# TIG casting in a mold



## omgsuperhax (Jul 4, 2020)

I have an absolutely insane idea I'd like to run by people.

I am a home jeweler, as in I 3d print and cast silver and gold. I'm getting married and I want a unique ring. I for some reason, have decided to try and make a rhenium ring.

I know rhenium has an insane melting point (and toxicity is unknown) but I just want to make it, I likely will never wear the ring, I don't wear jewelry. So I have a crazy idea that just might work but I wonder what other people think. Rhenium is normally melted/alloyed in a vacuum arc furnace, clearly that kind of equipment is beyond the hobbyist like me. But a TIG welder is not, and it's the exact same principle, non consumable electrode arc melting in an argon atmosphere. I know the crucible used in Vacuum Arc Remelting is a water cooler copper hearth, but casting copper is again something that is crazy difficult to do for me, but silver actually has a higher heat conductivity than copper (sterling silver is 10% lower, but it's the best I can do). 

I plan on casting a water cooled sterling silver mold of the ring, like a trench cut into the inner ring of a donut (probably split into thirds so I do not have to destroy the mold to release the ring). Then take rhenium powder or even wire or bar or previously arc melted samples, and use a TIG torch to melt it (I guess it would be brazing) into the silver mold. I have little experience doing any TIG welding, I know it could take a very powerful, water cooled unit to do the melting but tk me it seems possible. I only plan on melting a very small portion at a time, like about a gram or two. I know the structural strength of a ring would be lower than one cast as one piece but I don't mind. I am also aware that the argon blanketing would be imperfect and could result in some rhenium being burned up and a loss of material but I am ok with that. 

Does anyone have experience using a TIG torch to melt other high melting point metals like iridium, platinum, osmium, tantalum, etc? Does anyone have any clue if the underside of the weld would form to whatever shape or design the mold has, or would I need to have the outside machined as well? 

It seems crazy but it also seems like it could work. I'd love to hear feedback!


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## g_axelsson (Jul 4, 2020)

I would say that it's impossible to cast a ring in a metal mold like that, the physics would be insane. Even with an electron beam melter with vacuum bell and water cooled copper hearth. Not many hobbyists have one but I do. :mrgreen: 

To cast a ring the metal needs to flow inside the mold and not freeze before the mold is filled up. With a cooled metal mold it would just freeze at contact and clog the mold. If you overheat the metal it would melt the surface where you pour the metal. A ring is too thin to make an extreme cast like this.
If it was as easy to do as you describe it, then there would be a lot of people doing it already.

I've seen a video of a platinum bar cast in a water cooled copper mold and it had a lot of surface defects from the rapid cooling when it came in contact with the copper.
Found it! Check this thread and the video in it. https://goldrefiningforum.com/phpBB3/viewtopic.php?t=22917#p240759

Göran


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## omgsuperhax (Jul 4, 2020)

EDIT: I don't want to seem combative, I'm very grateful for your insight! 

Sure, I don't think it'll come out looking anything like normal lost wax investment casting, and there's no reason to do it this way other than the extreme temp needed to melt Rhenium (3185°C vs silver at less than 1000°C or even platinum under 2000°C). No one does it because you can melt gold/silver/platinum with more accurate and better tested methods. But when forming refractory metals into a bar or wire, they do use suction casting to pull the molten metal into a water cooled copper/graphite mold, its the only way to cast really high melting point metals. But that's for parts that are used in jet engines or the like and need to be strong. I definitely expect it to be much less structurally sound than a casting, and I don't need it to be workable or malleable afterwards either. 

But perhaps casting is the wrong term to use. It's more like the continuous casting of steel? Or just additive brazing/welding in a ring? Sort of like a 3d printer using a welding stick instead of plastic. I don't want to melt all of the estimated 12-17g of rhenium at once, maybe a gram at a time. Like I guess imagine normal ring, I'd melt a small bead of Rhenium on the inside diameter, then rotate the ring 10° and then weld another bead, rotate again and weld another bead. Eventually you'd have a brazed or welded ring of rhenium on the inside of the other ring. Kind of how when brazing the beginning of your weld is solid and cool by the time you weld the last part of your bead.


You do have a copper cooled hearth? I'm curious if you melt a large mass of metal how closely does the resulting button follow the shape of the hearth or is the rounded shape just the result of surface tension.


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## jimdoc (Jul 4, 2020)

Here is a rhenium ring that I have. I was told it needed an EDM to make it from a rod.


What's your favorite precious metal?


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## omgsuperhax (Jul 4, 2020)

I saw that when I was initially researching different metals! Very nice!


Here's another one I found too.

https://www.rwmmint.com/products/rhenium-re-24-karat-ring

They also make a pure iridium ring.


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## omgsuperhax (Jul 4, 2020)

g_axelsson said:


> I would say that it's impossible to cast a ring in a metal mold like that, the physics would be insane. Even with an electron beam melter with vacuum bell and water cooled copper hearth. Not many hobbyists have one but I do. :mrgreen:
> 
> To cast a ring the metal needs to flow inside the mold and not freeze before the mold is filled up. With a cooled metal mold it would just freeze at contact and clog the mold. If you overheat the metal it would melt the surface where you pour the metal. A ring is too thin to make an extreme cast like this.
> If it was as easy to do as you describe it, then there would be a lot of people doing it already.
> ...



Oh I had a friend give me a different way to put it!

He worded it as not "casting" but "using a rounded backing plate to shape a brazed bead"


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## Lou (Jul 4, 2020)

Rhenium is nontoxic and rolls, swages, can be drawn much like copper. A very nice, dense metal. Truly best enjoyed as fully dense pieces.

