Letter 27076

Need process for 108 hours in CASS Test  

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We have plated 25 micron medium phosphrous electroless nickel as under coat and 10 micron micro craked chromium as top coat. At CASS test it has failed after 44 hours against the requirement of 108 hours. Please adivse us what process can withstand up to 108 hours in CASS test.

K. Jagan
Director - Coimbatore, Tamilnadu, India

You should use an electroless nickel containing at least 10.5% P for severe corrosion services such those requiring CASS tests. Also, to obtain 104 hours resistance, you will probably have to increase the coating thickness to 50 or 75 microns.

Ron Duncan Palm International, Inc. - LaVergne, TN

Ed. note: It is our sad duty to alert the readers to the passing of Ron Duncan on Dec. 15, 2006. For those who would like to know more about him, a brief obituary opened Update No. 13 of our Metal Finishing Industry Update Podcast.

The recommendation from Mr. Duncan seems correct, since high phos EN is more resistant to corrosion and has less pores or voids. Although, another thing to keep in mind, besides porosity or discontinuities is that EN is hard. This means that the microcracks in this particular chrome, which were developed for ductile electronickel or copper underplates, might propagate through a fragile layer to the base metal.

Guillermo Marrufo
Monterrey, NL, Mexico

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