| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a cored bar capable of surely preventing a piercing plug from dropping out of the cored bar, when drawing the cored bar from a hollow tube stock after piercing and rolling, without deterioration of production efficiency. <P>SOLUTION: The cored bar 3 to be used in a piercing rolling machine for piercing and rolling a billet into a hollow tube stock to hold a piercing plug 2 at a tip thereof includes a tapered portion 3a provided adjacent to the held plug 2 in such a manner that the diameter is increased toward the tip. In the tapered portion 3a, preferably, taper angle α is 1-5°, and taper height H is half of the difference between the maximum diameter Dp<SB POS="POST">max</SB>of the plug 2 and the root diameter D<SB POS="POST">0</SB>of the tapered portion 3a or less, and 2 mm or more. <P>COPYRIGHT: (C)2013,JPO&INPIT |
