Granule Size as a Function of the Apparent Viscosity of a Suspension During Spraying (Agglomeration) in a Drying and Granulating Unit

Abstract

The spraying of a WC–Co–Cr powder suspension in a tower spray dryer was investigated in order to determine the most suitable apparent viscosity of the suspension for achieving a productive flow of the suspension, whose productivity is evaluated by the maximum content of agglomerates after spray drying. The maximum content of agglomerates of the required fraction is determined by subsequent shrinkage during sintering. After sintering and sieving, the powder is suitable for deposition of wear-resistant coatings by the gas-flame spraying method. An analysis of the starting materials was carried out in terms of the particle size and bulk density for preliminary mixing of the suspension; the optimal amount of added liquid relative to the dry material was determined with subsequent measurement of the apparent viscosity of the resulting suspensions. The apparent viscosities of the suspensions and agglomerate particle sizes after spraying in the drying and granulating unit were measured. The dependencies of the granule size on the apparent viscosity of the suspension during agglomeration in the drying and granulating unit were obtained. The maximum content of the required fraction was achieved at an apparent viscosity of 20.07 s. Agglomeration of composite materials by spray drying enabled us to obtain spherical particles of the specified fraction that are suitable for further compaction and subsequent spraying of the powder composite material onto parts for protection against wear and corrosion.