Castings on transit railcars often have complicated geometry. Varying thicknesses and limited space for shooting are difficult for radiographic testing of such castings. To reach the high-quality requirements of the density, accuracy, contrast, and sharpness of the films, a series of experiment were performed on one casting with complicated geometry to compare different results from different shooting methodologies.
Films with different ISO speeds are suitable for different wall thickness while their detection ranges overlap with each other. By adopting multiple film techniques, radiographic quality is enhanced when inspecting complicated castings geometries. The utilization of lead intensifying screen contributes to improve the image quality of the radiograph, so that the absorption of different sections is equalized and the prescribed quality level and density requirements are met. Latitude of film is improved by selecting appropriate voltage. Source-to-film distance is increased in order to minimize geometric unsharpness and ensure overall uniformity. Lead foil screens are utilized as a filter in front of films to absorb scattered radiation. In addition, back scatter radiation is reduced by placing lead plates behind the cassette. Large focal spot size is adopted. Short time of exposure is preferentially selected for the purpose of reducing the active time of scattered radiation. Moreover, the selection of other associated processing parameters helps to lessen the adverse effects caused by complicated casting geometries.
The results of these experiments show that the quantities of films and inspection cost can be reduced, efficiency of inspection can be improved; missing detection in complicated areas can be effectively avoided; the detection capability is increased and reliability of inspection results is ensured. In conclusion, the multiple film technique is a satisfactory methodology for radiographic testing of steel castings with complicated geometry.
