tungsten

Huh, why? Can't you grind Tungsten?

George H.

sure can, thats how they making milling cutters and such, but afaik it's not and issue, tungsten is brittle so rings shatter quite easy

-Lasse

You can grind it, but you can't cut it with dikes, which is the usual last resort. Between the inevitable burn, tissue abrasion, and probable lack of grinders in your average ER, you'd be far more likely to lose the finger with a tungsten ring. I certainly wouldn't wear one.

Cheers

Phil Hobbs

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I worked in a mortuary (mostly pushing a broom) when I was an aspiring juvenile delinquent. Rings are cut because at one time, the surviving relatives would weigh the ring, and declare that the mortuary was stealing the gold or whatever. It was obviously the chips produced by a saw that was causing the slight weight loss. Still, the tradition of using cutters instead of saws prevailed.

In the 1960's, we had some kind of fixture and cutter arrangement to cut the rings. I don't recall the details. For tungsten, which is quite brittle, there's the equivalent of the automotive "nut cracker":

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It does, of course, depend on how stupid or ignorant the people at the ER are.

Tungsten carbide is even harder than tungsten, and probably less brittle. Due to its brittleness, it's incredibly easy to remove:

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RoRo

Den torsdag den 17. september 2015 kl. 18.54.43 UTC+2 skrev Robert Roland:

it is arguably safer than other rings because it won't bent around your finger if you crush it.

-Lasse

Although it does depend on what grade it is. Very pure tungsten (unless it's actually a special alloy, I don't know) is ductile at room temp and will bend rather than break. Most isn't, and has the added bonus of being porous from the sintering process.

Carbide is a technical ceramic, so of course, very brittle, and rather unreactive*.

*However, the stuff of cutting tools isn't pure carbide, but an "alloy" with 10-20% cobalt. (Technically, it's liquid phase sintered; but I like to think of it as being brazed together, in the same sense that brass brazes steel, or solder brazes lead. That last one technically isn't brazing, but I like to think of it that way.) Hopefully they don't use that, because that would probably cause dermatitis and toxicity and stuff.

Neither of these matter for the rings that are inlay. Eh, fortunately and unfortunately, I suppose.

Tim

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Seven Transistor Labs, LLC 
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I don't know about electronic components, but aren't just about all PCBs made by drilling with Tungsten Carbide drill bits? Would that concern the customer?

--

Jeff

Tungsten carbide (W4C) is the mililng cutter material (granular W4C with some cobalt binder). Pure tungsten goes from soft to soft and brittle, depending on heat treatment, and would be easy to break/grind. I think the 'wedding ring' application uses the cobalt-binder carbide composite material.

Someone told be that all Tungsten was sintered, because you couldn't put it in anything and heat it above it's melting point. (I don't know if that is true or not.)

A quick search found this,

Which says you can get crystals formed without melting but just by sintering.. which I didn't know.

George H.

Squeeze it in a vise. No problem.

--sp

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Besides the already mentioned IC interconnect and TIG electrodes, I can think of

- some high current relays/contactors, which use tungsten pre-make contacts.

- Perhaps some GDT surge arresters use tungsten as electrodes.

- x-ray tubes use often tungsten in the anode.

- some high voltage assemblies (corona discharge, ion optics)

- Anyone knows whether tungsten wire is used in fuses with high current breaking capabilities?

None of those is probably relevant for your products, though.

Klaus

P.S. I sense a bit of confusion here. When a jeweler says 'tungsten' they actually mean *tungsten carbide*.

Similar to when a machinist refers to 'carbide' they usually mean tungsten carbide.

That's the matrial used for PCB drills and other cutting tools, the teeth brazed onto circular saws etc. It's very, very hard - a 9 on the Mohs scale (boron nitride and diamond are harder).

Virtually anyone who has used carbide tooling in anger knows how brittle it is.

--sp

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Best regards,  
Spehro Pefhany 
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Thanks for the clarification, Spehro.

You should never use your tools in anger. :^) (Well unless you need to Wildarize some component.) I have busted a bunch of small carbide drill bit in haste. :^)

George H.

That point was made. AIUI, ERs now have tools that will cut Tungsten rings. With the price of Gold, they've become fairly popular.

I had one of those rings and it broke just from hitting it on the counter once.

--

Rick

That's the point. I couldn't figure out how to give them a cert for materials I couldn't get certs for in the parts I use... plus, this is already as easy money as anyone can find.

--

Rick

Yeah, grain growth occurs at elevated temperatures, which is why most metals can be forged when hot, and why sintering and ceramics are possible (and semiconductors, incidentally). It's a diffusion thing. All sintering is not made equally though: you get more grain growth, and therefore densification, when doing it for longer durations and at higher temperatures, which is expensive. (It can also be a bad thing, for the metals that don't benefit from grain growth and segregation: many aluminum and steel alloys are included.)

Sintering can also be done under pressure, in which case it's called Hot Isostatic Pressing.

Refractory metals can be melted, but it's rather difficult for several reasons:

- You need an induction levitation system. This both heats the metal and supports it, since as you suppose, you can't hold it in a crucible.

- You also need a vacuum, because at those temperatures, it reacts with most things (like oxygen and nitrogen). While you could use argon or such...

- It's still not hot enough. So as long as you're in a vacuum, and you add an electron bombardment system (think e-beam welding) too.

Now you can finally, transiently, melt the stuff.

Theodore Gray has a wonderful story, taking a trip to a Russian facility that's one of the few (if not the only) with this type of equipment. He brought a sample of -- which one I forget, possibly osmium or iridium or rhenium, which he wanted to melt to find its highest density. (These are elements that he literally has just laying around, because he has an element collection. That he keeps stored, in part, in his Periodic Table. Yes, it's a table made of wood, and it's periodic too!)

The final challenge is another limitation: because the stuff is so hot, and being bombarded with electrons, it evaporates very quickly. So even if you melt it for just a fraction of a second, you lose much of your sample -- poof, evaporated onto the chamber walls. Have fun with that!

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Thanks for that Tim, I figured you were our local induction furnace guy.

Re: T. Gray and the elements, Yeah I have his book, well I bought it for my daughter so it's her book. She has a small element collection (mostly metals) I bought home a piece of Tantalum the other night and we read about it... it's nice that she still likes this sciencey stuff at age sixteen.

George H.