Computationally Modelling Ink Filling Systems To Identify Causes Of Bubble Formation

[stothy]

Hey all, I'm a bit of a lurker around here but I love checking in every so often. I am posting this around multiple sites at the moment as I am preparing to start my dissertation with the title "Computationally modelling ink filling systems to identify causes of bubble formation". This was a project I initiated myself as I wanted to be able to involve my interest in fountain pens in my work at university. Basically I am aiming to model how bubbles form in converters/feeds/pistons and even inkjet printers and to comment on their adverse effects on the performance of fountain pens/printers and solutions to this problem. I plan for it to be a fairly dynamic project so nothing is set in stone about what I am going to do, I have no idea where it will take me.

I was wondering if anyone in this fantastic community has done any work in the area or know anyone who has? If so, are there any papers you would recommend for me to read or is there something in particular that you think I should attempt? Any advice is appreciated and if anyone is interested in talking to me about my project then I would be more than happy to discuss it with you. If there is a particular interest in my project then I may even be inclined to make regular blog posts on my work and findings. Thank you in advance, I really look forward to any suggestions that you have!

Edited August 20, 2015 by stothy

[Pickwick]

You may well be the first in this field of analysis my friend. As far as I know this has never been thought out before and air bubbles forming is as old as the innovation of the fountain pen. Having been acquainted with pen and ink these past seventy years, the solution to expelling air bubbles when the sac or converter is empty is, immerse the nib and feed in the ink, fill, lift the pen free from the ink, expel the ink along with air bubbles which inevitably form, and then repeat until all the air is expelled.

 

These instructions were included with every new pen manufacturers produced many years ago, and to my knowledge even they have never done an investigation.

 

I have searched the web to see if anyone has done any scientific research, but found nothing except the above advice I have always followed.

 

Having written that, I would be interested to read any other members explanations on this subject who may have done an investigation.

[jar]

Detergent makers likely have all your answers.

[welch]

Start with pen company engineers. Try contacting whoever now runs Onoto; Parker and Waterman in France; Pelikan; Lamy. They must have "fluidic designers", that body of knowledge must have been transmitted from earlier pen companies.

 

Check the interview with Geoff Hollington, who designed the Parker Insignia, Sonnett, and Parker 100 at Tony Fischier's Parker Penography:

http://parkerpens.net/geoff_hollington_interview.html

 

Tony writes: "All of the interior, mechanical and fluidic design was done by Parker, but he worked closely with Parker's engineers to make sure space was efficiently used and that writing performance, cap fit, pushbutton action and so on were optimised."

 

Tony might know how to get into parts of the Parker archives that have design information from their pens. It would be glorious if Parker had saved sketches, blueprints, exact design details from the original Duofold, the Vacumatic, and both filling versions of the 51. Geoff Parker might have design documents that the archives don't...calls himself a "pack rat".

 

I read a biography of Henry Dreyfuss, who designed the Eversharp Skyline, but Dreyfuss says nothing much about fountain pens. Lots about chairs, rail cars, the interior of airliners, tractors...even the interior of WW2 tanks, I think. Not Eversharps.

Edited August 21, 2015 by welch

[stothy]

Wow, this response is overwhelming, thank you to everyone for showing an interest!

 

@welch, I really appreciate all the effort you have gone to to help me with my project, the resource that you have suggested sound ideal for what I am looking for, I will definitely make sure I contact the people you have suggested. Thank you again!

[jar]

Remember that fountain pens only work because bubbles get in. No bubbles means no workie.

[stothy]

Remember that fountain pens only work because bubbles get in. No bubbles means no workie.

My understanding is that fountain pens only work because air gets in whilst in use. The air is being replaced by ink when being filled so bubble formation is a sign of the pen being filled imperfectly.

 

I'm interested to know what you are suggesting as it could completely change the nature of my project from "how to reduce bubble formation" to "how to create the ideal amount of bubble formation". Thank you for your input!

[Pickwick]

My understanding is that fountain pens only work because air gets in whilst in use. The air is being replaced by ink when being filled so bubble formation is a sign of the pen being filled imperfectly.

 

I'm interested to know what you are suggesting as it could completely change the nature of my project from "how to reduce bubble formation" to "how to create the ideal amount of bubble formation". Thank you for your input!

