<<< Electrochemical polishing at home >>>

Hi.
I'm working on a project to restore a few small watch parts that need
be polished for further treatments. As the surface is uneven, it is
difficult to polish some surfaces and I trust EC Polishing to be my
solution.
However, I don't have the composition of the bath (for a simple home
setup) and other process parameters.
I would appreciate any tips and experiences on this topic.
Thank you,
Dan
Reply to
aldebaran
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Go ask a horology newsgroup. We're hairy-arsed engineers round here and our processes are crude and unsuitable for polite company.
For anodic cleaning and electropolishing dirty brass I've used the following. I _think_ it's based on Canning's Anodax cleaner formulation, but I've no idea how accurately.
1 part caustic soda (sodium hydroxide), 7 parts washing soda (sodium carbonate). Mix to a strength of 8oz / gallon. Use near-boiling hot (90°C) at a current around 30A/sq ft. and agitate it by bubbling air or CO2 through the bath. Max duration about 30 seconds. For electropolishing you probably want to tone it down a bit and do it for longer.
Wash afterwards, swill in hydrochloric acid pickle, then wash again.
I don't recommend this process on smallparts without experimentation. But it's cheap to make up, easy to work with, and might give you a starting point.
Reply to
Andy Dingley
What metal? The formula for the bath will vary based on that. I put one for stainless and aluminum in the dropbox about three years ago with a note identifying the originating patent.
Reply to
TheAndroid
I believe it's Stainless Steel; I need to chemically polish the slot in the head which is not accessible otherwise. Thanks.
Reply to
aldebaran
Big problem is that electropolishing doesn't like to penetrate down holes, and is very good at rounding off sharp edges like you probably have at the edge of your slot. You don't get significant polishing past about 10-20% of the diameter down a hole, and deeper than that (down to maybe 50% of the diameter) you can actually roughen and degrade the surface as the current density falls off below what gives good polishing. Don't know where you live but most any big city will have a few electroplating/electropolishing shops. Take your part for a visit and let a pro look at it in person.
-- Regards, Carl Ijames carl.ijames at verizon.net
Reply to
Carl Ijames
The hole problem can be addressed by placing "robbers" (conducting wires) through them. This is what chrome plating shops do for the exact same problem. Also, it helps to have the solution in motion via a pump. Rounding is a function of time left in. If you over-polish, you round the edge. Can't change the physics of that!
Reply to
TheAndroid
Thanks for answering. If I go to a shop they will laugh at me... The reason is that my parts (watch screws) are so tiny, about 1mm long. I would try electroless chemical polishing at home (I don't have more that 6 at a time) but I don't know the composition of the acid bath. Can you please help? Thanks, Dan
Reply to
Anonymous
Sorry, can't help with electoless polishing. What makes you think a shop hasn't seen lots of stuff like your screws already? If you are lucky they will relish the challenge :-).
-- Regards, Carl Ijames carl.ijames at verizon.net
Reply to
Carl Ijames
I get a lot of stainless electropolished commercially- they use a propietary solution, but the main ingredient is phosphoric acid. My guess is Ospho would probably work, or dilute phosphoric, which is used as a paint prep, and is often available at good paint stores.
Reply to
rniemi
For stainless, there is a citric-acid based product line called "Citrisurf". They offer cleaning, passivating, and polishing formulas and equipment. I wanted a small amount to do some electrocleaning and passivating of stainless for jewelry -- after some discussions with the company and a look at their MSDS, i decided to do some experimenting on my own. For the record, the company was very helpful and even offered to send me a few samples of their products, but the minimum purchase quantities are way more than I could ever use.
Anyway, I got good results on 416 stainless with a home-brew mixture of 10% food-grade citric acid, and 1% disodium EDTA, dissolved in distilled water and run at about 90 celsius. I was using a home-made brush plating setup (with reverse polarity, of course) at about 18 volts, and the "wand" was a piece of flattened copper tubing with a strip of fine scotch-brite wrapped over it and secured with a wire tie.
I got very good results with electrocleaning, being able to easily remove the brown heat-stain from prior silver-soldering. After final polishing, I then passivated the pieces with a 20-minute soak in the hot solution.
Cleaning and passivation seemed to work well -- I also noticed a reasonable amount of polishing action during the cleaning, though that was not my principal objective.
In this formula, the sodium EDTA serves as a chelating agent to hold dissolved metal in solution.
Reply to
Bob

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