Gluing Stainless Steel – Some Footnotes

UPDATE – See Final Footnote at Bottom re. the Armstrong Method.

A conversation with a friend included this comment:

Well, Brian, just how strong were these glued joins?

And from e-mail:

Did the join strength you tested confirm the claims of the manufacturers?

Were the joins strong enough to use adhesive applications in lieu of brazing? Well, were they?

We tested the strength of the joins – we tested dozens of joins… Unfortunately, we did not have any sophisticated apparatus to measure join strength – we relied on the “armstrong” method of testing by four able, middle-aged men tugging and pulling in various ways to force join failure. In general, we believe that manufacturer claims are reasonable. Here is what we found:

The lap join – the 1/2 sq-inch plate-to-plate joins were incredibly strong.

Of all the trials, the acrylic joins submerged in water for 10 months all failed with two men pulling together to break the join; these joins were strong enough that one man pulling could not break the join.

All other lap joins tested survived four men pulling to break the join. Wow!

The irregular surface join susceptible to peel – the rod and ring join showed a wide range of strength among the trials tested.

The H8610 acrylic join failed with the one man holding the ring stationary and another man twisting the rod – it took some “heaving” and “grunting”, but the join failed.  This adhesive was the strength standout for the acrylic adhesives, though, and all other acrylic trials failed with considerably less grunting!

The DP420 epoxy required two men twisting the rod to break the join. The E-214HP epoxy required a bit more strength from the two men twisting the rod to break the join than the DP420 epoxy. All other epoxy joins were broken with one man twisting the rod.

So, this is all rather subjective, but the conclusions were apparent to all four of who gathered around the pile of joins…

Some elements of application still need to be investigated to fully evaluate these adhesives. The most significant consideration we did not explore was adhesive thickness. We suspect that there is an optimum join thickness – greater than which and the join will fail by pulling the adhesive apart while leaving adhesive on both substrates, and less than which and the join will fail by pulling the adhesive from a substrate. We suspect that join thickness is less of an issue for epoxies in general. For our trials, we used a binder clip to apply uniform squeezing force on all joins, and the result was a thicker join for a more viscous adhesive. None of the manufacturers could give us guidance on optimum join thickness.

We are satisfied that a lap join can indeed replace a braze or a bolt. The irregular join where peel force is evident may fail in the real world application where the braze currently serves the application adequately; however, the manufacturer will give the epoxy a whirl and see if it survives!

Happy gluing.

Final Footnote – a friend asks,

Say, Brian, what is the Armstrong Method?  It sounds sophisticated, but nothing here is sophisticated…

Well, my good friend, the Armstrong Method is a play on the words “Strong” and “Arm”. When you don’t have a sophisticated tool, you are left with no other choice than brute force methods. You can shy away from that embarrassment by referring proudly to the “Armstrong Method”!

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