Wich material best suited for vacuum?

[veens705 0]

Hi,

 

I'm thinking about 3D-printing a mold for containing 'kathodes'. These kathodes I want store under vacuum in a bag. Th kathodes should not touch the walls of the bag, and that's what the mold is for. I'm looking for an inert material that does not degas, so a plastic with no plastisizers might do well.

What is the best material to use?

 

Our mechanical department uses PLA. Would that be OK or better to use something else?

 

Thanks!

 

kind regards Jan Veenstra

[SandervG 1,521]

That is a good question! I will ask around. 

[geert_2 557]

It might depend on how deep the vacuum has to be? Not only the plasticizers might be a problem, but also water and plain air. For example nylon absorbs a lot of water very quickly, which means it goes through easily. Also, some plastics are not oil-tight nor airtight: oils and solvents might seep through, as well as atmospheric air.

 

And what if it fractures? How big will it be, and how strong does it have to be? And what if it shatters: can that do harm or not? Big objects need to be incredibly strong.

 

If it has to keep its vacuum for a longer time, I think you would best go for metal or glass. If it is actively kept under vacuum by a pump, I think any reasonably strong plastic might work?

 

Your biggest problem might be how to print it airtight? Normally prints have huge amounts of tiny voids, canals, bubbles,... You will have to print very slow and in very thin layers to get it watertight, and on a single nozzle setting (no dissolvable supports).

 

I once tried to print a filter for my vacuum pump, first at default settings. To test it, I put it under pressure with tap water, but the water jetted out via lots of tiny holes. After printing again slow, cool, and in the tinnest layers possible, it is now watertight, and it seems reasonably airtight too. But the rest of the system isn't: silicone-tubing is not vapour-tight at all, and not oil-tight either, and the pump probably isn't too, so I can't really test my filter alone.

 

[veens705 0]

@geert_2:

The 3D-printed parts do not have to be air tight, or even water tight. (It might even be beneficial that they are not, so all the air can escape from the 3D-parts.) They just have to be firm enough to keep the 'kathodes' from touching the walls of the vacuumbag. To clarify I added a JPG with a picture of other (round) parts packed in the same kind of bag that I had in mind for the kathodes. So it is not the 3D-printed part that has to keep the 'kathodes' under vacuum. (From your comment I understand you might think this.)

 

The 'kathodes' are packed now in the same manner in a large plastic mold. But the amount of products we need in one run is far smaller than the size of the package, so we want to repack in smaller amounts, but we can not 'break up' the old mold in smaller molds. An idea was to 3D-print a smaller container.

 

(I foresee a question: What is the material of the old large mold?

Answer: I don't know, and a problem is that the manufacturer of the 'kathodes' does not exist anymore. but I might ask around because former employees still may be around somewhere...)

[geert_2 557]

Are the kathodes clamped in the mold, is it a sort of box, similar to a box for a camera filter or lens (e.g. UV-filter)?

 

If so, I think I would rather go for something that can withstand rough handling during transport, and that still prints easy enough.

 

PLA is hard but gets brittle, and snap-fits don't work well. Also it deforms in the sun, if left in a car, even in the trunk, outside of direct sunlight. It will keep deforming until the load and internal stresses are fully off. So, this might not be the best option?

 

Maybe PET could be a choice, in its most natural color? The fact that it is (or can be) food-safe, means that it shouldn't release too much dangerous or agressive stuff. And it has enough flexibility to survive snap-fit lockings, and has enough temperature resistance to survive a car in the sun. It does not easily fracture when dropped.

 

But vacuum can do weird things: apart from degassing, it can even chemically decompose materials: I have seen that under electron microscopes with some dental cements. I am not a chemist, so I have no idea if this is a factor with plastics?

 

[Framar 38]

adding to what Geert_2 said, natural PP might a second choice.