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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Does anyone know, please, if it is even possible to silver solder or braze to Copper-Tungsten sheet, or have any practical experience of making-to-metal joints to refractory metals?
My hottest flame is MAPP gas/air - 1980 Centigrad (~ 5300 Farenheit)
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Harry! I can finally help here! I have been a US Navy certified welder since 1995! The answer to your question is yes! It can be silver soldered, though there is no particular reason to use silver solder a brass/bronze braze would be much stronger and more effective. Your only real issue is going to be the heating of your base metal (the copper alloy) By the time you get the copper hot enough to accept the silver you wont need to have the flame anywhere near it. When the copper is hot enough you will see it change color. Be sure to use a liquid flux!!!!!!! IT IS A MUST. Preheat the copper and brush the liquid flux on it while its hot. Keep on heating it until you notice a slight change in color. Pull away the flame and apply the silver solder. Sounds easy, but i can assure you it is a major pain in the a@$. (the silver will flow wherever you apply the acid, so try not to be messy) If you have trouble getting the heat you need with the mapp try preheating the base metal in an oven at about 400-450f. Then be quick with the torch;-) How thick is the copper??
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
doctor electrons wrote ...
Harry! I can finally help here! I have been a US Navy certified welder since 1995! The answer to your question is yes! It can be silver soldered, though there is no particular reason to use silver solder a brass/bronze braze would be much stronger and more effective. Your only real issue is going to be the heating of your base metal (the copper alloy) By the time you get the copper hot enough to accept the silver you wont need to have the flame anywhere near it. When the copper is hot enough you will see it change color. Be sure to use a liquid flux!!!!!!! IT IS A MUST. Preheat the copper and brush the liquid flux on it while its hot. Keep on heating it until you notice a slight change in color. Pull away the flame and apply the silver solder. Sounds easy, but i can assure you it is a major pain in the a@$. (the silver will flow wherever you apply the acid, so try not to be messy) If you have trouble getting the heat you need with the mapp try preheating the base metal in an oven at about 400-450f. Then be quick with the torch;-) How thick is the copper??
Fantastrastroke! Nothing so good as to meet a man who knows what he is talking about!
Thicknesses are: 0.016", 0.026", 0.031" and 0.036". All are sized 1" x 3" and I am hoping to use them in an edge-firing spark gap of my own invention.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Any time! You can use Master Mechanic "all-purpose liquid soldering flux" "no pre cleaning necessary" It's $1.99 a bottle here. Not too sure what you have for hardware stores there but any liquid flux should work. The good ones have muriatic acid in them. You'll know right away when you brush it on if it is going to work. On copper and all of its alloys you will see an immediate color change. It will brighten, drastically! Also, mapp gas will be fine for the thickness you are working with. Thought you were going to say .125-.25! Either way the tools you have will do the job. I assume you have a mapp/oxy rig. If not, straight map and a decent plumbing torch will work. You WILL have to worry about distortion so the more concentrated (fine spot size) your flame the better! Thinner materials will tend to warp unless you heat them evenly. This is why the preheat in the oven will help greatly. Depending on the type of joint you are trying to form the heat will vary. The easiest in your application (the method of fusing) will most likely be a outside fillet. Inside fillet will be extremely difficult. Butt joints will be fairly simple but use a gap between your workpieces equivalent to 1/2 the thickness of the material and clamp a heatsink 4 times the thickness away from the seam (parallel to it) this will eliminate a good portion of the distortion. Leave it clamped until the material has cooled! You should be all set! Now you have a real practical use for those oven mitts I am more than happy to help, if you have any other questions please ask! If i have helped you, then i have justified my time here! Perhaps you'll share a photo of this sparkgap when the masterpiece is finished? I would love to see it! Almost forgot! When you have finished making the required joints be sure to remove all remaining flux! IE: just clean it.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Thanks so much for your help!
I have a Bernzomatic needle-point MAPP/air torch, which sounds just right from what you say.
I have both hydrochloric acid (US: "muriatic") and zinc chloride (old-fashioned: 'killed spirits'") - could I make suitable fluxes out of these, or would generic plumber's acid flux (cheap) be just as good?
I have several dozen pieces of the Copper-Tungsten sheet in the sizes mentioned, so I have a little room to get things wrong on a few trial samples before going for the full monty.
