Metal finishing Q&As since 1989

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Oxidation and red rust

 

My question is regarding zinc plated dichromated shaft material that is used on my product. These products are shipped via ocean and have arrived at my door with a white thick film and some red rust. This product is packed very loose in the box and has as much space as product. The plating on the 1/4" shaft is 3 to 5 mills and the shaft is dichromated. Is there a formula to determine the required amount of plating or dichromating to insure I don't have this problem? What other steps can I take, with regards to packaging? My goal is not to increase product cost, if possible. Also, is there a rule of thumb that would encourage stainless steel usage over zinc plating?

Your comments will be welcome.

Regards,

Dave Lucchetti
- Detroit, Michigan

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I don't believe that you have 0.003 to 0.005 inches of zinc on that shaft. Do you mean 0.0003 inches? Even 3 tenths of a mil should protect the steel for a few weeks in a box.

The chromate: Is it a trivalent formula? Is it blue or yellow, or iridescent in color?

A post dip of some sort, like a wax, will protect the product. You may need to wash it off after the trip.

Cost is the rule of thumb for making the part out of stainless steel.

  
Tom Pullizzi
Falls Township, Pennsylvania
 

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For this corrosion to occur you need moisture. Make sure your parts are absolutely dry prior to packing. Then make sure that packing is impervious to moisture while shipping. If any moisture is in an enclosed environment you end up with 100% humidity which will cause corrosion problems.

Geoffrey Whitelaw
- Port Melbourne, Australia