| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for seamless steel pipes that can suppress occurrence of uneven wall thickness during piercing, which tends to increase in the operationally unstable portion particularly near the front end during manufacturing of the seamless steel pipe. <P>SOLUTION: In the manufacturing method for seamless steel pipes, a plug 1 is attached to the front end of a bar 2, while the bar rear end is fixed. At least one position in the bar excluding the front and rear ends is held by a bar holding device 3. While a hot steel material with a round cross section is rotated in the circumferential direction along the cross section, the plug is pushed in and pierces the front end of the hot steel material. Referring to a relationship between the maximum uneven wall thickness ratio and the bar deflection amount given in the following equation (1), the upper limit of the bar deflection amount corresponding to the allowable upper limit of the maximum uneven wall thickness is decided. The piercing is executed while keeping bar deflection amount not higher than the bar deflection upper limit (preferably 0.5 mm). The maximum uneven wall thickness ratio (%)=c+b×logη+a×(logη)<SP POS="POST">2</SP>(1), wherein η: bar deflection amount(mm)=0.05-5 mm, a, b and c: coefficient (positive, real number). <P>COPYRIGHT: (C)2012,JPO&INPIT |
