I was at a boring accounting seminar today. How do they get the ink into those very narrow tubes that make up the cartidge. It seems the ink is very viscous so it won’t pour very well.
I suspect a very narrow needle that is plunged to the bottom then injects the ink as it is drawn up. But that seems like quite the technical challenge to get a needle in such a narrow tube and inject viscous ink without spilling any at all. Do they heat the ink up too to make it less viscous? Is such a narrow bore needle that difficult to manufacture that consistently works withbending, plugging or spilling ink?
Also, have you considered how many tiny cheap parts go into making a ‘giveaway’ pen? the one I had, has a little thin rubber cap on the butte end that didnt’ do anything but cover the end. Someone had to design, produce molds, manufacture and somehow attach it to the pen… its astounding how so many tiny little parts that have little function are manufactured by the millions so cheaply.
This page doesn’t get into much detail about that part of the process, but it does mention “injectors”, which sounds like your needle idea.
See - YouTube
(at 2 minutes 34 seconds)
That’s for the older-style pens with slightly fatter cartridges, but I imagine the process is similar for newer ones…
Or, not as close-up a view, but modern Bic pens getting injected at 7 minutes:
(at 7 minutes)
Well they can adjust the viscosity, and they worked out that if its really thick, then stickiness will hold it into the tube, while the rolling ball will grab some and transfer it to the paper, and that grabbing drags the whole bolus of ink down the tube.
The stickiness of the ink to the tube is what I think are what the OP missed… OP was thinking the ink is so think it would sit in shape if the tube was not there… no its definitely liquid, but its held in place by the stickiness of the ink , the way it sticks to the tube…
So the ink is liquid and will flow into the tube with just a little pressure, its just that gravity and general hand movements aren’t enough to make it move.
But there’s what I found… if you have a biro that seems to have run out of ink, check to see if there is ink in the tube… if so, just blow down the end of the tube… the additional force of your breath may well cause the ink to move down to the ball point… the stickiness isn’t that much is it ?
Smaller diameter circles/cylinders/ spheres have a higher ratio of circumference/surface area /surface area to area/volume/volume… Its why dust floats in the air… the ratio of surface area to weight is higher for smaller particles… the air-dust stickiness then holds onto the particle…
What amazes me even more about ball-point pens is the ball-point – They have to manufacture, to highly precise tolerances, those itty bitty ball bearings, and the sockets they sit in, and then assemble all of the parts together.
That rubber bit isn’t useless decoration. That converts the pen into a stylus for use on touchscreen tablets. You just “write” on the screen using the other end of what’s otherwise a ballpoint pen.
To make them now seems trivial, but the first ball point pen patent was awarded in 1888. Making a ball point pen back then was amazing.