As I understand the OPs project, it's the initial problem of the formation of bubbles in a sac or converter during filling.I only have a couple of pens with this problem on the initial fill. My conclusion is air is still getting in no matter how deep I immerse the pen in the ink. when filling.

 

Bubbles are not how the pen works during writing. If this was the case it would only cause a violent action similar to inverting an open bottle of water ninety degrees, forcing air to enter in bubbles. This would cause a fountain pen to shed the ink in a similar manner.

 

This is where the feed comes in. It's designed not only to collect ink, but also to allow air into the sac or converter in a controlled without forming bubbles, which could prove disastrous. It's essential in ensuring a continuous flow of ink onto paper.

[stothy]

That is exactly right Pickwick and it seems we have the same understanding of how a fountain pen works as well. Thank you for clarifying this but if anyone else has any alternative views on the matter, please let me know!

[jar]

My understanding is that fountain pens only work because air gets in whilst in use. The air is being replaced by ink when being filled so bubble formation is a sign of the pen being filled imperfectly.

 

I'm interested to know what you are suggesting as it could completely change the nature of my project from "how to reduce bubble formation" to "how to create the ideal amount of bubble formation". Thank you for your input!

The issue is not bubbles but rather where a bubble might be. Bubbles in ink are only a problem when surface tension holds a bubble at the very entrance to the feed.

 

That is pretty common in some converter pens and almost unknown in most other filling methods. The pen works as ink gets replaced by air. Filling has absolutely nothing to do with writing though so bubbles during filling are irrelevant.

 

The problem of a bubble being held at the neck of some converters is pretty well known as are the solutions; adding surfactant to the ink, inserting some obstruction that will break up a blocking bubble (beads, springs, ball bearings) and cleaning the inner wall of the converter with a surfactant that will bond (even if only temporarily) on that inner surface.

[Pickwick]

The issue is not bubbles but rather where a bubble might be. Bubbles in ink are only a problem when surface tension holds a bubble at the very entrance to the feed.

 

That is pretty common in some converter pens and almost unknown in most other filling methods. The pen works as ink gets replaced by air. Filling has absolutely nothing to do with writing though so bubbles during filling are irrelevant.

 

The problem of a bubble being held at the neck of some converters is pretty well known as are the solutions; adding surfactant to the ink, inserting some obstruction that will break up a blocking bubble (beads, springs, ball bearings) and cleaning the inner wall of the converter with a surfacant that will bond (even if only temporarily) on that inner surface.

I've just carried out your tip and cleaned the two converters giving me problems and they are working OK. Thank you.

[rwilsonedn]

Unless you have a research team and a computing lab at your disposal, it seems to me, you may want to limit the scope of your dissertation quite a bit. Even the meaning of the word bubble in this thread has changed enough to create several good dissertations. Do we mean the bubble in the top of the ink chamber? Or an obstructive bubble at the entrance to the feed? Or unstable bubbles that form during filling? (How unstable?) Or bubbles responsible for the transport of air through the feed during writing? Any one of those could be a significant project.

The one that I would vote for would be computational study of the exchange of ink and air in a feed/nib system during writing. It has always puzzled me. Most people say ink moves through the feed channels by capillary action. Then it reaches the nib, is drawn through the slit again by capillary action, and somehow transfers to the writing surface once it reaches the tip. But obviously at least some of the time capillary action is replaced by some other mechanism: I have ink blots on my journals to prove it. And sometimes transport stops altogether. Several possible mechanisms there. And I have never seen a convincing story about the reverse transport of air. As Jar points out, if air were not being continually moved up the feed into the ink chamber, a vacuum would form that would eventually draw the ink back out of the feed. But how is it moving: micro-bubbles? A tiny channel that is not blocked by ink? Diffusion? And how is the air intake restricted enough to prevent the pen from simply leaking when you hold it nib-down?

Enough questions for one day ... great topic!

ron

[stothy]

Unless you have a research team and a computing lab at your disposal, it seems to me, you may want to limit the scope of your dissertation quite a bit. Even the meaning of the word bubble in this thread has changed enough to create several good dissertations. Do we mean the bubble in the top of the ink chamber? Or an obstructive bubble at the entrance to the feed? Or unstable bubbles that form during filling? (How unstable?) Or bubbles responsible for the transport of air through the feed during writing? Any one of those could be a significant project.

