A kneader, also called a double arm sigma blade mixer, is composed of two z-shaped blades that rotate toward each other at differential speeds. The blades pass the trough walls and each other at close clearances, providing a shearing and tearing action on the product being mixed. At the end of the cycle, the trough of the mixer is tilted and the finished product is discharged for transfer to a downstream operation. The kneader extruder combines the efficiency of a conventional double arm sigma blade mixer with the convenience of an extrusion screw for discharging heavy and viscous materials. This discharge screw is located in a separate cavity just below the z-blades and helps feed batch material into the mixing blades. Once the mixing/kneading cycle is complete, the screw extrudes the product out through a discharge opening or die.