Products Finishing magazine is the No. 1 industrial finishing publication in the world. We keep our readers informed about the latest news and trends in plating, painting, powder coating, anodizing, electrocoating, parts cleaning, and pretreatment.
Issue link: https://pf.epubxp.com/i/131829
pl a tin gC L INIC pfonline.com/experts n Zinc corrosion Q. My company produces steel components. All of these assemblies are nitrogen-brazed components and then are subject to clear zinc plating. The plating bath is chloride, and we are using a clear chromate that has been approved for 120+ hours to white corrosion. After the plating line, we manually dip all our assemblies into a solvent-based rust preventive to help with the air pockets and bare spots that are common due to the design of the assemblies. Within the last year we have been experiencing white corrosion (zinc oxide) while the assemblies are in storage. What do you think is the root of our problems? G.N. A. Do you see these white areas on the uncoated areas of your parts, or is the zinc oxide seen only on areas that are completely plated with zinc? Assuming that the corrosion is appearing on the plated surfaces, I would suggest that your rinsing step after the plating in the zinc chloride bath should be investigated in more detail. If the plated parts are not thoroughly rinsed after plating you may have a residue of acid salts left on the surface that can cause the corrosion of the zinc, giving zinc oxide. You should also investigate how the parts are being stored. If you have a lot of humidity present in your warehouse, the moisture plus the residual salts on the surface will give you a white corrosion. Try storing your parts with a drying agent of some type. nTriple Gold plATinG Q. What does "triple gold plating" mean? Is this an actual combination of deposits or a marketing/sales selling point? K.M. A. An electroplater will tell you that triple gold plating is exactly as described: three layers of gold applied on top of each other. The idea is that three layers of gold will give you a heavier deposit that holds up to everyday wear and tear on watchcases and jewelry. That being said, in many cases the term also is used as a marketing/sales gimmick. Whether a piece of jewelry or a watchcase is truly triple-plated is not easy to determine without taking thickness measurements of the gold deposit, and, unfortunately this is not something that the average jewelry buyer can do. nplATinG on polyeTherimide Q. I recently received a request to plate gold on a material called Ultem. What is the composition of this plastic, and what is the best method for plating it with gold? P.K. A. Ultem is a member of the polyetherimide (PEI) family of thermoplastic resins. It was originally developed by General Electric, but now is produced by an offshore chemical company. PEI is chemically resistant, so special processes have been developed for metallizing this material. One of the classic ways is to use what is sometimes called the well and etch technique. In this process, an organic solvent is used to make the polymer surface swollen, and then it is etched using chromic acid or a chromic acid-like material. This type of treatment modifes the surface so that other coatings can adhere to it. There also are other proprietary methods that have been developed to minimize the surface modifcation. The key here is to create a surface that metal will adhere to. Metallizing the surface of PEI materials is usually done with proprietary chemicals that are available from vendors that specialize in this type of plating. The frst step is to deposit a copper layer on the surface of the plastic. Then you can deposit non-copper layers. The exact procedures must be worked out for each type of PEI. It helps to have good cooperation between the company that manufactures the plastic parts and the company that does the metallizing. Keep two things in mind: 1. Do not attempt to "reinvent the wheel." Use chemicals that have been commercially developed for this process. Trying to formulate "home brews" wastes a lot of time and energy. 2. Find a chemical vendor that specializes in this type of metallization, and work with it to develop your process. An older book on this subject, Metallizing of Plastics—A Handbook of Theory and Practice by Richard Suchentrunk, is out of print but is available from Amazon.com. ndecorATive or hArd chrome plATinG? Q. One of my customers wants chrome plating on brass handrails. He also expects a life of five years for these rails. Should I use decorative or hard chrome for plating these rails? J.P. ARTHUR S. KUSHNER, Consultant, platingclinic@pfonline.com 34 JUNE 2013