Abstract: A mixing apparatus for mixing material in a mixing chamber (19) is provided. A rotor (21) is mounted on a shaft (15) which is both rotated and moved axially simultaneously. Motors (13) through gears (14,16) rotate shaft (15) and rotor (21)' and hydraulic cylinders (9) move the rotor (21) axially. Motors (13), the gears (14,16), the rotor shaft (15), and the rotor (21) are all supported by carriages (11) which slide on horizontal rods (7). The rotor (21) has internal radial mixing slots (39). A rotor cleaning apparatus is provided which includes two separable collar parts (41, 41') having a plurality of cleaning prongs (43) in the form of a comb. The collar parts (41, 41') are supported by comb carriages (45, 45') which move the collar parts (41, 41') radially from a non-use position into cleaning position. When the rotor cleaning apparatus is in cleaning position, the cleaning prongs (43) are in alignment with the radial slots (39).