the invention relates to a rotor disk for inserting into a receiving container for treating polymers , comprising a disk body , on the upper face of which mixing and / or comminuting tools can be provided and on the opposite lower face of which a number of conveying ribs extending from the inside out is provided , by means of which conveying ribs polymer particles can be conveyed outward during operation or which conveying ribs exert a force directed outward from the center of the rotor disk on the polymer particles caught by the conveying ribs during operation . according to the invention , the thickness of the disk body is reduced toward the outside .