Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 157 of 331

application methods POWDER COATING EQUIPMENT BY NICHOLAS P. LIBERTO POWDER COATING CONSULTANTS DIV. OF NINAN INC., BRIDGEPORT, CONN. There are many ways to apply powder coating materials; however, the material that is to be applied must be of a compatible type. For instance, if the applica- tion method is fluidized bed, the powder coating material must be a fluidized bed grade. Conversely, if the method of application is electrostatic spray, the powder material must be an electrostatic spray grade. Once the material is correctly selected, the application method is chosen by part design and production goals. There are two forms of application methods: flu- idized bed application and spray application. These vary as widely as the appli- cations they suit. FLUIDIZED BED This application method was the first one used to apply powder coating mate- rials. It is still used on many applications where the cured-film thickness is above 5.0 mils. Typical items are wire products, electrical bus bars, etc. The fluidized bed application method can be performed in two ways. One way is the nonelectrostatic fluidized bed. This process requires preheating the part so that powder will melt and adhere to it. The hot part is placed into a fluidized bed of powder for coating. The amount of powder that is applied to the part is a function of how hot the part is and how long it is in the bed. It should be ob- vious that tight film-thickness control is not of primary concern when this method is used, as the total coating thickness often exceeds 10 mils. To gain more control of film thickness on the part, with a fluidized bed sys- tem, the principles of electrostatics are introduced. As shown in Fig. 1, the part Fig. 1. Electrostatic fluidized bed for powder coating. 156

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