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"Surface activator for adhesive bonding of stainless steel"





March 23, 2010

I need to bond two stainless steel sheet metal parts using adhesives. As SS is inherently passive material, the bond strength is very low and the epoxy adhesive used peels off. I checked on a site of an adhesive manufacturer regarding activating the surface of SS. They have suggested two methods. First method is dipping in two solutions at 60 deg C ; one containing sulphuric acid+oxalic acid and another containing chromic acid and sulphuric acid. the second method using a proprietary solution called Accomet-C
I tried the first method but the results are not consistent. Effect on 304 grade are better than that on 304-L grade stainless steel. The chemical suggested (Accomet-C) is simply not known to any of my chemical suppliers.
Can you suggest any better method or if possible, the supplier for Accomet-C, if it works?

Nitin Kibe
Product design - Pune, India
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First of two simultaneous responses -- March 25, 2010

The BEST way to get a good bond is to abrade the surfaces mechanically if this is possible.
You can also etch the surface with a nitric acid/ hydrofluoric acid solution, but this is quite hazardous.
I do not know how well the Accomet works. You need to go on your browser and search for it to see what their recommendations are.

lee kremer
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Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois

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Second of two simultaneous responses -- March 26, 2010

Nitin,

I prepare stainless steel for bonding in the following way:

Pre-clean (may include degreasing and alkaline cleaning), then rinse in clean running water.
Etch in Sulphuric acid (30% v/v, 58-62 °C, 3-8 minutes), do not rinse between this process and the next stage.
Desmut in Sulphuric/dichromate solution (15% v/v sulphuric acid, 2-3% w/v sodium dichromate, 60-65 °C, 3-5 minutes)

Rinse in distilled or demineralised water to remove desmut solution.
Wipe any residual smut from the surface using cloths soaked in distilled or demineralised water. Dry using a compressed air line.

At this stage I would now use a bonding primer within 4 hours of the etch process, this is when you get the best bonding properties.

I do not know what adhesive system you are using so there is little advice I can give on the primer or bonding, but if it is structural consider using something like 3M EC3901 primer and EC3960 structural adhesive.

Brian Terry
Aerospace - Yeovil, Somerset, UK
^

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