Tiny crucible for braze dipping ends of wire parts? - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 07:35:12 am
content: I want a tiny crucible, maybe 5mL, which I can heat full of molten braze, so I can heat with a OA torch on a stand so I can dip things into it to 'silver' them. I.e. melt nickel bearing silver braze and dip stainless steel wires ends into it, so they become solderable. So you can solder them to regular parts at a low temperature with regular solder.Any ideas on how to make this? I thought to take a graphite rod and form a chalice shape out of it. The idea is to have a small 'bowl' shape on top, where I can melt the silver and put flux on top, then dip the end of wire in there. Kind of like a high temp version of a solder pot.The idea would be to heat the neck so it acts like a heat exchanger to melt the solder in the tiny bowl (I imagine it would make good contact with the flame). I think it needs to be a bowl shape, trying to melt stuff in a strait bore is trouble IMO.Is there some crucible for this that I can buy? Is graphite a good material? I thought i could work it with a file / basic tools. I wanted to keep things kinda thin to make it easy to heat up. I wanted to make it so I can dip it, so the coating is uniform. There is too much difficult cleaning up little blobs from parts if you try to conventionally coat it.... I thought surface tension might help.I know you can get little charcoal crucibles for melting, but they are heated from the top. I need the top clear so I can dip delicate stuff in there carefully through the flux. It would glow and smoke but it should be workable.

author: TERRA Operative
author_rank: Super Contributor
timestamp: May 08, 2025, 07:40:20 am
content: How hot does it need to be?

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 07:42:52 am
content: Like melt pure silver I guess is upper limit of what makes sense. IDK what kinda adhesion I will get to various metals I wanna coat. The brazes are typically like 750C, the silver might go to 900?The idea being if you don't know how it will work, you can try different braze alloy, or whatever you got in the pot to see how it dip coats. Graphite rod stock is easy enough to work. At first I thought stainless steel, but the idea is to coat stainless steel. I don't want it like climbing the walls of a stainless crucible if it sticks. I think the 40% silver 2% nickel alloy braze is the most likely candiate for what will work

author: Analog Kid
author_rank: Super Contributor
timestamp: May 08, 2025, 07:45:19 am
content: Couldn't you make this out of steel? Its melting point is a lot higher than what you're trying to melt in it.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 07:46:05 am
content: It would coat it and then you need a new one for every experiment And if its just regular steel, I can see it creeping out of the pot. THat molten braze likes to travel. Not 100% sure it won't move up. And it might contaminate the stuff in the pot?.And like idk if you ever did it, but it gets like ugly. Parts never come out nice right after brazing with the fluxes I use, you need to clean em in acid and stuff.I thought if graphite cools down, you could just knock out the inside.I mean surely if they can make a reactor with graphite, my little contraption might work?I wanted it to work like a lab beaker. You can clean it out and its clean and ready for another experiment.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 08, 2025, 09:31:02 am
content: Hello coppercone2,Might something likethissuit to your requirement ?Alternative materials like Magnesia or ZrO2are also available.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 01:43:09 pm
content: is that suitable for heating with a torch directly?

author: Andy Watson
author_rank: Super Contributor
timestamp: May 08, 2025, 02:04:35 pm
content: Doesn't the jewellery trade already have the solution? Look-up "Jewellery crucible" on your favourite search engine. Lots of size options available, and in graphite too

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 08, 2025, 02:07:59 pm
content: Hello coppercone2,Quote from: coppercone2 on May 08, 2025, 01:43:09 pmYes Al₂O₃ is usable up to 1750°C (*), so for a C₃H₈-air or C₄H₁₀-air torch, this is OK. For a C₂H₂-O₂ torch, it's a no-go.However, I would suggest you confirm with the manufacturer/seller and ask which material has the best thermal conductivity and is not too fragile.(*) Al₂O₃ melts above 2000°C

