Saturday, November 6, 2010

Polishing Corny Kegs

As promised, here is more information on how to polish stainless steel. Mostly the process is the same as for any polishing, but there is one gotcha, so read on to the end. When you pick up used corny kegs, they are usually dented, scuffed and covered in decals. I spoke a little last time about removing the decals, but there is always glue and gunk left behind. Last time I mentioned Goo Gone, but if the gunk is stubborn, I have found that mineral spirits or paint thinner will work too. Be careful with this because if you get it on the top and bottom rubber bumpers it may damage them, although careful, gentle rubbing with mineral spirits can remove black scuffs from red and blue upper bumpers. Here is a good example of what your used corny will probably look like when you get it.
 I started with an 80 grit SandBlaster pad from 3M, moving in a small circular motion and periodically checking the pad to make sure it wasn't clogged. I then moved to a 320 grit SandBlaster pad, following the same procedure I used with the 80 grit pad. Then I worked the entire stainless steel surface of the keg with 1000 grit wet/dry paper.  Keep the paper wet with just enough water to make the paper easy to move, this will soften the cut and keep the paper from clogging. At each step, make sure you work out the scratches made by the previous cut. You could also use opposing cuts at 90 degrees, since this will help you see when you have removed all of the scratches from the previous cut.
Once you have completed all of the above steps, wash the keg with water and then dry with a soft cloth. You should now have something that looks like the picture below.
If you wish to continue polishing to a mirror finish, you could now work the keg with a buffer and various rouges, but I like to leave it at an even, rough finish so that future scuffs and dings don't show as much. Now here is the gotcha, after stainless steel is polished at the factory, it is then passivated. Without passivation, the exposed iron atoms in the metal surface would begin to oxidize, and you would soon see rust discoloration in the metal. Passivation is normally carried out with any one of several strong acids. In our case we can use oxalic acid to passivate the stainless steel. My favorite source for oxalic acid is Bar Keeper's Friend. This household cleanser is available in many places, I purchased mine at Home Depot, but I understand it is also found in most stores that sell cleaning supplies. A word of warning regarding oxalic acid and Bar Keeper's Friend, beside being a corrosive, it can also cause kidney damage if you ingest, breathe or adsorb any of it. Please consider wearing protective equipment when you use this stuff. I use PVC forearm length gloves, safety glasses and a dust mask when I polish my kegs. If all goes well, you will end up with a clean, nice looking long lasting finish of which you can be proud. Here is a before and after shot for comparison.
That's it for now, but there will be more soon.

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