Magnetic portable magnetic particle inspection machine test film display is not clear reason

1. The national standard test piece has a groove mark composed of a circle and a cross, the horizontal line represents the circumferential magnetization of the portable magnetic particle flaw detection machine, and the hard line represents the longitudinal magnetization of the fluorescent magnetic particle flaw detection machine. If the test piece only shows the horizontal or vertical line after the magnetic detection, please pay attention to check whether the circumferential or longitudinal magnetization current on the main control panel is turned on.

2. If the horizontal line on the test piece is not clearly displayed, the circumferential magnetization current can be appropriately raised, or the longitudinal magnetization current can be lowered until the display is clear. If the vertical line on the test piece is not clearly displayed, the longitudinal current can be raised, and the circumferential current can be lowered until the display is clear.

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3. When the current display is not clear after repeated adjustment, if we use water-based magnetic suspension, we need to check whether there is oil on the surface of the test piece. Oil and water are not compatible, and the test piece with oil will affect the adsorption of magnetic powder.

4, when how to adjust the current display is not clear, it is necessary to confirm whether the test piece is close to the workpiece, and the test piece can be clearly displayed only if it is closely attached to the workpiece.

5, when how to adjust the current display is not clear, you can detect whether the magnetic powder concentration in the magnetic suspension meets the standard. The magnetic suspension used for a long time should be replaced with a new magnetic suspension.

6, when how to adjust the current display is not clear, confirm whether the irradiance of the ultraviolet lamp is up to standard.

Sensitivity of flaw detection machine:

1. When the thickness of the inspected part is greater than 6mm, AC yoke should be used for detection.

2, when the thickness of the inspected part is less than or equal to 6mm, the effect of using the DC yoke is better than that of the AC yoke, and the deeper defects can be detected.

3. When verifying the sensitivity of the DC yoke, it must be verified on the thin plate. If only the lifting force meets the requirements, the sensitivity magnetic mark display on the thicker plate also does not meet the requirements or is fuzzy and invisible.

4, sometimes the standard specifies the application of direct current or rectifier current, must look at the size of the workpiece before use, if the yoke method must be negotiated with the technical side and jointly verify the detection effect, change the detection current. Of course, if other magnetization methods such as the current method are used, DC has a large advantage.

So what determines the size of the demagnetizing field of the flaw detection machine?

1, the size of the applied magnetic field determines the size of the demagnetizing field:

The stronger the external magnetic field, the better the magnetization effect, the stronger the magnetic field generated by the equivalent N and S poles at both ends of the workpiece, the stronger the demagnetizing field outside the workpiece.

2, the size of the demagnetizing field is inversely proportional to the L/D value of the workpiece:

L refers to the total length of the workpiece, D refers to the maximum diameter of the section of the workpiece, and for a hollow cylindrical workpiece, D refers to its equivalent diameter, whose value is (square square of the outer diameter and the inner diameter); For hollow, non-cylindrical workpieces, the D value is (the difference between the outer overall cross-sectional area and the inner hollow cross-sectional area is divided by the square of π and multiplied by 2).

It can be seen from the formula of the second point that the demagnetizing field of magnetized hollow workpiece is smaller than that of solid workpiece under the same conditions of L and D. Under the same D condition, the demagnetizing field generated by the workpiece with longer magnetization length is smaller than that of the short workpiece.

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3. The demagnetizing field is related to the geometry of the workpiece:

The demagnetization field of the workpiece with different geometric shapes is different. Under the same magnetization intensity, the demagnetization factor is different. For the completely closed ring sample, N=0; For spherical parts, N=0.333;

4. The demagnetizing field is related to the form of magnetization current:

Magnetizing current using alternating current will produce skin effect, than direct current penetration depth shallow, N, S pole magnetism formed at both ends of the workpiece is poor, so when alternating current and direct current magnetize the same workpiece, alternating current produces a small demagnetizing field.

Attention points of flaw detection machine in power and weld:

1, power:

1) When using the continuous magnetization method, it is necessary to clarify the power time to ensure that the magnetic powder can be used in the case of power;

2) When using the remanent magnetization method, the magnetization time is generally 0.2-1s, and when using the impulse current, it should be more than 10ms and be powered on continuously for more than two times. If the magnetic particle flaw detector can have sufficient magnetic potential when detecting the flaw, it can not be restricted in accordance with this regulation.

2. Weld

1) One is that when heat treatment is applied to the weld after welding, it is necessary to implement flaw detection after the final hot processing.

2) For the crack detection of the gap and pressure vessel after hot processing, the magnetization method should not use the direct current method.

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