The rays interact with the substance as they penetrate it and their intensity is attenuated by absorption and scattering. The degree of intensity attenuation depends on the attenuation coefficient of the substance and the thickness of the passage through the substance. If there is a defect in a part of the object (specimen) being illuminated, and the attenuation coefficient of the material constituting the defect is different from that of the specimen, the intensity of the transmitted rays in that part of the area will differ from that of the surrounding area, and as long as a certain detector is used to detect the difference in intensity of the rays, the film is placed in an appropriate position to be sensitised to light by the transmitted rays, and a negative is obtained by darkroom processing. The degree of blackening of each point on the negative depends on the amount of radiation exposure, due to defective parts and intact parts of the intensity of the transmitted rays are different, the corresponding parts of the negative will appear on the blackness of the difference. When the negative is placed on the viewing lamp, different shapes of images composed of different blackness areas can be seen, according to which the evaluator can judge the defective condition and evaluate the quality of the specimen.
Scope of application: applicable to all kinds of metal, non-metallic materials and composite materials testing; the most widely used in welding parts and castings.
(1) The visual image of defects can be obtained, qualitatively accurate, and the quantification of length and width dimensions is also more accurate.
(2) Inspection results are directly recorded and can be stored for a long time.
(3) Higher detection rate of volumetric defects (porosity, slag entrapment, etc.)
(1) Suitable for inspection of thin thickness of the workpiece but not suitable for thicker workpieces.
(2) For area defects (such as cracks, unfused, etc.), if the camera angle is not appropriate, it is easy to miss the detection.
(3) It is difficult to determine the position and size (height) of defects in the thickness direction of the workpiece.
(4) The detection cost is high and slow.
(5) The rays are harmful to the human body.