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1. The fineness of electrostatic powder particles: The significant difference between powder coatings and solvent-based coatings is that the dispersion medium is different. In solvent-based coatings, the use of organic solvents as a dispersion medium; and in powder coatings, the use of purified compressed air as a dispersion medium. Powder coatings are dispersed during spraying and the granularity of the coating cannot be adjusted. Therefore, the fineness of powder particles suitable for electrostatic spraying is important. The particle size of powder coatings suitable for electrostatic spraying is preferably between 10 microns and 90 microns (i.e. >170 mesh). The powder with particle size less than 10 microns is called ultra-fine powder, which is easily lost in the atmosphere and the content of ultra-fine powder should not be too much. In electrostatic spraying, the ratio of charge and mass carried by the particles is very small, the gravity of large particles of powder soon exceeds the aerodynamic and electrostatic forces, therefore, large particles of powder have a large kinetic energy, not easy to adsorption to the workpiece up.
2, powder coating resistivity and dielectric constant for powder electrostatic spraying process, the focus should be considered is the powder coating particles to accept the charge, maintain the charge and charge distribution, which directly affects the powder adsorption to the workpiece and deposition efficiency, in addition, it is important that the uncured powder coating must withstand the mechanical vibration of the transmission mechanism and not fall off the powder. In fact, the main factor affecting the powder particles to accept the charge and maintain the charge is the dielectric constant of the powder coating, the lower the dielectric constant of the powder, the easier the particles are charged, but the loss of charge is also easier, which reflects the powder on the workpiece suction force is not firm, slightly by vibration on the powder, for electrostatic spraying powder coating, should be as high as possible with high dielectric constant, it will make the powder adsorption force greatly improved. The coating film is more uniform. But the high dielectric constant of powder coating, charged more difficult, which requires the electrostatic powder spray gun structure to be improved, the use of multi-electrode forced charged structure. For powder coatings, it is composed of polymer compounds (such as: epoxy powder, polyester powder, etc.), they have two main adsorption force on the workpiece: Coulomb force (electrostatic force) and Van de Waals force (molecular force). Polymer compounds all have high resistivity, so the Coulomb force (electrostatic force) is large and reliable. The resistivity of the powder itself, will determine the powder in a certain electrostatic electric field strength charged state; such as: when the resistivity of the powder in 1013 ohms, electrostatic voltage as long as 30-50KV, can make the powder good charged; and the resistivity of the powder in 108-109 ohms, it is necessary to apply 100-120KV of electrostatic voltage to get the above charged effect. The relationship between the resistivity of the powder and the electrostatic voltage.
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