The one that I would vote for would be computational study of the exchange of ink and air in a feed/nib system during writing. It has always puzzled me. Most people say ink moves through the feed channels by capillary action. Then it reaches the nib, is drawn through the slit again by capillary action, and somehow transfers to the writing surface once it reaches the tip. But obviously at least some of the time capillary action is replaced by some other mechanism: I have ink blots on my journals to prove it. And sometimes transport stops altogether. Several possible mechanisms there. And I have never seen a convincing story about the reverse transport of air. As Jar points out, if air were not being continually moved up the feed into the ink chamber, a vacuum would form that would eventually draw the ink back out of the feed. But how is it moving: micro-bubbles? A tiny channel that is not blocked by ink? Diffusion? And how is the air intake restricted enough to prevent the pen from simply leaking when you hold it nib-down?

Enough questions for one day ... great topic!

ron

That is what I was aiming to do, I was going to do some further research and once I have enough information, decide on a specific type of bubble formation. Although that is interesting to me it is not where I will be directing my research, I am more concerned with bubble formation when the pen is being filled with ink. To model the writing experience a much more complex model would have to be used; one that is dynamic so that things such as the nib could move, unfortunately I do not have the resources to work on such a model.

 

Thank you for your kind words though, I really appreciate all the support!

[El Gordo]

Interesting, and I do not want to take the "fun" out of it, but just wondering whether you also need to consider the "fund" part? If so, interest might be higher if it is part of a bigger problem with wider economic impact? Some similar problems in other fields maybe?

Edited August 23, 2015 by El Gordo

[stothy]

Interesting, and I do not want to take the "fun" out of it, but just wondering whether you also need to consider the "fund" part? If so, interest might be higher if it is part of a bigger problem with wider economic impact? Some similar problems in other fields maybe?

I would be interested to know what you mean exactly, if you mean how it could potentially save money then I will definitely cover this, it is something that my academic mentor is very interested in as he specialises in inkjet printing and he wants me to make analogies to inkjet printers. If you mean something else, please let me know.

[El Gordo]

I would be interested to know what you mean exactly, if you mean how it could potentially save money then I will definitely cover this, it is something that my academic mentor is very interested in as he specialises in inkjet printing and he wants me to make analogies to inkjet printers. If you mean something else, please let me know.

 

Actually you already answered it yourself: what I meant is that if some external funding (or even justification of university funds) plays a role, people might question about the economic relevance (ROI) of research for a niche market. Inkjet and analogies in that field might be good and relevant connection on that side.

Depending on the actual modelling focus and comparison between both:

- on youtube (don't ask me where, guess it was a video from Lamy, could be wrong) there is at a certain moment a 3D drawing on screen of a feed. Could be simply for mould making, but I guess the file could as well serve as input for modelling work. Don't know. Never been there.

- It might also be worthwhile to dig in some "old" literature (late 1970's and 1980's or so) when inkjets and the micromachining of heads were still in the, say, precompetitive research phase and have a look of what has been done then and how it emerged to the current status (with a period in between that, I guess, would have more industrial development without publication too much details). In the early days a number of problems related to satellite formation, viscosity, etc were encountered, and modelling could be done as well, be it with less powerfull tools than today. No references come to my mind however.

[pepsiplease69]

Most modern feeds have an 'ink-delivery' side, which involves the ink channel and the ink-air exchange that the feed does at the mouth of the converter (for cartridge converter pens), and an ink-intake side.

 

This is the little opening on the underside of the feed that must be dipped in ink while filling the pen. Normally this opening stays free and clear during writing. Only during filling this opening is immersed in ink and some form of suction draws ink through this intake opening up into the ink reservoir. Naturally there's air in the intake opening in normal cases, and when the pen is dipped into the ink, there's some air that gets in front of the ink coming into the reservoir, therefore trapping a bubble of air along the way.

 

I'm not wanting to answer your original question, just sharing my own experience here.

[dneal]

jar is on the money with his posts. I'll try to expound / clarify them with some pictures.

 

First, the only problem with "bubbles" in the part of the pen that holds the ink is when (as noted) surface tension prevents the ink from moving to the feed.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/SurfaceTension015_zps1c980d6d.jpg

 

Although converters are the primary culprits, this can happen in any pen, with any type of filling mechanism. Here are some cartridges exhibiting the behavior.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/Stuck%20Ink%20001_zpsckzohboh.jpg

 

I have an M300 that loves to do this with Caran d'Ache ink, so piston fillers aren't immune (although they seem to be less susceptible).

