Metal Finishing Guide Book

2013

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can often be used for waterbornes. Usually only the atomizers will need to be modified for waterbornes, or replaced with atomizers specifically designed to handle waterborne materials. The remaining equipment and distribution system can be reused unless made of materials that will corrode in waterbornes or be damaged by exposure to them. Well-engineered conversions from solvent-based coating materials to waterbornes result in the highest possible operating efficiency at low cost and with maximum operator safety. The operating cost, in terms of TE, should be about the same as that of a good solvent-based paint system. To get high TE, electrostatics must operate at peak efficiency. This means directly charging the material with electrostatic voltage, but limiting the hardware that gets charged. Voltage-blocking devices confine high electrostatic voltage to only the atomizer and hoses to the atomizer. This means that the rest of the coating material application system can be the same or similar to the system before the conversion is made. The electrostatics will still operate at high efficiency because the coating material can be directly charged so the TE will be comparable before and after conversion. Because system capacitance, or the capacity to store electrical energy, can be controlled to "safe"' levels, safety issues with the converted systems are not prohibitive. In other words, a voltage-blocked waterborne system is as close as possible to the solvent-based material system it replaces with a coating material that conducts electricity. To summarize, here is how to convert an application system from solvent-based coating materials to waterbornes: (1) Reuse the existing process and hardware if it is up to date and performing well for the existing solvent-based system. Change components where materials are not compatible with waterbornes. (2) Turn each atomizer into a mini-isolated system by installing a voltage block in the coating material hose, as close to the atomizer as possible. Directly charge the material for maximum TE. (3) Lower the voltage to maximize TE, extend equipment life, and reduce shock hazard. (4) Take advantage of the fact that waterbornes conduct electricity. Remove the electrostatic cables from the atomizers and charge at the voltage blocks. Cables will last longer and the guns will move easier. 203

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