The function of magnetic powder is as a display medium, and its types include:
a. Black magnetic powder - the composition is iron tetroxide (Fe3O4), black powder, suitable for workpieces with light or bright background.
b. Red magnetic powder - the composition is ferric oxide (Fe2O3), which is in the form of iron red powder, suitable for workpieces with dark background.
c. Fluorescent magnetic powder - the ferroferric oxide magnetic powder particles are coated with fluorescent substances, which can emit yellow-green fluorescence under ultraviolet irradiation. It is suitable for workpieces with dark backgrounds, especially due to the color sensitivity of the human eye. Compared with other magnetic powders, fluorescent magnetic powder has higher sensitivity for magnetic particle inspection of magnetic medium.
d. White magnetic powder - The ferrite magnetic powder is coated with white substance, which is suitable for workpieces with dark background.
In order to facilitate the use of on-site inspection, there are many types of commercial magnetic media, in addition to black, red and white magnetic powder, fluorescent magnetic powder, spherical magnetic powder (hollow, colored, for dry powder method), and pre-configured magnetic paste , concentrated magnetic suspension, and magnetic suspension spray cans, etc., as well as surface brighteners (contrast enhancers) to improve the testability of workpieces with dark backgrounds or rough surfaces.
In order to ensure the reliability of the magnetic powder inspection results, the magnetic powder (including magnetism, particle size, shape) and the concentration, uniformity and suspension of the magnetic suspension must be verified before use, and also need to be used regularly during the use process. In addition, the white light illuminance of the environment during observation and evaluation, or the ultraviolet intensity of the ultraviolet lamp used in the fluorescent magnetic particle inspection, etc., are also verification items to ensure the inspection quality.