Abstract: Two horizontally opposed winged rotors move in synchronism to define a cyclically varying window between them such that improved mixing results are achieved. The wings are provided in diagonally opposed pairs such that the leading ends of all wings move in pairs through the horizontal plane of the window.

Abstract: A batch mixer has position monitoring means for the ram operably coupled to the ram moving motor to move the ram within a range of positions adjacent the ram's "down" position to improve mixing by allowing limited upward movement of the ram as a result of internal pressures inside the mixer. Excessive ram return movement is prevented however, and the limited ram movement is achieved by feedback control influence on the pressure to the fluid actuator that operates the ram. Also disclosed is a feed-back control for batch size to assure that optimum use is achieved for the mixer during each batch mixing interval.