Apparatus for manufacturing plastics blanks

An injection molding apparatus for forming plastic blanks, comprising a generally tubular mold cavity defined by an outer mold and a concentric mold mandrel, a retractable tubular sleeve telescoped over the mandrel to substantially occupy the mold cavity prior to the injection of plastic material, said sleeve being displaceable from the cavity at a rate dependent upon the rate of injection of plastic material into the cavity, means biasing said retractable sleeve toward a position to substantially occupy the mold cavity so that sleeve displacement is in response to plastic material completely filling the mold cavity, a fixed cylinder for receiving and accumulating moldable plastic material, said outer mold including an injection port providing communication between the mold cavity and the fixed cylinder, the outer mold being moveable into the cylinder to force material from the cylinder through the injection portion into the mold cavity, and a retractable shaft extending through the fixed cylinder for controlling communication between the cylinder and the mold cavity.