Cold expanded of large diameter straight welded pipe is a use of hydraulic or mechanical means urging the steel pipe from the steel wall along the radially outward dilatation pressure molding process. Mechanical than hydraulic mode, the device is simple and more efficient use of steel in high-precision machining conditions more precise, in the reservoir emptying large diameter pipe joints straight no need to use, now the world's most advanced several large-caliber straight seam steel pipe expanding pipeline processes are adopted, the process is as follows:
Mechanical expanding is the use of the split-side diameter-enlarged portion of the expansion segments radially, so that the longitudinal direction of the tube in a stepwise manner, the full length of the tube segments to achieve plastic deformation process. It is divided into five stages
1, The initial stage of a full circle. Segments open until all the segments are exposed to the pipe wall, this time in the step length range within steel tube radius of each point are almost identical, steel preliminary full circle.
2, Nominal inside diameter of the stage. Anterior segments from the start position to reduce the speed of movement, until reaching the required position, this position is within the finished pipe quality requirements circumferential position.
3, Springback compensation stage. Segments 2 at the position of the start phase further low speed, until reaching the required position, this position is within the requirements of the design process of elastic recovery before the pipe circumferential position.
4, Pressure stable stage. Segments before playing the complex inner pipe circumferential position remain intact for some time, this is the stable phase packing equipment and expanding process requirements.
5, Unloading regression phase. Circumferential segments starting position quickly retracted from the inner pipe bomb before the complex until the arrival of the initial position of the enlarged diameter, which is expanding process requirements shrink the diameter of the smallest segments.
