Effect of drying on powder coating efficiency and agglomeration in vibro-fluidized bed

Glass beads of 43 mum were coated in a vibro-fluidized bed by atomizing a f ine silica powder together with polyvinyl alcohol aqueous solution. The coa ting efficiency and weight fraction of the agglomerated particles were meas ured under various experimental conditions, and their dependencies on the f requency and the direction of vibration were investigated. The coating effi ciency and the degree of the agglomeration among core particles correlated well with an index R. The index R was introduced to evaluate quantitatively the drying conditions in a fluidized bed. Application of vertical vibration on the fluidized bed lowered the coating efficiency somewhat, while it prevented agglomeration. From the experimenta l results it was confirmed that coating with high quality and high efficien cy, where few agglomerates were produced and silica powder was utilized eff iciently, was possible in a vibro-fluidized bed with adequate vibration fre quency and orientation of the vibration vector.