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A standard for the amount you can bend alkaline zinc without flaking?

 

We produce power steering fittings from low carbon steel tubing. We have them plated with alkaline zinc and yellow chromate. My question is with an 8 to 18 micron thickness (customer spec) how far can we expect to be able to bend these without having flaking problems, providing the plating line is maintained correctly? Is there a written standard for this anywhere that can be referenced? Also our customer is now wanting to specify 13 to 23 microns on some new parts that receive a bend up to 114 degrees after plate is this consistently possible? Any and all help will be appreciated. Thanks.

Kevin Davis
- Versailles, Kentucky, USA

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There are several things I can say:

1. You could hire a consultant to research current standards and zinc plating technology and determine which types of plating and line maintenance techniques should be used for your desired finish (possibly overkill).

2. You can consult with your plater or another knowledgeable plater and discuss your requirements and arrive at what all feel are achievable levels of quality, process control and testing for insuring the part will be bendable. You might suggest that the plater also discuss this with his chemical supplier who may be able to offer additional advise, process revisions, etc..

Gene Packman
process supplier - Great Neck, New York

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That's true, and good advise, Gene. But I think Kevin is looking for feedback from suppliers and platers as to whether this specific requirement sounds reasonable. Hopefully someone is reading this who can comment in that spirit.

I am not such a person myself, but I feel that a mandrel test--wrapping the part around a specific diameter mandrel--is a far more accurate and repeatable test that trying to make a sharp bend to a specific angle when there actually is no such repeatable thing as a sharp bend anyway. Bend it against your thumb and it may easily pass to 180 degrees every time; bend it with a press brake on a hardened anvil and it may fail at 45 degrees every time.

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