| 摘要 |
PURPOSE:To form an excellent insinde stepped tube free from concavity on the outer surface by using a mandrel provided with an annular curved concavity smaller in diameter than the small diameter part at the base of the small diamenter part at the tip in froming an inside stepped tube from a hollow billet by hot extrusion. CONSTITUTION:For the small diameter part 22 of required length at the tip, a large diameter part 24 connected thereto through a tapered part 23 and a small diameter part 22 in front of the tapered part, a mandred 21 provided with an annular curved concavity 25 smaller in diameter than the above is used. This mandrel 21 is fitted to a mandrel holder 3, and a hollow billet (a) put in a container 5 is pressed through a dummy block (a') by forward movement of a stem 4 that follows the movement of a crosshead 2. At the same time, the mandrel 21 is put in a caliber 18 of a die 4, and metallic material of the billet (a) is extruded between the two. Thus, an inside stepped tube is formed without forming concavities on the outer surface where the inside tapered part is positioned. |
