On Wed, 13 May 2015 21:34:39 +0800, snafu wrote:

On 12-May-15 9:47 PM, William Graves wrote:
On Mon, 11 May 2015 06:34:04 -0700 (PDT), "
wrote:

On Monday, May 11, 2015 at 9:10:21 AM UTC-4, snafu wrote:
On 11-May-15 9:03 PM, wrote:
On Monday, May 11, 2015 at 8:23:10 AM UTC-4, snafu wrote:

Does anyone have any suggestions as to what chemical means might be
useful to lock or bond the (probably stainless) metal connector to the
PVC to prevent unscrewing?

Boat/Marine supply stores have tons of sealants that bond to multiple
materials including PVC and stainless. You might consider Dow Corning
795 - I have used it to bond plexiglass windows to stainless hatches.
It probably would work with PVC but check the materials sheet.



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.

--
Ed Huntress