There are two types of non-destructive testing methods for spring surface quality: infiltration method and magnetic particle inspection method. The principle of the infiltration method is to use the capillary action to check the surface opening defects. First, spray the cleaning agent on the surface of the spring, then spray (or dip) the penetrant, then remove the excess penetrant, and then spray the developer, the penetrant can The microcracks seep on the surface of the spring, and the developer clearly shows the crack. The principle of the magnetic particle flaw detection method is that after the ferromagnetic material or the workpiece is magnetized, the magnetic lines of force are deformed at the defects on the surface of the workpiece and the near surface, and the surface of the workpiece is escaping to form a magnetic pole and a leakage magnetic field. When the surface of the workpiece is sprinkled with magnetic powder or poured with a magnetic suspension, The magnetic powder particles are adsorbed by the leakage magnetic field at the defect, showing the position, shape and size of the defect.
The detection method generally clamps the spring to the two poles of the magnetic particle flaw detector, and generates a magnetic field after being energized. The magnetic field line is cut at the place where the spring surface has a crack, and when the magnetic suspension is poured, the magnetic powder accumulates at the crack. Both of these methods are surface flaw detection, which have limitations, that is, the internal defects of the material cannot be detected. The infiltration method can only inspect surface open defects, and the magnetic particle inspection method can only inspect surface and near surface defects. Their biggest disadvantages are low efficiency, poor precision, easy to cause false detection, missed inspection, and surface scarring, slag inclusions and dents are not easy to find. Ultrasonic flaw detection relies on echoes reflected by the ultrasonic waves to be received by the probe, and is detected, amplified, and displayed on the instrument to detect defects inside the object (or surface). Due to the long length of the spring, the sound wave is seriously attenuated. However, since the spring is cylindrical, the ultrasonic wave enters the inside of the spring and the sound wave reflected by the inner circular arc surface produces a focusing effect. The sound wave does not have a large divergence loss, and has sufficient detection sensitivity, and can ensure sufficient energy after multiple reflections. . In fact, after the ultrasonic wave is reflected more than 4 times, an ultrasonic channel is formed inside the spring. At the same time, because the ultrasonic wave speed is extremely fast, the shear wave velocity inside the spring reaches 3250 m/s, and the ultrasonic wave enters the spring end face angle at a moment, and the reflected wave is very Easy to accept by the probe. Therefore, the method is simple, the detection result is intuitive and the accuracy is high, and not only the internal defects of the spring but also various defects of the spring surface can be detected.
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