Silver soldering/brazing
Silver soldering/brazing
What do others use to soft and hard solder SS. Flux and torch? What would be a good torch to use and should I use propane/oxygen?
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Richard Hull
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Re: Silver soldering/brazing
Soft soldering is weak, but in non-vibrating and fixed setups is quite satifactory provided no temperature extremes are the norm. (work weakens the joints due to expansion and contraction).
Soft soldering rarely heats a piece beyond 500 degrees F.
Soft soldering of large metal parts can easily be done using a common propane torch. Fluxes vary based on the material to be soldered. SS is the toughest of materials to soft solder and copper and brass, among the easiest. Acid core solders and fluxes must be neutralized and treated following soldering or you will never pull a decent vacuum due to outgassing.
All soft soldering should be done with a tin-silver solder like 97% tin and 3% silver. Expensive indium solders allow for glass to metal joints.
Soft solder will fill gaps and joints very well if the temperature is controlled at the joint well. pieces to be soft soldered can have gaps and be ill fitting to a degree.
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Hard Soldering is another whole world where the pieces to be joined need to reach temperatures beyond 1000 degrees F. The easiest source of heat is the common oxy-acetylene torch with graded tips to match the work to be done.
Mapp gas torches with special nozzles can braze and silver solder smaller items, but only oxy-gas units can handle larger sized pieces.
Brazing, hard soldering and silver soldering are all the same and demand the above items. Brazing usually involved a brass alloy feed rod. Hard soldering or silver soldering traditionally involves a high silver content rod >30% silver.
For scientific purposes, one should always use silver contents beyond 50% with 75%-90% being preferred. Hard soldering for vacuum work should only involve silver and copper in the brazing alloy, though some antimony is allowed. Avoid cadmium in such alloys!
Ultimately, all fits in silver or hard soldering must be relatively smooth snug fits. It will amaze you as the silver solder wicks nearly instantly up into the joint and leaves a clean, shiney, very strong joint following cleaning. The one thing that silver soldering will not do is fill or bridge a gap or a void. The surface tension is so great that it will flow like a rocket ship over vast surface areas rather than fill a gap.
NOTE: In all soldering operations, hard or soft, but especially soft, you will gain a tremendous advantage by "Tinning" all joints prior to assembly. When tinning, sand the surfaces to be joined to a brilliant shine. Next, flux is applied to the part of all pieces where they are to be joined. These are then heated prior to assembly and a small amount of solder is allowed to coat the piece where it is to be joined. While still hot, the piece is wiped quickly with a wet rag leaving a surface mirror coating of the solder. When assemlbed and reheated very little solder need be applied as the solder instantly flows to all parts of the tinned surfaces leaving no voids and a firm solid joint.
Richard Hull
Soft soldering rarely heats a piece beyond 500 degrees F.
Soft soldering of large metal parts can easily be done using a common propane torch. Fluxes vary based on the material to be soldered. SS is the toughest of materials to soft solder and copper and brass, among the easiest. Acid core solders and fluxes must be neutralized and treated following soldering or you will never pull a decent vacuum due to outgassing.
All soft soldering should be done with a tin-silver solder like 97% tin and 3% silver. Expensive indium solders allow for glass to metal joints.
Soft solder will fill gaps and joints very well if the temperature is controlled at the joint well. pieces to be soft soldered can have gaps and be ill fitting to a degree.
************************************************************
Hard Soldering is another whole world where the pieces to be joined need to reach temperatures beyond 1000 degrees F. The easiest source of heat is the common oxy-acetylene torch with graded tips to match the work to be done.
Mapp gas torches with special nozzles can braze and silver solder smaller items, but only oxy-gas units can handle larger sized pieces.
Brazing, hard soldering and silver soldering are all the same and demand the above items. Brazing usually involved a brass alloy feed rod. Hard soldering or silver soldering traditionally involves a high silver content rod >30% silver.
