Polishing Of Ss

[TomP]

Paul,

A good source for both the tools and materials as well as a wealth of knowledge in their forum is available at http://www.caswellplating.com/buffs/buffman.htm

They seem to carry those odd shaped cones and pads that make polishing that much easier.

Oh, and regards to Renoir. He is right on with his technique though I think 1 amp at 25 volts is a little high. We use 12VDC and the amperage is based on the surface area in the bath, rough .1A per 1 inch of surface area for a .00005 coverage. Oxalic acid would not be my choice. It is not agressive enough. I would use a 33% solution of nitric acid. A little more agressive.

The passivation method we use, and refers to ASTM A380 treatise are:
Grades with at least 16% Chromium (except free machining grades e.g. 303)
20-50% nitric acid
Room temp. to 40?C
30-60 minutes

Grades with less than 16% Chromium (except free machining grades e.g. 416)
20-50% nitric acid
Room temp. to 40?C
60 minutes

Free machining grades such as 303, 416 and 430F
20-50% nitric acid + 2-6% sodium dichromate
Room temp. to 50?C
25-40 minutes
We keep our acid tank at about 38C. Any hotter and emissions become a problem.

Electropolishing is by far more favored and much much less labor intensive. But it has its own set of issues. Namley that you can turn your garage into an EPA Super Fund site if you are not extraordinarily careful. Here is the flow chart we use for this process:
Heavy Alkaline soak and clean (Ph 10) we use caustic soda ash. Garunteed clean
Cold Water Rinse
Acid (Sulfuric) descale
Cold Water Rinse
Electro polish
Drag out (looses the heavy metals)
Polish rinse
Nitric Acid bath
Cold Water Rinse
Hot Water Rinse
Cheesecloth wipe and buff.

It is theoreticaly possible to set this kind of operation in your garage, but by the time you have everything needed to start: heaters, tanks, FUME HOOD AND AIR SCRUBBER, and the power rectifier (which, for a small one can run close to $1000), chemistry supplies, and lots of beverages for your neighbors when they complain about the smell. Might just be easier to find a local polisher.

Hope this helps.

Originally Posted by Paul Seamons

I have occasion to have various SS fittings, bases etc. fabricated at my local machine shop. These are fine and functional but with a "mill finish". Anyone have any experience polishing SS from the mill finish I get at my shop to the nice, almost mirror, finish found on most marine hardware?