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Parts too big to passivate?

 

I work for a contract manufacturer of OEM equipment. We currently have a project that requires a frame weldment (80îH x 144î W x 45 D), material is SS 304 with a #4 brush finish. The weldment requires passivation. My problem is, none of the local finish shops has a tank large enough to dip the entire frame. Can the frame be double dipped in the passivation process? Will this damage the material in the overlapped area? Please let me know.

Thanks,

Chuck E. Rogala
- Phoenix, Arizona

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I think it would be perfectly acceptable to "double-dip" the part in the tank for passivation. The areas of overlap would be re-passivated. Care should be taken not to overexpose the part to the passivation solution in the first dip. Since the tank is not big enoughh to begin with, the only concern I would have is how you handle the part, not damaging scratching on the side of tank or areas where the parts is being held. Platers tape or some other type of rubber gasket material wrapped around the area to be held by the hook or rack from the hoist thick enough to sufficiently prevent the part from being scratched, re-soiled or reintroduced to iron from the hook. And finally, the obvious, good Quality Control of the solution, i.e temperature, concentration, will ensure proper control in the 1st and 2nd dip of the operation.

David M. Weaver [deceased]
- Toccoa, Georgia

Ed. note: With great sadness we must advise that David passed awayt on Aug. 15, 2003.

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Chuck:

Should be not problem with 304ss, even using nitric acid for passivation. citric acid formulations are available that will give good results with no problems in double dipping. You can also get products that can be sprayed or brushed on the part outside of a tank. See our web page.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois