PURPOSE: To detect whether welding is normal or not, by arranging plural magnetic detecting elements dispersedly along the butt part between the rear end of a preceding steep plate and the front end of a trailing steel plate.
CONSTITUTION: The magnetic detecting elements for magnetic field distribution detection are arranged dispersedly along the weld zone. Namely, when they are equipped to an electrode, grooves 60 are formed in the electrode 30 on the top surface side in a comb-tooth shape; tips (on a steel plate end side) of the teeth are made deep to arrange detection coil 7 therein, intermediate parts are made shallow to run lead lines 7a of the detection coils 7 therein, and the other-end common part is made slightly deeper to allow the lead lines to run therein. A magnetic field produced by a current flowing through the steel plate during flashing and upsetting is detected to find =>1 of a flashing frequency distribution, flashing mean current distribution, flashing heat input distribution, upsetting mean current distribution, and upsetting heat input distribution from respective output voltages of the detecting elements, thereby detecting whether the welding is normal or not.
NAKAYASU TAKESHI
FURUI KIMIHARU
