Eddy current flaw detection of eddy current flaw detector is a kind of flaw detection method which uses an electromagnetic induction principle to detect surface and near-surface defects of conductive components. The principle is that the eddy current is generated in the conductive component by the excitation coil, and the change of eddy current is measured by the detection coil, so as to obtain the information about the defect of the component. According to the shape of the detection coil, it can be divided into three types: through type (used for wire, bar and pipe detection), probe type (used for local detection of the component surface) and insertion type (used for internal detection of tube hole).
The eddy current flaw detector is portable and suitable for on-line, off-line and field flaw detection of various metal parts, automobile parts, metal pipes, bars and wires. It can be used for automatic flaw detection of the pipe wall, drill plate, bearing ring, hole slab, square billet, round billet and other mechanical parts. It has a relatively independent test channel, which can drive a combined probe consisting of absolute and differential coils. The test channel can collect data simultaneously. It can be used to detect longitudinal and transverse defects (such as bars), blind and open cracks in metal pipes, rods and wires during production. It has high sensitivity.
It is very important for eddy current flaw detector technology to have cracks on the surface of mechanical parts because it will produce serious quality problems. In order to ensure the safety and reliability of the processed parts, visual inspection alone can not meet the requirements, thus increasing the inspection requirements of the workpiece processing surface. Therefore, in order to achieve the required quality of the production line, it is indispensable for the eddy current flaw detector to adopt a non-contact measurement method and detect all parts in a short time. The eddy current detection of conductors is an electromagnetic induction inspection, and its typical application is eddy current inspection.
The detection of eddy current flaw detector is that the conductor is close to the coil with alternating current, and the alternating magnetic field is established by the coil. The alternating magnetic field passes through the conductor and acts with it by electromagnetic induction to establish eddy current in the conductor. The eddy current in the conductor also produces its own magnetic field. The effect of the eddy current magnetic field changes the strength of the original magnetic field, which leads to the change of the coil voltage and impedance. When defects occur on or near the surface of the conductor, the strength and distribution of eddy current in eddy current flaw detector will be affected. The change of eddy current will cause the change of voltage and impedance of the detection coil. According to this change, the existence of defects in the conductor can be known indirectly. Because of the different shape of the test piece and the different locations of the test piece, the shape of the test coil and the way of approaching the test piece are different. In order to meet the needs of various detection, people have designed a variety of detection coils and eddy current detection instruments.