Assessment of the coating quality in a top-spray fluidized bed coater: An experimental study

The effects of multiple factors on the coating process in a top-spray fluidized bed coater were systematically investigated. The intra-particle coating variability could be assessed by the SEM measurement. Fluidizing gas temperature (0.5–0.9, normalized by the boiling point of water), injection velocity (0.115–0.397 m/s) and concentration (2.1–5.2 wt%) of the coating liquids, atomizing pressure (1.0–3.0 bar) and nozzle height (378 and 470 mm) were found to impact particle agglomeration, coating efficiency and thickness dramatically. Their impact trends and mechanisms were analyzed in detail. The effect of the particle size (0.22–1.26 mm) on particle agglomeration behavior was highlighted. Critical injection velocities and the corresponding agglomeration ratios were experimentally determined. Finally, it was established that there were no universal optimum conditions for the spray coating process, and they can be experimentally determined according to the attributes of interest. [Display omitted] •Evaluating the coating thickness by theoretical calculation and SEM measurement.•Establishing SEM measurement to assess the intra-particle coating variability.•Investigating the effects of multiple factors on the coating process.•Determining critical spray rates and agglomeration ratios for six particle sizes.