Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Larry Zitko, ChromeTech, Inc.
Chromic Acid Level in Bath
Q. We have been maintaining the chromic acid level of two inches below the tank but
we are unable to control the fumes/mist even though scrubber is working
perfectly. Can you help? Also, how far below the surface of the liquid should plated parts be?
A. The liquid level in your hard chrome plating tank is too close to the rim of
the tank and the inlet slots of your exhaust hood. This situation can
dramatically increase the amount of chromic acid that is conveyed to the
inlet of the scrubber, as you have noticed.
During hard chromium electroplating, the electrolysis of water also occurs,
generating hydrogen gas at the cathode and oxygen gas at the anode. These
gasses rise to the surface of the plating solution, then escape to the
atmosphere immediately above the surface. A significant amount of plating
liquid is released with these gasses. If the liquid level is down far enough
from the rim, a portion of this liquid is returned to the plating bath. Any
portion of the liquid that does not fall back into the bath (typically the
smaller sized droplets) must be captured by the local exhaust hood.
I like to see the liquid level down at least 6" from the rim.
With regard to your second question, it is best to keep the plated regions
down at least 2" below the surface of the bath. This will ensure that all
that gas activity near the surface will not insulate the plated region from
the plating electrolyte.