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| Parts
are racked for anodizing. Fort Wayne Anodizing does a lot
of automotive finishing, however it also provides quality
finishing for the medical, electronics and appliance industries
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Electropolishing
is the electrolytic removal of metal in a highly ionic solution
by means of an electrical potential and current or, in other words,
reverse electroplating. So what are the benefits of using electropolishing
as part of an anodizing process? Plenty, as Fort Wayne Anodizing
has found out. Not only does electropolishing provide a decorative
surface and act as a replacement for bright dip, it improves the
aluminum surface prior to anodizing by smoothing out the peaks and
valleys.
Electropolishing
removes metal from the surface while producing a unidirectional
pattern that is stress and occlusion free, microscopically smooth
and highly reflective. Deburring is accomplished quickly because
of the higher current densities used, enabling the constant exposure
of the burr tip. The combination of no directional lines from mechanical
finishing, plus a surface relatively free of hydrogen, results in
a hygienically clean surface.
Electropolishing
aluminum does not produce toxic fumes, require fume hoods, produce
corrosion or require high temperatures. To control the bath, FWA
takes the specific gravity and checks the aluminum metal content.
"We see it as a big advantage over bright dipping," stated
Dennis Fulford, sales manager. "Bright dipping aluminum produces
nitrogen dioxide, which is toxic. Also, you have to run the bath
at a higher temperature (194-205F), which requires more heat and
hence more money. Another issue is that the bright dip bath has
several variables that need to be controlled in order to produce
good work."
Neither
is an aluminum electropolishing bath the same as a stainless steel
electropolishing bath. Chemistries as well as parameters differ.
See Table I.
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TABLE
I: Electropolishing Baths
|
| |
Stainless
Steel |
Aluminum |
| Temperature |
120F |
150-160F |
| Voltage |
6-9v |
12-24v |
| Amperage |
10
asf |
20-40
asf |
| Time |
6
min avg. |
6
min avg. |
| Chemistry |
H2SO4,
H3PO4 additives |
H3PO4
based |
| Agitation |
some |
vigorous |
However,
much like their steel counterparts, aluminum pieces are cleaned
prior to electropolishing. Aluminum parts first go through degreasing,
unless they are heavily soiled, in which case they are etched. FWA
tries to avoid this as much as possible because the etching can
mar the surface of the aluminum. After degreasing and rinsing, parts
are desmutted and run through more rinses before entering the electropolishing
tank. After electropolishing, parts are rinsed and run back through
the desmut tank to clean off any oils they may have picked up in
the rinse tanks. Now they are ready for either conventional or hardcoat
anodizing.
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|
Aluminum
electropolishing baths are more vigorously agitated than steel
electropolishing baths. Many other parameters are also different,
such as chemistry, amperage and voltage.
|
FWA
offers both conventional anodizing, as well as hard coat anodizing,
chromate conversion coating, vacuum impregnation and the Metabrite
Process. The customers who have requested the electropolishing have
been mostly from the medical field, appliance and heavy truck industries.
Many want the bright electropolish with an anodized and clear finish
for items such as headlamp bezels, side mirror brackets and grilles.
The medical industry requests the process because of how well it
removes burrs, which is extremely important when dealing with surgical
equipment. These items are also dyed. FWA has eight standard colors
it offers from black and clear to purple and yellow. Some of the
medical equipment is color-coded.
Fort
Wayne Anodizing's slogan is "It's not how it's made. It's how
it's made to last." And now it offers its customers one more
way to make their products last longer and look better. "Traditionally,
our customers relied on FWA to provide them with a matte or stain
finish. With the electropolish, we can give them more options for
a brighter anodize," stated Mr. Fulford.