If you can imagine one long 3" side as "the firing edge" I want to make a joint to ordinary (and thicker) copper sheet along the entire length of the opposite 3" edge, to keep inductance as low as possible.
Two Cu-W sheets are held apart by really split down mica, to form a linear 3" gap of great fineness and accuracy, a sandwich construction which (in theory) will fire at as low as 750V. It need not survive a great number of shots.
I am also trying find out about refractory adhesives to hold my metal-mica-metal sandwich together. There are plenty of commercial products advertised on the net, but the prices are truly horrific. It's also important that the adhesive should not add significantly to thickness of the sandwich, and be easy to keep free or micro-bubbles that would lead to arcing and misfiring. A tall order, I think, but sometimes an older technology can provide a simple and less expensive solution that you might have heard off. Physical strength of the adhesive joint is not important so far I can see from my current knowledge, since there will be an outer clamp/heat sink to further reinforce the sandwich.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
You can use the hydrochloric, it will work fine by itself. The Cheap plumbers liquid flux may actually work better though. There's some sort of magic ingredient in there someplace. As far as the adhesive, you may want to check out penetrating adhesives. They are used for all sorts of things, possibly exactly what you are looking to accomplish! You could clamp together your "sandwich" and apply the adhesive to the edge and it would penetrate all the way across. The clamping would eliminate any large bubbles or imperfections. Penetrating adhesives come in conductive and nonconductive versions (when they're dry of course). I would stand the piece (or sandwich) up vertically and apply a penetrating adhesive until it ran out of the bottom evenly. That should ensure that you have filled every pore. Then i would let it dry laying flat. Sounds cool!! It seems you have it well thought out!! Get er goin!!
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
doctor electrons wrote ...
You can use the hydrochloric, it will work fine by itself. The Cheap plumbers liquid flux may actually work better though. There's some sort of magic ingredient in there someplace. As far as the adhesive, you may want to check out penetrating adhesives. They are used for all sorts of things, possibly exactly what you are looking to accomplish! You could clamp together your "sandwich" and apply the adhesive to the edge and it would penetrate all the way across. The clamping would eliminate any large bubbles or imperfections. Penetrating adhesives come in conductive and nonconductive versions (when they're dry of course). I would stand the piece (or sandwich) up vertically and apply a penetrating adhesive until it ran out of the bottom evenly. That should ensure that you have filled every pore. Then i would let it dry laying flat. Sounds cool!! It seems you have it well thought out!! Get er goin!!
Roger on the flux. I'll get some regular plumber's acid flux from a hardware store.
I've found a cheap adhesive called REGY25 which is a 'Glass Yarn Fixative' for bonding glass rope seals to metal oven doors, and is guaranteed to be good to 850 centigrade - which sounds like a similar case to bonding mica to Cu-W - though isn't really 'refractory' - once you get into the adhesives that can survive 1500 centigrade and more you're talking about hundreds of dollars rather the ten bucks for the oven door glue.
This high temperature glass glue looks pretty thin stuff, so it might flow into the sandwich by capillarity, as you suggest. Anyway I can try this out with some cheap 'dummies' without having to use my precious stock of Cu-W sheet.
The heavy copper heat-sink/clamp will start just 1mm back from the long firing edge, so when the adhesive vapourizes out of the edge tip itself, I can't see the de-lamination spreading further back - and there would be no advantage to the spark to snuck inside the lamination instead of going via the air - when we're talking about 750 - 1000V, electricity is fairly well behaved, without having too many ideas of its own about short-cuts we hadn't thought of!
This isn't like a TC gap which has to survive boo-koo discharges - this is for single shot initializing of a 250J Rayleigh line half-microsecond discharge across a bigger linear solid tungsten gap. (Two triangle-section tungsten rods 2.75" long - just shorter than than mica sandwich firing gap ) It would be nice if it could survive 50 shots or more, but there's no way to find out but put it together and see how it goes. It wouldn't be an experiment if I already knew the outcome!
Just so you can see the picture in your mind - imagine the triangle-bars of solid tungsten as the main gap, with the mica-sandwich device just between them as a trigger device. On the opposite side is a 4" hard UV lamp irradiating both the main gap and the mica Cu-W sandwich trigger gap. 5 alpha sources (ex smoke detectors!) are also placed equidistantly just south of the gap, so we have short-UV aided and abetted by alpha particles adding to the pre-ionization fun.