For scientific purposes, one should always use silver contents beyond 50% with 75%-90% being preferred. Hard soldering for vacuum work should only involve silver and copper in the brazing alloy, though some antimony is allowed. Avoid cadmium in such alloys!
Ultimately, all fits in silver or hard soldering must be relatively smooth snug fits. It will amaze you as the silver solder wicks nearly instantly up into the joint and leaves a clean, shiney, very strong joint following cleaning. The one thing that silver soldering will not do is fill or bridge a gap or a void. The surface tension is so great that it will flow like a rocket ship over vast surface areas rather than fill a gap.
NOTE: In all soldering operations, hard or soft, but especially soft, you will gain a tremendous advantage by "Tinning" all joints prior to assembly. When tinning, sand the surfaces to be joined to a brilliant shine. Next, flux is applied to the part of all pieces where they are to be joined. These are then heated prior to assembly and a small amount of solder is allowed to coat the piece where it is to be joined. While still hot, the piece is wiped quickly with a wet rag leaving a surface mirror coating of the solder. When assemlbed and reheated very little solder need be applied as the solder instantly flows to all parts of the tinned surfaces leaving no voids and a firm solid joint.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Carl Willis
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Re: Silver soldering/brazing
Hi Brian,
I have used a couple kinds of cadmium-free silver brazes. Bellman-Melcor A50N works very well on stainless steel parts. McMaster-Carr's "high fill silver" will actually do a pretty good job of filling cracks, which as Richard mentioned, is not something that hard silver solder naturally tends to do.
As for flux, there are two kinds: "white" flux and "black" flux. Both are mostly a fluoride salt--so be careful about getting your face in the fumes. I use the white stuff myself. I have used the black stuff at work. I am not really sure what the functional differences are. Black flux seems harder to clean up but I think is supposed to work better with stainless steel. White works fine on stainless in my opinion. I like to dilute it slightly with water and apply it with a toothpick. One thing you generally do not want is a lot of stray flux because the solder will follow it very aggressively on a surface.
The parts should be glowing at least a dull red color when they are ready for solder. The flux will fuse and become a clear liquid. One of those little handheld butane pinpoint torches is adequate for parts around 1/4 inch diameter or less (has some trouble with copper because it's too conductive). Anything much bigger and it is a job for an oxy-gas torch of some kind.
-Carl
I have used a couple kinds of cadmium-free silver brazes. Bellman-Melcor A50N works very well on stainless steel parts. McMaster-Carr's "high fill silver" will actually do a pretty good job of filling cracks, which as Richard mentioned, is not something that hard silver solder naturally tends to do.
As for flux, there are two kinds: "white" flux and "black" flux. Both are mostly a fluoride salt--so be careful about getting your face in the fumes. I use the white stuff myself. I have used the black stuff at work. I am not really sure what the functional differences are. Black flux seems harder to clean up but I think is supposed to work better with stainless steel. White works fine on stainless in my opinion. I like to dilute it slightly with water and apply it with a toothpick. One thing you generally do not want is a lot of stray flux because the solder will follow it very aggressively on a surface.
The parts should be glowing at least a dull red color when they are ready for solder. The flux will fuse and become a clear liquid. One of those little handheld butane pinpoint torches is adequate for parts around 1/4 inch diameter or less (has some trouble with copper because it's too conductive). Anything much bigger and it is a job for an oxy-gas torch of some kind.
-Carl
Re: Silver soldering/brazing
Thanks for the advice. The reason I am asking is that I am about to solder on my BeO ebay insulator to a 2 3/4" conflat that should arrive monday. I was doing some practice on some scrap SS last night. I am not sure what I was doing wrong. I have acid flux and 5% silver solder , the surface was sanded bright and cleaned with Methanol. I applied flux and heated to red with a propane torch. The small amount of solder melted and flowed. But should it have alot of black residue in and around the solder? It looked really bad! What does the jobs you two have done look like before you clean away the flux. Is there a possibility of too much oxygen keeping the flux from keeping the oxidation off the metal? If that makes any sense. Should the flame be confined to a small area at the soldering point, a fine tip? Maybe I just need more practice. Is this an art that takes awhile to get good at? I would just like to avvoid wasting good flanges , damage from too much heat or just look really bad.
