On Thursday, May 18, 2017 at 8:05:00 PM UTC-4, Chris Jones wrote:
On 18/05/2017 11:47, wrote:
On Wednesday, May 17, 2017 at 9:32:23 PM UTC-4, Aussie wrote:
On 17-May-17 11:51 PM, wrote:
On Wednesday, May 17, 2017 at 8:46:04 AM UTC-4, Chris Jones wrote:

. The epoxy should form a good seal to the bare copper.

My understanding is that most epoxy does not adhere to copper. I think I read that somewhere. But you can find epoxy that will adhere sold for glueing copper plumbing together.

Dan




I wonder if it bonds to tinned (Pb/Sn solder) wire.

The difficulty with epoxy bonding to many metals is that it's actually bonding to surface oxide. Depending on the metal and the thickness and nature of the oxide, this results in weak joints in stainless steel, aluminum, copper alloys, and, of course, anything containing lead. There are other problem metals.

There are ways around it. One is to abrade the surface of the metal while it's coated with the mixed epoxy. This is sometimes called "scratch-in" preparation. I use it all the time, and it works great on stainless and aluminum.

I don't know for sure about copper. I've been asked about it before but I never tried it or looked into it, but I suspect it will be the same as for other metals.

This abrasion method is not practical in most commercial applications: aluminum aircraft wing skins being a prime example. To work fast and to get more reliable results, industrial users have worked out various conversion coatings and etches for specific metals that need to be bonded with epoxy and other adhesives. On aluminum, for example,they use phosphoric acid anodizing, PAA, and I've heard there are newer, better conversion coatings for aluminum.

There is an entire literature on this, but when I have a question, I just call 3M or Loctite, or whomever, and ask to speak to an engineer. Or I did. I was a trade magazine editor and I could use that leverage to get through. Now that I'm retired, they might just tell me to go **** up a rope. d8-)



Ok, then I wonder whether epoxy will bond to the urethane enamel of
solderable magnet wire instead, used in the same way.

I wonder, too.

Urethances are formulated in so many different ways that I can't begin to guess. FWIW, the conventional wisdom is that epoxy will bond to urethane (and to polyester and methacrylate) better than any of them will bond to epoxy.. Just watch out for the extreme elongation (ductility) of most polyurethanes, compared to the low elongation of epoxy. The difference can result in shear failure right where they're bonded.

--
Ed Huntress