comcom
by Dave Wright
Senior Technical Representative
Texo Corporation
Send your Questions to davewrit@execpc.com
Q. We have a two stage washer. We have some new parts that we had
to slow the line down to get a good cure. Since that time, everything
wants to flash rust. All the parameters in the washer are within
specifications, and we have even dumped and recharged to no avail. Do
you think it is the steel?
A. It could be, but more than likely it is the decrease in line speed
that is hurting you. You didn't say how much you slowed the line
down, but could you have slowed it enough that parts have an
excessive dwell time in between stages, or are even drying down? I
would check this first. If this seems like the culprit, try
installing misting nozzles in between the stages or extending a riser
from the rinse or first stage into the "dead" area. This may help
keep the parts wetted out. Another option might include trying to
increase the cure temperature so that you can bring the line speed
back up.
Q. It is difficult to maintain pH in the specified range of our
five stage, iron phosphate washer. The pH keeps creeping back up. If
we add phosphoric acid as our chemical supplier recommends, we get
lousy looking parts. What is happening?
A. I'll bet you are on well water that is very "hard". The reason for
this is the alkaline nature of the makeup water. As the water
evaporates and is made up with fresh water, you are continually
adding alkaline salts (primarily Calcium and Magnesium) which tend to
elevate and "buffer" the pH level. As this buffering increases, it
will take more and more acid to maintain pH. The easiest and most
cost effective solution is to provide low solids (deionized or
reverse osmosis), make up water. Low solids water has very little of
the alkaline salts of normal (good drinking) water. It will not
buffer the pH to the alkaline side nearly as much. Other benefits can
include reduced sludge volume and increased corrosion resistance.
Although a "system" will be less costly to operate, a replaceable
cartridge system, is perfectly acceptable and an inexpensive way to
prove it out. If you would like the details of how to set one up, let
me know and I will describe it to you in more detail than we have
space for here.
Q. We process steel and now occasionally some aluminum through our
seven stage washer. When we run aluminum, the parts sometimes come
out with a dark gray looking material that you can wipe off. Although
we have no real salt spray requirements for the aluminum, adhesion of
our powder is significantly worse than the steel. Any ideas?
A. Did you tell your chemical vendor that you were (or are) going to
run aluminum? I'll bet not. Sounds to me like you are using a cleaner
that is not "multi-metal" safe. By that we mean that it is probably a
Sodium or Potassium hydroxide based cleaner that is not inhibited
against attacking aluminum or zinc. Talk to your chemical vendor and
let them know your plans. They should be able to come up with a
"safe" cleaner that is either inhibited against attacking aluminum or
one that is caustic fee that will do the job. While you are at it,
ask about a phosphate that contains fluoride to etch the aluminum for
better adhesion. You really don't deposit an appreciable amount of
iron phosphate on aluminum, but that is another topic altogether!