a kneader with a vent function , including a kneading extruder , which permits the continuous viscous flow of material to be kneaded even at a high speed rotation to prevent the generation of cuttings and exhibiting sufficient venting capability . the kneader includes a barrel having kneading chambers defined therein , a rotor rotatably inserted into the kneading chambers , and having a feed portion on an outer peripheral surface thereof . a vent port is in communication with the kneading chamber of the barrel at a position around the feed portion . the feed portion in a vent zone includes a screw tip having a material feed surface with an outwardly curved surface in section .