a mixing silo for free - flowing finely divided solid materials , in particular for powdered , fibrous and / or granular mixed material , especially polymer granules , specifically suited for mixing polymer granules , having an excellent mixing quality and at the same time a simplified and improved suitability for washing out in order to avoid cross contamination . the mixing silo may be used for homogenizing possibly inhomogeneous polymer granule batches in the form of a stream of product from a process producing polymer granules .