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Carl Willis
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- Joined: Thu Jul 26, 2001 7:33 pm
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Re: Silver soldering/brazing
Hi Brian,
For SOFT silver solder, which is what it sounds like you have, there is no need to get the part red-hot. The solder will melt at pretty much the same temp as "regular" lead-tin solder. A lot of flux is typically needed. Heat the part, squirt some acid flux on, wait for it to boil, add solder (which should flow easily). If the solder starts balling up and refusing to flow, the answer is usually to add new flux rather than more heat. Black could be one of two things: metal oxides that have saturated the flux, or something organic that got in there (such as if you use cotton or sponge or camel-hair brush to apply the flux). Neither should be there, ideally. Make sure to aggressively clean the work when finished because that acid flux has an appetite for, well, anything and everything.
-Carl
For SOFT silver solder, which is what it sounds like you have, there is no need to get the part red-hot. The solder will melt at pretty much the same temp as "regular" lead-tin solder. A lot of flux is typically needed. Heat the part, squirt some acid flux on, wait for it to boil, add solder (which should flow easily). If the solder starts balling up and refusing to flow, the answer is usually to add new flux rather than more heat. Black could be one of two things: metal oxides that have saturated the flux, or something organic that got in there (such as if you use cotton or sponge or camel-hair brush to apply the flux). Neither should be there, ideally. Make sure to aggressively clean the work when finished because that acid flux has an appetite for, well, anything and everything.
-Carl
Re: Silver soldering/brazing
This is probably not the answer your looking for but, in my opinion Tig welding is a better way that using a gas torch. The issues with the using a gas torch (butane, acetlene, mapp) is that it puts a lot of heat into the work pieces and requires a lot of flux to turn out a clean weld. It also takes a lot more work to clean up, and detect/fix leaks. with Tig welding its much easier to avoid distortion since it only heats up a small spot where your welding, and replaces the flux with a shield gas. You still have to be careful with managing heat load using a TIG torch but is still easier that using a gas torch. After I got a TIG, I've have not used my gas torch. It is so much superior.
Another issue with using flux is that it can get inside of your joint and cause outgassing/leak issues later on. If you look at the majority of all UHV components the use TIG welds. In cases where a brazing is required, the pieces to be joined are place in a brazing furnance using hydrogen as the shield gas.
Since your joining a ceramic piece, you want to avoid excessive heat that could cause a leak in the ceramic to metal brazing join. One possible method is to use a tig torch to braze SS with Silver. Ive never personally tried it, but I did come across a few discussions\\articles from google searches. Obviously this could be tested on a couple of scrap pieces first to see if the results are acceptable. The advantage is using brazing over welding is the lower temperature required which would reduce heat distortion that might damage the ceramic to metal brazed joint.
If the cost of a TIG is to expense, you might be able to rent one from a rental shop or alternatively buy one on ebay with the intent to resell back on ebay so your out-of-pocket money isn't that big of deal. If you decide to rent a TIG, you will need a couple of days for practice. It isn't extremely difficult. It just takes a little practice to hold the torch steady will introducing a welding rod into the pool. Unlike a gas torch you can't hit the TIG electrode to either the work piece or the welding rod since it will short out the arc. You also need to hold the TIG torch much closer to the work surface. The closer the electrode is to the surface the less current and heat load will be put into the work piece.
FWIW: I use a Miller dynasty 200DX. I bought this TIG because it you can adjust it's output (current/duty cycle/etc) and it can handle aluminum which requires AC. I think the 200DX cost me about $2k with the torch and foot petal. Steel and stainless can be TIG welded using DC. I also recommend that you purchase a 1/16 electrodes and use a Alumina Nozzle #5. The standard electrode is 3/32 which is a little too big for fine detail work and requires more current to maintain a stable arc. the #5 Nozzle provides good shield gas coverage while providing you good visibility near the electrode (important so you can keep an eye on the torch and welding rod so that the electrode doesn't touch). You will also need a bench grinder to sharpen the electrode tip. Occassionally the electrode will touch the weldment and will need to be ground off to keep the plasma arc clean.
