Effect of air bubbles in a paste when subjected to spinning

[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

 

[jerromyjon]

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.

Yes, I thought about that and then thought of having a line of these containers falling down a long flight of shallow steps. Judging by the image of the container, the plunger would need to be supported though. I can't help but wonder if the plunger being supported or not would have any effect on impact.

 

[gery katona]

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

We love interns! As a matter of fact, we have one here right now.

 

[DaveC426913]

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.

I think the issue here is that, whatever amount of force is enough to extract bubbles from the viscous paste, may equally be enough to separate out its ingredients.

No matter though. Easily correctable. I suggest that you add a post-de-bubble final mixing step into your procedure. But it will have to mix gently enough so as not to fold air back in, or you will be right back in the same boat.

 

[boneh3ad]

I think the issue here is that, whatever amount of force is enough to extract bubbles from the viscous paste, may equally be enough to separate out its ingredients

That would depend on the relative density of the bubbles versus the particles. If the particles are much more dense it shouldn't be a problem.

 

[stedwards]

I'd rather stop problems at their source. Extract samples along the process. Examine each for gas bubble contaminates. Establish a measure. Change the process where the greatest contamination occurred.

Maybe the majority of the problem is due to the ancient seal on the hand pump used to get part A out of the drum. Maybe it occurs in the mixer when the first 500 milliliters are also mixing with air, and this fraction should be discarded.

 

[gery katona]

I think the issue here is that, whatever amount of force is enough to extract bubbles from the viscous paste, may equally be enough to separate out its ingredients.

No matter though. Easily correctable. I suggest that you add a post-de-bubble final mixing step into your procedure. But it will have to mix gently enough so as not to fold air back in, or you will be right back in the same boat.

Yes, that may be needed. The problem is it is mixed in a separate bowl mixer and the transfer process to cartridge is where the gets introduced.

 

[gery katona]

I'd rather stop problems at their source. Extract samples along the process. Examine each for gas bubble contaminates. Establish a measure. Change the process where the greatest contamination occurred.

Maybe the majority of the problem is due to the ancient seal on the hand pump used to get part A out of the drum. Maybe it occurs in the mixer when the first 500 milliliters are also mixing with air, and this fraction should be discarded.

Understood and agreed. The problem thus far has been controlling a number of points along the process that are potential problems. It is compounded by the fact you can't visually see the air in the material since it is a paste and not transparent. One of those points that has thus far been uncontrollable is the very beginning when the material is first dispensed into the cartridge. Even with the piston all the way up, there is air surrounding the crown due to its design. As the material is introduced through the top, it automatically traps air that is around the crown which cannot be avoided. this is just one example of several things that have been uncontrollable, thus we have been focusing on removing the air afterwards even thought it is an extra step(s) in the process.

 

[stedwards]

So much for my attempt to think out of the box. But there is one thing. Since you are finding bubbles at the end of the process, could a similar method be used within to process to test samples?

You're mixing a powder into a fluid, right?

 

[gery katona]

Since the bubbles are mostly invisible, we can't see them during the process. Only after injecting the material into a mold, curing it, and opening the mold do we see the result. That of course is the worst time to find them. Maybe some kind of x-ray system like an airport scanner could see into the material, I don't know. Even the step of extracting the mixing blades out of the material can leave air pockets which can get trapped when the material folds over it. Yes, there are several powders used and the mixing is done under vacuum which probably removes all air in the mix, but then it has to get handled to dispense it into the cartridge. It is in those process steps where air finds its way in.