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PLATING parts has to do with cleaning of the base material prior to plating. There are two possible causes for blackening of your cadmium plate. One may be how the parts are stored or shipped. The blackening of cadmium deposit can be caused by presence of sulfur-containing materials such as wrapping papers and corrugated board. Try shipping your parts in non-corrugated containers and use wrapping paper that does not contain sulfur. Another possibility is that your plating bath contains copper contamination. You should analyze your bath and look for copper and other heavy metals. If you do have copper contamination in your cadmium plating bath, it can be removed by adding small amounts of sodium sulfide and precipitating the copper as copper sulfide. The amount of sodium sulfide and must be determined by determining the amount of copper present. If your analysis does show the presence of copper, you must also address where this is coming from. The most likely source is your buss bars. CLINIC A. It could be that your rinsing is not adequate and small amounts of material on the surface turn dark in a short period of time. Since this problem seems to surface primarily in the humid and wet winter seasons, the most likely cause is improper storage of the parts. If they are being stored in a warehouse that does not have climate control, the excess humidity will speed the formation of black spots. How can you solve this problem? The parts should be stored in a climate-controlled environment. If they are stored individually in plastic bags, a desiccant should be added to each bag to control the humidity. If the parts are stored in corrugated boxes, the sulfur compounds that are commonly found in corrugated and paper materials can also hasten the appearance of these black spots. Try storing your parts in plastic containers with a desiccant in each container. Black Spots on Acid Chloride Plated Fasteners Q. We have an auto chloride zinc plant for fasteners where we do trivalent clear and iridescent passivation. Sometimes we get black dots on fasteners after a few days of storing. This is commonly observed during rainy and winter seasons where humidity in our area will be around 95 percent. Is this problem related to drying or storage? —V.O. The Plating Zone Have a question? E-mail Art or check out our vast library of plating articles. pfonline.com/zones/plate Annual Anodizing Conference Anodizing 360…Discover a New Perspective! October 1-3, 2013 Hyatt at Olive 8 Seattle, Washington, USA $ave • General Sessions • Technical Tracks • Boeing Plant Tour (AAC Members only) with wallet-friendly options including early and team registration discounts. Hurry! Early discount ends August 31. Visit www.AACconf.org for details! • Networking Events • Optional Anodizing Quality Workshop (Level 2) • Plus much more! PRODUCTS FINISHING — pfonline.com 59