Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Default Victory!

http://www.flickr.com/photos/2768312...in/photostream

Keep the hydrogen bubbles away and good things happen!

Michael Koblic,
Campbell River, BC
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Rex Rex is offline
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Default Victory!

On Nov 6, 7:03*pm, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Keep the hydrogen bubbles away and good things happen!

Michael Koblic,
Campbell River, BC



Looks great. details?
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On Wed, 9 Nov 2011 13:32:59 -0800 (PST), Rex
wrote:

On Nov 6, 7:03*pm, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Keep the hydrogen bubbles away and good things happen!

Michael Koblic,
Campbell River, BC



Looks great. details?


It is really a follow-up to my previous thread "What causes that?"

Doing the same piece previously I ended up with a lot of small holes
in one area and there was a debate as to what causes them. I went
through some tests which are also documented on my flickr site. To cut
the long story short I believe that hydrogen bubbles which are formed
on the cathode should be kept away from the anode (the workpiece). I
believe that what one was seeing was a cavitation effect of these
bubbles.

I run the process with the electrodes side-by-side and about 3 inches
apart and this seems to have done the trick.

When I finish with the current work (Christmas rush!) I shall see if
this also solves the problem of foul biting I have had with some
pieces: I believe that the cavitating bubbles blasted little holes in
the resist.

Michael Koblic,
Campbell River, BC


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Default Victory!

Congrats on the progress. I still think stirring will help, if you ever
find some time to try it. The farther apart the electrodes are the less
important their relative shapes and the fewer problems with non-uniform
current density. For electropolishing 304 and 316 SS I like to basically
line the tank so there is cathode everywhere the anode "looks", just use a
large enough tank so the distance to the cathode is greater than feature
sizes on the anode and preferably larger than the anode itself. For
workpieces in the 1" cube or smaller range I make the anode-cathode distance
3-4" at least, and if I'm manually holding the piece I stir it around some
to vary the geometry as it polishes. As for your question on why bubbles
form on the resist, remember, you are constantly producing gas at both
electrodes so you are keeping the electrolyte supersaturated with dissolved
gas. Any nucleation site will result in bubble formation, even if there is
no current flow there. This is one reason stirring can help, it keeps
knocking the bubbles off the active anode surfaces. The bubbles act like
little insulators so while a bubble is stuck in one spot that spot is not
being electrochemically etched. There is an upper limit, however, because
right at the active surface you get a thin film that is more viscous than
the bulk solution due to the dissolving metal, and this film helps level the
current density and gives uniform etching (the higher viscosity slows the
etching and it's more viscous at the bottom of a pit where the film isn't
readily rinsed off so the bottoms of pits etch slower; the tips of high
spots stick up out of the film and the sharp tip concentrates the electric
field, both of which increase the rate of etching to knock the high spot
down to the average surface). You need this film but you also need to rinse
it away to maintain maximum current density, so some stirring helps both
ways. Go extra crazy stirring and you can totally sweep this film away and
back come the pits. I played with this some with citric acid electrolyte
and electropolishing SS, and it took some heroic stirring to cause problems
so I mention it mostly for completeness sake, I doubt you will see it.

-----
Regards,
Carl Ijames
wrote in message ...

On Wed, 9 Nov 2011 13:32:59 -0800 (PST), Rex
wrote:

On Nov 6, 7:03 pm, wrote:
http://www.flickr.com/photos/2768312...in/photostream

Keep the hydrogen bubbles away and good things happen!

Michael Koblic,
Campbell River, BC



Looks great. details?


It is really a follow-up to my previous thread "What causes that?"

Doing the same piece previously I ended up with a lot of small holes
in one area and there was a debate as to what causes them. I went
through some tests which are also documented on my flickr site. To cut
the long story short I believe that hydrogen bubbles which are formed
on the cathode should be kept away from the anode (the workpiece). I
believe that what one was seeing was a cavitation effect of these
bubbles.

I run the process with the electrodes side-by-side and about 3 inches
apart and this seems to have done the trick.

When I finish with the current work (Christmas rush!) I shall see if
this also solves the problem of foul biting I have had with some
pieces: I believe that the cavitating bubbles blasted little holes in
the resist.

Michael Koblic,
Campbell River, BC


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Default Victory!

On Wed, 9 Nov 2011 20:52:59 -0500, "Carl Ijames"
wrote:

Congrats on the progress. I still think stirring will help, if you ever
find some time to try it. The farther apart the electrodes are the less
important their relative shapes and the fewer problems with non-uniform
current density. For electropolishing 304 and 316 SS I like to basically
line the tank so there is cathode everywhere the anode "looks", just use a
large enough tank so the distance to the cathode is greater than feature
sizes on the anode and preferably larger than the anode itself.


That's pretty much what I got now.

For
workpieces in the 1" cube or smaller range I make the anode-cathode distance
3-4" at least, and if I'm manually holding the piece I stir it around some
to vary the geometry as it polishes. As for your question on why bubbles
form on the resist, remember, you are constantly producing gas at both
electrodes so you are keeping the electrolyte supersaturated with dissolved
gas.


I found no evidence of gas being produced on the anode in my set-up.
At one stage I even isolated the electrodes and tried to collect the
gases. However, if you change the electrodes (e.g. both cathode and
anode stainless) there is gas production at the anode. I assume it is
chlorine but there is much less of it than hydrogen on the cathode.

I think the bubbles on the anode are the same ones that develop
elsewhere in the tank e.g. on its walls - the bath gets heated and
dissolved air comes out like in a tea kettle (the last run was
consuming almost 30W).

Any nucleation site will result in bubble formation, even if there

is
no current flow there. This is one reason stirring can help, it keeps
knocking the bubbles off the active anode surfaces. The bubbles act like
little insulators so while a bubble is stuck in one spot that spot is not
being electrochemically etched.


I will argue that the situation is opposite: The bubbles burst and
produce microcavities.

There is an upper limit, however, because

right at the active surface you get a thin film that is more viscous than
the bulk solution due to the dissolving metal, and this film helps level the
current density and gives uniform etching (the higher viscosity slows the
etching and it's more viscous at the bottom of a pit where the film isn't
readily rinsed off so the bottoms of pits etch slower; the tips of high
spots stick up out of the film and the sharp tip concentrates the electric
field, both of which increase the rate of etching to knock the high spot
down to the average surface).


That is true. I found the process to be wonderful at removing machine
marks.


You need this film but you also need to rinse
it away to maintain maximum current density, so some stirring helps both
ways. Go extra crazy stirring and you can totally sweep this film away and
back come the pits. I played with this some with citric acid electrolyte
and electropolishing SS, and it took some heroic stirring to cause problems
so I mention it mostly for completeness sake, I doubt you will see it.


I found stainless to be quite a different beast from mild in this
process.

Michael Koblic,
Campbell River, BC


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Default Victory!

Going back to my days of etching circuit boards....

Aquariums make good containers. Can be free or really cheap if you find
the right yard sale or craigslist posting.

Heat can help. Aquarium heaters are handy for that.

One method of stirring is to run an aquarium bubbler-stone under the
workpiece. Aquarium pumps/filters can also be used. You may see a theme
developing here....

Don't try to use (or let someone else use) an aquarium used for plating
or etching for fish...

You may want to experiment with different electrolytes. Washing soda
(sodium carbonate) or baking soda (sodium bicarbonate) instead of salt,
for instance.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.
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Default Victory!

Ecnerwal wrote:

(...)

One method of stirring is to run an aquarium bubbler-stone under the
workpiece.


The etchant will disintegrate the stone.

AMHIKT, go ahead.

--Winston
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