Abstract: A method of manufacturing extruded seamless hollow materials characterized in that, prior to extruding a hollow billet from container liner through extrusion dies, a process wherein a centering jig for holding the tip portion of mandrel at the center of extrusion is provided on the extruding side or in the extrusion dies on the extruding side of the container liner, a process wherein the tip portion of mandrel is inserted into the centering jig to be held and a process wherein the hollow billet is pressurized to fill up said billet in the container liner are included.

Abstract: A method and apparatus utilizing a core is located at a central portion of a molten metal storing portion in a vertical semi-continuous mold. The molten metal is poured into the molten metal storing portion, and casting takes place with the inner diameter of a solidified distal portion of the molten metal being controlled by a distal portion of the core. This approach provides a reliable method for the manufacture of high-quality hollow billets which are free from internal defects.

Abstract: A tubular material drawing apparatus for manufacturing precision tubes comprises a plug set device, provided to a back bench, for holding a plug rod in a horizontal state, a travel base to be movable backward with respect to the back bench in a horizontal direction, a holding mechanism, provided to the travel base and capable of holding a rear end portion of a tube element, for holding the rear end portion of the tube element and moving the tube element in a horizontal direction to fit the tube element on the plug rod upon movement of the travel base, a clamp, movably provided to the travel base in a horizontal direction, holding the rear end portion of the tube element and then bringing the rear end portion to the holding mechanism, a carriage guide horizontally extending, a carriage which is guided by the carriage guide and is movable forward, die provided between the back bench and the carriage, and a chuck portion, provided to the carriage and capable of holding a front end portion of the tube element.

Abstract: There are provided a current detecting resistance element connected in series with a loop for supplying current to a telephone set, a switching circuit including a three terminal semiconductor switching element connected to be ON.OFF controlled by the voltage drop across the resistance element, and an impedance element controlled by the ON.OFF operation of the switching element to be connected across the loop for adding AC loss.