Apparatus for injection molding of rubber

Claim 1

In a cyclically operable reciprocating screw injection molding machine for molding a succession of articles of an elastomeric material, said machine including a reciprocable, rotatably driven screw disposed within a barrel having an outlet adjacent its front end and an inlet displaced rearwardly from said outlet, mold means operably connected to said barrel outlet, means for rotating said screw for masticating and heating said material while feeding it toward said front end of the barrel and while said rotating screw is recprocated toward the rear of said barrel, means for causing forward rEciprocation of said screw to inject said heated material through said barrel outlet into said mold means, and means for heating said mold means to effect at least substantial curing of said elastomeric material, the improvement comprising: means for causing the screw to rotate during an initial part of the rearward reciprocation of the screw in each cycle at a first speed sufficient to elevate the temperature of said elastomeric material to a first level; means for causing increased rotational speed of the screw during the remaining part of said rearward reciprocation of the screw in each cycle to elevate the temperature of said elastomeric material accumulated in rearward portions of the barrel to a level close to the temperature of the elastomeric material near said outlet; and means for feeding elastomeric material into said barrel inlet at rates determined by the demand of the screw for new material at any speed of rotation of said screw.