How are magnetic particles applied during MPI?

The application of magnetic particles during Magnetic Particle Inspection (MPI) involves creating a suitable environment where the particles can effectively indicate the presence of surface and near-surface discontinuities. The correct method involves either immersing the component in a bath of magnetic particles or spraying the particles onto the surface while a magnetic field is applied.

This approach is effective because the application of the magnetic field helps align the particles along the lines of magnetic flux, making it easier to detect any discontinuities. When defects are present on the surface of the material, the magnetic path is disturbed, causing the particles to cluster at those points. This clustering highlights the imperfections, allowing for better visualization and evaluation of the material's integrity.

The other methods mentioned, such as heating the material before application, layering the particles manually, or embedding them within the material, are not standard practices for MPI. Heating could potentially alter the material properties and affect the inspection results, while manual application does not ensure that the particles align appropriately with the magnetic field. Embedding particles within the material would not allow for the identification of surface imperfections since they would be concealed and not responsive to the magnetic field.