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thus require less frequent maintenance. Other operating variables such as voltage defne the fxture maintenance; the higher the voltage, the more time you can get out of a rack before it needs clean up. There is no single recommendation for a rack fxture maintenance schedule that can satisfy all specifc conditions and applications. The schedule for your specifc conditions and application needs to be estimated or calculated using a rack validation procedure to determine the number of no-coats or partial coats over time. The validation study is based on the premise that a perfect maintenance schedule should produce zero no-coats and partial coats, and that an acceptable maintenance schedule should produce no more than 0.5 percent defective parts. Getting more than 0.5 percent no-coats in your line is a sure giveaway that your rack maintenance schedule is not adequate and needs to be re-evaluated. Best practices include incorporating a racking and load bar ID system so that proper tracking and evaluation can be performed. I have seen e-coat facilities where 100 percent of the racking fxtures are cleaned on a monthly basis and others where they are cleaned annually. Other facilities do not clean 100 percent of their racking at once, but use a rotating schedule. For example, weekly maintenance on 25 percent of the fxtures means 100 percent will be cleaned once per month, or 1/12 monthly equals 100 percent once per year. Some facilities only clean the specifc contact areas, not the entire fxture, to minimize cleaning costs and paint consumption from re-coating. Others have positive grounding systems or automatic fxture cleaning systems, eliminating the need to clean and maintain racking based on no-coats or partial coats, and cleaning only to prevent e-coat accumulation. In all these cases, racking performance has been more than acceptable, which supports the idea that a single racking standard can't be developed and implemented in all facilities to reach desired results. When racking fxtures are structurally large and heavy, like I-beams or tubular stock, or when partial rack cleaning is performed, large amounts of electrocoat residue can build up on portions. Grounding may not be an issue with these racks because the part may get the ground externally or through a positive grounding mechanism. Because no-coats are not the issue with this type of fxture, the rack fxture validation procedure must be modifed to include other criteria such as material consumption, and smoke and odor in the oven. Because this e-coat buildup is very porous and absorbs large amounts of process chemicals and paint, it feeds off itself and accelerates the e-coat buildup over time. This buildup can carry large amounts of permeate into the oven, contributing to permeate drips, dirt, signifcant smoke and excessive odor. Anolyte Flow RAte Q. What is the best anolyte flow rate for anode cells? S.H. A. The purpose of having anolyte solution circulate through the anodes is to remove the excess acid generated during coating and maintain electrocoat bath pH. A secondary purpose of the anolyte circulation system is to dissipate waste heat generated during coating and maintain anode temperature. Without proper anolyte fow, the paint bath pH will decrease over time and the life of the anodes will be compromised. Suppliers of anode cells typically recommend having at least 0.2 gpm to 0.4 gpm for each square foot of anode surface area, although higher fow rates would not be a problem. Because the anolyte solution recirculates inside of membrane anodes, care must be taken not to reach discharge pressures that could damage the membranes. Anolyte circulation systems require the anolyte fow but also require very little discharge pressure. The discharge pressure output must be just enough to overcome the pressure losses encountered in the system (due to piping and elevation changes) and just enough pressure to return the necessary fow to the anolyte reservoir—nothing more. Pressures around 1 psi are typical in the industry. electRicAl chARge on conveyoRs Q. I see conveyors used for e-coating. How do you not get charge traveling from the e-coat tank along the conveyor? R.D. A. The reason is simple: the anodes are charging the paint. Typically, this paint is isolated electrically from the electrocoat tank walls by a roll-on coating that is non-conductive. Then the conveyor and all other metallic structures are connected to the ground from the rectifer and grounded to earth. This is the setup for a cathodic system; the polarity is reversed in anodic systems. Other electrocoat systems use liners or dropin FRP or polyethylene tanks as electrical insulators. If the insulating material fails, there will be a short circuit in the system. LearnMORE Find an Ecoat Supplier Looking for the coatings and electrocoat equipment discussed here? Access hundreds of suppliers by category at short.pfonline.com/EcoatSupp. pfonline.com 41