For internal defects, commonly used non-destructive testing methods are radiation detection and ultrasonic testing. Among them, the radiation detection effect is the best, it can obtain an intuitive image reflecting the type, shape, size and distribution of internal defects, but for large castings with large thickness, ultrasonic testing is very effective, and the position of internal defects can be measured relatively accurately. , equivalent size and distribution.
1) Ray detection (micro focus XRAY)
Radiation detection, generally using X-rays or gamma rays as the source of radiation, requires equipment and other ancillary facilities for generating radiation. When the workpiece is placed in a ray field, the radiation intensity of the radiation is affected by internal defects of the casting. The intensity of the radiation emitted through the casting varies locally with the size and nature of the defect. The image of the defect is formed by radiographic recording, or detected by real-time observation through a fluorescent screen, or by a radiation counter. Among them, the method of recording by radiographic film is the most commonly used method, which is commonly referred to as radiographic inspection. The defect image reflected by radiography is intuitive, and the shape, size, number, plane position and distribution range of the defect are all Can be presented, but the depth of the defect is generally not reflected, and special measures and calculations are needed to determine. The application of ray computer tomography in the International Casting Network has become expensive due to its high cost and high cost. However, this new technology represents the future development of high-definition ray detection technology. In addition, the use of a microfocus X-ray system that approximates the point source actually eliminates the blurred edges produced by the larger focus device, making the image outline clear. Using a digital image system can increase the signal-to-noise ratio of the image and further improve image clarity.
2) Ultrasonic testing
Ultrasonic testing can also be used to inspect internal defects by using sound beams with high-frequency acoustic energy to propagate inside the casting and to detect reflections when they encounter internal surfaces or defects. The magnitude of the reflected acoustic energy is a function of the directivity and properties of the inner surface or defect and the acoustic impedance of such a reflector, so that various defects or acoustic energy reflected from the inner surface can be applied to detect the presence, thickness or surface of the defect. The depth of the lower defect. Ultrasonic testing is a widely used non-destructive testing method. Its main advantages are: high detection sensitivity, which can detect small cracks; and large penetration ability to detect thick section castings. The main limitation is that it is difficult to explain the reflection waveform of the detachment defect with complex contour size and poor directivity; for undesired internal structures such as grain size, microstructure, porosity, inclusion content or fine dispersion Precipitates, etc., also hinder the interpretation of the waveform; in addition, reference to the standard test block is required for the detection.
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