The magnetic particle method is widely used in ferromagnetic materials due to its simple, fast and low-cost applicability, which is used in the detection and location of surface and near-surface defects.
In this method, the determination of surface defects depends on the size of the defect and its proximity to the surface, and it is applied only to ferromagnetic, that is, magnetizable materials. The basic principle of the method is based on the magnetization of the examined material. The magnetization process is carried out by passing an electric current or a direct magnetic flux through the part. Ferromagnetic materials do not show any resistance to this magnetic flux, on the contrary, they contribute to the passage of this magnetic flux.
Magnetic behavior of metallic materials:
a) Non-magnetic material
b) Magnetic material
If a magnetic field is applied to the surface of a material with faults, if ferromagnetic powders are sprinkled on the surface, these dusts are attracted by the leakage fluxes formed in the areas where the faults are located, and collect on these discontinuities and form a bridge for the passage of the leakage flux. Thus, the locations of the existing discontinuities are determined.
Not applicable to non-ferromagnetic materials. If the discontinuity is not positioned at an appropriate angle to the direction of the applied magnetic field, it cannot be determined. Large parts may require very high magnetizing currents. If the inspection surface is too rough, it affects the result negatively. If there is paint or coating on the inspection surface, its thickness directly affects the inspection result. If the magnetic powders are dry, they are in the form of flour-like powder. Powders are of two types, wet and dry, depending on where they are used. In addition, these powders are chosen in a color that will contrast with the ground on which they will be used, or with fluorescence content.
Application stages of magnetic particle method;
- Pre-cleaning of the inspection surface
- Demagnetization if necessary
- Application of magnetizing current
- Spraying of ferromagnetic powders
- Interruption of the magnetizing current
- Examination
- Evaluation and report preparation
- Demagnetization and final cleaning