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Issue link: https://pf.epubxp.com/i/156873
CLINIC ELECTROCOATNG Too Much E-Coat Q. We outsource black e-coating on the automotive seat belt cable assemblies we manufacture. Our customer is complaining there is too much e-coat, which is making our cable assemblies too stiff. Our competitor's parts clearly have less coating than ours. We only have to pass a 70-hr salt spray test, but I am told ours would pass 1,000 hrs. Our suppliers tell us they cannot put on any less coating. Wouldn't less time or current yield less coating? —M.T. pfonline.com/experts depend on many specific factors, including film thickness, weight, square footage and geometry of the parts, annual volumes, and environmental costs. Typically, the larger the part and the greater the environmental costs, the more the cost analysis will favor the powder. A. Your supplier could make some changes to the way it runs your parts and, as a result, obtain lower film thickness. The stiffness comes from the cured e-coat film bridging over the small gaps between wires. This bridging takes away the desired flexibility from the cable assembly. At lower film thicknesses, the bridging and stiffness will decrease significantly. Critical parameters that your e-coat supplier could change and that have a direct impact on film thickness are voltage, percent solids, deposition time, bath temperature, and current or load density. Some are easy to change for your specific part production runs, while others not only affect your part production runs, but also those of other customers getting their parts coated at the same supplier. If your supplier is using a black cathodic epoxy e-coat, the film could be adjusted from 10-12 microns or less all the way to 34-38 microns. The e-coat technology is capable of providing a wide range of thicknesses by varying application parameters. That is one of the advantages of e-coat. For your specific application and salt spray performance, you would only need to apply 14-16 microns, or even less. At this low film, your seatbelt cables will have some bridging but will still remain perfectly flexible after cure. The 70-hr requirement for salt spray performance is not difficult to obtain at those electrocoat films. Keep in mind that typical epoxy electrocoat technologies should be capable of going over 1,500-2,000 hrs salt spray at typical film thicknesses of 20 to 25 microns. Why does your supplier gives you more film thickness than you really need? It may be that it does not adjust the process parameters for your specific parts. It may have established the parameters based on other high-volume parts and is not adjusting the process to the lower square footage obtained when running your parts. Your supplier not only could apply lower film thickness and improve field quality, but also could reduce material and application costs and convert a problem into a win-win for both of you. You could also give your supplier more volume so it could hone in its process more to your specific application. Powder vs. E-coat Costs Q. We are going to paint our stampings with either e-coat or powder. Which is cheaper? —A.G. A. It depends. The material cost of applying powder or e-coat, for the same conditions of performance and quality, will 62 SEPTEMBER 2013 — pfonline.com Feed-Over Test Q. Could you tell us about the "feed-over test"? We are trying to replace our current electrocoat supplier and want to use this test, but we have JOSE A. TIRADO / Consultant not been able to electrocoat@pfonline.com find any literature about it. —G.G. A. The feed-over test is a simulation test performed in a laboratory. It is used to determine the operational feasibility and chemical compatibility of two different electrocoat paints when mixed together in the e-coat tank. The feedover test is necessary to confirm and verify the potential replacement of one electrocoat paint supplier with another without outside disposal of the existing electrocoat bath. Electrocoat suppliers do not like their paints to be mixed with another supplier's paint and, in most cases, will not recommend the user to do that. In some cases, the e-coat user has no other alternative, however, and the feed-over test is the necessary due diligence to ensure proper functioning and proper performance of the electrocoat bath. For example, your electrocoat tank is operating with paint A and you would like to start using another e-coat paint, paint B. Additionally, you would like to start feeding paint B over your existing e-coat bath with paint A without having to dump the entire existing bath. Your strategy is to start feeding the new paint B over the existing paint A as regular paint make-up feed. The feed-over test will determine the minimum initial percent of paint B necessary in the bath for the tank to operate and perform properly. The test typically covers mix ranges from 20 to 90 percent of new paint versus old paint. In most cases, the electrocoat bath needs to have at least 20 percent of the new paint for the bath to deposit properly. Depending on the compatibility of resins, solvents and operating pH, greater percentages may be needed. The greater the starting percentage of new paint, the lower the risk with the future feed-over and conversion. The feed-over test itself involves coating out panels at