if one mixer blade 124 breaks the sector 120 having that blade can be replaced with a spare sector while the broken or damaged sector is being repaired also only blade sectors 120 need to be stocked as spares and not entire blade assemblies 76 moreover for large apparatus 14 entire blade assembly 76 may be very large and heavy and difficult to manufacture as one piece in contrast individual blade sectors 120 are much easier to machine and handle in the manufacturing stage than the entire assembly 76 furthermore although all blade sectors 120 are preferably identical to one another constructing blade assembly 76 from a plurality of individual blade sectors enables the substitution of different blade configurations as may be desirable for experimention purposes when optimizing blade size and shape for different particulate materials 102 and also permits the intermixing of different blade configurations as may sometimes be desired as shown in fig3 6 each blade sector 120 includes in addition to blade 124 a flat base portion 126 to an outer end region of which is connected a lower end the associated blade as is more particularly described below blade sector portions 126 are configured so that upon interconnection of all blade sectors 120 by ring 122 a central circular aperture 128 fig3 and 6 is defined through which upon assembly of appparatus 14 shaft 74 extends.