A device for discharging or mixing lump materials from a shaft furnace with a hollow body for discharging the reaction materials open at the bottom and/or at least to one side, has screws arranged in a star-shape in the hollow body. These screws have shafts of different lengths in a plane and/or one screw is a continuous screw. In one of the possible combinations of floating shafts (2) of three different lengths, the shafts are arranged in the shaft furnace (1) so as to form an eight-pointed star, the opposite floating shafts (2) having the same length. The 'dead' or non-stirred area at the centre of the shaft furnace is extremely reduced in this combination.