# Effect of air bubbles in a paste when subjected to spinning

1. Jun 3, 2015

### 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.

2. Jun 3, 2015

### A.T.

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

3. Jun 3, 2015

### 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.

4. Jun 3, 2015

### 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.

5. Jun 3, 2015

### gery katona

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

6. Jun 3, 2015

### gery katona

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

7. Jun 3, 2015

### 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

8. Jun 3, 2015

### jerromyjon

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

9. Jun 3, 2015

### gery katona

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.

10. Jun 3, 2015

### jerromyjon

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

11. Jun 3, 2015

### 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.

12. Jun 3, 2015

### 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?

13. Jun 3, 2015

### rumborak

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

14. Jun 3, 2015

### DaveC426913

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.

15. Jun 3, 2015

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.

16. Jun 3, 2015

### 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.

17. Jun 3, 2015

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.

18. Jun 3, 2015

### 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.

19. Jun 3, 2015

### jerromyjon

Perhaps bouncing repeatedly?

20. Jun 3, 2015

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.

21. Jun 3, 2015

### gery katona

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

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22. Jun 3, 2015

### gery katona

It may not, but the material IS magnetic.

23. Jun 3, 2015

### gery katona

Yes, that would help.

24. Jun 3, 2015

### rumborak

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?

25. Jun 3, 2015