Method and system for monitoring quality of phosphate coating
AssigneeHughes Aircraft Company
InventorsFrank A. Ludwig, Bruce M. Eliash
Life of this patent
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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 or potential between the metal surface and one or more counter electrodes while they are in the phosphating solution and superimposing a constant ac signal thereon. 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 electrode and the substrate. The ac impedance spectra provide an indication of defects in the phosphate coating even when the defects are located within a relatively small region of the total surface area of the metal surface.
Claims17
A method for monitoring the quality of a phosphate coating applied to a metal substrate having a large surface area, wherein said phosphate coating is applied by exposing said metal substrate to a phosphating solution, said method comprising the steps of:
- (a) applying a selected dc current or potential between said metal substrate and a counter electrode while said substrate is exposed to said phosphating solution;
- (b) superimposing a constant ac signal on said dc potential or current applied between said metal substrate and said counter electrode, said ac signal having a peak-to-peak potential or current, and a frequency;
- (c) providing said counter electrode positioned in contact with said phosphating solution;
- (d) providing at least one reference electrode positioned in contact with said phosphating solution and in proximity to said substrate, wherein said reference electrode is located between said counter electrode and said substrate;
- (e) measuring the ac potential between said metal substrate and said reference electrode, said measurement of ac potential being expressed as an ac spectra which provides a continual, real-time indication of defects in the phosphate coating applied to said metal substrate wherein said defects are located within a small region of said large surface area of said metal substrate.
A method for monitoring the quality of a phosphate coating according to claim wherein said counter electrode surrounds said metal substrate on at least two sides and is distant from said metal substrates
A method for monitoring the quality of a phosphate coating according to claim wherein said metal surface is immersed in said phosphating solution.
A system for monitoring the quality of a phosphate coating on a metal substrate having a large surface area, said system comprising:
- (a) a phosphating tank containing a phosphating solution in which said metal substrate having a large surface area is immersed to apply a phosphate coating thereon;
- (b) at least one counter-electrode located in contact with said phosphating solution;
- (c) means for applying a selected dc current or potential between said metal substrate and said counter electrode while said metal substrate is immersed in said phosphating solution;
- (d) means for superimposing a constant ac signal on said dc potential or current applied between said metal surface and said counter electrode, said ac signal having a peak-to-peak potential or current, and a frequency;
- (e) at least one reference electrode located in proximity to said metal substrate and located between said metal substrate and said counter electrode;
- and
- (f) means for measuring said ac potential between said metal substrate and said reference electrode, said measurement of ac potential being expressed as an ac spectra which provides a continual, real-time indication of defects in the phosphate coating applied to said metal substrate.
Dependencies are inferred from the claim text.