Overview:
Magnetic particle inspection is a method that uses the above magnetic phenomena to find surface and near-surface defects in ferromagnetic materials or workpieces. When a ferromagnetic workpiece is placed in a magnetic field that saturates it, magnetic field lines are directed through the workpiece. If the magnetic field lines encounter discontinuities in the workpiece material (i.e. defects such as cracks, slag inclusions, pores, etc.), and in order to maintain their continuity, the magnetic field lines must bypass these defects to form magnetic flux leakage. If these defects are located on the surface or near the surface of the material, but because the magnetic field lines in the workpiece have reached saturation, the magnetic field lines will bypass these areas with lower magnetic permeability (larger magnetic resistance) and leak out of the workpiece surface to form "leakage". magnetic field". In this way, magnetic poles will be generated on both sides of the defect. When magnetic powder (or magnetic suspension) is sprayed on the surface of the defective workpiece, the defective magnetic pole will attract the magnetic powder and form obviously visible linear or point-like accumulation of magnetic marks.
History of development:
1) It was discovered that people discovered the phenomenon of magnetism earlier than the phenomenon of electricity. As early as the Spring and Autumn Period and the Warring States Period, the working people of our country discovered the phenomenon of magnets attracting iron, and used magnets to attract iron. The "Sinan Spoon" was made, and the compass made on this basis was one of the great inventions in ancient my country and was first used in the navigation industry.
2) Establishing the theory In the 17th century, French physicists conducted quantitative research on magnetism. In the early 19th century, Danish scientist Oersted discovered that there is also a magnetic field around currents. At the same time, French scientists Biot, Savard and Ampere conducted systematic studies on the distribution of magnetic fields around currents and came up with general rules. . Faraday, who grew up in England, pioneered the concept of magnetic induction lines. These great scientists set glorious milestones in the history of magnetism and laid the theoretical foundation for the creation of magnetic particle testing.
3) Invention As early as the 18th century, people had begun to engage in magnetic flux leak detection tests. In 1868, the British Engineering Journal first published a report on the use of a compass and magnet to detect magnetic flux to discover discontinuities in cannon (gun) barrels. Eight years later, Hering obtained a U.S. patent for using a compass and magnets to detect discontinuities in rails. In 1918, American Hoke discovered that metal powder ground from a hard steel block held by a magnetic clamp would form a certain pattern on the surface of the steel block, and this pattern was often consistent with the shape of cracks on the surface of the copper block. It is thought to be caused by the longitudinal magnetization of the steel block, which prompted the invention of magnetic particle testing. In 1928, de Forest developed the circumferential magnetization method in order to solve the fracture failure of oil well drill pipes. He also proposed the idea of ??using magnetic particles with controlled size and shape. After unremitting efforts, the magnetic particle detection method was basically successfully developed and More reliable detection results were obtained.
4) Successful application In 1930, the dry magnetic powder developed by de Forest and Doane was successfully used in flaw detection of welds and various workpieces.
5) The advent of magnetic particle flaw detection machines. In 1934, MagnaHux (American Magnet Company), which produces magnetic particle flaw detection equipment and materials, was founded, which played a great role in promoting the application and development of magnetic particle flaw detection machines. During this period, an experimental fixed magnetic particle flaw detector device was developed for the first time to demonstrate magnetic particle inspection technology. Magnetic particle testing technology was early used in aviation, navigation, automobile and railway sectors to detect fatigue cracks in engines, wheel axles and other high-stress components. In the 1930s, fixed and mobile magnetic particle flaw detectors and portable magnetic particle flaw detectors were successfully developed and applied and promoted, and the demagnetization problem was also solved. In 1935, oil magnetic suspension began to be used in the United States.
6) Current situation Today in the twentieth century, magnetic particle testing has been widely used. Countries attach great importance to magnetic particle testing. As a non-destructive testing equipment, magnetic particle testing equipment has the lowest testing cost and the highest safety. Used extensively by various industries.