Process for controlling a sand and gravel sorting and sizing device

Process for controlling the product composition in an apparatus for sizing and sorting mineral raw materials, comprising a feed means for the raw material feed and at least one chamber serving for the separation of low density materials from the sand product fraction, including a sand product removal means and an overflow for the low density materials, the chamber being designed to operate as a sorting region according to the fluidized bed process in order to sort the raw material feed, said process comprising the steps of:

• performing in the chamber (14) by means of the level (h.sub.FS) of the fluidized bed (15) present in the chamber additionally a sizing separation of the sand fraction into a sand product mass (m.sub.Pr) and into a micro particle sand fraction (m.sub.FSS), to be discharged via the overflow (17);
• controlling, for the adjustment of a pre-set concentration of micro particle sand in the sand product mass (C.sub.<Prsoll), the fluidized bed level (h.sub.FS) such that the micro particle sand fraction (m.sub.<A) in the supplied raw material mass is divided, by means of the fluidized bed (15), as a function of the pre-set admissible concentration (C.sub.<Prsoll) into a micro particle sand fraction (m.sub.<PR) to be discharged into the sand product mass (m.sub.Pr) and a micro particle sand fraction (m.sub.FSS) to be discharged via the overflow (17);
• predetermining, for all geometrically similar constructive designs of the apparatus, the fixed yield distribution (V), defined as a ratio of the micro particle sand fraction (m.sub.FSS) to be removed to the micro particle sand fraction (m.sub.<A) in the supplied raw material mass, as a function of the fluidized bed level (h.sub.FS) in the form of a calibration curve as a parameter specific to the apparatus;
• and,
• deriving, based on the calibration curve, the fluidized bed level (h.sub.FS), corresponding to the required yield distribution (V.sub.soll) as a function of the determined micro particle sand content (m.sub.<A) in the supplied raw material mass, as a set value for the level adjustment of the fluidized bed (15) present in the chamber (14).