An apparatus is provided for the pulverization of vulcanized rubber pea-size pellets. The apparatus consists of a barrel entrance, an extruder forcing section, a multiple rotor barrier section and an end discharge which presents the extrusion to a high speed wire brush-like member which shatters the extrusion into extreme small pieces. The hopper forcing section is provided with an extremely long hopper opening the design of which permits an insert which completes the barrel bore to 360 degrees. By adding inserts, the length of the forcing section is adjustable and adiabatic extrusion can be achieved. The now adjustable forcing section is followed by a section of rotor barriers, which consist of a wide top diagonal barrier crossing the extruder groove in a manner which requires all of the process material to pass through the clearance barrier top to barrel bore. The wide top barriers are provided with a set of circumferential grooves which start at capacity and end downstream at zero capacity. Spaced between said grooves is a second set of circumferential grooves which start at zero capacity and increase to capacity at the down stream side of the extrusion groove. The accepted material is directed down stream to an extrusion head which extrudes the material as a wide, thin sheet to atmosphere and a high speed wire brush-like member which shatters the exiting material into extremely small pieces. Material can be injected onto the brush to mix with the extruded particles.