Finally the best welds (no matter if you use gas or TIG) is to machine the work pieces with an exact fit. any gaps between the two work peices will result in distortion when the two pieces are joined. With a exact fit, TIG welding doesn't required a welding rod. You can weld the pieces directly together. This creates an extremely clean weld.
One last thing with TIG welding, You need to clean the work area of the work peices absolutely clean. Any dirt or oxidized material will cause splatter which is extremely annoying or affect the quality of the weld. I usually clean up the work area using a solvent (alchol, acetone, etc) and then use a stainless steel wire brush on work area.
I would also recommend using an electronic auto-darkening helmet and a foot petal to control the TIG arc.
I Hope this was useful to you.
AG
Another issue with using flux is that it can get inside of your joint and cause outgassing/leak issues later on. If you look at the majority of all UHV components the use TIG welds. In cases where a brazing is required, the pieces to be joined are place in a brazing furnance using hydrogen as the shield gas.
Since your joining a ceramic piece, you want to avoid excessive heat that could cause a leak in the ceramic to metal brazing join. One possible method is to use a tig torch to braze SS with Silver. Ive never personally tried it, but I did come across a few discussions\\articles from google searches. Obviously this could be tested on a couple of scrap pieces first to see if the results are acceptable. The advantage is using brazing over welding is the lower temperature required which would reduce heat distortion that might damage the ceramic to metal brazed joint.
If the cost of a TIG is to expense, you might be able to rent one from a rental shop or alternatively buy one on ebay with the intent to resell back on ebay so your out-of-pocket money isn't that big of deal. If you decide to rent a TIG, you will need a couple of days for practice. It isn't extremely difficult. It just takes a little practice to hold the torch steady will introducing a welding rod into the pool. Unlike a gas torch you can't hit the TIG electrode to either the work piece or the welding rod since it will short out the arc. You also need to hold the TIG torch much closer to the work surface. The closer the electrode is to the surface the less current and heat load will be put into the work piece.
FWIW: I use a Miller dynasty 200DX. I bought this TIG because it you can adjust it's output (current/duty cycle/etc) and it can handle aluminum which requires AC. I think the 200DX cost me about $2k with the torch and foot petal. Steel and stainless can be TIG welded using DC. I also recommend that you purchase a 1/16 electrodes and use a Alumina Nozzle #5. The standard electrode is 3/32 which is a little too big for fine detail work and requires more current to maintain a stable arc. the #5 Nozzle provides good shield gas coverage while providing you good visibility near the electrode (important so you can keep an eye on the torch and welding rod so that the electrode doesn't touch). You will also need a bench grinder to sharpen the electrode tip. Occassionally the electrode will touch the weldment and will need to be ground off to keep the plasma arc clean.
Finally the best welds (no matter if you use gas or TIG) is to machine the work pieces with an exact fit. any gaps between the two work peices will result in distortion when the two pieces are joined. With a exact fit, TIG welding doesn't required a welding rod. You can weld the pieces directly together. This creates an extremely clean weld.
One last thing with TIG welding, You need to clean the work area of the work peices absolutely clean. Any dirt or oxidized material will cause splatter which is extremely annoying or affect the quality of the weld. I usually clean up the work area using a solvent (alchol, acetone, etc) and then use a stainless steel wire brush on work area.
I would also recommend using an electronic auto-darkening helmet and a foot petal to control the TIG arc.
I Hope this was useful to you.
AG
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Donald McKinley
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- Joined: Tue Nov 01, 2005 10:53 pm
- Real name: Donald McKinley
Re: Silver soldering/brazing
At our shop for our red heat silver soldering, We use city natural gas out of the pipe along with oxygen in a small Victor torch.
