Study on Design of Magnetic Flux Leakage Testing Instrument for gun

Abstract: The paper describes the magnetic Dipole model of magnetic flux leakage(MFL) based on the principle of MFL testing, proposes the effects of surface defect width and depth on MFL field, and presents the peak-peak amplitude algorithm that the features of defect signal are extracted. The peak-peak amplitude and separation, signal gradient variation are used as the distinguish criterions of defects. The principle of instrumental hardware design is also introduced. The introduced gun MFL testing instrument is successfully employed in the nondestructive evaluation of gun. Keyword: magnetic flux leakage; defect; nondestructive evaluation; peak-peak amplitude algorithm; hardware design CLC number: TG115.28;TJ306 Document code: A Article serial number:1008-0570 The parts of gun often create crack when used for a period, in order to avoid accident caused by crack, we must detect it periodically, this is very important for the safely operation and the safety of the operator. The magnetic flux leakage(MFL) detecting method is very sensitive to the crack on ferromagnetic materials, and with low cost and simple arts and crafts. So it is very widely used in the crack detection for gun. The principle of MFL non-destruction is as follows. The gun's parts is first magnetized by a magnetizer containing high-strength Nd-Fe-B(Neodymium-Iron-Boron) permanent magnets, then if there is crack on the surface of gun part, the magnetic conductance of the position with crack will be lower than usual, the magnetic resistance will be higher, and the magnetic line will be focused below the crack and magnetic field will leak out of the ferromagnetic material, then we can detect the leakage magnetic field and find the crack. With different kinds of shape of the cracks or different kinds of size, the leakage field will be different. The leakage field can be detected by Hall-effect sensor, and we can estimate the size of the crack by the leakage field gained by Hall sensor. And so we can implement the non-destructive detection for the gun. 1 The model of MFL for crack The distribution of leakage magnetic field varied with different kinds of the geometric shape of the crack, we can know from information that by statistical almost all of the shape of crack are V-shape, so we adopt the V-shape crack model to study the leakage field and try to find the connection between the crack size to leakage magnetic field. It is non-linearity for the magnetization of the parts of the gun's material, so, in order to simplif