Better adhesion WITHOUT prepping surface?????

[bama01]

My epoxy saga just gets stranger by the week. I'm doing some testing on how best to epoxy AL to 301 1/2 hard SST. I've found an epoxy that works almost OK. I've been trying to find a reliabe method for preparing the surface to maximize the surface bond strength. It appears that, if I rough up aluminum-yes, I can get some crazy bond strenght. HOWEVER, it appears the surface bond strength on the SST, is notably less when I either sand blast or rough it up with sand paper.

How can this be, it's counter-intuitive! I get better adhesion by just simply cleaning the SST, than roughing it up?! Up is down, black it white! What's going on!

Jim

 

[EdStainless]

Put samples under microscope and look at the surface. My hunch in that either there is a good surface texture to start with, or your roughening is leaving too much residue on the surface.
Have you tried a light acid etch or pickle on the SS? That might be a more reliable surface to work with.

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Plymouth Tube

 

[bama01]

Well, after I sandblasted and/or abraded with sandpaper, I cleaned as well as I could with Alcohol, so residue, I don't see how. But the "stock" surface finish looks to me to be almost mirror finish, I just don't see how that's a better surface to work with than roughed up.

Isn't the whole idea of roughing up a surface to INCREASE the contact surface area.

I think this product has acidity to it already, because on the parts that failed, I can see where it's no longer shiny, it looks etched.

I need Dr. House and his cronies to run differentials on this topic.

Jim

 

[IRstuff]

Actually, it might be worse off, depending on the viscosity and coverage of the epoxy. I can sort of imagine that an epoxy might simply "bridge over" small enough crevices, thereby actually resulting a weak joint, compared to a microscopically smooth surface, where the epoxy has uniform contact to the surface.

TTFN

FAQ731-376

 

[EdStainless]

The adhesion scale is microscopic. It doesn't matter how the surface looks.

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Plymouth Tube

 

[Ron]

The alcohol could be the adhesion problem. Try MEK or acetone.

 

[Helicopterjunky]

Investigate "adhesive promoter" and follow manufacturers instructions.

 

[tomwalz]

Try a commercial, caustic based cleaner with a rinsing agent added. We have a couple cans of Easy Off oven cleaner around for this sort of thing.

Not a stainless guy but this thought occurred to me.
If 301 SST is 310 stainless steel then the surface has different properties than the underlying material because stainless steel forms an oxide layer. When you roughen the surface you remove that layer which did bond pretty well. After you have roughened you need to reestablish the surface.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.