The circular housing of a fiberizer mill has a rotationally driven shaft on which there is a disk haivng a conical face and spaced apart rows of teeth. A stationary disk has on its face a multiplicity of annular grooves which define teeth. There is a small gap between the tips of the rotary teeth and the tips of the stationary teeth. The gap extends at an acute angle relative to vertical plane passing perpendicular to the shaft axis so that particles being disintegrated experience a horizontal component of force. The result is that particles, after having been exploded by striking the teeth on the stationary disk, are emitted generally radially outwardly from the gap. Hammer bars on the periphery of the rotary disk are surrounded by a toothed circular breaker plate member concentric to the orbital path of the hammers on the rotary disk. The flow of fibers and particles outwardly of the gap between the rotary and stationary disks continues into the path of the hammers which smash the particles against the teeth of the circular breaker plate. The plate has a gap in it through which the air entrained fibers are passed to an outlet.