1070-4272/04/7709-1469C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 9, 2004, pp. 1469!1475. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9,
2004, pp. 1481!1486.
Original Russian Text Copyright + 2004 by Karavaev, Litovka.
AND CORROSION PROTECTION OF METALS
Optimization of Electroplating Processes in Drum Baths
To Obtain a More Uniform Coating
V. I. Karavaev and Yu. V. Litovka
Tambov State Technical University, Tambov, Russia
Received April 6, 2004
Abstract-The optimization of the electroplating process in drum electrolyzers to minimize the standard
deviation of the coating thickness is considered.
The uniformity of a deposited metal layer is one
of the main quality parameters of electroplated coat-
ings obtained in baths with drums. The problems of
achieving a prescribed or the minimum possible vari-
ance of the coating thickness arise both in design of
electrochemical systems and in control of the proc-
esses. Solution of these problems is complicated by
the lack of a well-developed theory of the process and
by inconsistency of experimental data on how param-
eters of an electrochemical system affect the uni-
formity of a coating.
Technical specifications for fabrication of articles
with electroplated coatings commonly give the mini-
mum acceptable thickness of deposits, which predeter-
mines the electrolysis duration. If the coatings
deposited are nonuniform, then, on obtaining the
minimum possible deposit thickness in some parts of
an article, the thickness of deposits in other regions
may exceed the minimum value severalfold. This
leads to an unproductive increase in the expenditure of
a metal deposited, electrolyte, and electric power,
lowers the output capacity of the electroplating ap-
paratus, and makes higher the production cost of
the articles manufactured.
The choice of the electrolyte composition and elec-
trolysis parameters, as well as of the design of the
electroplating equipment and feeding units is governed
by the necessity for obtaining articles with the highest
possible thickness uniformity in their different parts.
As an optimization criterion is commonly used the
root-mean-square deviation (also termed standard
deviation) s of the thickness of a coating on articles
from its average value.
The main factors that affect the chosen criterion are
the current I, drum filling C
, drum rotation frequency
w, and drum parameters: diameter D and degree of
wall perforation f
. Let I, C
, and D be variables.
Then, to optimize the drum electrolyzer, it is neces-
sary to find the current I, drum filling C
, and drum
diameter D at which the standard deviation of the
coating thickness, s(I, C
,D) is the smallest:
,D) 6 min,
at constraints determined by the equations of a math-
ematical model and by process limitations.
A particular case of the optimization problem to be
solved is a search for process variables: current I and
for an available drum. In this case, it is
necessary to find the current I and drum filling C
at which the standard deviation of the coating thick-
ness, s(I, C
), is the smallest:
) 6 min.
To relate the chosen criterion to the variables, we
construct a system of equations of the mathematical
model. Theoretical concepts of the process and gen-
eralized experimental data formed a basis for the con-
straint equation suggested in , which relates the
standard deviation of the thickness of a coating de-
posited onto articles in a rotating drum to the param-
eters of the system:
s = K
where K is the scatter factor; h, average coating thick-
ness; and Dt, electrolysis duration.
The average coating thickness is found from the
h = ÄÄÄÄÄÄ,