Strange Observation of Ink in Ball Point Pen

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SUMMARY

This discussion centers on the behavior of ink in ballpoint pens when inverted. Participants observed that ink does not flow downward until the pen is actively used, attributing this to the high viscosity of the ink and the design of the pen that prevents air from entering. The conversation also highlights the role of capillary action, adhesion, and cohesion in ink flow, as well as the effects of gravity and pressure changes when writing upside down. The design features of specific pens, such as Space Pens and Papermate's pump system, are noted for their ability to function reliably in various orientations.

PREREQUISITES
  • Understanding of fluid dynamics, particularly viscosity and capillary action.
  • Familiarity with the mechanics of ballpoint pen design.
  • Knowledge of adhesion and cohesion in relation to liquid behavior.
  • Basic principles of pressure and vacuum in sealed systems.
NEXT STEPS
  • Research the mechanics of capillary action in liquids.
  • Explore the design and functionality of Space Pens and their pressure systems.
  • Investigate the properties of different inks and their viscosities.
  • Learn about the physics of adhesion and cohesion in fluid dynamics.
USEFUL FOR

Students, engineers, and anyone interested in the physics of fluid dynamics, as well as pen enthusiasts and manufacturers looking to enhance ballpoint pen designs.

  • #31
Are you saying that the air gets in there because of ('negative') hydrostatic pressure of the ink column or because it is 'dragged in' by the action of the rolling ball?
It seems to me that what goes on just behind the ball is quite complicated.

btw, I don't think the school kids' Ink Cartridges can be pressurised. When connected, and the stopper / ball at the mouth is pushed in, nothing actually squirts out. If it did, then there would be an excellent weapon for the kids and they don't use cartridges as a weapon! They manage to get it all over their fingers, though - something that the ball point pen is less prone to.
 
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  • #32
sophiecentaur said:
Are you saying that the air gets in there because of ('negative') hydrostatic pressure of the ink column or because it is 'dragged in' by the action of the rolling ball?
It seems to me that what goes on just behind the ball is quite complicated.

I don't know what you mean with hydrostatic pressure. But I was saying that once you start writing upside down, after a few seconds you consume the ink that is just below the ball, so now there is a small gap of air between the ball and the ink column, so the ball isn't 'picking up' more ink as it rolls.
 
  • #33
sophiecentaur said:
When connected, and the stopper / ball at the mouth is pushed in, nothing actually squirts out.

Ball...? Stopper...? What on Earth are you referring to?
This must be some newfangled version of the thing that I'm talking about. Mine used a totally sealed plastic tube. There was an input needle built into the base of the nib, which punctured whichever end of the tube you inserted. (The best analogy that I can think of is the vacuum blood-sample needle setups that you use in a medical clinic.)
 
  • #34
Danger said:
Ball...? Stopper...? What on Earth are you referring to?
This must be some newfangled version of the thing that I'm talking about. Mine used a totally sealed plastic tube. There was an input needle built into the base of the nib, which punctured whichever end of the tube you inserted. (The best analogy that I can think of is the vacuum blood-sample needle setups that you use in a medical clinic.)

I have seen both cartridges close the way you described and cartridges closed the way sophiecentaur described - they had a plastic tube at the end but instead of being sealed with a piece of plastic, there was a small plastic ball inside the tube - and when you installed the cartridge ball was forced inside. Same effect, but once the cartridge was empty you could open it and take the ball for... whatever. I recall having several in a box when I was a teenager.
 
  • #35
Borek said:
I recall having several in a box when I was a teenager.

You must be a hell of a lot younger than you look. :-p
I've never seen such a thing.
 
  • #36
Remember I live good 8000 kilometers away from you, this is so far that it makes strange things to time.

Actually these with balls were earlier than those just sealed. One day there was no ball in the cartridge, that was a shock I am still fighting PTSD.
 
  • #37
Borek said:
Remember I live good 8000 kilometers away from you, this is so far that it makes strange things to time.

Actually these with balls were earlier than those just sealed. One day there was no ball in the cartridge, that was a shock I am still fighting PTSD.

:smile:

Man, every time that you post, I stop and wonder why it is that North Americans ever started telling Polish jokes. :biggrin:
 
  • #38
The "cartridge pen" inserts are not pressurized!

I use, almost exclusively, refillable cartridges called "converters".

When ink is drawn out due to capillary action, air gets in the same way. A sudden drop of pressure, like in air travel, will make the pressure of the air in the ink sack / cartridge to squirt out the ink.

Some pens have snorkels which serve to equalize the pressure. But that is by no means necessary for them to work -- it just makes them easy to fill.
 
  • #39
So the air must come in around the sides of the ball? The issue is what forces are making it happen when upside down.
The only difference between the situations upside down and right way up is the difference in hydrostatic pressure, remember. Adhesion and cohesion are independent of gravity.

Also, if you store cheap pens 'ball upwards' they soon refuse even to start to work. There must be a lot more leakeage round the cheap ball.
 
  • #40
Danger said:
Ball...? Stopper...? What on Earth are you referring to?
This must be some newfangled version of the thing that I'm talking about. Mine used a totally sealed plastic tube. There was an input needle built into the base of the nib, which punctured whichever end of the tube you inserted. (The best analogy that I can think of is the vacuum blood-sample needle setups that you use in a medical clinic.)

All the kids use the ball/stopper kind these days. Are you sure you're not referring to the Charles Dickens / Bob Cratchett type quill pens which you use on a high stool in Mr Scrooge's Office?
 
  • #41
sophiecentaur said:
All the kids use the ball/stopper kind these days. Are you sure you're not referring to the Charles Dickens / Bob Cratchett type quill pens which you use on a high stool in Mr Scrooge's Office?

Enough out of you, you young whipper-snapper. :-p
I had to use these damned things in school from '65 to '67. At that time, they were absolutely the only option between fountain pens and ball-points. Believe me, I would far prefer that the school had mandated even the cheapest ball-points over those crap cartridge things. I suppose that it was economically significant that we students paid more than $1.25 for those damned pens and a 5-pack of cartridges, rather than the school system shelling out $0.10 each for ball-points.
 
  • #42
I left School some time before that, actually, so I must have missed the 'puncturing' variety. It was only about 20 years ago that I started teaching and came across the 'ball' variety. Despite quite a neat design, kids are quite capable of getting in almost as big a mess as they / we used to with conventional fountain pens with a squeezy bulb and a bottle of Parker Quink Blue-Black.
 
  • #43
I generally use Private Reserve brand ink, which is washable. I know I might make a mess, some day, and plan accordingly. Only drawback is getting notes rained on...

(I'm currently writing with a Pelican M600 filled with Visconti brown that has a tiny bit of blue-black added. It has a built-in plunger, not a cartridge at all.)
 

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