Once the discharge starts in an oxygen-free environment, then extreme UV <200 nm will also (hopefully) add steepness to the breakdown wave-front.
If you wonder why I'm going to such lengths to produce hair-trigger levels of pre-ionization, it's because it's essential that the main linear gap fire evenly across its entire length, rather than have raggedy edges, or firing from just one point along its 2.75" length, which would completely ruin the point of this ultra-low inductance device.
I'm sure I'll need to talk again when I've refreshed my supply of absurdly expensive MAPP gas, as this is a bit out of my usual league of ( now illegal ) lead/tin Ersin Multicore soldering.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Harry! Sounds cool! You seem to have come up with a very plausible design. At least it works in my head. Yours to i believe! Have you ever thought about putting the whole thing in a sealed acrylic box and purging it with an inert gas like argon? Or Co2? I think that would help it live longer. No oxidization would take place after firing. Actually the more i think about it argon would be much better than Co2 because Co2 will actually cause the arc to burn hotter. Thats why it is a common shielding gas for MIG welding. What do you think? That gap reminds me of a TEA laser. When i messed with those things i used cheap ebay micrometers mounted to a plate to adjust my arc rails!
Sorry if this leaned off of the original topic, but this is good stuff!!
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
doctor electrons wrote ...
Harry! Sounds cool! You seem to have come up with a very plausible design. At least it works in my head. Yours to i believe! Have you ever thought about putting the whole thing in a sealed acrylic box and purging it with an inert gas like argon? Or Co2? I think that would help it live longer. No oxidization would take place after firing. Actually the more i think about it argon would be much better than Co2 because Co2 will actually cause the arc to burn hotter. Thats why it is a common shielding gas for MIG welding. What do you think? That gap reminds me of a TEA laser. When i messed with those things i used cheap ebay micrometers mounted to a plate to adjust my arc rails!
Sorry if this leaned off of the original topic, but this is good stuff!!
Hi Doc!
There's a lot of stuff about why I am using high pressure nitrogen gas in another thread, which I suppose ought to be amalgamated with this one for the sake of those who want to look at the whole picture.
Apart from the 5 bar pressure issue, I would expect an acrylic box to be blown to pieces when 250J is switched in half a microsecond, so it will have to be something a lot tougher than even the die-cast aluminium boxes which are my solution to almost every kind of housing and container issue.
I must say I'm really delighted by both your expert assistance and your enthusiasm for my idea. Like you, I can 'see' it working in my head, though I'm sure it won't work at anything like its full potential without loads of tweaks and iterations, but that's what engineering is all about.
It has to go in a pressure vessel that can safely withstand 5 bar N2, plus the (unknown) blast overpressure. Size isn't an issue with Mark One, so I wonder how difficult it would be to saw off the end of a gas cylinder to install the gap module inside, (with very hefty feedthrus going through the cylinder wall) and then machine threads into the cut off ends in order to screw the head back on. It's not something I have the skill or equipment to do, but I could take it to a machine shop and get them to do it for me if it looked like the best way to go. The cylinder would be lined with a thick etched PTFE/Teflon sleeve both as an insulator and an an elastic buffer element to dissipate some of the shock/blast overpressure before it can distend the cylinder wall beyond the point of failure.
But maybe you can think of some entirely different high pressure housing that would be less expensive to produce, doc? I'm completely open to suggestions, because I'm trying to find my way to a place where few hobbyists have been before, and most of us have to have to have as much skill in working with micro-budgets as we do with electrical engineering, constructional skills, and theory - a greater variety of skills than are ever expected of any single person in industry.
I've just sent out for a Dominos Pizza with everything, and a six-pack of Bud, so that'll give me a bit of a break from the drawing board, and from the backache that goes with it, while I mull over all the good stuff we done talking about.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
Just a thought; if this runs hot enough to need tungsten then I don't see the mica standing up to the heat. Mica can stand about 900C. Plain copper will survive nearly 1100 and it's easy to solder, has a low resistance and is cheaper.
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Soldering/Brazing of Cu/W alloy sheet
Nothing so good as to meet a man who knows what he is talking about!