Best bet is to press into rod from powder, sinter under H2 (Re volatilizes), then cut that with EDM (or drill hole). Fabricate from there by turning on lathe.



Also, Research135 is correct that zirconia is also used as backup. I’ve used zircon sand, but zirconia (ZrO2). So excuse my jerk behavior to him. He is a member I regret losing.


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## omgsuperhax (Jul 4, 2020)

Lou said:


> Rhenium is nontoxic and rolls, swages, can be drawn much like copper. A very nice, dense metal. Truly best enjoyed as fully dense pieces.
> 
> Best bet is to press into rod from powder, sinter under H2 (Re volatilizes), then cut that with EDM (or drill hole). Fabricate from there by turning on lathe.
> 
> ...




Using zircon sand as what? To cast platinum? 
Is this a continuation of the post from where the post with that video?

I see that copper blocks were used to cast platinum ingots, that's pretty interesting.

I agree that sintering would be the best bet, but I don't have the ability to do that. I am a hobbyist and have the equipment to cast silver and gold, but I'm willing to borrow a TIG welder to try this lol


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## Lino1406 (Jul 5, 2020)

TIG welder will not do that. It is a point welder


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## Yggdrasil (Jul 5, 2020)

I beg to differ Lino.
TIG welding is the predominant method for stainless steels and other non ferric metals.
DC welding as used in SS can be superbly focused, AC welding as in Aluminum is more spread and as such less focused.
It can reach very high tempertures in concentrated areas, in many respects the welding is done by a plasma beam at around 10000 deg C.
It has the benefit that if you design the parts correctly, you do not have to add material to the weld and as such the weld will be very homogenous.
It will not reach electron beam/laser temperatures though.


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## Lino1406 (Jul 5, 2020)

You mean a ring with an acceptable form can be made of point weldings?


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## Yggdrasil (Jul 5, 2020)

No!! 
I believe we have a misunderstanding here. :wink: 

What I mean is that a TIG welder is not a point welder, even if it can be used for point welding.
Persionally I have successfully welded a Titanium pipe with additive material made of strips cut from the same as the base material.


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## Lino1406 (Jul 5, 2020)

Thanks for clarifying YD


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## omgsuperhax (Jul 5, 2020)

Lino1406 said:


> TIG welder will not do that. It is a point welder




Sure. I wasn't attempting to melt all the material for a ring at once into a single mold. I meant point melting a small drop of rhenium inside of a shaped channel, then moving a bit and melting another small piece. I know melting a whole blob would be impossible, but is it possible to shape a weld by constraining it in a cooled mold. 

In my head it seems like applying papier-mache to a mold, you apply it bit by bit, and it's definitely not one solid piece, but it comes close to the final form you want it to be. Obviously the inside diameter or the ring would need cleaning up as it would be like the top of a weld.


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## omgsuperhax (Jul 5, 2020)

I will attempt to draw a diagram so it makes sense lol


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## FrugalRefiner (Jul 5, 2020)

I think it's an interesting idea, but I don't know that you'll find anyone with experience to guide you. You're a pioneer. Follow the beat of your own drummer and let us know how it turns out. I'm looking forward to seeing pictures!

Dave


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## omgsuperhax (Jul 5, 2020)

FrugalRefiner said:


> I think it's an interesting idea, but I don't know that you'll find anyone with experience to guide you. You're a pioneer. Follow the beat of your own drummer and let us know how it turns out. I'm looking forward to seeing pictures!
> 
> Dave




Ya, I kind of hoped it wasn't this lol. It makes sense in my head that it would work, but I really didn't want to make the leap of it doesn't work, the fiance will be mad for me wasting time and money on it haha. But the pay off is the most unique ring on the planet to match the Apollo moon dust ring I made for her engagement ring.
I know it's sort of like intentionally failing to make a proper weld, so no one is trying to fail this way.


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## jimdoc (Jul 5, 2020)

What are the limits of induction heating? And have you looked into that?


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## Lino1406 (Jul 5, 2020)

Here is the expected result, best case


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## omgsuperhax (Jul 6, 2020)

jimdoc said:


> What are the limits of induction heating? And have you looked into that?



I've considered it. I think rhenium's magnetic properties don't bode well for induction melting, at least that's what I've read in the scientific sources I've managed to find.


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## Lou (Jul 6, 2020)

You can sinter it.

Take said welding power supply and improvise one of these:

https://en.wikipedia.org/wiki/Spark_plasma_sintering


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## butcher (Jul 6, 2020)

I would look into twisting or braiding multiple strands of the PGM thermocouple wires and wrap wire braid into a ring shape then using tig torch to weld the braid together using more of the same thermocouple wire as a filler rod.


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## omgsuperhax (Jul 6, 2020)

Lou said:


> You can sinter it.
> 
> Take said welding power supply and improvise one of these:
> 
> https://en.wikipedia.org/wiki/Spark_plasma_sintering




So it would be more like resistance heating it, not really hitting with an arc. So kind of like fusing it together by heating it up like a lightbulb filament? I'd have to evacuate the air somehow or blanket it with argon first though. I could try to think of a way to do that


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## snoman701 (Jul 6, 2020)

Much better off starting out with an ingot of vacuum arc remelted rhenium and having it wire edm'd out.

Melting any of these metals mentioned in this thread (except platinum) will require every bit of vacuum you can get out of a good rotary vane pump. 

You *MIGHT* be able to pull a ring into a copper hearth ingot mould, but I doubt it.


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