disclosed herein is size reduction apparatus such as a granulating machine of the type for cutting plastics and the like . the granulating machine includes a chamber provided with a driven rotor having a series of cutting knives affixed on the periphery thereof . the cutting knives cooperate with stationary bed knives to comminute material fed into the cutting chamber . one or more screens are positioned in the bottom of the chamber and allow for the discharge of the material after it has been reduced to a predetermined size . a series of fluid nozzles are arranged to deliver fluid such as air under pressure into the chamber in the zone below the axis of rotation of the rotor . the air acts to effect a scrubbing of the granulator screen , improve cooling of the cutting chamber and cool the cutting knives . by such scrubbing and cooling in the area of the discharge screen heavy build up of material on top of the screen is precluded as the material is circulated and suspended . also , melting of the thermoplastic material in the chamber is prevented .