Nondestructive testing - magnetic particle testing method

Detection method
According to different classification conditions, the magnetic particle detection methods are classified as follows:
Carrier for applying magnetic powder: dry method (fluorescent, non-fluorescent), Wet method (fluorescent, non-fluorescent)
Timing of applying magnetic powder: continuous method, residual magnetic method
Magnetization method: axial energization method, contact method, coil method, yoke method, center conductor method, cross yoke method

Principles of magnetic particle testing methods:
1. Both the continuous method and the residual magnetization method can select the continuous method first.
2. For wet and dry methods, wet method is preferred.
3. For the six detection methods classified according to the magnetization method, the selection should be based on the shape and size of the workpiece and the ease of operation.

Continuous method: When the continuous method is used, the magnetization of the workpiece to be inspected, the process of applying the magnetic powder, and the observation of the magnetic trace should be completed within the magnetization energization time. The energization time is 1 s-3 s, and the magnetization can be stopped after the magnetic suspension is stopped for at least 1 s. . In order to ensure the magnetization effect, the magnetization should be repeated at least twice.

The limitation of the energization time is that the defect has sufficient time to form a magnetic trace; stopping the magnetization after stopping the application of the liquid for at least 1 S is to form and retain the magnetic trace.

Residual magnetic method
1. The residual magnetization method is mainly used for a workpiece to be inspected with a coercive force of 1 kA/m or more and a sufficient residual magnetic field (remaining magnetization of 0.8 T or more).
2. When the residual magnetic method is used, the magnetic powder should be applied after the end of energization, and the general energization time is 0.25S-1S. Before applying magnetic powder or magnetic suspension, any ferromagnetic object shall not touch the surface of the workpiece to be inspected.
3. When AC magnetization is used, a power-off phase controller should be provided to ensure the magnetization of the workpiece.

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