A YT content provider who specialises in collecting odd warning signs was intrigued by a large one spotted outside a titanium factory which read “NO BALL POINT PENS ALLOWED ON PLANT SITE”

https://www.youtube.com/shorts/R8lB6A-riIY

Somewhat intrigued, he did some research to find out why, and discovered that ball point pens have tungsten carbide tips. If a production engineer has some of these in a breast pocket and leans over the railing of an overhead gantry, the pens could fall down and contaminate the feed-stock of a titanium furnace. The plastic components of the pen would be instantly destroyed, but the tungsten carbide ball in the tip which has a higher melting point could survive and introduce a microscopic inclusion flaw into a titanium casting. As these melts tend to be used for mission critical high precision components in the aerospace industry, possible points of failure have to be kept to an absolute minimum.

1 hour ago, toucana said:

A YT content provider who specialises in collecting odd warning signs was intrigued by a large one spotted outside a titanium factory which read “NO BALL POINT PENS ALLOWED ON PLANT SITE”

https://www.youtube.com/shorts/R8lB6A-riIY

Somewhat intrigued, he did some research to find out why, and discovered that ball point pens have tungsten carbide tips. If a production engineer has some of these in a breast pocket and leans over the railing of an overhead gantry, the pens could fall down and contaminate the feed-stock of a titanium furnace. The plastic components of the pen would be instantly destroyed, but the tungsten carbide ball in the tip which has a higher melting point could survive and introduce a microscopic inclusion flaw into a titanium casting. As these melts tend to be used for mission critical high precision components in the aerospace industry, possible points of failure have to be kept to an absolute minimum.

Curious.

I rather like this one, from an Australian (where else? 😁) construction site: