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'Skip' problem when doing black passivation in stainless steel baskets

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Q. Hi,
While doing online black passivation on barrel parts in stainless steel (SS304) basket some of the parts are not getting fully passivated. Due to this, rejection is around 30-40%. Whereas when the same parts from the same barrel are passivated manually in the plastic basket then all parts are good and no 'skip' passivation is observed.

(good parts on left, bad parts on right)

Could you please tell me the issue and how to resolve this in automatic online process?

Veerendra kumar
- Gurugram/ Haryana/India
September 25, 2023

A. Hi Veerendra.
I assume these parts are zinc plated or zinc alloy plated, and are then transferred to either stainless steel or plastic baskets for chromate conversion coating?

You are asking us to do an awful lot of reading between the lines, and we could make faster progress if you were more explicit about exactly what you are doing.

But could it be as simple as the load in the plastic baskets being smaller and being manually agitated by an operator? You are not going to get consistent passivation in the middle of a big blob of screws sitting, non-agitated, in a tank of passivation chemicals; you can see the iridescence indicating extremely thin passivation. Tell us what happens to the parts after they leave the plating barrels please.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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