Loctite, Brass & Steel

[petertha]

Double back tape works great for that application also .

Yup have that too and an arsenal of various epoxies. It was just the Loctite that perplexed me.

 

[petertha]

I'm test bonding some C360 brass to the same steel & also 6061 aluminum. I'll let it cure & report back. Maybe my imagination but seemed like it was already setting up.

 

[mmcmdl]

I now have an aluminum bar stuck to the steel .

 

[AGCB97]

Seems to me there are 2 types of bonding strength, shear and tensile. The Loctite has great shear strength but not so good tensile (pulling apart).
Sometimes it's hard to get our head around things like that without real thinking.
Aaron

 

[ArmyDoc]

I'm not sure, but I'm going to guess it's because it is shim stock and not an un-interrupted circle of metal. As I understand it, the way this stuff works is that the crystal lattice expands as it cures. In a solid piece, that would cause pressure between the rod and the surrounding metal that would hold it in place. If the surrounding metal can expend, there wouldn't be any pressure.

 

[projectnut]

Most Loctite thread locking and sealing products ae anaerobic, meaning they will not cure in the presence of oxygen. They have dozens of different products that work in different atmospheres, on different substrates, and different temperature ranges. Here's a link to the products available.

Search

www.henkel-adhesives.com

You'll need to outline the materials and the atmosphere they work in to see if they have a product available that will accomplish what you're looking for

 

[chips&more]

Sorry, Loctite 680 is for joining cylindrical parts. It will not work for your application…not. I would read-up on Loctite products and their proper application first. Good luck…Dave.

 

[petertha]

I tried a scrap of regular C360 brass to the same 1018 steel blank with #680 retainer, no primer. That's the round slug. Also tried regular red LT on 6061 aluminum (corner scraps). This is more like what I was expecting. It held well enough to turn it down thin without failing the adhesive. Its not a lot of force under cutting but it certainly didn't fall off like the brass shim did. Both lifted with an Exacto blade, the #680 held firmer. I think brass doesn't adhere with LT the way steel does, but this wasn't a super finish or anything either.

 

[petertha]

Sorry, Loctite 680 is for joining cylindrical parts. It will not work for your application…not. I would read-up on Loctite products and their proper application first. Good luck…Dave.

Yes 'cylindrical' is what I've read on their spec sheets. But how does the adhesive film know its in a gentle arc vs. a flat plane as in my example post #18 example? Here is graph from #680 spec sheet, steel pins & collars at different controlled gaps. I interpret this to mean the annulus is 100% adhesive filled, no metal contact. The middle blue line of 0.25mm ~ 0.006" gap cures slower for sure. Only 75% strength is achieved after 24 hours vs say 90% strength for the black line 0.05mm = 0.002" gap over the same period. I will repeat this with steel on steel & I'm pretty sure it will be a more permanent bond, but lets see.

You can see on the pics the green film adhesive remnant is fully hardened & has to be filed or sanded off the steel. So (my terminology) it is 'curing' but it is not 'bonding' to the brass shim. An analogy might be epoxy layup in a mold. The epoxy cures, it has hardened, it is fully bonded to the reinforcement cloth layer, but is has not bonded to the mold with release agent on it.

 

[francist]

I wonder if it doesn’t have more to do with the flexible nature of the shim rather than the brass material itself? I mean, the thin shim would almost peel itself off rather than having to separate the whole adhesive layer at once with a thicker and therefore stiffer section.

Just thinking out loud, not always a good thing....

-frank