Re: Electropolishing
- From: "Carl Ijames" <carl.ijames@xxxxxxxxxxxxxxxxx>
- Date: Tue, 01 Nov 2005 03:21:51 GMT
> Thanks Carl. Despite my efforts, I'm still doing electro-dulling! Your
> comment about using copper for the cathode might be what I'm missing.
> I've been using SS for the cathode. I think my lack of success is due
> to a combination of things. Wrong cathode material, electrolyte out of
> balance, and low electrolyte temperature. I have however played with
> various current densities. One other thing I have learned is that by
> using 308 stainless wire (commonly used in MIG welding) as wire
> hangars, there must be enough of an iron content to dirty up the
> electrolyte with a reddish-brown emission.
You're welcome. It's so rare I have anything to contribute here, and
I've learned so much over the years. I don't understand it, but I've
seen test workpieces (usually scraps of 1/4" OD 304 tubing, about 1-3"
submerged, I scotchbrite to dullness and then polish to test the setup
each time I turn everything on before going on to the workpiece) go from
great to ugly as I change nothing but the cathode from different pieces
of 304 stainless steel sheet to copper to lead sheet. The lead and
copper "always" work (famous last words :-)), but apparently identical
pieces of 304ss work or don't work at random. I wound up splitting two
1' long pieces of 5/8" copper tubing from the scrap bin with some small
snips to get two sheets 2"x1', and bent each into an L that stuck up out
of the solution and went ~1/3 of the way across the bottom of my work
tank. Connected them together with a piece of 8 ga wire and I've been
using them for 3 years now. My work tank is a plastic 1/2 gallon ice
cream container - nice rectangular shape and big enough for the 1-2"
sized stuff I usually do. I used to use concentrated H2SO4-H3PO4 but
that stuff is nastier if you get it on you and is hygroscopic (it sucks
water out of the air and will gradually overflow the tank). I've been
happy with the citric acid-H2SO4 solution once I worked out the best
ratio (equal parts battery acid and citric acid powder by volume, heat
to dissolve and use warm-to-hot, I usually run at 90 deg C but I have a
nice thermostatted water bath that I keep at that temp for other stuff).
Also it's easier to get battery acid and citric acid (auto parts store
and www.mcmaster.com) than it is to get concentrated H2SO4 and H3PO4. I
pretty much always use 308 wire for hangars and I've never seen the
solution go reddish brown. It starts out clear and slowly turns green
from the chromium (plus bluish from the nickel).
Oh, watch out for the hangar wire - you _will_ burn yourself a few
times. 304SS is actually pretty close to nichrome, composition-wise,
and pushing 5-25 amps down a 1/16" diameter piece of 308 will get it to
glow red hot pretty often. It's the times it doesn't glow that get you,
it's so easy to forget how hot it gets.
-----
Regards,
Carl Ijames carl.ijames at verizon.net
.
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