Magnetic particle detection method
Magnetic particle detection is a method of observing defects by using magnetic particle as display medium. According to the type of magnetic powder medium applied during magnetization, the detection methods are divided into wet method and dry method. According to the time of applying magnetic powder on the workpiece, the inspection methods are divided into continuous method and remanent method.
1.Wet and dry
Magnetic powder suspension in oil, water or other liquid medium is called wet method, it is in the detection process, the magnetic suspension evenly distributed on the surface of the workpiece, using the flow of liquid and magnetic leakage magnetic field to magnetic powder attraction, showing the shape and size of the defect. In the wet method, the magnetic particles can be used because of the dispersion and suspension properties of the magnetic suspension. Therefore, it has a high detection sensitivity. Especially suitable for the detection of surface defects, such as fatigue crack, grinding crack, etc. Wet methods are often used in conjunction with stationary equipment, as well as with mobile and portable equipment. The magnetic suspension used for the wet method can be recycled.
Dry method is called dry powder method, in some special occasions, can not be used to test the wet method, and the use of special dry magnetic powder is directly applied in accordance with the program on the magnetized workpiece, the defect of the workpiece that shows the magnetic trace. Dry inspection is mainly used for local inspection of large casting, forgings, large structural parts and welding parts. It is usually used in conjunction with portable equipment.
2.Continuous method and remanence method
(1) continuous method, also known as accessory magnetic field method or current magnetic method, is to apply magnetic powder or magnetic suspension to the workpiece under the action of external magnetic field for magnetic particle inspection. The observation and evaluation of the workpiece can be carried out under the action of the external magnetic field or after the interruption of the magnetic field.
(2) remanence method means that the workpiece is magnetized first, then the workpiece is poured with immersion suspension, and the magnetic powder is observed after aggregation. This method is used to detect the residual magnetism of materials, so it is called remanence method.
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