A weighing apparatus for the preparation of a mixture of granular components that comprise batches of material required by a plurality of processing machines in a plant for the manufacture of plastic products is described. The apparatus comprises a Multi-Channel Gravimetric Batch Blender (MCGBB) configured to weigh predetermined weights of the raw materials and to combine the weighed portions of raw materials into batches according to a predetermined recipe for each processing machine and a computer that controls the operation of all components of the MCGBB. The MCGBB comprises several weighing units arranged in a way that allows material weighed in each of the weighing units to fall through individual chutes via a common funnel into a manifold that distributes the weighed batches to several processing machines via a system of delivery pipes.