Yellow Stains on Nickel Plate
Why do yellow stains form in low-current-density areas of the mild steel furniture hinges we nickel barrel plate?
Q. Yellow stains form in low-current-density areas of the mild steel furniture hinges we nickel barrel plate. The Hull cell test is satisfactory, and I have dummied the plating bath. The current density is 190 amps at 13 V, and I am maintaining pH between 4.2 to 4.6. The barrel rotations are 14 per min. My pre-clean process is degreasing, rinsing, anodic cleaning for 15 min in the barrel at 50°, rinsing with water, sulfuric acid etching and rinsing, then I start plating in the barrel for 1hr and 15 min. The post-cleaning process involves two water rinses, a trivalent chrome dip for 2 min, rinsing and drying.—P.D.
A. Your plating specifications appear to be in good order. Do you see the yellow stains before you place the nickel-plated parts in the chrome plating bath? How many parts do you plate in your barrel at one time? I’m inclined to think that you are overloading your barrel and not getting adequate plating in the lower-current-density regions of your hinges. I suggest that you reduce your barrel load and see if this helps with your problem. Also, you could investigate your rinsing process after the nickel plate to determine if additional rinsing gives you better results. I have sent you a copy of the “Nickel Tank Doctor.”
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Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.