water sealing 3d printed parts

RatLabGuy

RatLabGuy

You look like a monkey and smell like one too
Joined
May 18, 2005
Location
Churchville, MD
Looking for some advice/ideas on sealing a large 3d printed part so its water-tight.

Need a spray, or maybe brush-on material that will dry smooth, but can be applied to something that is an irregular bowl-shape (each side of the inverse mold to cast a human head).
Typical printed ABS is slightly porous at each layer, so fluids tend to seep inside. Need to seal that while maintaining a smooth finish (or at worst leaving the print layers, but ideally they go away too).

Would the infamous Flex Seal work? Other kind of silicone spray? An epoxy finish that runs juuuust enough to not leave brush strokes but not pool toward the bottom?
We tried a handful of thin layers of Plasti dip spray and still got a small amount of leeching. Maybe not enough b/c you can still see the print lines...?
 
Flex seal would probably work with 10-12 really thin coats with it drying in between. It looks bubbly and rough but drys decently smooth


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Are the ABS parts being "polished" (with acetone) afterwards? That generally "melts" the outer layer, effectively smoothing & sealing them...
 
I'm assuming your using a FDM printer. I have read about the ABS smoothing effect by wiping the part down with acetone to help fuse the layers together, never actually tired it.

You could also try
- increasing the wall/shell thickness
- increasing the layer thickness
- switching to an SLA printer which can produce a continuously sealed layer
 
Caver Dave said:
Are the ABS parts being "polished" (with acetone) afterwards? That generally "melts" the outer layer, effectively smoothing & sealing them...
Click to expand...
We discussed that, and even tried it. The problem is that it is difficult to get a controlled "melt". Its a really big part (FYI it take 4.2 liters to fill a void the size of an average head and upper neck) so you have either (1) do it by hand, which leaves streaks etc and not real smooth or (2) by vapor, which warps the sealing surface.
 
snipes243 said:
I'm assuming your using a FDM printer. I have read about the ABS smoothing effect by wiping the part down with acetone to help fuse the layers together, never actually tired it.

You could also try
- increasing the wall/shell thickness
- increasing the layer thickness
- switching to an SLA printer which can produce a continuously sealed layer
Click to expand...

Doing SLA of something this size would be difficult. But, super cool... hell I'll look into it.

A big part of the goal here is to develop a process that any person (lab) can easily and cheaply follow, so they can built a similar device. So requiring access to an expensive SLA printer is not ideal.
Otherwise we'd just have it milled from aluminum ;-)
 
RatLabGuy said:
Doing SLA of something this size would be difficult. But, super cool... hell I'll look into it.

A big part of the goal here is to develop a process that any person (lab) can easily and cheaply follow, so they can built a similar device. So requiring access to an expensive SLA printer is not ideal.
Otherwise we'd just have it milled from aluminum ;-)
Click to expand...

Yeah Cheap and SLA isn't a real combination. We tried to buy one to print a 96 gallon trashcan plug for a roto mold, lets say boss man didn't like the price tag.


So now my curiosity has kicked in have you tried vapor polishing? Might be able to smooth the layers out, without the excess melting that comes with dipping.
How To: Vapor Polishing ABS 3D Printer Filament | MatterHackers
 
snipes243 said:
Yeah Cheap and SLA isn't a real combination. We tried to buy one to print a 96 gallon trashcan plug for a roto mold, lets say boss man didn't like the price tag.


So now my curiosity has kicked in have you tried vapor polishing? Might be able to smooth the layers out, without the excess melting that comes with dipping.
How To: Vapor Polishing ABS 3D Printer Filament | MatterHackers
Click to expand...
We did, and in fact we have a vacuum oven in the lab :D. we tried it with a small part but it didn't do much. I suspect bc we didn't use enough acetone for the volume in te hoven - to do this with such a large piece (2 really ) it would take a massive amount. And again - most people don't have a vacuum oven laying around.
The other problem with this is it's not real predictable if it will 100% seal.

I'll pick up a can of Flex Seal and try that.
 
I've seen a few 2-part resin products for this purpose that are higher priced (and probably more chemically...dangerous) than the XTC-3D above. I've also seen some penetrating cyanoacrylate products for pore sealing but they're probably not good for continuous immersion. I don't generally deal with FDM though (not great mechanical properties) so the circles I travel in have been different processes and different RP materials.

There's also the traditional materials for sealing porous molds make from plaster, etc., which are paste wax and PVA (polyvinyl alcohol), or one of the other film-forming alcohols. Also brushable urethanes.

Also, what are you doing at the parting line to seal the mold, and do you have any mechanical registration between the halves?

How long does the liquid stay in there? Minutes or hours probably, if you're casting something?


Are you trying to cast a human head out of ballistic gelatin?
 
Fabrik8 said:
I've seen a few 2-part resin products for this purpose that are higher priced (and probably more chemically...dangerous) than the XTC-3D above. I've also seen some penetrating cyanoacrylate products for pore sealing but they're probably not good for continuous immersion. I don't generally deal with FDM though (not great mechanical properties) so the circles I travel in have been different processes and different RP materials.

