61, pp. 88-92. 204/434; 204/DIG. s; 427/4411'; 427/4351 P'im'l" Examine”? “"18. [
58] Field ..... Ferrocote 61 AUS oil, which was subsequently wiped to leave just ...
'
.
US005324399A
United States Patent [191
[11] Patent Number:
5,324,399
Ludwig et al.
[45] Date of Patent:
Jun. 28, 1994
[54] METHOD AND SYSTEM FOR MONITORING QUALITY OF PHOSPHATE
mer’s Encyclopedia of Chemical Technology, third ed., pp. 304-308, (1981)". .
COATING
Freeman, “Phosphating and Metal Pretreatment-A
[75] Inventors: Frank A. Ludwig, Rancho Palos
Guide t° M°d=m Pmcess and “acme”, Industrial
verdcs; Bruce M. Eliash, L05
Press, Inc._, 1986', Chapter 2.
Angeles, both of Calif,
Sadkowsk1 et a1, “Evaluatlon of the Effect of Surface
_
_
[73] Assign“: 12:81:15
Pretreatment on Metal Phosphating by Impedance
Company’ L08
ge es’
Measurements”, Proceedings of the Symposium on
'
Advances in Corrosion Protection by Organic Coat
[21] Appl. No.: 881,586 .
_
ings, Apr. 11-14, 1989‘, Cambridge, England. '
[22] Filed‘
Zantout et al, “Electrochemical Acceleration of Phos
May 12’ 1992
phating Process” Transactions of the Institute of Metal
a; cg ................................ “5627;530:115”2x224
Finishing, 1983‘, vol. 61, pp. 88-92.
204/434; 204/DIG. s; 427/4411’; 427/4351
P'im'l" Examine”? “"18
[58] Field of Search ............ .. 204/1511, 434, DIG. s,
Ammey- 488"‘, 0' F'm-M- E~ Lwhman; M- w- Sales;
204/412; 427/443.1, 435
[56]
w- K- Demn'LW
References Cited
[57]
Us PATENT DOCUMENTS
ABSTRACT
A method and system for monitoring the quality of a phosphate coating on a metal surface having a large surface area. The method comprises applying a current
2,132,439 10/1938 2,766,423 10/1956 3,841,988 10/ 1974
or potential between the metal surface and one or more
4,019,129 4/1977
counter electrodes while they are in the phosphating
4,310,389 1/1982
solution and superimposing a constant ac signal thereon.
4,500,391 2/1985 1?
An ac impedance spectra is obtained by measuring the ac potential between the metal substrate and one or
’
’
/
more reference electrodes located between the counter
FOREIGN PATENT DOCUMENTS 0107491 5/1984 European PM OK .
electrode and the substrate. The ac impedance spectra provide an indicauon of defects in the phosphate coat
8605381 10/1986 PCT In" Appl. .
mg even when the defects are located witiun a rela
2153854 8/1985 United Kingdom .
tively small region of the total surface area of the metal
OTHER PUBLICATIONS “Metal Surface Treatments (Chemical)” in Kirk-Oth-
34:
17 Claims, 13 Drawing Sheets
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