Introscope for Quality Control of Castings Made of Aluminum and Magnesium Alloys

D. I. Sviryakin, A. D. Maksimenko,
A. A. Dmitrov, V. S. Pertsev

(Presented by the scientific seminar of the Research Institute of Electronic Introscopy)

Nondestructive in-line quality control of cast, forged, and welded blanks intended for the manufacture of complex and expensive products has a major economic effect, since it makes it possible to reject items according to such defect criteria as, at the early stages of production, do not yet manifest themselves in any way and lead to rejection only at the end of the technological cycle of manufacturing the product. However, because blanks at the beginning of the technological process, as a rule, have not even undergone rough machining, it is very difficult to detect defects in them against the background of technologically permissible but interfering factors, often exceeding rejection levels. For this reason, the selected inspection method must possess a definite selectivity with respect to defects or must provide information in a form convenient for processing and analysis by an electronic computer or by a human operator, as a result of which a conclusion can be drawn as to whether the blank is defective or suitable for further technological processing.

X-ray introscopy, like radiography, in many respects meets these requirements and in a number of cases can supplement it. That is, in in-line production it is most advantageous to carry out 100% express inspection of blanks by visual examination of their internal structure with the aid of an X-ray introscope, and only in those cases where it is necessary to have a document should radiography of defective blanks be performed on the basis of the preliminary results of introscopic express inspection.

To carry out such comprehensive X-ray inspection of large-sized (600 × 600 × 100 mm) cast blanks made of aluminum and magnesium alloys, in 1972–1973 the Research Institute of Electronic Introscopy developed and manufactured an X-ray television introscope with an electron-optical radiation converter, and developed an inspection procedure. The introscope set (Fig. 1) includes an X-ray radiation source (a RUP-120-5 or RUP-200-5 apparatus) with a vertical displacement device; a manipulator table for securing, moving, and rotating the inspected blanks on it; a radiation receiver (located beneath the manipulator table), which converts the flux of X-ray radiation into a visible image and then into video signals; a video monitoring device (VKU), which reproduces the X-ray image of the inspection objects; a control panel for the video channel and the manipulator table; and a control panel for the X-ray apparatus. The introscope is located in two rooms. In one room, where the ra

Fig. 1. X-ray television introscope for inspection of cast products made of aluminum and magnesium alloys

The operator’s workplace, the control panels, and the video-control unit are located in one room; in the other are the radiation source and receiver and the manipulator table. To ensure radiation protection for the service personnel, the rooms are separated by a lead wall and a double door with interlocks.

When the RUP-120-5 unit is used, the introscope makes it possible to inspect the quality of cast blanks with wall thicknesses up to 40 mm; when the RUP-200-5 unit is used, up to 75 mm. The optimum flaw-detection sensitivity (Fig. 2) of the introscope, determined using aluminum grooved reference standard No. 3 of GOST 7512—55 at thicknesses of 25—75 mm, is 2.2—3%. With water cooling of the X-ray tube, the introscope can provide three-shift operation. The inspection productivity, in comparison with radiography, increases by a factor of 15—20; therefore only

Fig. 2. Graph of the dependence of the flaw-detection sensitivity of the introscope on the thickness of the aluminum being transilluminated

Vertical axis: Sensitivity, %
Horizontal axis: Aluminum thickness, mm

individual blanks in which defects of interest to technologists have been detected with the aid of the introscope. Images analogous to radiographs can also be obtained by photographing the X-ray images from the VCU screen, but the quality of the images in this case is inferior to that of radiographs, since photography followed by printing on photographic paper leads to the disappearance of some image details because of a reduction in the signal-to-noise ratio at the intermediate stages of information transmission. Therefore, in the quality-control procedure for cast blanks it is recommended, by scanning, to carry out complete visual introscopy of every blank entering the production stream. For more reliable detection of cavities, pores, foreign inclusions, and open cracks in places of increased thickness, ribs, and angular transitions, it is necessary, by rotating the table, to change smoothly the direction of transillumination and to use the adjustable lead diaphragm installed on the radiation receiver. This diaphragm makes it possible to eliminate partially the scattered radiation that lowers the contrast of the X-ray image; however, along with increasing the image contrast (when the transillumination area of the diaphragm is reduced), it reduces the inspection area. After viewing the entire blank, the operator decides whether further machining of the blank is advisable. In the event of mass defects, the operator makes a radiograph of one or two blanks with the most characteristic defects, prepares a description of these radiographs, and submits them to the process engineers/foundrymen or to higher quality-control bodies for the products. To check the quality of adjustment of the introscope units, it is recommended periodically, once a week, to carry out inspector checks of the image quality on the VCU screen of the introscope against radiographs of the products inspected during that period, and at the same time to determine the defectoscopic sensitivity using the groove-type reference standard installed on various sections of the products.

REFERENCES

1. V. A. Dobromyslov, S. V. Rumyantsev. Radiation Introscopy. Atomizdat, 1972.

2. S. V. Rumyantsev. Radiation Defectoscopy. Atomizdat, 1968.

3. Television (General Course). Edited by P. V. Shmakov. “Svyaz,” 1970.

4. Nondestructive Testing. Handbook, edited by R. McMaster. “Energiya,” 1965.

5. F. N. Kharadzha. General Course of X-Ray Engineering. “Energiya,” 1966.