How is it a ballpoint pen which did not work previously, miraculously starts working again when you make a few scratches with it on paper? What’s the mechanism behind it?
In: Engineering
If you look at a magnified image of the pen’s tip, it shows a rolling ball, hence the name ballpoint pen. If it gets unused after a short while, the ink will most likely dry up and will temporarily make the ball “stuck”, making it unable to transfer on paper.
Scratching the pen on paper will roll the ball in the tip of the pen and apply force, which will make the ball unstuck and get it rolling again, in which allows the ink to flow again.
Ballpoint pens have a steel ball sealing the ink in the pen. The ink is too thick to flow around the ball. However when you drag the ball over a surface it will spin and drag some of the ink with it therefore metering the ink onto the surface. However if you leave the pen unused for a while the ink around the steel ball can dry up locking the ball from rotating. You need to write on a surface with some friction in order to free the steel ball from the dried up ink to allow it to rotate again.
Ballpoint pens, as the name suggests, [have a ball on its tip](https://i0.wp.com/ipwatchdog.com/images/writing-instrument.jpg) which makes contact with paper, displacing ink from it in the process. When a pen is not in use for a while, the ink on the exposed side of the ball dries out and gunks up the tip, blocking new ink from flowing out. Rolling the ball vigorously tends to break off the gunk and get the ink to flow again.
The ball itself was probably stuck from a piece of dust. Dragging it across sufficiently rough paper managed to free it again.
The ball is supposed to roll ink on as you write but they occasionally get jammed.
Think about what “ballpoint” means. It’s basically a tiny ball bearing held at the end of a tube of ink. As it rolls, it transfers ink from the inside of the tube to the paper. So if you don’t use it for a while, the ink on the outside will be dry or rubbed off; “scratching” it on paper gets the ball rolling again so the transfer of ink can resume.
There is a literal ball in the end, and as you move the pen it rolls around, bringing ink on it’s surface from inside the pen to the paper. If it sits for a while, the ink dries, but a quick scribble rubs off any dried ink and gets fresh ink flowing again.
The ink also serves to lubricate the action of the ball bearing. When not in regular use it can get stiff. Once you get a couple of turns on the ball it is again sufficiently lubricated.
I am not an expert, but it’s a tiny ball that rolls in every direction, picking up ink from the stem and leaving it on the paper. At times, it feels like the ball gets stuck for some reason, and and the hard pressure of scribbling in multiple directions on paper seems to “unstick” it.
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