A. In my experience, it is unusual to completely shut
down and start up a phosphating line multiple times
in a week. I would think this would be problematic for
several of the ingredients in the phosphating stage.
Some of the ingredients may be soluble at the elevated
operating temperatures, but insoluble as the bath is
allowed to cool on the off days. This precipitation, along
with a natural tendency to form sludge in this tank, will
be exacerbated by the frequent line cool downs. One of
the ingredients that could precipitate would be the iron
phosphate or free iron.
The first thing I would do is insure that the tank is
fully up to its specified temperature range before starting
any production. Then perform any required titrations
from your supplier, typically total acid, free acid and
pH. Some suppliers also have procedures available to
check the accelerator and grain refiner concentrations (if
formulated) as well as free iron. An old method to rapidly
increase free iron would be to add some steel wool to
the phosphate tank to provide it with a quick supply
to dissolve. However, this should only be done if you
confirm the tank is low in iron. I would also recommend
contacting your supplier of the phosphating chemicals.
They should be familiar with the chemistry of the bath
and would be able to tell you more specifics regarding
what is going wrong.
Consider
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