Best method to seal and bond two pieces of PETG to be watertight?
I have a practical print that consists of two pieces, both printed in PETG. It's an oversimplification, but think of it as the first part being a "box" with an inlet and the second piece is a "lid" that serves as the outlet for water.
Normally, for PETG I would just use Super Glue and that will bond the "lid" to the "box" just fine.
But in this case, this "box" will have water (think of a standard sink pressure) flowing through it.
I've already coated the exposed surfaces in XTC-3D for additional internal waterproofing.
The question I have is: what would be the best product (or combination of products) to seal the two pieces of PETG together that can stay bonded under (mild) pressure and will provide a water-tight seal?
I was originally thinking to use automotive RTV silicone as that makes a nice "gasket" but the top piece isn't bolt-on. It's currently designed to be "glued" in. But now I am thinking that the RTV silicone may seal the gap well, but won't provide enough bonding to keep the "lid" from being blown off when water pressure is applied. Water exits the "box" through the "lid" so the pressure won't be enormous but the flow out is lower than the flow in, so there will be some pressure built up.
I feel the (copious applied) crazy glue alone will probably hold the two pieces together better than the RTV - but I don't know how "waterproof" crazy glue is and wonder if the water will leak. So looking for suggestions about alternatives.
With a lot of extra printing, I could make several copies and do trial-and-error (and still might), but wanted to check here furst in case anyone has had some practical experience bonding PETG in a waterproof (with some positive water pressure) application. Each copy of the model takes many hours so if I can save myself a lot of printing time and filament to avoid (or at least minimize) too much trial-and-error, that would be ideal.
Thanks in advance
RE: Best method to seal and bond two pieces of PETG to be watertight?
You could coat it with pain or some sort of paintable adhesive.
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Chuck H
3D Printer Review Blog
RE: Best method to seal and bond two pieces of PETG to be watertight?
If it's not possible to redesign the parts to bolt together, I'd make a printed part to clamp the two parts together.
If however a redesign is possible I'd bolt the two parts together and us an O ring or similar sitting in a pocket. If you prefer to use a liquid gasket any shaping you do to the mating faces will increase the mating surface area.
RE:
Standard cyanoacrylates are not water resistant long term.
There are some 'waterproof' superglues, your nearest marine chandler will have some and other glues too, if you're inland try a fishing tackle store.
Most PET is glued with either low temperature low-melt adhesive - tricky but doable, or with spray adhesive and possibly contact adhesive ...
There is another option, it's possible to use a 3D pen as a sort of plastic welder - think MIG or TIG with the wire replaced by filament.
And read: https://blog.prusa3d.com/the-great-guide-to-gluing-and-assembling-3d-prints_44908/
Cheerio,
RE: Best method to seal and bond two pieces of PETG to be watertight?
Yeah, I am leaning towards re-designing it to be bolt together. Though because of space constraints, it will be somewhat complicated. And while I would love to use an O-ring in a grove as you suggest, this being a very custom piece with very unique dimensions, I suspect I won't be able to source a commercially-available rectangular-shaped O-ring in the dimensions I need, thus will have to use liquid gasket maker.
Maybe I can combine the two ideas and make a mold so that I can use the RTV silicone to form (essentially) that custom gasket that could sit in a pocket. I have some pretty tight dimensional constraints so everything will have to be "thin" - maybe ~2mm wide gasket/seal and probably M3 bolts and nuts.
Thanks!
If it's not possible to redesign the parts to bolt together, I'd make a printed part to clamp the two parts together.
If however a redesign is possible I'd bolt the two parts together and us an O ring or similar sitting in a pocket. If you prefer to use a liquid gasket any shaping you do to the mating faces will increase the mating surface area.
RE: Best method to seal and bond two pieces of PETG to be watertight?
Thanks for the useful information and that link. Great answer. Though I think I am going to first try to redesign the part to use bolts. Challenging as there isn't a lot of spare room in the part for bolts, but I am thinking if I use M3 nuts and bolts I can probably make that work. I'll try that first but if that doesn't work out, I'll look into those marine "waterproof" CA. The 3D pen "welding" is also an interesting solution. But I thought those pens can only use PLA. I wonder how "welding" PETG together with PLA would work. Probably won't try that for this application, but that is a good idea in general and maybe I'll get one of those pens for the future.
Thanks again for such a thoughtful and complete answer.
Standard cyanoacrylates are not water resistant long term.
There are some 'waterproof' superglues, your nearest marine chandler will have some and other glues too, if you're inland try a fishing tackle store.
Most PET is glued with either low temperature low-melt adhesive - tricky but doable, or with spray adhesive and possibly contact adhesive ...
There is another option, it's possible to use a 3D pen as a sort of plastic welder - think MIG or TIG with the wire replaced by filament.
And read: https://blog.prusa3d.com/the-great-guide-to-gluing-and-assembling-3d-prints_44908/
Cheerio,
RE: Best method to seal and bond two pieces of PETG to be watertight?
Most of the pens can reach temps higher than pla. The one I have can just about do abs too so petg should be within its scope. Not that I’ve tried it with petg.
RE: Best method to seal and bond two pieces of PETG to be watertight?
For O-ring alternative, would something like a silicone rubber cord work? You can cut it to whatever length you need.
RE: Best method to seal and bond two pieces of PETG to be watertight?
Until now, I had not even heard of this. Now that I looked it up, I think that will actually work quite well (and be easier than making a custom two-part mold myself) and just ordered some from Amazon. Thanks for the info.
For O-ring alternative, would something like a silicone rubber cord work? You can cut it to whatever length you need.
RE: Best method to seal and bond two pieces of PETG to be watertight?
I am late to the game here, but I just used the Oatey brand of Purple Primer for PVC and CPVC. They make a clear one as well that has the same chemicals according to theur MSDS. Anyway, a light coat of it bonded two test pieces of PETG together. They are smaller pieces and one is a square and one is a flat piece. I cant pull them apart.
Since it is an action of melting a thin layer of material, I imagine it is water tight. But I have not tested that. I was just excited about a fairly cheap solvent to join PETG.
RE: Best method to seal and bond two pieces of PETG to be watertight?
I'm not the expert by any means but I just don't think many 3d prints can be considered watertight. Even with sealants, you've got lots of nooks and crannies that won't hold water.
RE: Best method to seal and bond two pieces of PETG to be watertight?
For a more forgiving bond, I use Aileen's The Ultimate Multi Surface Adhesive. My guess is that it will be watertight if applied carefully with no holidays.
If I expected any parts to be truly watertight, I would print them with solid infill.