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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?
Product design - Pune, India
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.
Stellar Solutions, Inc.
Second of two simultaneous responses -- March 26, 2010
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.
Aerospace - Yeovil, Somerset, UK