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Zinc plate spec on drawing

My name is Steve Ennis I am a product engineer for a hose coupling manufacture. I have received reports from a end user that a zinc plated schedule 40 steel coupling is rusting. Our drawing for this part calls out zinc plate with no other info. A secondary component to this coupling has a zinc spec called out ASTM B633 Type 1 Class 3. My questions are: 1)Does the drawing have enough info to correctly plate these parts. 2)The parts are used in south Calif. outside; why would they rust. 3) Would a swage operation (push the coupling thru a die) effect the zinc plate and contribute to the parts rusting?

Thanks in advance for your assistance.

Steve Ennis
hose coupling manufacture - Chestertown, Maryland
2005

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Hi, Steve. I would suggest that you get a copy of the Quality Metal Finishing Guide for Zinc Plating from MFSA (www.mfsa.org). It will make most of these issues clear. Zinc plating deters rust in proportion to its thickness, but at best it doesn't last indefinitely. Swaging operations are deleterious to zinc plating, but not necessarily fatal; inspection of samples after swaging should insure that the plating is not severely damaged. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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2005

The drawing calls ASTM B663. This standard gives pretty enough information for the zinc plater:

Type I: as plated, w/o supplementary treatment.

Class 3: 12 microns.

ASTM B663 calls for another ASTM tests: salt spray test, peeling test, etc.

The swage operation may peel off the zinc plate, so one should test by ASTM B571 (referenced in b663) and check if yet there is a problem of peeling in the plating. Maybe what it is specified is not enough to stand the operation. If it is so, you can modify the spec or modify the operation.

Nevertheless checking the operations is one point to check.

Remember all failures can come from humans, machinery, environment, procedures. Review the FMEA of your product if it has one.

Saludos.

Guillermo Castorena
- San Luis Potosi, Mexico

adv.