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 08:42:01 pm
content: I know it theoretically works but its being blasted from one side and stuff. Graphite I think its ridiculously tough for heat. The other stuff, I know it can take an oven, but a torch? Like its gonna end up being hit with a torch from one side. Literally put welding torch in fixture and aim it at the melter. I feel like those furnace crucibles might not survive this.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 08:43:03 pm
content: Quote from: Andy Watson on May 08, 2025, 02:04:35 pmIf its meant for torch heating they heat it from the top with the flame, I never saw anyone try to heat it from the bottom. I need a dipping pot not a caster. I have a top heater 10mL charcoal one. You can smelt small things if you pour it. I need to keep it hot while I carefully dip small objects in there and slowly remove them. I can't have flame near the work piece. I think those typical torch ones rely on you heating the metal, which acts as a heat exchanger (molten silver) and uniformly heats the crucible. In this case you are not uniformly heating the crucible from the outside. And not with electricity. Electric coils are also uniform.The idea is quick. I can do this with my muffle furnace but its slow as balls. I want a thing I can setup and use in like 2 minutes so its not an all day affair in the work shop to make some little experimental BS. I feel like I can buy a graphite rod and make the thing in like 1/2 an hour with some files and maybe a grinder burr and it will cost $10.If I went through the trouble to wind a heater on a crucible and get a power supply and this and that I can also do it, but I wanted to know if anyone here has enough thermal knoweldge to tell me if this simplified and low effort setup might work. I am worried that the graphite might crack. I don't know how much abuse it can take.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 10:52:58 pm
content: I think the parameter I am after is thermal shock resistance. I think the higher it is, the more it can take un-even heating. Is this true?Graphite beats aluminaBut i just realized, the flux will probobly trash graphite.If I need to spread out burners or something, I might as well go electric. It was only appealing because I thought maybe you can put it infront of a torch with little workWhat I was thinking is to bang a divet into a stainless steel 'bus bar' and wire it to a resistance transformer so the middle gets hot. But that is also hard to deform, I doubt I can do it by hand without heroic effort, when I bent brackets out of that flat bar it was already totally bananas hard. Some stupidity with a ball bearing and sledge hammer might work or injure me severelyI probobly should just go electric and solve the wire gauge/coil size/wattage/voltage engineering/math problem.Though, only if it turn out I can use what I have to power it, because the main reason is I don't want another clunky heater appliance in my shopor just settle for one use crucibles made from drilled steel rods and throw em out/waste silver. Its not that bad price wise for experimenting I guess.Main idea for this was to make the end of a spring solderable so you can add a pogo pin to it. You can buy 1 brand ready made but I thought it would be cool to make a 'dimensionally correct for the problem' oscilloscope ground spring probe with pogo pin for the specific application on hand. Indium solder kinda works but its a little weak and I am scared it could pop off and short out a board, though I did manage to break the probe before it broke off once. I would be confident if I can solder it with regular solder to the stainless. I trust a silver braze much more then electro plating tooSO the idea was that you get a box of spring grounds, shape and cut them the way you like, silver it, solder on a pogo probe, and have a custom pogo pin spring ground low inductance probe. Using the springs grounds is infuriating. If you silver it manually, you end up with a ball forming, and the end of the spring needs to be carefully filed/sanded before soldering and I hate shaping tiny short wiresAnd there is other applications like solderable leads for DIY resistors and stuffLol, though I think there might be another solution that people won't like. Make a 'flicker' mechanism so you basically 'flick' the spring, covered with molten silver, so that molten silver gets flung off. That should get rid of the ball and leave a nice surface finish, but its about the most medieval solution I ever came up with, flinging molten silver at stuff lol... hmm or maybe compressed air. It might do the work I am trying to put off to surface tension.Ohhhh shit. Or, high temperature solder wick. Wow actually I wonder what would happen if I got some thick solder wick and put black brazing flux on it and try to wick molten silver. !!!! That might actually be a easy safe solution to this problem.

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 05:55:33 am
content: https://www.msesupplies.com/products/mse-pro-high-purity-99-95-molybdenum-mo-crucibles?variant=32267153244218Perfect. China already let me down on Mo before, so I got this.but i will ride it like i stole it . It wont' get no argon

author: coppercone2
author_rank: Super Contributor
timestamp: May 10, 2025, 10:51:01 pm
content: well molybdenum is heavy

author: pqass
author_rank: Super Contributor
timestamp: May 11, 2025, 12:45:40 am
content: I remember usingceramic cruciblesfor science lab.They can take the heat (1100*C) but not sure about their durability though.