For higher temp we have plain acetylene w no oxygen. I really like the city gas approach, it's cheap and works very well.
Carl, where do you buy the Bellman-Melcor A50N?
Anonymous, did you mean to say nitrogen in your second paragraph above? I would hate for one of our novice craftsmen to leave us with a loud bang one of these days.
Don M.
For higher temp we have plain acetylene w no oxygen. I really like the city gas approach, it's cheap and works very well.
Carl, where do you buy the Bellman-Melcor A50N?
Anonymous, did you mean to say nitrogen in your second paragraph above? I would hate for one of our novice craftsmen to leave us with a loud bang one of these days.
Don M.
Re: Silver soldering/brazing
I think I just need more practice. After trying again tonite I got alittle better results, but not near perfect. Less oxidation and better flow. I think I need a smaller tip to concentrate the heat to the soldering area. I am seriously thinking about getting a small inverter TIG unit but still need to master this art. I have to just perfect my own technique. Who knew it was this hard. Nothing like soldering copper pipe. Any other ideas or suggestions are welcome.
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Donald McKinley
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- Joined: Tue Nov 01, 2005 10:53 pm
- Real name: Donald McKinley
Re: Silver soldering/brazing
Brian
Are you fixturing your parts before applying the heat? Ideally the parts should be held together with a little pressure so that they will not move while the heat is applied. If you are using the torch in one hand and the solder in the other, you have to start juggling things around if you want to secure your parts if they start sliding around when things go liquid.
Jig up, be neat & tidy & your joints will start to look better and better.
I use a fire brick to rest my parts on occasionally while silver soldering. The fire brick reflects the heat back onto the parts so that they heat up faster. The heating should happen fast so that you don't start to produce more oxide than the flux can handle.
I like the bi-floride containing white paste. It really does the trick.
If you post a few small pics of your problem joints, you will get some real helpful hints that will go beyond generalities. Like they say, a picture's worth a thousand words
Don
Are you fixturing your parts before applying the heat? Ideally the parts should be held together with a little pressure so that they will not move while the heat is applied. If you are using the torch in one hand and the solder in the other, you have to start juggling things around if you want to secure your parts if they start sliding around when things go liquid.
Jig up, be neat & tidy & your joints will start to look better and better.
I use a fire brick to rest my parts on occasionally while silver soldering. The fire brick reflects the heat back onto the parts so that they heat up faster. The heating should happen fast so that you don't start to produce more oxide than the flux can handle.
I like the bi-floride containing white paste. It really does the trick.
If you post a few small pics of your problem joints, you will get some real helpful hints that will go beyond generalities. Like they say, a picture's worth a thousand words
Don
Re: Silver soldering/brazing
This is a really good thread. Thanks for everyone's post.
It would be good if AG can elaborate on the hydrogen atmosphere approach. When heat treating tungsten filaments, we used a hydrogen gas environment in an inverted open bell jar. But I don't recall doing any brazing directly in it.
If you weren't careful, and brought in some air, it could puff out, which was generally harmless, although rather startling the first couple of times.
I agree, too that TIG is the way to go, if you can afford the unit. Some rather nice 90 -150 Amp units from Hobart, Clarke, and Miller cost in the $300 to $700 range. (Northern Tool and Welders.com are places to see the units side by side) .
Still will be a bit of money for some. Miller seems to have the better quality hardware, and the adjustable current feature is very handy.
Dave Cooper
It would be good if AG can elaborate on the hydrogen atmosphere approach. When heat treating tungsten filaments, we used a hydrogen gas environment in an inverted open bell jar. But I don't recall doing any brazing directly in it.
If you weren't careful, and brought in some air, it could puff out, which was generally harmless, although rather startling the first couple of times.
I agree, too that TIG is the way to go, if you can afford the unit. Some rather nice 90 -150 Amp units from Hobart, Clarke, and Miller cost in the $300 to $700 range. (Northern Tool and Welders.com are places to see the units side by side) .
