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"Electrical resistance property of Class 3 coatings"

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I have heard that chem films using the potassium ferrocyanide [affil link] accelerators such as Alodine 1200 do not work well for Class 3 coatings. These products produce low electrical resistance at first but given some time this property is lost. For the Class 3 coating to retain its low electrical resistance, a product without the accelerators such as Alodine 600 should be used. Does anyone have any supporting information on this?

William Calvert
- Orlando, Florida

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I don't have any supporting evidence, but if someone needs a reliable contact resistance on chromate conversion coated aluminum, they use a fastener that cuts into the aluminum, obviating any need for knowing the aging characteristics of the film.

  
Tom Pullizzi
Falls Township, Pennsylvania