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"Parts returned for Plating too thin"


We are a sheet metal manufacturing company. Parts were returned to us for incomplete plating, plating that is not thick enough. The standard on the drawing is Type 2 (gold). SC2 class B. Minimum .0003". The part being plated is a 22.720 channel with thru holes one side of the flanges. Can this be done? Maybe this specification is unreal and cannot be done. The amount of plating is .00023 on the outside of the channel on the inside is .00011. Can you give the info. The metal is cold roll steel and is .105 thick.

Shirley Marsh
metal products - Santa Rosa, California


A. Your plater should be able to produce a minimum thickness of 0.0003 inch gold. You don't say what specification is being sited on the drawing but Mil-G-45204 gives the following information: Type II is 99.0 gold purity, Grade A through D refers to deposit hardness, Class 00 through 6 refers to thickness (Class 4 is 0.0003 inch thick minimum). Also, unless the drawing specifies otherwise, only surfaces which can be touched by sphere 0.75 inch diameter need meet the minimum thickness.

Neil Bell
Red Sky Plating
supporting advertiser
Albuquerque, New Mexico
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December 19, 2012

A. Hi. My guess is that Shirley means to talk about zinc plating with a 'gold' colored chromate, perhaps ASTM B633 [affil. link to spec at Techstreet] , rather than gold plating. Regardless, Neil's point that it is customary for a minimum thickness specification to only apply to areas touchable by a 3/4" diameter ball remains a good one.

It should be relatively easy to increase the plating thickness somewhat, but the approximate 3:1 thickness ratio between the thickest plating on the part and the thinnest is not real surprising. And if you truly need .0003" minimum, it may be worthwhile to improve the racking, switch to a type of plating with more even throwing power, or consider auxiliary anodes -- because .0009" on the thick areas is probably more than you would reasonably want.

Good luck.


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

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