Characterization of particle size evolution of the deposited layer during electrostatic powder coating processes (original) (raw)
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Journal of Electrostatics, 2009
This experimental study investigated the influences of two different powder systems (coarse and ultrafine) on particle charging and deposition characteristics during electrostatic powder coating processes. Results disclosed that, despite their differences in particle sizes, the two powders behave similarly in deposition process, commonly resulting in a cone-shaped deposited pattern in the inner portion of the substrate and an increase of deposited particles in the fringe region. However, their different properties lead to the discrepancies in their deposition efficiencies, which account for a higher efficiency with the coarse powder. The study further revealed that the coarse powder is superior to the ultrafine powder in charging in-flight particles, which directly contributes to its higher deposition efficiencies. Furthermore, it was disclosed that the two powders exhibit distinct characteristics in charging deposited particles. Compared to the coarse powder, the ultrafine powder is more uniform in charging deposited particles, mainly owing to its greater particle number and higher specific surface area but less mass. In particular, the charging efficiency of overall deposited particles decreases for the ultrafine powder but increases for the coarse powder with increased charging voltage, closely related to their particle properties. However, both powders decrease in charging efficiency of deposited particles with extended spraying duration due to back corona intensifying with spraying.
Influence of powder properties on the performance of electrostatic coating process
Journal of Electrostatics, 1997
Properties of powder, e.g. particle size distribution, chemical composition, triboand corona charging characteristics, electrical resistivity, hygroscopicity, fluidity and shape distribution play significant roles on the performance of powder coating such as transfer efficiency, film thickness, adhesion and appearance. Our focus in this paper is on particle size distribution, fluidity, charging characteristics and their effects on the first pass transfer efficiency. Even a minor difference in powder properties showed differences in the applications process illustrating the importance of characterizing physical parameters and control techniques to achieve desirable performance.
EFFECTS OF PARTICLE SIZE ON MIXTURES DURING NONELECTROSTATIC AND ELECTROSTATIC POWDER COATING
Journal of Food Process Engineering, 2011
Two mixtures, 44 and 256 mm NaCl and 64 and 191 mm starch, were nonelectrostatically or electrostatically coated onto an aluminum target. The coating processes cause the proportion of each powder in the mixture to be different on the target than in the initial mixture. First, some loss of powder occurs during the targeting step; thus, not all of the powder land on the target. This targeting loss is caused by the individual powder characteristics and interactions that occur between powders in the mixture. Also, an uneven distribution is produced on the target due to the way the powder is dispersed. Finally, adhesion loss occurs on the target, also due to individual and mixture characteristics. During nonelectrostatic coating, the largest cause of the change in proportion was targeting losses. During electrostatic coating, the largest cause was adhesion loss. Interactions in the mixture decreased the change in proportion, except for nonelectrostatically coated NaCl.
Observations During Electrostatic Deposition of High Resistivity Powders
Transactions of the IMF, 1974
Electrostatic deposition of insulating powders has been studied by observing the processes occurring, during and after coating, directly with a cine camera and through an image intensifier. A correlation has been found between surface discharges, the final appearance of the coating and the movement of powder particles on the surface. A mechanism to explain these phenomena has been suggested.
Innovative Food Science & Emerging Technologies, 2004
Particle size, density, cohesiveness and chargeability of powders were correlated to their electrostatic and non-electrostatic transfer efficiency and dustiness in gravity fed tumble drum and pneumatically fed conveyor belt coating systems. The effect of particle size on transfer efficiency was opposite in the two systems, while the other properties were similar. For non-electrostatic coating, smaller particles give more efficient coating in the gravity drum whereas in the pneumatic conveyor system larger particles coat better. Electrostatics improves the coating efficiency of small particles so that size is no longer important in the conveyor system, while small particles continue to be better in the tumble drum. The more free-flowing the powder, the greater the non-electrostatic and electrostatic coating transfer efficiency for both systems. Electrostatic coating transfer efficiency increases in both coating systems for powders that are readily chargeable. Density was typically not significant. The powders that were worst non-electrostatically showed the greatest percent improvement with electrostatics. Small particles create more dust in both coating systems.
Morphology of powder particles produced by spray atomization and other processes
Vojnotehnicki glasnik, 2015
The physical and mechanical properties of coatings are heavily influenced by the technologies of powder production and by the parameters of the plasma spray process. One of the most important parameters that affects the physical and mechanical properties of coatings is the morphology of powder particles-homogeneity, granulation and granulation range, directly related to the technologies of powder production. This paper describes the technological processses of powder production most commonly used and shows the SEM micrographs of powder morphologies. Depending on the manufacturing process, powder particles have different characteristics regarding their shape, size, specific gravity, purity, etc. Since these characteristics have a significant impact on the quality and properties of deposited coatings, it is necessary to possess knowledge about the characteristics of powders in order to better control the behavior of particles in the plasma jet, in order to produce the expected characteristics of the coating.Powders have a variety of characteristics to be set for the operating parameters of the deposition in order to obtain the desired coating characteristics.
Journal of Food Process Engineering, 2011
Nonelectrostatic and electrostatic coating processes cause the proportion of each powder in a mixture to be different on the target than in the initial mixture. First, some loss of powder occurs during the targeting step; thus, not all of the powder lands on the target. This targeting loss is caused by the individual powder characteristics and interactions that occur between powders in the mixture. Also, an uneven distribution is produced on the target because of the way the powder is dispersed. Finally, adhesion loss occurs on the target, also because of individual and mixture characteristics. During nonelectrostatic coating, a mixture of fine NaCl and starch particles changed in proportion due to the differences between individual targeting, and mixture adhesion, losses. Little change in proportion occurred in the coarse NaCl and starch mixture. During electrostatic coating of both mixtures, proportions changed because of differences between individual adhesion losses. PRACTICAL APPLICATIONS Food coatings usually consist of mixtures of powders with different densities and compositions, which cause separation of the powders. For maximum consumer acceptance, the powder should be evenly coated on the surface, with the same proportion of ingredients as in the original powder. In fine powder mixtures, during nonelectrostatic coating, targeting loss is the biggest cause of separation. Therefore, when mixtures of different density and composition are used, the coating systems need to be designed to minimize the targeting loss difference between the powders. Electrostatic coating reduced targeting loss of the fine powders by a large amount; therefore, it is one way to
Measurement of the electrostatic powder coating properties for corona and triboelectric coating guns
Journal of Electrostatics, 2005
Measurements have been made of the deposited powder layer for conventional electrostatic corona powder guns and triboelectric guns. By selectively removing the powder layer under computer control conditions, measurements of the powder thickness, and the adhesive properties of the powder layer have been obtained for variation in the coating process and detailed comparisons have been obtained for both coating systems. r