摘要 |
PURPOSE:To manufacture an electric welded steel pipe excellent in shape and quality of the weld zone in cage roll forming accompanied by downhill forming, by preventing occurrence of edge wave of joint edge part of the blank pipe by combining press forming conditions properly. CONSTITUTION:A strip 10 undergoes initial and intermediate forming by a break down rolls 12, edge forming rolls 14, outside cage rolls 16 and inside cage rolls 18 and further finish formed by fin pass rolls 20, 22, 24 to become a blank pipe 26. This is upset welded by squeeze rolls 28 to obtain an electric welded steel pipe 29. In these processes, the blank pipe is formed under following conditions: downhill coefficient eta is within the range of 0.3-1.3; fin pass total reduction R is within the range of 0.4-1.5 with the lower limit rising to a peak of eta=0.8 and the upper limit lowering making eta=1.05 a peak; the first fin pass reduction distribution ratio delta is >=50% and the lower limit rises making eta=0.8 a peak. |