Conductive Paint On Castings

Q. I am the Finishing Engineer in a custom job shop. We specialize in show-quality chrome plating. We are encountering a lot of die cast parts that are corroded so severely that we can’t get them to plate. We drill out and fill the pits, but the gray and white corrosion in the metal causes problems. I have been tasked to find the solution to the problem. During attendance at trade shows and technical society meetings, I’ve heard that some shops are coating similar cast parts with a conductive paint and then plating on top of it. Can you please tell me where can I find some information on this process. J.K.

A. Electroplating issues are usually solved by the Wizards, you know, the guys with the tall pointed hats emblazoned with the moon and stars. However since you used the “p” word, I’ll give you my answer. Long ago and far away, in the Laboratory of the company formerly known as Westinghouse, I had a similar project. We made cosmetic repairs to pitted casting using epoxy and polyester filling compounds. After smoothing the surfaces by filing, sanding and buffing, the castings were coated with conductive paint and then sent to the plating lab, where our Wizards worked their magic. Talk about magic, after viewing the finished products, even the Director of Research was unable to tell they were once pitted castings.

Although we found the epoxy filling compounds to be more durable, the polyester compounds were smoothed more easily. The filling compound we used were body putties purchased at an automotive parts store. These compounds are also available at craft and paint stores. Conductive paints are available from suppliers listed on page 300, of the Products Finishing 2007 Directory and Technology Guide under Metallizing Sprays and Conductive Paints (www.pfonline.com/suppliers.html).