Device to detect disturbances in an electromagnetic field induced by

Abstract

Device to detect surface faults in a hot metallic bar or wire rod (11) travelling at speeds up to 130 meters per second, the device comprising upstream and/or downstream rough alignment lead-in means (38), in which device are included first coils (29) and at least one pair of second coils (13) coaxial with the first coils (29), the first coils (29) generating an alternating magnetic flow which causes on the surface of the bar (11) parasitic currents that generate in the second coils (13) a magnetic feedback flow, the first (29) and second (13) coils defining a measurement assembly (12), at least two measurement assemblies (12) being included and having their lengthwise axis able to move from an open position defining an intake hole (15), in which the various lengthwise axes coincide substantially with the nominal axis of the feed of the bar (11), to an inspection position defining a resulting inspection hole (15R), in which inspection position the lengthwise axes are substantially parallel to the nominal axis of the feed of the bar (11) and are positioned substantially at an equal distance apart on about a circumference the centre of which lies substantially on that nominal axis of the feed of the bar (11), in which device the index of filling of the resulting inspection hole (15R) is greater than 0.8 and tends to be 0.95 or more, the index of filling being defined by the ratio between the area of the cross-section of the bar/wire rod (11) and the area of the resulting inspection hole (15R).