PFA bonding: plastic welding? Adhesive? 1

[Nanimo]

Hello,

I have some flexible tubes of PFA (1/8" OD 1/16"ID) that I need to bond to a larger PFA tube (rigid). I was wondering what was the best way to do that. I just ordered some epoxy for PFA and I was also looking into plastic welding. What would be your advise on the best way to do that? The assembly will go to a pressure of ~3bar.
If plastic welding is a good option, which kit do you recommend me to buy? I am willing to put up to 400$ in that thing.

I also need to do the same stuff but with PTFE. Now PTFE will be more annoying as it does not really weld and does not really stick. The adhesive I ordered is also rated for PTFE (treating agent + epoxy), but I wanted to know if you had any good options for me to consider. Same dimensions

Thanks a lot!

 

[moltenmetal]

You're presumably using PFA for a reason. Epoxy isn't PFA, either in terms of temperature/pressure or corrosion resistance, so it may or may not work. Shocked to hear that any kind of chemical "activator" can make epoxy reliably stick to PFA- any kind of activator I'd want to mess with, anyway. PFA is very chemically inert below 300 C.

PFA can be bonded thermally by heating, either via infrared radiant or hot air heating. You'll need to heat until the part becomes transparent rather than bluish translucent (the point at which you can flare it) and then a bit farther than that- don't know the temperature for sure but it will definitely be above 300 C. Inert gas may be needed in that process to develop a full proper weld- don't know, but know that you can literally just heat PVDF up on a ceramic hot plate top until it starts to melt, then stick the two pieces to one another to result in a messy but strong butt weld- you may be able to do that with PFA but I've never tried.

Doing an attachment of the geometry you're talking about will be tough- not just to get the parts to stick to one another but also to keep that 1/16" hole open.

Sorry I don't have a nice easy solution for you. You may need to revise your design geometry to make this possible- or you can just try stuff until something works.

 

[Nanimo]

Thanks molten metal. I'm using stuff I'm not extremely familiar with and nor are my colleagues, so it's good to have some (constructive) input!

 

[Nanimo]

Forgot to add:
the PFA epoxy I had was not good at all, it was just some regular epoxy and they have put lots of materials they "suppose they can bond" in the description.
I got another kit more "professional", with an etcher and a special 2-tubes epoxy, for 130 bucks. I still need to try that one, I'll need a fume hood as the MSDS shows how nasty is that thing ...

 

[moltenmetal]

Radiation/ion beams and liquid alkali metals and stuff even worse than these are the only things I know of that have a hope of modifying the surface of PFA chemically to make it happy to accept an adhesive, but I guess since you've bought the stuff and it's apparently "for PFA", it's worth a try. Abrasion to generate surface roughness to make tongue and groove-type physical adhesion joints would also be necessary- that's how you get PFA and other fluoropolymer non-stick coatings to remain on the surface of a frying pan etc.