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Principle and method of ultrasonic flaw detector

Technical Knowledge 2020-07-15 15:40:51
The original design was designed to reflect and refract the medium when it propagates through the ultrasonic wave when it encounters the medium. If there are no defects in the material, the other end of the material propagated by the ultrasonic wave will be reflected. After being captured by the probe, according to the sound speed and actuality of the wave in the material The time spent between the transmitted wave and the received echo during the inspection to determine the thickness of the material. If there is a defect, there will also be a reflected echo, which will be captured by the probe. Then the defect echo will return more than the other side (bottom) of the material Wave travel is short, and it can be judged whether a defect is formed by being reflected on the equipment.

Use steps of ultrasonic flaw detector:

1. Connection of flaw detector

Before using the ultrasonic flaw detector, first prepare the workpiece to be tested, then insert the probe cable plug into the socket above the host, tighten the plug, and connect the corresponding probe to the probe connector BNC. When using the single-probe method in detail, the two connector sockets are also practical (internal parallel connection). When using a dual-crystal (TR) probe (one chip emission, one chip absorption) or two probes (one emission, one absorption), Be careful to connect the transmitter probe to the left socket and the absorption probe to the right socket. After connecting the flaw detector, press the button. After the flaw detector emits a short beep, release the finger and the flaw detector will be turned on automatically.

2. The basic settings of the flaw detector

After the flaw detector is turned on, it is necessary to set up the basic parameters of the flaw detector's detection channel, scanning method, display tree mold, material sound velocity, probe method, gate width, gate start, gate height and other parameters based on the actual inspection.

3. Straight probe zero calibration

For steel forgings, since the sound velocity of the material is known, the probe zero point can be adjusted directly. Select the "fundamental" function group, and then select the "Probe Zero" function menu with the corresponding menu key of the diligent menu, place the probe on the test block, adjust the sound path of the flaw detector, so that the sound path measurement value (S) of the status line and the test block The known thickness of is the same, and the zero point of the probe obtained at this time is the correct zero point of the probe.

4. Tilt probe calibration

Oblique probe calibration usually requires the following steps: ① calibrate the incident point (probe front) ② calibrate the probe angle (K value); ③ calibrate the sound velocity of the material; ④ calibrate the probe zero point.

(1) Detection coverage rate

During the inspection, each scan of the probe should ensure that the coverage ratio of the scanned sound beams is greater than 15% of the probe diameter.

(2) The moving speed of the probe should not exceed 150mm/s. When the active alarm device is accepted for scanning, it is not subject to this limitation.

(3) The scanning agility is at least 6dB higher than the reference agility.

(4) Coupling agent

Engine oil, paste, glycerin, etc., without damaging the appearance of the detected workpiece.

5. Detection surface

(1) The inspection surface and inspection scope are almost fixed. It should be ensured that the entire product of the inspected workpiece is scanned by the sound beam. The sound beam scans the entire product of the inspected workpiece.

(2) Straight probe axial and radial detection

When the straight probe is used for axial detection, the longitudinal wave sound beam is incident in the axial direction, and a transverse defect perpendicular to or close to the axis can be found; when the straight probe is used for radial detection, the probe is placed on the outer circular surface of the shaft, and the longitudinal wave is the main The sound beam is incident incident along the radius of the shaft, and the most common longitudinal defects in the shaft are formed by forging deformation. For other poor forgings, the detection method of the straight probe is also different. The same as the shafts, usually only the axial and circumferential detection cakes and ring rings should be important to receive the radial and outer circumferential detection of the end surface.

(3) Diagonal probe circumferential and longitudinal detection

For the defects of radial diffusion in the shaft, the above-mentioned straight probe detection method is difficult to detect. Therefore, it is necessary to select an oblique probe with an appropriate refraction angle for circumferential detection on the outer circular surface of the shaft. At this time, the sound beam is obliquely incident on the shaft Internally, the radial pressure has a high acoustic pressure emissivity. When it is actually detected, the curvature of the inclined probe is consistent with the circumferential curvature of the shaft. It can be obtained when grinding the plexiglass acoustic wedge. A single probe or dual probes can be used (one send and one receive) Probing.

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