PURPOSE: To obtain a titled high quality ribbed tube of high rib height ratio even in case of material difficult to work by manufacturing a metallic tube having a straight rib on inner face by hot extrusion, and twisting it in circumferential direction by tensile force smaller than the yield strength of the tube material.
CONSTITUTION: In manufacturing a tube having intenal spiral rib used mainly for a heat transmitting tube, a hollow round heated metallic piece 5 coated with glass lubricant on inner and outer faces is put from the back into a container to which a die 2 is attached in the front. A stem 7 is put in from its back, and at the same time, a mandrel 8, which has a straight groove 9 on the outer peripheral face and moves axially in the stem 7, is inserted in the piece 5. Then, the stem 7 is advanced, and the material is pushed out between the hole of the die 2 and the mandrel 8, and a tube 10 having internal straight rib is obtained. One end and another end of the tube 10 are chucked by a heat stock 12 and a tail stock 13 respectively, and the tube 10 is twisted while a applying axial tensile force, and a tube having internal spiral rib is obtained.
NISHI MICHIO
TAKEMURA TOSHISADA
IDEMITSU PETROCHEMICAL CO