There's also the traditional materials for sealing porous molds make from plaster, etc., which are paste wax and PVA (polyvinyl alcohol), or one of the other film-forming alcohols. Also brushable urethanes.
Click to expand...
can't use waxes and alcohols because we may use the mold for certain materials that require heating at low temp in an oven, and non-aqueous gelatins that they might mix/react with.
Also, what are you doing at the parting line to seal the mold, and do you have any mechanical registration between the halves?
Click to expand...
there's a groove and a silicone cord gasket that gets slightly crushed to create a seal.
How long does the liquid stay in there? Minutes or hours probably, if you're casting something?
Are you trying to cast a human head out of ballistic gelatin?
Click to expand...
Curing takes several hours, depending on temperature. Goes in at maybe 45-50 C, eventually gets chilled to 5 C.

Yes, casting a head out of ballistics gel (for now), although it's not normal gel, it's doped with NaCl to match the electrical conductance of scalp and has embedded wires and electrodes that create current dipoles to simulate brain activity :D.
Today, we cast w/ BG, and assume that's what most other labs will do but we're working on much more complex materials and designs, like a "scalp" made of cabroxymethylcelulose and skull of a porous semi-conductive ceramic... or ionic non-aqueous gelatins etc.

The casing and manufacture process will be open-source released so anybody can do it on a minimal budget.
So, yeah, we make fake heads. And occasionally they have to be, er, destroyed... its rather convenient and satisfying this one is based on an MRI of my old boss...
 
I'm going to go with an epoxy that's low enough viscosity to have good flowout after brush application, and good void filling, and acceptable adhesion to ABS obviously. I'm assuming that's what the XTC-3D is. Something in a cartridge or 2-pack syringe would probably be plenty of volume for a head mold.
 
yeah, I tried playing around with Flex Seal spray on some wood... it's way too thick and "lumpy" for this, I'm sure it would seal it but the coat would be really thick and sloppy. Coated a test piece in some polycrylic I had on hand, suspect it is too low viscosity and adhesion, we'll see.
It's too bad the XTC-3d is priced like its made of gold.
 
Haven't tried it yet, but I picked up a can of silicone modified conformal coating. Naturally, everything in my house has to be "modified." ;) Anyway, I bought it to try and seal PLA prints for grins and giggles. Might be worth a shot. I haven't tried it yet. I'm assuming it will go on thin and smooth, like an average conformal coating. Oddly, the website that recommended it was using it to seal printed sex toys, and seemed to take bacterial growth very seriously, so I think I can trust their research. Would it be food safe? Probably not. I think it would eventually wear off. But for your application, it may be perfect, and easier than a brush-on 2-part epoxy product. It comes in a spray can. I'll try to find a link.

Found it. https://www.amazon.com/gp/product/B008O9YGQI/ref=ppx_yo_dt_b_asin_title_o04__o00_s00?ie=UTF8&psc=1
 
We've used Flex Seal on SLA models at work...but the purpose was for the texture, not necessarily for sealing. Didn't even check to see if it made the parts water tight, but I'd assume being SLA printed, they were already water tight. So I guess my post doesn't really help anything at all... :lol: Sorry about that :lol: other than to say "sure, Flex Seal would probably work, but it'll leave a bumpy-lumpy texture." There, I helped.
 
catfishblues said:
Haven't tried it yet, but I picked up a can of silicone modified conformal coating. Naturally, everything in my house has to be "modified." ;) Anyway, I bought it to try and seal PLA prints for grins and giggles. Might be worth a shot. I haven't tried it yet. I'm assuming it will go on thin and smooth, like an average conformal coating. Oddly, the website that recommended it was using it to seal printed sex toys, and seemed to take bacterial growth very seriously, so I think I can trust their research. Would it be food safe? Probably not. I think it would eventually wear off. But for your application, it may be perfect, and easier than a brush-on 2-part epoxy product. It comes in a spray can. I'll try to find a link.

Found it. https://www.amazon.com/gp/product/B008O9YGQI/ref=ppx_yo_dt_b_asin_title_o04__o00_s00?ie=UTF8&psc=1
Click to expand...
Where did you pick it up? That has a 1-2 month lead time.
 
I found a similar polyurethane product that will be here tomorrow...
 
FYI I did a test run using some polycrylic sealer (intended for wood finishes) I had laying around, applied with a good old 1.5" paintbrush. It's a little too runny and tended to pool in the base a little, but it sealed it just fine. If it were a relatively horizontal surface it would be fine. I suspect the polyurethane spray will be more ideal.

Also, I was quite surprised when I got up in the morning after spraying the Flex Seal, and it had really flattened out a lot. Could see all the original grain in the wood board I sprayed on. Wasn't expecting that.
It's still not ideal for this case b/c of the high volume it comes out in, it'd be hard to control for small details or an area that is not large. I'm sold on it for a big thing though... like a screen door on a boat...
 
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