Double-Z-kneaders are characterized by counter-rotating kneading arms with different varying rotational speeds (usually in the ratio of 3:2) in semi-cylinders, the interesection which forms a saddle piece and meeting tangentially just above this. The mixing action is a combination of bulk movement, shear action, stretching, folding, dividing and recombining as the material ist pulled and squeezed against blades, saddle and trough ends.