Still will be a bit of money for some. Miller seems to have the better quality hardware, and the adjustable current feature is very handy.
Dave Cooper
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Richard Hull
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Re: Silver soldering/brazing
TIG will not braze well, at least I have never heard of it being done. You would really have to dial it back and work on large pieces only, I suppose. I wouldn't even want to think about it much less try it. TIG is pretty much a similar metals weldment process where the metals are fused without filler rod. Both pieces to be joined should be of the same alloy for easy welding. SS and normal steel is a crap shoot for TIG.
Grossly dissimilar metals like brass and SS, Copper and nickel, etc., are best handled by brazing/sillver solder in one off joinings. In mass production, such items are almost always furnace silver soldered.
Richard Hull
Grossly dissimilar metals like brass and SS, Copper and nickel, etc., are best handled by brazing/sillver solder in one off joinings. In mass production, such items are almost always furnace silver soldered.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Re: Silver soldering/brazing
Keep the area carbon free.
Do not handle work piece or !!SOLDER!! with bare hands or gloves exposed to oils.
Practice attaining the correct temperature/flux for the thickness (and types) of materials.
Use a clean stainless steel brush. Store the brush and solder properly when not in use.
Tin that surface, tin that surface, and tin that surface.
Joe Sal
Do not handle work piece or !!SOLDER!! with bare hands or gloves exposed to oils.
Practice attaining the correct temperature/flux for the thickness (and types) of materials.
Use a clean stainless steel brush. Store the brush and solder properly when not in use.
Tin that surface, tin that surface, and tin that surface.
Joe Sal
Re: Silver soldering/brazing
>Anonymous, did you mean to say nitrogen in your second paragraph above? I would hate for one of our novice craftsmen to leave us with a loud bang one of these days.
Its Hydrogen not Nitrogen or Argon. Ceramic to metal brazing is done in a sealed furnace chamber. I believe the hydrogen helps wet the brazing alloy to the ceramic. A google seach on ceramic to metal brazing should turn up some information. I believe it was also discussed here a while ago.
Its Hydrogen not Nitrogen or Argon. Ceramic to metal brazing is done in a sealed furnace chamber. I believe the hydrogen helps wet the brazing alloy to the ceramic. A google seach on ceramic to metal brazing should turn up some information. I believe it was also discussed here a while ago.
Re: Silver soldering/brazing
Heres a post on groups.google.com
http://groups.google.com/group/rec.craf ... 4559b1e073
I've not tried it. The advantage would be to reduce the heat load into the working pieces since silver melts at a much lower temperature than SS. I would be very concerned TIG welding a SS workpiece with a nearby Ceramic to metal brazed seal. In this situation brazing would be the better choice.
>SS and normal steel is a crap shoot for TIG.
I think using a stainless welding rod would help. Ive welded cold rolled steel with 308L SS welding rods with good success. Although I never had a need to weld SS with steel.
>In mass production, such items are almost always furnace silver soldered.
This reminds me. You want to avoid using Silver welding rods with phosphate, cadium or other agents since they can cause outgassing and virtual leaks. I believe JW Harris sells a line of Silver (Safety-Silver) that doesn't contain these contaimants. There are used for welding SS for food processing equipment. Be aware that these probably have a higher melting temperature which may make it more difficult to get a good clean weld and avoid distortion.
This OT but might be useful:
You can Solder SS (using plain electrical solder) if you coat the SS work piece in a liquid flux and use a small SS wire brush to remove the thin oxide layer. I used this method to create a few low ohm resistors by soldering some copper wire to SS foil. You have to be careful to keep the scratched surface from exposer to air during the process. I would not recommend using this method to create vacuum seals, but it could be useful if you need to join SS with some other metal. Note that electrical solder would be inapproprate for vacuum work since most brands contain rosin, lead or other non-vacuum friendly substanances. Perhaps a tin/silver solder alloy might work.