In this paper we carry out a first order engineering analysis of the spheronisation process. We examine numerically the rounding of a single extrudate particle in a vessel chosen to apply apparently random impacts to the particle. The process parameters are chosen in relation to the practical situation; however, the mechanical properties of the extrudate are substantially simplified: a simple elasto-plastic constitutive model is used and the yield strength of the material is reduced so that spheronisation is obtained after a relatively small number of impacts. This study illustrates first order effects during rounding of particles and discusses the interplay between material and process parameters. (c) 2010 Elsevier B.V. All rights reserved.