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Letter 35082
Acid based electrolytic cleaning
[Connecticut]
+++++
I'm in the process of learning more about surface cleaning,
finishing, and coating. I'm using the
ASM
Volume 5 for reference. I was wondering if anyone ever used acid
for cathodic electro cleaning of carbon steel. Cathodic cleaning uses
hydrogen ions for the scrubbing action instead of hydroxyl ions, so I
was wondering why a basic solution is recommended for both anodic and
cathodic cleaning.
Keith Davis
fuel cells - Danbury, CT, USA
1st of three simultaneous responses--+++++
Bases or alkalies are preferred because they are effective in
dissolving greases and oils. Acids are not, also some unwanted
metallic species may be present dissolved in the cleaning baths.
Cleaning in forward polarity may result in their reduction and
consequent deposition over the surface of the part instead of leaving
the bare metal clean. For that and other reasons, like the
brittleness of high strength steels, acid cleaning is preferred as a
mid or final step after alkaline cleaning and mostly used on reverse.
G. Marrufo-Mexico
Guillermo Marrufo
Monterrey, NL, Mexico
2nd of three simultaneous responses-- +++++
In addition to the scrubbing action of the generated gasses,
alkaline cleaners are able to saponify oils and greases. Acids
generally have no effect on O&G.
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Jeffrey Holmes,
CEF
- Spartanburg, SC, USA
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3rd of three simultaneous responses-- +++++
The scrubbing action is only one aspect of the cleaning process.
All things being equal, it's a lot easier to remove organic soils
with alkaline cleaner formulations than with acidic products. An
acidic product also has the potential of attacking the steel surface,
while you can pack the caustic into an alkaline cleaner and not do
any harm to the surface.
George Gorecki
- Naperville, Illinois
+++++
My particular application for electrolytic cleaning is to remove
rust and scale, therefore the breaking down of soils with an alkaline
solution isn't paramount. Acid dipping is another method for
attacking the oxides and I was wondering if acid in either an anodic
or cathodic environment would be most effective.
Keith Davis
fuel cells - Danbury, CT, USA
First of two simultaneous responses -- +++++
US patent 6294072 seems to be relevant to your enquiry.
But one must ask - if you wish to use acid, why add the complexity of
an external electrical system? - just let the acid dissolve the
oxides, as is done in countless thousands of pickling tanks around
the world. Electrolytic descaling has the advantage of not needing
anything as aggressive as the usual pickling acids, but it swaps one
set of operating problems for a different set. To superimpose an
electrolytic system on an acid system seems to force on you the
difficulties of both, for no overall benefit.
Bill Reynolds
- Melbourne, Victoria, Australia
Second of two simultaneous responses -- +++++
Not enough information and far too many variables for a finite
answer. Anodic acid might work great for a while and then the amount
of iron or copper or chloride ions reach a magic point and the parts
would be pitted beyond use. Temperature is a factor as is the voltage
applied. In acid cathodic, you reach a point where crud will plate
out on the part which can be difficult to get off.
For heavy rust and mill scale, abrasive blasting is probably the best
option.
Approach free advice with great caution.
James watts
- FL
+++++
The reason I was contemplating using electrolytic cleaning in
conjunction with the acid is to get the benefit of the scrubbing
action of hydrogen/oxygen. I can't use abrasive blasting because it
will not reach internal cavities. These internal cavities have rust
(cast iron manifolds, pump housings). Normal passivation does not
actively remove the scale, and I've had good luck doing both acid
cleaning, and alkaline electrolytic cleaning, and I was just
wondering if the combination would add some benefit. Maybe I'll check
out that patent.
Keith Davis
- Danbury, CT USA
+++++
In Cathodic Electrolytic Cleaning a current impressed on the
cathode. This impressed current reduces the hydrogen cations to H2
gas, which then causes a mechanical scrubbing action on the surface
of a material. This mechanical scrubbing has the potential to remove
scale, but has an assortment of problems associated with it. The
biggest problem is contamination from other metal cations. These
cations will plate on the surface of the cathode. Make sure your
anode is anodically inert. Graphite should be used. Because of
contamination issues many references recommend an alternating
current. However, my company has used cathodic electrolytic treatment
successfully on the pilot scale. Hope this helps.
Luke Autry
Electroplating - Ellington, CT
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