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The principle and usage of the ultrasonic flaw detector will be explained in detail by the Shanghai Bashu technicians:
First, the principle of ultrasonic flaw detector:
By ultrasound in the material spread encounters medium reflection and refraction on the original design may occur. If the material is not defective, then the other end of the material, the ultrasonic wave propagation reflections will occur, after the probe capture, according to sound velocity and the actual in the material The time between the transmitted wave and the received echo is used 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 be returned to the other side of the material (bottom surface). The travel time of the wave is short , and it can be judged on the equipment to determine whether a defect has formed.
Second, the ultrasonic flaw detector use steps:
1) Connection of the flaw detector
Before using the ultrasonic flaw detector, prepare the workpiece to be tested, then insert the probe cable plug into the socket above the main unit, tighten the plug, and connect the probe to the probe connector BNC . When using the single probe method in detail, the two connector sockets are equally practical ( internal parallel connection ) , when connecting a twin crystal (TR) probe ( one wafer emission, one wafer absorption ) or two probes ( one emission, one absorption ) , To carefully connect the transmitter probe to the socket on the left, connect the absorption probe to the socket on the right. After connecting the flaw detector and pressing the button, the flaw detector emits a short " beep " sound, then release the button finger and the flaw detector is actively turned on.
2) The basic settings of the flaw detector
After the flaw detector is turned on, it is necessary to set the basic parameters such as the detection channel, scanning method, display mode, material sound velocity, probe method, gate width, gate start, and gate height of the flaw detector.
3) Straight probe zero calibration
For steel forgings, the probe zero point can be directly adjusted due to the known sound velocity of the material. Select the " Essential " function group, and select the " Probe Zero " function menu corresponding to the menu button corresponding to the Diligence menu. Place the probe on the test block and adjust the sound path of the flaw detector so that the sound path measurement value (S) and the test block of the status line are made. The known thickness is the same, and the zero point of the probe obtained at this time is the correct probe zero point of the probe.
4) Oblique probe calibration
Oblique probe calibration usually requires a step: 1 calibration incident point ( probe front ) 2 calibration probe angle (K value ); 3 calibration material sound velocity ; 4 calibration probe zero point.
1 , detection coverage rate
During the test, each scan of the probe shall ensure that the coverage of the scanning beams is greater than 15% of the diameter of the probe .
2 , the probe movement rate should not exceed 150mm / s . This is not restricted when the active alarm device is scanned.
3. Scanning agility is at least 6dB higher than the benchmark agility .
4 , coupling agent
Oil, paste, glycerin, etc., and does not damage the appearance of the workpiece.
5 , detection surface
(1) The detection surface and the detection category are simply fixed, and the sound beam should be scanned to the entire workpiece to be inspected.
The sound beam scans the entire workpiece to be inspected.
(2) Straight probe axial and radial detection
When the straight probe is used for axial detection, the longitudinal wave beam is incident in the axial direction, and a transverse defect perpendicular to the axis or perpendicular to the axis can be invented ; 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 mainly The radius of the sound beam is incident along the axis, and the most common longitudinal deformation of the sheet formed by forging deformation can be invented. For other forgings with different tolerances, the detection method of the straight probe is also different. The shaft type should generally be the same as the radial and outer circumferential direction of the end face even if the axial and circumferential detection of the cake and the ring are accepted.
(3) Circumferential probe circumferential and longitudinal detection
In order to deal with the defects of radial diffusion in the shaft, the above-mentioned direct probe detection method is difficult to detect. Therefore, it is necessary to use an oblique probe with a proper angle of refraction to perform circumferential detection on the outer circumference of the shaft. At this time, the beam is obliquely incident on the shaft. Internally, the sound pressure emissivity of radial defects is higher than that of force. In the actual detection, the curvature of the oblique probe and the circumference of the shaft are increased. It can be used to repair the plexiglass transparent sound wedge. It can be used with single probe or double probe ( one shot and one output ). Detection.
Through the above introduction, have you understood the principle and usage of the ultrasonic flaw detector? If you have any questions, please feel free to contact us!