| 摘要 |
PURPOSE:To obviate generation of a weld defect in the stage of producing an electric welded steel pipe by a high frequency welding method by determining the correct value of the rate of melting in the central part of the plate thickness from the surface heating conditions in the stage before the converging point of a V-edge, and controlling the voltage of an electric power source in accordance with said value thereby determining the quantity of heat input. CONSTITUTION:The surface width in the V-edge part 4 of a steel plate formed to a pipe shape is measured with an image sensor camera 18, and a signal corresponding to the width is emitted and is inputted to a comparator 13. On the other hand, the thickness and pipe forming speed measured with a thickness measuring device 15 and a pipe forming speed measuring device 16 are inputted to a setting circuit 14 for reference value of surface melting, which determines the reference value of the melting width of the plate surface according to the thickness and pipe forming speed during the formation of the pipe and inputs the signal to the comparator 13. In the comparator 13, the actually measured value for the melting width of the surface with the camera 18 and the above-described reference value are compared. The voltage of a welding electric power source is controlled with a control circuit 17 for source voltage until the difference thereof is made zero, whereby desired weld heat input is obtained and weld defects such as cold well and penetrator are obviated. |
