We know that magnetic particle testing is relatively simple compared to ray testing and ultrasonic testing, and the detected defects are relatively less harmful defects, so magnetic particle testing operators often ignore some details.
1. The magnitude of the current is only guaranteed to be no less than 1050A during the test (this value is for the workpiece of the author, and the current magnitude of other different workpieces must be different), and it is not obtained through testing with standard test pieces. optimal current.
Solution: The defects of each workpiece are different, so the optimal current when detecting defects may be different. When we detect different types of workpieces, we should use standard test pieces to determine the optimal current and magnetization direction.
2. The intensity of the black light or the intensity of the white light was not tested before the test, and the blackness of the dark room was not measured. Test specification requirements: the intensity of the black light at a distance of 380mm is ≥1000UW/cm2, and the visible light intensity should not be greater than 20LX. The intensity of white light at a suitable distance is ≥1000LX, and the illuminance on the surface of the inspected workpiece should not be lower than 500LX. These basic details are often overlooked.
3. The prepared magnetic suspension has not been tested for wettability (water break test).
Solution: The wettability test of the prepared magnetic suspension should be carried out before each test. The test method is to apply the water magnetic suspension on the surface of the workpiece. If the magnetic suspension is poured continuously, it will form a piece on the entire surface of the workpiece, indicating that the wetting performance is good; if the water magnetic suspension film on the surface of the workpiece is broken, the workpiece has a bare surface (that is, a water-broken surface), indicating that the wettability of the water magnetic suspension is unqualified. At this time, a wetting agent should be added or the surface of the workpiece should be cleaned to achieve complete wetting.
4. The preparation of the concentration of the magnetic suspension is unreasonable. The author, I found in my work that some personnel are not very sensitive to the concentration of magnetic suspension. Although unreasonable concentrations can detect defects, the concentrations required by the inspection specifications are all optimal concentrations, and the defect detection rate is correspondingly low. will improve.
Solution: The concentration of the magnetic suspension should be configured according to the requirements. The standard concentration of the magnetic suspension should be: Fluorescent magnetic powder: 0.1-0.4mL/100mL non-fluorescent magnetic powder: 1.2-1.4 mL/100mL
5. The impact of testing personnel. Some operators wear myopia glasses, which affects the ability to find defects; some operators do not wear protective glasses.
Solution: At present, the myopia glasses that people wear are generally photosensitive lenses. This kind of glasses will darken when black light is irradiated. Such glasses are not allowed in the test. Since ultraviolet rays are not allowed to directly or indirectly enter human eyes, in order to avoid human eyes being exposed to ultraviolet radiation, inspectors should wear ultraviolet-absorbing goggles, which can block ultraviolet rays and most violet and blue light. However, it is necessary to ensure that the goggles cannot reduce the ability to detect yellow-green fluorescent magnetic particle marks. Wearing goggles is also a protective measure for inspectors.
6. Carry out standard partitioning on the workpiece, which is 150mm×150mm according to the standard requirements, but some partitions are too different and the overlap is less than 25% during magnetization.
Solution: The partition should be as close to 150mm×150mm as possible, because the shortest distance between contacts should not be less than 75 mm. This is due to the excessive current density within 25mm near the contact, which will produce excessive background, which may cover up the relevant display. The distance between the contacts should not be too large, because if the distance is too large, the magnetic field will be weakened, which will affect the display of defects.
Made in China has developed from the era of speed to the era of quality, we must start from the details to ensure quality and quantity.