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.
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.
White Bronze, Copper-Tin-Zinc Tri-metal: Expanding Applications and New Developments in a Changing Landscape
This paper deals with the renewed interest in applications for white bronze tri-metal (Cu-Sn-Zn alloy).
Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.
An alternative product for passivation...