Etching or abrading stainless steel for adhesive bonding

A. Hi Mike. 3M has a good video on prepping for VHB, including isopropyl vs. acetone [on eBay or Amazon], roughing up the surface and priming:

We appended your question to a thread about abrading the surface vs. chemically etching it, but I think the mirror polish is the problem -- it may leave soils which the isopropyl alcohol isn't removing, and it minimizes the surface area available for bonding. If it's practical to abrade the stainless surface where the VHB sheet will be going to increase its area, that sounds like a great first step.

Luck & Regards,

I am thankful for being directed to the appropriate thread. I still need to mount components to 304 stainless, but will resort to using screws.
The use of sulfuric acid to 30% is as far as I wish to go. I've worked in shops with chromic acid and HF, and feel that they are best handled by professionals.

A. Yes, it is used to clean plastics, metals, glass etc. Majority of applications involve cleaning, activating the surface and rendering it hydrophilic which promotes bonding.
It is a clean pollution-free process. This could be expensive compared to chemical techniques. Cost depends on the size of the vacuum chamber required, vacuum pump, power supply etc. It also depends on the level of sophistication (which may or may not be essential) as well as the country of origin. I suppose there are several suppliers in the US.
Plasma cleaned parts have a definite shelf life- different for different materials. It is therefore a common practice to have an in-house facility.

A. According to my experiences some RTV silicones or 2 component epoxies bond much better to metal and nylon than PUR. Anyway try looking at www.delo.de
They provide service for our adhesive issues. Maybe some of the PUR Series of them can help. I have tried bonding HNBR Rubber on to DIN 1.4105 Stainless part and a PUR Adhesive from DELO works.
Best regards,

A. Dear Gamal,
Try any reducing acid ... HCl may be the best solution ... but I'm not a chemist.

A. David, I would recommend using a blast media such as Stainless cut wire shot, 304 or 316 alloy or even glass beads to rough up the inside of the Tee fitting. The outside threads can be maked with a vinyl sleeve. I have seen both used prior to painting stainless steel. Tim

A. Stainless is not the most predictable when it comes to surface preparation prior to bonding with epoxy. You may need to try a couple of methods before you pick the right one.

Henkel have the following reference www.henkelna.com/us/content_data/14258_LT4536_TT_Aerospace_Surface_Preparation_Guide.pdf
ASTM D2651 also will provide you with some options.

Thanks for your response Tim. Interesting you propose mechanical methods, since I have been investigating this approach since our disappointing acid etch tests. Do you know if a mechanically abraded surface is as good as a chemically etched one? These parts are really small and the surface deep, so getting in there with a blast nozzle is a problem. I have used both a diamond point bit and a small grinding stone but have not tested the bond in application yet. Other thoughts or ideas? David Martin [returning] - Santa Barbara, California A. The problem with blasting is that you get poor bond durability. The only successful methods I have used have involved hazardous chemicals unfortunately. Probably the most successful method I have come across is 30% sulfuric acid at 60 °C for 2-5 minutes, followed by a desmut of 10% sulfuric acid/2% sodium dichromate at 55-60 °C for about 10 minutes. I have tinkered with ferric chloride[on eBay or Amazon]solutions with varying degrees of success, the best probably be 30% ferric chloride[on eBay or Amazon]at 70 °C. After that we are getting into the really nasty stuff such as hydrofluoric acid containing etches. Just my personal experience. Hope it helps. Brian Terry Aerospace - Yeovil, Somerset, UK

A. David, granted, most of our applications have been for large Stainless Steel components where a customer has specified a epoxy coating. How small are you part ID's? 1/4" , 1/8" or smaller? How deep ? Can the part be fixtured to hold in place? What quantity of parts need to be epoxy painted?
The stainless as cut wire shot is readily available in .020", .017", .014". The stainless cut wire shot has a minimum hardness of Rc 45 ,but is typically Rc 50-55. If these size are suitable to use, they should be able to rough up the 316 alloy. What hardness is the 316 alloy fitting?
You would have to test blast some parts to see if this process yields acceptable epoxy adhesion.

In response to Ciaron-
Thank you for the Henkel document reference. It's very detailed, and certainly adequate for our purposes. It is interesting to me that Nitric acid is not even one of the constituents in any of the three baths recommended by this Spec.

Additional response to Tim-
Subsequent production units will all be larger, but our smallest current parts have a 1/8"ID, and also 1/4"ID. At this stage the quantity is small: probably not more than about 30 pieces. The depth of these holes extends to about 1", so the angle of attack for the blast media would be very shallow, especially at max. depth and may not allow enough surface roughness. These are stock and special cast Swagelok parts, but I don't know the hardness. Thanks for your help.

In response to Brian-
Thank you for your procedure. It is a simple one which doesn't involve the least desirable acids. Very helpful.