Development of magnetic powder inspection technology and calculation of electric welding modes

1. Development of magnetic powder inspection technology

1.1 General information about magnetic powder method of flaw detection

Magnetic control methods, a special case of which is magnetic powder flaw detection, are based on the registration of magnetic scattering fields that occur over defects, or on the determination of magnetic properties of controlled products. In addition to detecting defects such as material defects (cracks, hairs, sunsets, flocks, etc.)magnetic methods make it possible to solve problems of structure research, to determine quality of heat treatment of parts, presence and quantity of residual austenite, magnetic anisotropy, to control process of solid solution decay and dispersion hardening, to determine mechanical characteristics of ferromagnetic steels and cast iron by change of their magnetic characteristics, as well as to control thickness of cemented or nitrated layers and thickness of surface hardening layer of articles. The magnetic powder method is one of the most common methods for detecting defects such as metal discontinuity. The method has the following advantages: high sensitivity; easy control and possibility of checking parts of different shape and dimensions on the same flaw detector; possibility of inspection of parts in the structure; comparatively high control performance. The magnetic powder method is based on the detection of magnetic scattering fields over defects using ferromagnetic particles.

Magnetic flux in the defect-free part does not change its direction. If in the magnetic flux path there are areas with reduced magnetic permeability, for example, defects in the form of metal continuity rupture (cracks, non-metallic inclusions, etc.)

Where they exit the part and enter it back, local magnetic poles and a magnetic field above the defect arise. After removal of the magnetizing field, the magnetic field above the defect and the local poles remain due to the presence of residual induction.

The nature and magnitude of the scattering field over the defect are influenced by variable factors; magnetizing field strength; magnetic properties of the material; size and shape of the controlled article; size, shape, location and direction of defect on the article. To detect magnetic fields above defects, ferromagnetic particles are applied to controlled areas of the article, which are suspended in liquid - water, kerosene, mineral oil (wet method) or in air (dry method).

Thus, the task of magnetic powder flaw detection is to create a magnetic field above the defect and detect a defect on the product by the presence of a magnetic scattering field.

Conclusion

Based on the results of the course work, I obtained the necessary skills to justify the selection of possible methods of IPC, the justification of the choice of methods of magnetizing the part, the calculation of magnetization currents, the justification of the selection of equipment for IPC, as well as the justification of the welding or surfacing method for a particular product, the selection of power sources and additive material, as well as the calculation of rational surfacing modes.