Metal Finishing Guide Book


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Page 131 of 903

30���60 sec, ambient 30���60 sec, ambient 30���60 sec, ambient 30���60 sec, ambient 30���60 sec spray, 120���140��F 60���90 sec spray, 120���140��F 30���60 spec spray, ambient 60 sec dip, ambient 60 sec dip, ambient 120���180 sec dip 120���140��F 30���60 sec, ambient 60 spec dip, ambient 30���60 sec, ambient (Recirculating) 30���60 sec dip, ambient Fresh DI water riser spray, ambient 120 sec, 120���140��F 120 sec, 120���140��F 60���120 sec, ambient (two rinses preferred) 60���120 sec 120 sec, 120���140��F 60���120 sec, ambient (two rinses preferred) Cleaning Cleaning Rinse Activation Zinc Phosphating Rinse Rinse Seal DI water rinse DI water rinse 60 sec, 110���130��F 60 sec, 110���130��F 30���60 sec ambient 30 sec, ambient 60���120 sec, 120���140��F 30���60 sec, ambient Spray/Dip Combination Dip Process Spray Process Table V. Process Examples 128 phosphate crystals tend to be larger in comparison to other accelerators. Since peroxide accelerators do not produce any side products other than water, these are the most compatible where environmental issues are of concern. Recently, nitroguanidine has been introduced into low-zinc phosphate technologies. This is the only accelerator in use that is not self-decomposing. Another major benefit is its wide working range, which provides a very robust process. NICKEL-FREE PHOSPHATING Nickel has long been known to significantly improve paint adhesion and corrosion protection; however, nickel compounds are noxious and closely regulated in the effluent stream. Nickel-free processes, therefore, are desirable to satisfy health and environmental demands. Nickel-free processes are available and in use. Most processes replace the nickel with very low concentrations of copper. The corrosion protection of these copper-modified processes on steel is excellent; however, further progress is still needed if hot-dipped galvanized steel is part of the treatment mix. The paint adhesion under cathodic electrocoat as in use in the automotive industry is not sufficient with these processes to match the performance of nickel-containing processes on hot-dipped galvanized steel. PROCESS SETUP PRIOR TO PAINTING Several different processes can be utilized with zinc phosphating. Straight spray installations are popular as well as straight dip operations; combinations of both are also used to make them advantageous. When complex parts are being processed where a lot of recessed areas have to be treated and painted, a combination of spray

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