Magnetic particle inspection

Magnetic particle inspection is also called MT inspection. After the ferromagnetic material is magnetized, if there are discontinuities (defects) on the surface or near the surface, the magnetic field will overflow to form a leakage magnetic field. The ferromagnetic particles applied to it will accumulate at the leakage magnetic field to form magnetic marks. By observing the characteristics displayed by the magnetic marks, the surface or near-surface quality of the object can be evaluated. Magnetic particle testing is simple to operate and the test results are intuitive and easy to read. It is suitable for surface and near-surface defect detection of ferromagnetic materials, but it cannot be used for non-ferromagnetic materials. Magnetic particle testing objects: ferromagnetic materials

1. Wet and dry
The use of magnetic powder suspended in oil, water or other liquid media is called the wet method. During the inspection process, the magnetic suspension is evenly distributed on the surface of the workpiece, and the flow of the carrier liquid and the leakage magnetic field are used to attract the magnetic powder to display the shape and size of the defects. In wet detection, due to the dispersion and suspension properties of the magnetic suspension, the magnetic particles that can be used are smaller. Therefore, it has high detection sensitivity. Especially suitable for detecting small surface defects, such as fatigue cracks, grinding cracks, etc. Wet methods are often used with stationary equipment, but also with mobile and portable equipment. The magnetic suspension used in the wet process can be recycled. The dry method is also called the dry powder method. In some special occasions, when the wet method cannot be used for testing, special dry magnetic powder is used to apply directly to the magnetized workpiece according to the program, and the defects of the workpiece will show magnetic marks. Dry inspection is mostly used for local area inspection of large castings, forging blanks and large structural parts and welding parts. It is usually used in conjunction with portable equipment.
2. Continuous method and residual magnet method
(1) Continuous method The continuous method, also known as the accessory magnetic field method or the current magnetic method, applies magnetic powder or magnetic suspension to the workpiece under the action of an external magnetic field for magnetic particle flaw detection. The observation and evaluation of the workpiece can be carried out under the influence of an external magnetic field or after interrupting the magnetic field.
(2) Residual magnetism method: The residual magnetism method first magnetizes the workpiece, then pours the suspension on the workpiece, and observes it after the magnetic powder gathers. This is a detection method that uses the residual magnetism of materials, so it is called the residual magnetism method.

●Domestic standards: NB/T 47013, GB/T 18851, GB/T 26953, GB/T 9443, JB/T 9218, etc.
●International/EU standards: ISO 3452, ISO 4987, EN 10228-2, EN 1371, ISO 23277, etc.
●American standards: ASTM E1417, ASTM E165, ASTM E433, ASTM A903, etc.

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