Friday, April 8, 2011

The Pickling Bucket



Almost all of the hardware I purchase, lag screws, nuts, bolts, machine screws and such are galvanized. That's fine for general use around the shop but if I want to weld it or create a special black, rust or bronze surface finish the galvanizing must be removed. I have always called this "pickling" but that might technically just apply to removing oxidation and this process should be called degalvanizing.

For several years I have been using a simple outdoor setup to do it. On the north porch just outside the forge room door I have a 5 gallon plastic bucket about half filled with muriatic (hydrochloric acid). When not in use I keep it covered with an upside-down rubber 3 gallon feed pan. A sieve device makes it easy to remove and rinse the cleaned pieces.

The sieve is a plastic container with about two gallon volume which originally, I think, contained kitty litter and easily fits inside the five gallon bucket. I cut away part of the top below the handle, tied a rope loop around the handle for hanging and then drilled about twenty 3/8" holes in the bottom.

It works like this. I put the galvanized pieces in the sieve and lower it into the acid. There is a screw in the wall on which the rope loop can hang so it doesn't fall down into the acid while the pickling process is taking place. Initially there is a vigorous boiling type action as the acid dissolves the zinc. After a few minutes this stops and the sieve can be lifted and drained. I run water from a hose into the sieve to rinse away the acid, dump out the hardware and let it dry on a newspaper. The sieve hangs on another higher wall screw and the lid is place over the
bucket to keep out rain and debris.

As the hardware dries a thin rust film forms - oxide - which usually seems to complete the passivation process. There have been a few occasions where I actually rinsed a more complex workpiece in a dilute baking soda (sodium bicarbonate) solution to assure the acid action was fully ended.

I have used the same acid for at least three years and it still seems to have the original potency but has changed from a clear yellow color to a deep rust color. A few times I have been distracted and forgotten to remove the hardware until the next day and the steel has survived well.

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