Effect of air bubbles in a paste when subjected to spinning

[gery katona]

I hope this isn't too simple for this site. I have had a challenge at work trying to eliminate air bubbles from a paste in a 20oz cartridge. The cartridge has a piston in one end to push the material out and the other end tapers to a small threaded 3/8" opening.

I won't take the time explain how the bubbles are introduced in the first place, let's assume it is an uncontrollable variable.

I know vacuum can suck the bubbles out, but this paste has a high viscosity and it does not work. the vacuum ends up sucking the material out of the tube. Also, vibrating the material can cause the bubbles to float to the surface, but again, the viscosity is the problem.

I'd like to try spinning the cartridge in something resembling a centrifuge. My first question is this: will the heavy paste moving to the outside of the spinning cartridge displace the air, forcing it to the center? If I end up with a cartridge of paste with a cylindrical tube of air in the center, I would still need to figure out how to extract the air, but at least it would be contained in a defined area. Is this theory on where the air would end up correct?

Also, does anyone know how I can test this theory? Seems easy enough, but I have not been able to come up with anything.

Any advice is much appreciated.

 

[A.T.]

Is this theory on where the air would end up correct?

Yes, the only question is how fast you have to spin it to achieve this in reasonable time.

 

[rumborak]

I don't see a problem with your approach, the centrifugal approach is exactly what I do when trying to force air cavities up a viscuous fluid.
In terms of testing, I would think building a centrifuge is the obvious way of doing so.
Disclaimer: Centrifuges can be dangerous when self-built. Use caution.

 

[jerromyjon]

The cylinder of gaseous center you imagine would occur if you spun the tube and its contents along the center axis parallel to its length. A centrifuge would pull the heavier semi-solid towards the outer radius and the gaseous bubbles would "rise" towards the inner radius of the centrifuge.

I despise air bubbles in tubes of sealant, toothpaste, adhesives, etc. so I have quite a few techniques for various applicabilities if you could be a little more specific. Just storing in air-side-up orientation will usually correct it, eventually.

 

[gery katona]

Yes, the only question is how fast you have to spin it to achieve this in reasonable time.

Much appreciated! Thank you. That's a start!

 

[gery katona]

I don't see a problem with your approach, the centrifugal approach is exactly what I do when trying to force air cavities up a viscuous fluid.
In terms of testing, I would think building a centrifuge is the obvious way of doing so.
Disclaimer: Centrifuges can be dangerous when self-built. Use caution.

Yes, I'm pretty much resigned to building one ourselves. I will heed your advice regarding the safety aspect.

 

[rumborak]

I was saying this from personal experience of trying to build a fan from Lego as a kid. That thing had a habit of disassembling violently from a certain speed on :p

 

[jerromyjon]

I hope this isn't too simple for this site.

If you considered using balanced opposed pairs as too simple, you would be amazed at the ignorance which frequently gets presented here.

 

[gery katona]

The cylinder of gaseous center you imagine would occur if you spun the tube and its contents along the center axis parallel to its length. A centrifuge would pull the heavier semi-solid towards the outer radius and the gaseous bubbles would "rise" towards the inner radius of the centrifuge.

I despise air bubbles in tubes of sealant, toothpaste, adhesives, etc. so I have quite a few techniques for various applicabilities if you could be a little more specific. Just storing in air-side-up orientation will usually correct it, eventually.

Yes, my thought was along the axis parallel to its length. I have invested an enormous amount of time on this bubble problem. The paste gets injected into a mold and makes aircraft parts. If an air bubble gets injected into the part, the resulting void can sometimes be repaired which is entirely non-value-added work, but half of the time the part is scrapped and they cost thousands of $. The material is mixed under vacuum, but there are many paths for air to get introduced between the mixing bowl and getting the paste into the cartridge that we cannot see/control. I would rather not worry about all those paths and just extract the air after the cartridge is filled. After filling, it is placed in a freezer until it gets used, usually around a week later. The cartridge is stored right side up with a cap on the top. The air can be anywhere within the material, so I don't think there is an air-side-up. Being frozen with a cap on top is not conducive to it bleeding to the top unfortunately.

 

[jerromyjon]

Yeah, sounds like a problem.
Just out of my league, unfortunately. I'll ponder it.

 

[jerromyjon]

The more I think about it, the more speculative it becomes. I have ideas but they would be challenged here. While the premises may be sound, I lack the ability to prove it mathematically nor find references to support them.

 

[jerromyjon]

What the heck, I'll just ask you a question. What effect could a magnetic field have in the state transition into the freezer. Is there any chance the curie temperature can be utilized?

 

[rumborak]

Has the topic of this thread suddenly changed? How do Curie temperatures play into this?

 

[DaveC426913]

Yes, my thought was along the axis parallel to its length.

Your bubbles will reach the surface faster (thus reducing the spin time) the shallower the paste is. So a tray with maximal surface area will "de-bubble" faster than a tall, narrow tube.

 

[boneh3ad]

Rather than spinning one tube around its axis, put two tubes opposite each other with the "top" (or wherever you want the bubbles to be for easy extraction) toward the center (i.e. lay the tubes on their sides) and then spin them around at a high rate like an actual centrifuge would. That should bring all the bubbles to the top where you can easily extract them while forcing all the paste to the bottom. Just hope the paste is mixed well enough that you don't start separating its constituent parts in the process.

