Abstract: Old rubber tires from cars and trucks are first cut up by a coarse pregrinder into pieces of about 100 to 200 millimeter size. These cuttings are then comminuted in successive stages down to particle sizes of about 5 millimeters. For that purpose they are passed through grinding mills with fluted rollers which deform the particles so as to rupture and expose their textile components. The comminuted particles produced in the various stages are screened to separate metal containing from metal free particles. In subsequent screening and comminuting stages the metal free particles are further reduced to separate masses of graded rubber flour substantially free of metallic and fibrous tire components.