Generally speaking, the square tube of the finished product that has been processed has a small degree of tortuosity, or it depends on the proofreading of the machine. Generally, to eliminate the bending of the square tube, it is necessary to pass the cold straightening, and the square tube The bending may be due to the fact that the mill is not adjusted for adjustment. Therefore, the remaining force in the rolling is formed by cooling or the like along the section and length of the pipe. Therefore, it is not possible to use a rolling mill to directly obtain a very straight pipe, and it is necessary to pass the cold straightening pipe to satisfy the non-bending of the pipe.