(using clean water), tape-pull testing
or white glove testing can also provide
valuable data. Cleanliness testing is
always relative; bench mark levels need
to be established that can be associated
with acceptable performance, and the
operation should be kept within upper
and lower limits at all times.
Aqueous washers, like all chemical
processes, need to be monitored and
maintained. Typically, a titration is
performed to determine the concentra-
tion of the chemistry, and should be done
once per shift. Documenting param-
eters like concentration, pH, conduc-
tivity, spray pressure and temperature is
good standard operating practice, and
a suitable data logging system must be
implemented.
An aqueous cleaner removes the soils,
and in an ideal system, those soils are
continuously removed from the washer.
Filtration can remove insoluble material
from the tanks, such as metal chips or
swarf. With ferrous programs, magnetic
separators can be combined with bag
filters. Oils can be removed from the
washer using skimmers or coalescers,
and a cleaning compound designed
to reject oils can aid the soil removal
process. The catch is to be certain that
cleaned parts are not removed through a
blanket of oil to prevent redeposition of
soils back onto the parts.
Even with good housekeeping and
maintenance, all chemical programs will
eventually reach the point when they
need to be recharged. Knowing when
recharging is required contributes to
success. With cleaners, utilizing free to
total alkalinity titration can help process
efficiency. Many alkaline cleaners are
controlled by free alkalinity titrations,
so this value will remain constant as you
replenish the solution with fresh product.
But over time, the total alkalinity will rise
in value (typically using indicators with
a color change at a pH close to 4, such
as methyl orange), as soils build in the
solution. You can record this ratio value,
and make plans to recharge before it
hits an upper limit associated with poor
cleaning.
The health of a cleaner bath can
also be measured by the amount of
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PRODUCTS FINISHING — pfonline.com
35
PARTS CLEANING