 

Again, it's all about surface tension. If you're writing a technical paper then that should be your focus.

 

More generally (and as noted by jar), pens work by exchanging ink for air. As the ink leaves the pen, something must replace it or a vacuum is formed and no more ink will come out. You can observe this happening. Using a piston filler with a clear window, or a converter with the barrel removed, fill the pen with clear water. Then, wrap the nib in a paper towel (so it will draw the ink out) and while holding the pen nib-down, observe the reservoir. You will see small bubbles rising from the feed to the top of the ink reservoir.

 

This is not complex. Here is a simple ebonite feed from an Omas. You can see that there is one channel cut into the feed, but that it is slightly narrower at the bottom than the top. Ink travels along the narrow portion of the channel and air is returned to the reservoir via the wider portion of the channel

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/OmasFeed003_zpsdd5efb25.jpg

 

This picture is of the top of the same feed. Note that the nib-end of the channel is "ramped" up toward where the nib will lay. Capillary action pulls the ink up to the nib, along the slit and to the tip; which is why it is important for the nib to be in contact with the feed (or with a very, very slight gap at most). Getting proper contact is what you're achieving when you "set" the nib and feed. Some will say to increase the gap between the nib and feed for a "wetter" flow, and it will work to some extent; but it is much better to widen the gap between the tines for a wetter flow.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/OmasFeed002_zps1e2e9777.jpg

 

Here is a vintage ebonite feed with two channels and a larger main channel for air return. This is common in pens designed to flex, since it allows a greater flow of of ink (and return of air) when flexing the nib. The "ramp" I mentioned earlier is more visible in this feed.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/Kaweco%20Sport%20712/712004_zps30e361b6.jpg

 

Lastly (since someone will ask), let's talk about the cuts in the side of the feed. These are buffers to hold ink when the air in the reservoir expands (usually from warming) and forces ink out of the pen. The ink will go somewhere, and without these buffers it's usually somewhere you don't want it... Some Noodler's hacks I've seen posted instruct to cut these away, or make additional cuts to link them to the main ink/air channel. That's not their purpose. All they do is increase the surface area of the feed (to allow the ink to go somewhere besides dropping on your paper or pants).

[FarmBoy]

I think you will find that HP (Hewlett Packard) has modeled the the ink jet printer in so many ways they actually patented the idea and marketed it. You may or may not know that ink is not the only fluid that is jetted to print.

[stothy]

 

Actually you already answered it yourself: what I meant is that if some external funding (or even justification of university funds) plays a role, people might question about the economic relevance (ROI) of research for a niche market. Inkjet and analogies in that field might be good and relevant connection on that side.

Depending on the actual modelling focus and comparison between both:

- on youtube (don't ask me where, guess it was a video from Lamy, could be wrong) there is at a certain moment a 3D drawing on screen of a feed. Could be simply for mould making, but I guess the file could as well serve as input for modelling work. Don't know. Never been there.

- It might also be worthwhile to dig in some "old" literature (late 1970's and 1980's or so) when inkjets and the micromachining of heads were still in the, say, precompetitive research phase and have a look of what has been done then and how it emerged to the current status (with a period in between that, I guess, would have more industrial development without publication too much details). In the early days a number of problems related to satellite formation, viscosity, etc were encountered, and modelling could be done as well, be it with less powerfull tools than today. No references come to my mind however.

That is all very useful information, thank you! I fear that the model of the feed will not be useful for me but I will have a look to see if there is anything I can use it for.

 

Most modern feeds have an 'ink-delivery' side, which involves the ink channel and the ink-air exchange that the feed does at the mouth of the converter (for cartridge converter pens), and an ink-intake side.

 

This is the little opening on the underside of the feed that must be dipped in ink while filling the pen. Normally this opening stays free and clear during writing. Only during filling this opening is immersed in ink and some form of suction draws ink through this intake opening up into the ink reservoir. Naturally there's air in the intake opening in normal cases, and when the pen is dipped into the ink, there's some air that gets in front of the ink coming into the reservoir, therefore trapping a bubble of air along the way.

