Thread locking - Stainless steel into PVC

I can't tell you what to use, but I can tell you what NOT to use -- Loctite. It attacks most thermoplastics.

And I'll second that from experience. Loctite would be a big mistake...

No experience, but I would try the pvc pipe adhesive.

Dan

Thanks, I didn't know that. I was thinking of one of the Sika urethane adhesives perhaps.

Hi Dan, I thought of that too, but figured it would simply soften the PVC which would then re-harden after the solvent has evaporated. It's an easy test so I should give it a go. Thanks.

It might work better if the threads are rough rother than nice smooth surfaces.

Dan

If it has a hex area above the thread, perhaps you could plastic-weld some more PVC material up around that to keep it from unscrewing.

Tell an Electrical Supply store that you need to see their NMC fittings.

Good idea - unfortunately its cylindrical.

Take the connector out. Mill a slot up one side to half of the depth per width (1/8" wide slot Mill 1/16" deep). Install the connector and use a drill bit to "transfer" the slot to the PVC and finish the hole to size. (1/16" in the connector 1/16" in the ABS). Now take a chunk of PVC welding rod or ??? that is 1/8" and apply some PVC glue and insert it into the hole. Once it cures the connector won't move. Basically a linear locking spline. Same idea as used on key lock thread inserts. However instead of using the steel pins those use you have PVC. That way if you ever did need to remove it you could heat the connector and turn it to shear the PVC spline.

That's a great idea but there is likely to be >1000 of these made (I should have mentioned that earlier). I'll save the idea for next time I've got a use for it.

Boat/Marine supply stores have tons of sealants that bond to multiple materials including PVC and stainless. You might consider Dow Corning

Then I'd try epoxy.

I'll check it out - gave me an idea - I might look at Sika 291, its a urethane adhesive that I *know* sticks very well to PVC & stainless.

Part of the question here is whether you want to *permanently* lock those threads, or if you want to be able to disassemble the joints in the future. The commercial thread-lockers, including both Loctite acrylics and the commerical epoxy beads used in production, are calibrated to keep a tight joint and to tolerate a lot of vibration, but also to have a low breakaway shear strength that allows the joint to be unscrewed when necessary. Loctite, for example, comes in different degrees of breakaway shear strength for different jobs.

If you don't care about future disassembly, ordinary household two-part epoxy should do the job. The amine hardener is pretty active, however; I've never checked to see which plastics are safe with it, but it should be easy to Google. Unlike the epoxy beads made specifically for thread-locking, household epoxies are not made for specific breakaway shear strength.

If you do want to be able to disassemble, I'd go for one of the gooey pipe-thread sealants. I've used a liquid Teflon-containing sealant for decades, and it both locks joints tightly and allows joints to be unscrewed. I have them all over my house, in plumbing and (hot water) heating, and they work perfectly. I have some of them on metal-to-PVC threaded joints and I've never noticed any deterioration of the PVC.

You application doesn't sound particularly demanding. It should be easy to find some sealant that has decent joint strength without permanently binding the joint, and without destroying your PVC. Read the labels on the tubes in some hardware-store plumbing departments. They'll probably answer the PVC question.

That IS a great idea. You could also

The PVC ought to deform into the score marks.

Hmm ... from the description, snipped a few posts upthread, the connector sounds like a BNC. And it is common for those to have a D-shaped threaded stem, so it will be non-rotating in a punched hole in sheet metal. If so, then the solvent (not really an adhesive, I think) would soften the hole and allow it to deform partially into the flat of the 'D', so that would likely work.

As for the material of the connector -- assuming it is a real BNC, it is likely a copper alloy, plated with either nickel for the low grade ones, or with silver for the really high quality ones.

BTW The BNC is also supplied with a square flange with four corner holes for screws, so you could drill and tap the holes for those in the PVC if that would work better for you.

Chemical Bond: there is an adhesive for bonding ceramic 2 part delivery injection type doser mixes the proper amount as it comes out.

The grit s will jam if it unscrews - thus locked. or put sand in the threads. Glass beads etc.

Idea? groove , wet grit, assemble, let dry, slam down, grit release, jams threads.

Eh?

Hey Don, it's a large bayonet style connector. It has half a dozen conductors but uses a bayonet fitting about 2x the diameter of a BNC to lock & seal. Judging by the price and the look of the thing I'm pretty sure its a custom made connector housing.