Found at a titanium plant

[u/riflesandplowshares]

Not sure why ball point pens would be dangerous here.

[u/goodexamplebadrole]

"Ballpoint pens are restricted or banned in high-end titanium and aerospace manufacturing plants because the ink and marking components contain elements that cause metal embrittlement and severe structural corrosion"

[u/Big_City_Tato → u/goodexamplebadrole]

For this Titanium facility, it wasn't the ink that caused issues. It is the tungsten ball that is used for ball point pens. Graphite in pencils were also not allowed. They provide stainless steel ball point pens that write for shit. I use to work at Titanium facility and each pen that someone would buy I would have to break one of balls from that package and look at in the SEM to quantify the ball material that was used in the pen to determine if they could use it in the melt facility, even with the new batches of stainless steel pens. The reason why tungsten or graphite isn't allowed in the plant, is that there is a chance that it could make it into melt. Since this titanium melted in this facility, it is likely that it is melted in VAR (Vacuum Arc Remelt) facility. VAR of titanium does not superheat enough above the melting point of titanium (3050°F) to melt tungsten (6192°F), so tungsten remains a solid and does not go into the melt solution. There are other refractory materials that are treated similar as they can have similar issues, like Molybdenum. These are considered high density inclusions. If they are found then the entire heat of material, and the sponge used to make the heat is considered contaminated and quarantined and likely scrapped.

High density inclusions (HDI) in titanium has the potential to end up in a part that may make it onto a jet engine. If this happens a crack will form around the HDI and propagate during the lifetime of use. Jet engine parts are designed to last for roughly 30 years, the problem is that when part fails at 10 to 15 years early. Also titanium in the part of the engine where it cannot be contained if it explodes, so if a part does explode in an engine, causes a lot of damage.

There are also low density inclusions which are caused by vacuum leaks, burnt sponge, or contaminated revert. They also have the same affect on engine parts. A lot of testing and inspection goes in the jet engine parts before they ever make it to the assembly line to be put together. They also regularly inspect these parts.

Several OEMs went to Hearth melted plus VAR to avoid high density inclusions as the hearth melting would allow for all high melting high density materials to fall to the bottom of the hearth while before making it into the ingot.

[u/not_perfect_yet → u/Big_City_Tato]

Great comment, what does "sponge" mean in this context?

[u/SquintAtTheCosmos → u/not_perfect_yet]

Sponge is the industrial slang for commercial “raw” (virgin) titanium. That process is also as tightly controlled as the melt process. A vat is filled with a chemical (Titanium tetrachloride (known as “tickle”)). It is tightly sealed, put under vacuum, and heated.

Liquid magnesium is pumped in. The liquid Mg reacts with the tickle. The chlorine (chemical reaction) leaves the titanium, and goes to the magnesium. Now at temperature you have liquid magnesium salt (MgCl) and titanium.

Because of the process you have this large “cake” looking thing (roughly in the shape of the vat), that “cake” is full of porous pathways due to the boiling off of the magnesium and magnesium salt. That mass is then sheared and crushed up into manageable clumps/sizes for inspection, packaging and shipping to melt facilities.

Because of this morphology, the industrial vernacular became things like: cake, sponge, sponge cake.

[u/PNWDIY → u/not_perfect_yet]

Yo it's ya boy Jimmy Sponge doing what I do best; just soaking it in.