 

I'm not wanting to answer your original question, just sharing my own experience here.

That's fantastic information, I had my suspicions that this part of the feed would cause bubbles to form but I had no conclusive evidence. I will look into this further. Thank you!

 

jar is on the money with his posts. I'll try to expound / clarify them with some pictures.

 

First, the only problem with "bubbles" in the part of the pen that holds the ink is when (as noted) surface tension prevents the ink from moving to the feed.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/SurfaceTension015_zps1c980d6d.jpg

 

Although converters are the primary culprits, this can happen in any pen, with any type of filling mechanism. Here are some cartridges exhibiting the behavior.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/Stuck%20Ink%20001_zpsckzohboh.jpg

 

I have an M300 that loves to do this with Caran d'Ache ink, so piston fillers aren't immune (although they seem to be less susceptible).

 

Again, it's all about surface tension. If you're writing a technical paper then that should be your focus.

 

More generally (and as noted by jar), pens work by exchanging ink for air. As the ink leaves the pen, something must replace it or a vacuum is formed and no more ink will come out. You can observe this happening. Using a piston filler with a clear window, or a converter with the barrel removed, fill the pen with clear water. Then, wrap the nib in a paper towel (so it will draw the ink out) and while holding the pen nib-down, observe the reservoir. You will see small bubbles rising from the feed to the top of the ink reservoir.

 

This is not complex. Here is a simple ebonite feed from an Omas. You can see that there is one channel cut into the feed, but that it is slightly narrower at the bottom than the top. Ink travels along the narrow portion of the channel and air is returned to the reservoir via the wider portion of the channel

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/OmasFeed003_zpsdd5efb25.jpg

 

This picture is of the top of the same feed. Note that the nib-end of the channel is "ramped" up toward where the nib will lay. Capillary action pulls the ink up to the nib, along the slit and to the tip; which is why it is important for the nib to be in contact with the feed (or with a very, very slight gap at most). Getting proper contact is what you're achieving when you "set" the nib and feed. Some will say to increase the gap between the nib and feed for a "wetter" flow, and it will work to some extent; but it is much better to widen the gap between the tines for a wetter flow.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/OmasFeed002_zps1e2e9777.jpg

 

Here is a vintage ebonite feed with two channels and a larger main channel for air return. This is common in pens designed to flex, since it allows a greater flow of of ink (and return of air) when flexing the nib. The "ramp" I mentioned earlier is more visible in this feed.

 

http://i200.photobucket.com/albums/aa163/roomdog/Pens/Kaweco%20Sport%20712/712004_zps30e361b6.jpg

 

Lastly (since someone will ask), let's talk about the cuts in the side of the feed. These are buffers to hold ink when the air in the reservoir expands (usually from warming) and forces ink out of the pen. The ink will go somewhere, and without these buffers it's usually somewhere you don't want it... Some Noodler's hacks I've seen posted instruct to cut these away, or make additional cuts to link them to the main ink/air channel. That's not their purpose. All they do is increase the surface area of the feed (to allow the ink to go somewhere besides dropping on your paper or pants).

That is very interesting, thank you for your detailed explanation. What I can make from what you have said is that the surface tension of the ink in slimmer systems can cause an air gap to form, I have even noticed it on my TWSBI 580s with particular inks. Personally, I'm not sure I would call this a bubble but it has some similar characteristics. This air gap can cause trouble with writing experience as it can cause the pen to skip, something we have all experienced.

 

I have a couple of comments on this phenomenon in relation to my project: It appears that this occurs neither when filling or writing, it occurs when the pen is being moved and there are sudden changes to the inks position in the barrel. Whilst this is something that might be easy to model, it may be something I need to avoid as I can't make any analogies to other ink filling systems, I will discuss it with my mentor though as it has always fascinated me also. Again, thank you for all your help!

 

I think you will find that HP (Hewlett Packard) has modeled the the ink jet printer in so many ways they actually patented the idea and marketed it. You may or may not know that ink is not the only fluid that is jetted to print.

I will look into this but I am sure that I will be fine, my mentor works solely in the field of inkjet printers and he has put me in contact with some of his colleagues who have modelled them in the past. I do find the idea of using other liquids in inkjet printers fascinating though; their uses seem to be endless, from printing circuit boards to 3D printing as well now!