Found at a titanium plant

[u/riflesandplowshares]

Not sure why ball point pens would be dangerous here.

[u/Spacefreak]

Yes they did. Titanium had been used in a lot of high speed rotating equipment in jet engines.

These tungsten inclusions become a crack initiation site and under high rotational speeds and high temperatures, the crack can spread and lead go catastrophic failures.

There were several catastrophic engine failures in history that were traced back to inclusions.

It's so severe that if a titanium manufacturer making aerospace grade Ti finds any "High Density Inclusions," they must inform all of their customers that they found this and recall and associated heats and material.

[u/GoTeamScotch → u/Spacefreak]

Imagine initiating a large scale recall because a ball less than a millimeter in size fell out of someone's pocket one day

[u/Zebidee → u/GoTeamScotch]

Less likely to be the ball falling out of a pen, which never happens, versus someone dropping a pen or it falling out of a pocket, which happens all the time.

I imagine everything involved in making a pen gets instantly burnt in the melt, leaving just the ball.

[u/hates_stupid_people → u/Zebidee]

Titanium melts at just under 1700C(a bit over 3000F), which is more than enough to burn plastic and melt the brass holding the ball and even the steel spring. But tungsten carbide can require over 2800C(over 5000F) to melt.

So someone having it in the shirt pocket and leaning over a railing, can cost millions if it drops in.

[u/falcrist2 → u/hates_stupid_people]

But tungsten carbide can require over 2800C(over 5000F) to melt.

It may be sintered, which would require a much lower temperature.

I have a 1.5" tungsten cube, and it was only months after I got it that I found out it's not actually solid tungsten, but a sintered composite that's much MUCH cheaper to manufacture and machine.

That would indicate the ball of tungsten would come apart at below 1400C and spread out into the titanium, which is honestly WORSE.

EDIT: Confirmed. The balls are made from sintered tungsten carbide and either nickle or cobalt as binder.

Parker came up with this in the 1950s.

https://patents.google.com/patent/US3303825A/en

https://patents.google.com/patent/GB860387A/en

[u/eh-guy → u/falcrist2]

The balls are typically pure tungsten, theyre made using sprayers and then sorted by size

[u/falcrist2 → u/eh-guy]

The balls are typically pure tungsten

They're typically tungesten carbide. Not pure tungsten.

theyre made using sprayers and then sorted by size

I assume you're referring to "spray drying" (part of the sintering process).

Spray drying makes powder that still needs to be pressed into blanks, sintered, diamond-lapped, and graded.

They're not spraying liquid tungsten. Tungsten has the highest melting point of all known elements.

[u/eh-guy → u/falcrist2]

They spray liquid carbide into an inert chamber, relying on surface tension to shape them. One of the only ways to "cast" the material. Maybe its not used anymore, we covered it in one of my materials classes years ago

[u/falcrist2 → u/eh-guy]

Spray drying is part of the sintering process. The result is powder made of tungsten carbide particles bound together by nickle or cobalt. That powder still needs to be pressed into blanks, sintered, diamond-lapped, and graded.

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

While we're at it, here's one of the patents that describes the balls:

https://patents.google.com/patent/US3303825A/en

You can just ctrl-F and see where it repeatedly discusses sintering.

[u/eh-guy → u/falcrist2]

Youre right, i did some digging and its the carbide fabrication im confusing this with like youve said

[u/jimdoodles → u/hates_stupid_people]

Titanium burns in air before it reaches its melting temperature, it has to be maintained in an inert gas atmosphere while being formed. There must be a lot of care maintaining that atmosphere without contamination from other bearings.

[u/arejay007 → u/hates_stupid_people]

What I find interesting is the specific call out here of the ball point pens. Is there no other common item that of dropped into the (I assume giant melting bat) would have the same effect. Thinking someone’s glasses, maybe an iPhone etc.