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I have an issue with chemical plating of Iron, the component is immersed in Methyl Ethyl Ketone for a time span and then Zinc galvanized plating starts to corrode. I am not understanding what measures should I take. I am not at all into chemical engineering I am embedded engineer and trying to sell my products to companies.enter image description here

My advisor said I should get them alkaline coated.

This effect takes place after 3 days and there are no immediate results to the test.

Thank you You guys are awesome.

Ritesh Sharma
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  • Your big challenge: Given your moving parts and usage, what portions would wear out a chemically resistant coating via physical damage? How strong would a material need to be in those regions? There are likely better ways, but it is likely possible to build a sealed semi-flexible case around the part, potting it where it transitions to materials that are not suffering and without hampering the purpose much. – Abel Jan 22 '22 at 12:56
  • TBH these are metal clamps for Drums used in industrial packaging. So we cannot really enclose them, the pieces are small 2 inches and weigh 32 grams. i have tried getting them galvanized till 35 microns and same things happen. Although I am getting the component Alkaline solution dipped now I am worried about the aftermath. Strength required is 1 Tons tensile not shear. And the component has passed that test. – Ritesh Sharma Jan 22 '22 at 13:14
  • methyl ethyl ketone is nasty stuff for common gaskets, epoxies and the like. Not sure how long alkaline solution will buy. there are several polymers that are resistant (including ptfe) but theyre not particularly strong or wear resistant. People do need to take care not to scratch that teflon coating. – Abel Jan 22 '22 at 13:26
  • I am also getting it lacquer coated. – Ritesh Sharma Jan 22 '22 at 13:27
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    given the locations where your parts are expected to grind against one another, my reccomendation would be to swap the zinc galvanized for electroless nickel plating. doesn't help salvage your current part, but should work well for new ones. – Abel Jan 22 '22 at 13:31
  • Is the MEK a cleaning solution? Needless to say, if it is being used to clean the drums, all kinds of stuff is going into solution. You need a proper industrial chemist to test the solvent. You probably need to offer multiple coating options to your customers and then it sort-of becomes their problem. Pure MEK has a PH of 5.5, and galvanized coatings are already a lot less effective at that PH. Any lower and the coating is just not doing much. – Phil Sweet Jan 22 '22 at 15:10
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    There are different zinc-based galvanized coatings that are tuned to different environments. It may as simple as better prep and a slight modification to the coating. Or you may need to manage the cleaning solution better. – Phil Sweet Jan 22 '22 at 15:10
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    Run a test with acetone as the solvent instead and see if the same thing happens to your part. Acetone has a PH of 7. – Phil Sweet Jan 22 '22 at 15:18
  • yea it looks like an imperfect plating job? Thin zinc plating gives minimal protection, often just enough to keep parts fresh while they're still in the box pre being sold. Electroless Ni per Abel above is worth a shot. Search on finishing.com for a good knowledge base on all things to do with metal finishing / plating tweaks vs corrosion – Pete W Jan 22 '22 at 20:09

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Ritmesh, just to be clear: are the iron parts cleaned in MEK before zinc coating, or are the zinc-coated iron parts corroding after being exposed to MEK during service as drum clamps? I ask because the the usual process for pre-zinc dip coating is an initial acid wash and rinse/dry, not an MEK cleaning dip.

Also please note 35μm of zinc is not very thick and may not be able to cover up all the pits & scratches in the iron.

Also I notice that the corrosion is pitting corrosion associated with the sheared edges of these parts which suggests pinholes in the zinc in the roughened zones. Two things to try: a tumble deburring of the parts before zinc coating to remove any sharp edges, and a thicker zinc coat.

Finally, if the problem is pinholing then you should be able to rapidly produce it by dipping the parts into a warm, well-oxygenated weak acid solution with a little salt in it and then watching closely for gas evolution at the zinc surface, where the pinholes are. You can also do the pinhole test by assembling an electrochemical cell where one electrode is copper and the other is your zinc-coated part and the solution is a weak acid. this will resolve pinholes in seconds if you do it right.

Fred
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niels nielsen
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