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Anodizing aluminum is as simple as putting a bunch of parts
on a rack, and dunking them in a sequence of tanks (each with
a different chemical of dye in it). Between the chemical tanks,
you must rinse the parts off or the chemistry will quickly become
contaminated. Anodizing aluminum uses a huge amount of water
in rinsing. Nearly all of the water used is for rinsing parts
off before they go into the next bath of chemicals. 2/3 of the
tanks in our lines are rinse tanks, to illustrate the point.
Just like the air quality system, you start by minimizing the
amount of waste you generate. Here, we looked hard at how to
use less water. We set up spray harnesses that rinse off the
parts with clean water as the robot lifts them from the bath
of chemicals. This has 2 benefits, first one, the rinse water
will last a really long time before it needs to be refilled,
second, we get to keep our expensive chemicals in the tank that
we put them in, not in the rinse tank. This is called "reducing
chemical drag-out" and has become the key to our water use reduction
plan.
 Counter-flow
rinsing is an old method that is still great. Between the
chemical tanks, instead of just a single rinse tank you have
2. The first rinse tank is the overflow from the second, cleaner
rinse tank. Parts get rinsed in the dirtier tank first, then
the cleaner one. You add water to the second (cleaner) tank
and let it flow into the first (dirtier) tank. This saves
a bunch of water and gives a better rinse, your clean rinse
stays clean longer. We did this method one better. We flow
rinse water in a key area of our line through 4 rinse tanks,
only adding clean water to a single tank which overflows into
3 tanks, one after the other in a series. This saves us a
lot of rinse water without compromising quality.
We use conductivity meters in our rinse tanks.
When water is incredibly pure and clean, it doesn't conduct
electricity well at all, as contaminants get in the water,
it conducts electricity better and better. We monitor the
conductivity of our rinse tanks to control when (or if) more
water needs to be added due to increasing contamination. Nearly
everybody else doing this just sets the rinse tanks on a timer
(add 10 gallons every 3 minutes, for example). This is overly
simplistic and wasteful.
 Water
Recovery
One of the biggest reasons why we need to use as little rinse
water as we can is because we distill and re-use all of it.
If we generate thousands of gallons of rinse water a day,
we will need to distill and re-use it all. That would take
an incredible amount of energy. Our anodizing line is completely
closed loop, no water is released to the sewer.
We use a vacuum distillation system that is
incredibly elegant and efficient. We pump the dirty water
into sealed containers and vacuum the containers out, reducing
the pressure inside the container to about 40mmHg, about 1/20th
of atmospheric pressure. This reduces water's boiling point
enormously. The container has a Freon coil around it and the
Freon is super hot. That is the heat that boils the water.
The Freon then goes outside through a big radiator (just like
the part of an air conditioner that is outside) that cools
it off. The cooled Freon is then used to condense the water
vapor which collects in a tank. The Freon just goes around
and around and we get our clean water. The contaminates stay
behind in the containers to be reduced down to a dust and
cleaned out for appropriate disposal. It is a beautiful system.
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