Air tight materials

[pineirod 2]

Hi there,

 

We want to print a closing shell. It will be ca 1 meter in diameter, 0,5 meters long and 4mm thick.

 

We will flush this volume with dry air or Nitrogen. I was thinking about printing something with 100% infill.

 

First doing a prototype in our Ultimaker to then go to something big, like a Bigrep.

 

What materials would you recommend that are air tight?

 

thanks

regards

[Framar 38]

Air tight??? I think it is more related to the settings in the slicer. That being said, I had good result with PP as the layer adhesion is excellent I was able to print water tight objects that are also impact resistant. I would give it a try to test it's ability of being air tight...

 

Good luck!

[geert_2 557]

Most materials should be reasonably airtight if printed *slow*, in *thin layers*, and with good flowrate. So you get good layerbonding, and absolutely no underextrusion (important). A little bit of overextrusion could also help, but might create blobs. Do not use separate support materials (PVA) that dissolve: if they made strings in a print, these will dissolve and become holes.

 

But all models will have tiny "canals" and pores where bacteria can grip and grow. It's just that the water or air won't blow through.

 

For shell thickness, I would use at least 2 lines (=0.8mm for a 0.4mm nozzle), maybe 3.

 

Don't pressurise 3D-prints: they might explode at a much lower pressure than injection moulded models.

 

For huge models (1m), I would rather apply a coating, I think? Maybe even reinforce them with glass fiber mats, and then apply epoxy resin? Do tests if a 3D-print can handle the required loads and temperatures (PLA softens and warps in the sun).

 

[pineirod 2]

Hi there,

 

In the end we will use tough PLA, we got a BASF 2.5kg spool.

 

I always print with the standard options so I am not expert in touching many of the options.

 

 - For this purpose I have changed the infill to 100%, the "wall line count" to 10 (to make sure it the print head goes around 10 times and not the zigzag filling)

 

 - The printing speed is set at 50mm/s by default. Would you recommend to change it?

 

 - Layer height 0.15mm. It takes already 2.5 days. With 0.1mm takes 3.5 days, would you recommend to to to 0.1mm?

 

 - All flow options are at 100%. Which ones would you recommend to change and how much?

 

 - Would you suggest any other changes?

 

The coating idea is very good. We can paint it inside and out. Since we are testing first the small part with the Ultimaker, we will do a leak test, then paint and do it again

 

thanks

 

[geert_2 557]

I just printed a filter for my vacuum pump, to prevent it from sucking up big particles when suddenly applying vacuum. The filter was printed on an UM2, thus in a single material, no supports.

 

I printed the first model at 0.3mm layer height, 25mm/s. This was *not* airtight: when I put tap water on it, maybe 10 tiny jets spurted out of the shell, through tiny holes. The holes were where the layer-changes and take-offs and landings from traveling had occured.

 

The second model was printed at 0.06mm layer height, and 50mm/s. This model is *absolutely watertight*. Yes it took a lot longer, but it works now.

 

This filter is quite small, 30mm diameter, with 8mm, 10mm and 12mm bulbs for attaching tubing. So it has a thin shell. Bigger objects might need a *much thicker* shell to withstand pressure.

 

Major slicer settings:

- 0.06mm layer height,

- 50mm/s (don't go too slow at thin layers, otherwiste the material sits in the nozzle for too long and might decompose),

- shell 0.8mm (=2 lines, 0.4mm nozzle),

- infill 50...60%,

- top and bottom: 0 (=no solid top and bottom layers, so the filter is porous);

 

I could have printed it in one shot, vertically. But this would require custom supports for stability. I did not want it to wobble or fall over. So I preferred to split and print it in two parts, and glue them together with cyanoacrylate glue. And then I sanded it lightly and acetoned it, for a good fitting of the tubing.

 

 

Both parts need to be glued together, bottom to bottom, carefully applying cyanoacrylate around the edge, without gaps, but also without flooding and blocking the filter.

 

Anyway, before doing a large print that takes days, try different settings very carefully on a smaller testmodel. Go from where it sure leaks, and then gradually to where it is surely tight. Then keep a safe margin.

 

Also consider post-processing, acetoning, coating, glueing, whatever,... to make sure it is airtight. A thick varnish, coating or paint might also solve the problems.

 

Print without dissolvable support if you can. Otherwise strings of support through the print would cause holes after dissolving.

 

[pineirod 2]

Hi there,

 

thanks for the extensive information.

 

So you have 0.8mm wall thickness. We have 4mm. I attach some pictures. It's a "box". It will be glued to an aluminium frame (which will be screwed with an o-ring to an aluminium plate).

 

No support, the design was made in a way that it is not needed.

 

I'm thinking about going to 3mm thickness (for structure) and then do the painting/coating (for tightness)

 

thanks

 

 

[pineirod 2]

Hi,

Here more news about this project in case somebody is interested.

It was printed, glued to an aluminium connector and screwed to an aluminium plate with a flange for measuring the tightness.

 

We used helium to see the leaks in the system. With the probe at the bottom (see it in the picture, it is the front face of the printed part) the leak rate was pretty high. It could hold water, but it is not air tight.

 

The idea now would be painting it with some resin. But we are not sure since the over pressure - normal cycle might damage it

 

cheers,

 

 

[geert_2 557]

Maybe use a flexible PU coating? PU tends to glue well to most materials, and is quite resistant.

[pineirod 2]

It sounds like a very good option. We will look into that

thanks

 

[Labern 774]

You could use chloroform vapour to slightly melt the outer layer. I just went to my chemist and they gave me a bottle. 

Suspend the part in a container, put some chloroform in the bottom and put on the printers heat bed. A mist will form and polish the outer surfaces of you print which should seal it off. 

[geert_2 557]

50 minutes ago, Labern said:

You could use chloroform vapour to slightly melt the outer layer. I just went to my chemist and they gave me a bottle. 

Suspend the part in a container, put some chloroform in the bottom and put on the printers heat bed. A mist will form and polish the outer surfaces of you print which should seal it off. 

 

I have heard about this method before, but never really seen it. If you have success, could you share a few photos of before and after, or treated/untreated next to each other?

 

Is the effect more like acetoning ABS (high-gloss, very strong smoothing effect) or like acetoning PLA as cloakfiend does (satin, very mild effect)?

 

[Oliveros 11]

You could also print it with a resin printer, those make completely sealed parts from what i've tried, making some smaller fittings for small pumps, they seem to hold up okay, at least they don't leak.

[Labern 774]

It's more like acetone ABS, smooth and shiny. 

I don't have a before but you can see it's very smooth. 

Depends on how long you leave it depends on how much it smooths it. 

You can also use Chloroform to melt 2 parts together. 

[pineirod 2]

Hi,

I am not sure if I can get the chloroform... I will talk to some chemist in my working place, as far as I heard some time ago it is not easy to get the permission. I'd rather avoid "nasty" chemicals...

 

About the resin print: It is very nice, we have a Form2, but out part is too big, and in the future we plan to make a 1 meter x half a meter part. It won't be easy (or cheap!)

 

thanks