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Issue link: https://pf.epubxp.com/i/131829
A. The frst point to discuss with your customer is whether a bright shiny fnish or a matte fnish is required. As you are no doubt aware, decorative chrome gives you a bright, attractive fnish, while hard chrome gives you a matte appearance and is less attractive to many people. The hard chrome will probably last a lot longer on the handrails, but in my experience most handrails are usually plated with a bright fnish. This means a decorative chrome process should be used. nhARd-to-BuFF SilveR dePoSit nMAtte BlAck Zinc PlAting A. Start by checking the current density in the bath. Low current density will enable you to deposit silver, but if it is at the very low end of the suggested range you can get harder-than-normal silver deposits. There are several types of impurities that will cause silver deposits to become hard and diffcult to polish and buff, including the presence of iron and high chlorides. Lead, tin, nickel and organics also can cause this problem. To remove the unwanted organics, flter the plating solution through activated carbon. Keep in mind, however, that activated carbon treatment will also remove desirable organic additives, so you will most likely have to reconstitute the bath with the required additives. To remove most of the "tramp" metals mentioned above, dummy the bath at 2 asf for 12 to 24 hrs. n Q. What is the reason for using matte black zinc plating? L.R. A. The typical reason for using a chemical conversion coating on zinc plate is for added corrosion protection. Using a black such coating does not, in most cases, give you any more corrosion protection than what is commonly called a clear conversion coating does. Based on salt spray testing, both the clear and the black will give approximately the same number of hours to white corrosion. Classically, a black chemical conversion coating (chromate conversion coating) contains a small concentration of silver ions. With the advent of newer conversion coatings and the removal of hexavalent chrome from these formulations, the technology has changed, so you should talk to your chemical vendor about these types of coatings. Q. I work for a specialty silver plating company that restores silver-plated candelabras, silverware and other household items. Our silver plating bath has been wellmaintained in terms of testing and maintaining proper chemical composition, but we have noticed over the last few months that the plated deposits are more difficult to polish and buff. Do you have any suggestions for resolving this problem? S.L. nReAl-tiMe BAth MonitoRing SySteM Q. I am looking for a real-time monitoring system for a plating line to eliminate monthly coupon testing and weekly solution testing. Are there computer-based systems that will troubleshoot processes when they "go south?" D.A. A. What you are really looking for is a "robotic plating technician," and to my knowledge there currently are no systems that will enable you to do all the things you want to do. There are systems available that will control chemical additions and monitor your plating baths on a real-time basis. Perhaps some of our readers are aware of such a system and will respond. nMoRe on BlAck FiniSh on StAinleSS In the April issue, I answered a question regarding getting a black fnish on 430 stainless steel. I suggested the classic hot black oxide process. One of our readers has suggested that another process might also work: using a thermochemical treatment such as shallow nitriding followed by post oxidation. The magnetite that is formed on the surface is black and has good corrosion resistance. Thanks to E.R. for this suggestion. pfonline.com 35