author: coppercone2
author_rank: Super Contributor
timestamp: May 11, 2025, 01:03:04 am
content: Well I tried it and it works great and 56% silver with black flux coats little things nicely and very thin and makes it easy to solder . Not sure if the crucible got contaminated I will give it a soak in vinegar after.If you drill out a large bolt to make a shallow well, it would work fine I suspect. I thought there might be shenangians with the flux type, but no worries, and it works with mapp torch (I always try it first before OA). Molybdenum might have been over kill lolI thought it might be a endless quest like with electroplating lol. Not sure I even want to buy the Ni bearing solder, because the fluidity rating is lower. These parts look basically like electroplated when you pull em out from under the flux. The 7ml crucible has enough latent heat that you have a short period of time to work after you remove the torch before it starts solidifying.I did my work on a fluffy firebrick coated with two ITC coatings (the under coat and top coat), which I believe is zirconia basedand its nice and clean, minimal smokeI have silver bearing lead eutectic solder IIRC that I can use to solder the parts to stuff later, as I suspect the silver braze coat is rather thin. But I trust it alot more then electroplated coating !Exactly what I wanted. That crucible can be dedicated silver coater now for most materials, no need for experiments.If I want to use the cricble later even if its contaminated I can probably give it a soak in some kind of acid to clean it up. I just need to get some kinda bell jar type cover so after I use it I can let it cool down away from drafts so it hopefully does not crack (after I mostly empty it)and it actualy seems to heat better if you move the torch around the sides rather then heating it from up top like a charcoal one, however I suspect the char coal one might not need flux (since the gasses from it flux the inside). If you don't mind using a ounce of silver and a OA torch its probobly a better betHmm you know what else might be nice, for a next project, To see if you can dip braze aluminum. The zinc braze is a lower temperature but it should make it solderable. Perhaps in a cheaper iron crucible. Or, dip solder by filling a solder pot with one of those low temp aluminum soldering alloys (the best thing that works). That should make it easy to solder a aluminum rod. The process for plating Aluminum is a total dog. That is some where around 550C.Regular aluminum solder is 270C-300C. That you should be able to do in a regular solder pot.And I did read something along ago that perhaps 56% braze could actually bond aluminum, with the main problem being is the melting points. But perhaps a very quick dip might be the answer to getting silver on aluminum without messing it up too much. The melting points are equal, but aluminum is a good conductor of heat so maybe the right size part could survive and get a coating. But this would need a precise control (silver braze is 652, aluminum is 660. 8 degrees margin, for some aluminum alloys, I think most melt at a lower temp then the braze). Maybe someone more interested then me can experiment with this fine line. Perhaps I can try to dunk an aluminum rod in there, but it would probobly waste 2 sticks of silver brazeThough the problem is I forgot what the hell I was even trying to do with aluminum that made this interesting. Must have been a decade lol. Now its a process without a point.Real nice. I need to try with pure silverit looks like pickling takes care of the residue in therebthe molybdenum turned purple from fireI think ima buy a graphite one and try it. I see this stuff is not as dangerous or flowy as I thought it would be on the surfaces I am using, so if it cracks so be it. Picking does seem to work on it but it might be effecting the crucible a little bit and it seems foolish to use it if the solder sticks to it, I thought it would all come out super nice. I guess this is one of those questions of metals, when you are boiling one meant to stick everything together with fire under molten salt the game is a little different then the vacuum furnace they expect lol. I know I can use this molybdenum crucible for a higher purpose them silvering leads. It cools so fast in these small amounts it does not travel far. I was thinking like it might make a big hazard if it gets out. Its alot more intimidating when it flows under a OA torch on a red hot big piece of copper then it is in this situation (queen with no creep).Little graphite crucibles are a dime a dozengot some different element pellets too for doing solder/braze experiments.

author: coppercone2
author_rank: Super Contributor
timestamp: May 21, 2025, 06:03:53 am
content: the graphite is the best for silver solder by far, works with a mapp torch.I tried a zirconia and melted pure silver (slow) but it cracked on me, you can't be foooling around with a hand torch on that material as good as the reputation is. I assume the silver may have frozen and unfrozen with my bootleg freehand approach. Maybe if you make a fixture it could work but I don't know if that type of material even tolerates bare flames like that for those temperatures. I am guessing no. Very interesting to see the thin ceramic crack though when being heated, you see that there is a thermal barrier and the glow changes because heat is not going sideways or something like this.But you can do silver solder (56%) with graphite. And it heats up fast. One of those push button blow torches would be best so you can turn it off, or a extender tube with a torch holder.And their cheap. Get alot of them and its disposable (there is a ebay usa seller, looks like its turned on a lathe). If you got a proper furnace and alot of money I think it would be good to dip coat big objects like thatVery satisfying, I made a bunch of pogo pin ground probe adapters from my old ground spring collection. If you get the gold plated ground springs though, they solder just fine without doing anything to them. I don't think there is a good reason why you can't braze a splice in their either. Its like easy to control it being molten with a hand torch. Carbon really absorbs the flame heat good.I am still happy to have the molybdenum for my chill-plate experiments (peltier) to use as a cooling cup. It does react more with some acids then I thought it would, howeverWhat I think I am interested in is Ag72Cu28 alloy. I wonder if its the brazing alloy that has the lowest EMF since its mostly silver and no other metals and has the lowest melting point of the combo. But I forgot the application at this point. You can get it as some kind of foils onlineAnd the Mo works, but it probobly designed for vacuum use. With that flux boiling in there, the silver solder DOES stick to it in some places and its a right pain in the ass to get out (with pickling). I assume it would work fine for a silver boiling tub in vacuum, but not for my dirty business with black fluxand the graphite is durable, I dropped one 4 feet on tile floor before I used it and it was fine, I thought it might be mega brittleI am kind of thinking a silver solder pot is kind of indispensable from a workshop, combined with a few dollar graphite crucible. Really impressed how nice and easy it is with only plumber torch, compared to the business with setting up to electroplate tiny objects.What I like is that you can probobly get a butt load of spring grounds to solder to a PCB this way, since any cheap crap will work on this (no need for gold plated), to make durable test points for high frequency circuits, without having to wrap custom springs to solder on!

author: coppercone2
author_rank: Super Contributor
timestamp: May 28, 2025, 04:22:45 am
content: very clever way to use the wire as a coupler in that video.The proper way you make graphite coupler appears to be steel channels with shims to bend them out a little so they grip a graphite, if you can't metalize