them if I decide not to use it.

How hot will I need to get the SS to solder them together? I need to join a .1" thick hollow pipe to a 7/32" rod, would this air-acetylene do the job or will I have to invest in the oxy-acetylene rig for this?

BTW, thanks for the tip on using the radiant heat method for joining the copper parts Geoff... that sounds like a good idea to me.