| 摘要 |
<p>An object of the invention is to provide a technology of manufacturing seamless pipes excellent in quality features with high productivity. Thus is provided a method of manufacturing seamless pipes by carrying out piercing-rolling using a piercer provided with a pair of inclined rolls which method is characterized in that it has the following features (a) to (d):
Feature (a): That the piercing-rolling is carried out under conditions such that the plug tip draft (TDFT) is not higher than 0.04 or the root of the product of the plug tip draft (TDFT) and the number of billet revolutions (N), namely (TDFT x N) 0.5 , is not greater than 0.4. Feature (b): That the positions of the inclined rolls are selected so that the gorge draft (GDFT) indicating the ratio of the roll gap (Rg) which is minimal in the gorge section between the inclined rolls to the billet outside diameter (Bd) may satisfy the relations defined by the formula (1) given below. Feature (c) : That the piercing-rolling is carried out using a plug having a shape satisfying the relations defined by the formula (2) given below. Feature (d): That the billet is pushed by the pusher at least in the unsteady region of the piercing-rolling. - 0.01053 × EL + 0.8768 ‰¤ GDFT ‰¤ - 0.1765 × EL + 0.9717 - 0.95 × TDFT × N 0.5 + 1.4 ‰¤ L �¢ 2 / d �¢ 2 ‰¤ - 1.4 × TDFT × N 0.5 + 3.15
In the above formulas, TDFT is 1 - (d1/Bd), where d1: minimum roll-to-roll distance (mm) at the plug tip position and Bd: billet outside diameter (mm), and N = (Ld x EL)/(0.5 x n x Bd x tan²), where Ld: projected contact length (mm) from the billet gripped point to the plug tip, EL: piercing ratio, ²: roll feed angle, L2: rolling section length (mm) of the plug, and d2: outside diameter (mm) of the plug at the boundary position between the rolling section and reeling section thereof.</p> |
