MANUFACTURE OF SQUARE STEEL TUBE WITH LARGE DIAMETER WITH EMPHASIS ON IMPROVING QUALITY AND UNIFORMIZING RADIUSED SHAPE OF CORNER

摘要

PURPOSE: To uniformize the shape of corner part and prevent degradation of material by roughly forming square steel plate with the outer diameter slightly larger than the normal size and performing hot drawing at a temp. higher than A₃ transformation point of the steel material. ;CONSTITUTION: A solid thick steel plate is adjusted for width at both side edges and worked by an edge preparation machine 3. It is then worked by a forming press 4, applied by cold plastic working, and formed into a steel plate with a pentagon approximating section. Then, the plate is inserted into a tack welding machine 6 for tack welding, put through a forming roll, and formed into a rough formed square steel tube. This steel tube is rotated at 180° around the longitudinal axis, inserted into an internal welding machine 8, normally welded from inside, rotated again at 180°, inserted into an external welding machine 10, and normally welded from outside. After that, it is inserted into a heating furnace 12 and evenly heated around 750 to 950°C. Then, it is roll-formed by a hot forming roll 14 so that the outer radius of curvature is made almost 1.5 to 3.0t at the radiused shape part of the sectional corner of the tube and that the outer diameter is of the normal outer diameter size. Then, the plate is cooled to the ordinary temperature and straightened by a straightening roll 17.;COPYRIGHT: (C)1995,JPO