 

[rumborak]

A somewhat cheap way of forcing bubbles up might be by letting it drop from a certain height. In the end, centrifuges essentially work by increasing the "gravity" on the substance. Dropping something from a certain height has a similar (albeit more short-lived) effect.

 

[boneh3ad]

A somewhat cheap way of forcing bubbles up might be by letting it drop from a certain height. In the end, centrifuges essentially work by increasing the "gravity" on the substance. Dropping something from a certain height has a similar (albeit more short-lived) effect.

If the paste is very viscous, though, the acceleration may not be enough to be non-negligible and the fall may not be long enough to bring the bubbles all the way to the top.

 

[rumborak]

I totally agree. The dropping solution is only applicable for a much smaller range of fluids. But, I figured I'd point it out nonetheless, as it is a very easy and cheap thing to do.

 

[jerromyjon]

If the paste is very viscous, though, the acceleration may not be enough to be non-negligible and the fall may not be long enough to bring the bubbles all the way to the top.

Perhaps bouncing repeatedly?

 

[boneh3ad]

Perhaps bouncing repeatedly?

I suppose as long as by "bouncing" you mean letting it fall, then picking it back up and dropping it. Otherwise I'd think the acceleration bouncing back up would at least partially undo your progress.

 

[gery katona]

What the heck, I'll just ask you a question. What effect could a magnetic field have in the state transition into the freezer. Is there any chance the curie temperature can be utilized?

Well, the material IS magnetic, but I don't understand how the curie temperature could play a role.

 

[gery katona]

Has the topic of this thread suddenly changed? How do Curie temperatures play into this?

It may not, but the material IS magnetic.

 

[gery katona]

Your bubbles will reach the surface faster (thus reducing the spin time) the shallower the paste is. So a tray with maximal surface area will "de-bubble" faster than a tall, narrow tube.

Yes, that would help.

 

[rumborak]

It may not, but the material IS magnetic.

Oh, interesting. Well, under the assumption that whatever makes the substance magnetic will stay so even when applying an external magnetic field (i.e. it's not just suspended particles that will all settle at the bottom), could doing so possibly increase the virtual weight of the substance, and thus force the bubbles up?

 

[boneh3ad]

But if the magnetic particles are only suspended in the paste, doing it that way risks simply pulling them out of the paste and to the bottom on their own.

 

[rumborak]

Well, that's why I put that thing in the parentheses in my post

 

[gery katona]

Rather than spinning one tube around its axis, put two tubes opposite each other with the "top" (or wherever you want the bubbles to be for easy extraction) toward the center (i.e. lay the tubes on their sides) and then spin them around at a high rate like an actual centrifuge would. That should bring all the bubbles to the top where you can easily extract them while forcing all the paste to the bottom. Just hope the paste is mixed well enough that you don't start separating its constituent parts in the process.

That is logical and would simplify the extraction once the air was isolated. Actually it would eliminate the need for extraction altogether because simply pushing up on the piston would extract it out the top. Cool! Some kind of balancing process would be needed since it would be unusual for two cartridges to have the same weight. I can't say how likely it would be for separation of the constituent parts would be. The material is thicker than toothpaste for sure and would be more conducive to staying together I guess.

 

[gery katona]

If the paste is very viscous, though, the acceleration may not be enough to be non-negligible and the fall may not be long enough to bring the bubbles all the way to the top.

Our production people are excellent at dropping things, so they wouldn't need much training.

 

[gery katona]

A somewhat cheap way of forcing bubbles up might be by letting it drop from a certain height. In the end, centrifuges essentially work by increasing the "gravity" on the substance. Dropping something from a certain height has a similar (albeit more short-lived) effect.

Interesting. Yea, that would be cheap for sure.

 

[gery katona]

If you considered using balanced opposed pairs as too simple, you would be amazed at the ignorance which frequently gets presented here.

I did not until another post below because I was slow to grasp the merit.

 

[Khashishi]

Can you heat the substance to change its viscosity?

 

[gery katona]

Oh, interesting. Well, under the assumption that whatever makes the substance magnetic will stay so even when applying an external magnetic field (i.e. it's not just suspended particles that will all settle at the bottom), could doing so possibly increase the virtual weight of the substance, and thus force the bubbles up?

I like the concept. Boneh3ad's concern about dragging the magnetic particles down is something to consider and I wonder what strength of magnetic field it would take.

 

[gery katona]

Can you heat the substance to change its viscosity?

Good question, but that cures it.

 

[gery katona]

To sum up, we have several possibilities:

- Repeatedly drop the cartridge to increase the "gravity" forcing the air up and out. Easy to test. Can inject an air bubble with a syringe and measure the movement with each drop.
- Spin the cartridge in a centrifuge using either a single cartridge spun along the center axis parallel to its length or two opposing cartridges. A single cartridge system would be simpler to build and test as a starting point. If that worked, then a two cartridge system would eliminate the air extraction issue after spinning with the one cartridge system.
- Applying a magnetic field to increase the "virtual gravity" of the material thus forcing the air up and out. Elegant, but more complicated to implement.

Ok, I have some work to do and really appreciate the input. Don't hesitate to suggest other ideas!

 

[rumborak]

- Get an intern with a syringe who removes all the bubbles manually