Abstract: This invention relates to a self-cleaning type extruder including a cylinder and at least two screws therein adapted to rotate in the same direction, the screws being in such a relation that at any position in at least a part of the screws which lies in the longitudinal direction of the extruder, the contour of one screw in a cylinder cross-section taken at right angles to the screw axes is in substantial contact at one point with the contour in the same cross-section of another screw intermeshing therewith. A conventional self-cleaning type extruder lacks the ability to knead a resin stock uniformly and sufficiently.

Abstract: The present invention enables the efficient production of integral baseball bats made of metal tubing by use of a unique process utilizing a forming machine without welding or joining individually processed portions, this process comprising substantially the following major steps:The step of rotationally forming the body portion by pressing a plurality of spinning rollers of three or more in number synchronously on the tubing with a pre-formed mandrel inserted therein;The step of rotationally forming the grip portion by urging another plurality of rollers against the tubing at the rear portion thereof after retracting the tailstock; andThe step of rotationally forming the other end portion of the tubing which is re-chucked after an interruption of working followed by a turn-over of the tubing which has been removed from the mandrel.