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在X射线探伤摄片中,欲获得黑度基本均匀一致的X光底片,除曝光条件合适外,还取决于对焦的准确程度。尤其是弯曲度较大的工件,对焦问题显得更为突出。球罐因其本身特点,焊缝纵横分布整个球面,透照时,要求射线束垂直于焊缝表面,即形成一个通过对焦中心点与球体的正切平面垂直位置。否则,X光底片对称两端容易产生明显的黑度不匀的现象,严重影响射线照相底片的质量。因此,如何保证对焦准确性便成为球罐射线照相中较关键一环。平常使用的射线探伤时对焦方法已经难以适应球罐透照需要。专用支架对焦法是在原对焦方法基础上的一种新改进,它比较适用于大型球状体压力容器的射线探伤。
In X-ray radiography, to obtain a substantially uniform black level X-ray film, in addition to the appropriate exposure conditions, but also depends on the accuracy of the focus. Especially the larger curvature of the workpiece, focusing problems appear to be more prominent. Spherical tanks because of its own characteristics, vertical and horizontal distribution of the entire weld spheroids, transillumination, the beam perpendicular to the weld surface requirements, that form a through the center of the focal point and the ball perpendicular to the tangential plane. Otherwise, symmetrical two sides of X-ray film tend to produce obvious unevenness of blackness, which will seriously affect the quality of radiographic film. Therefore, how to ensure the accuracy of the focus becomes the more important part of the radiography of the spherical tank. Commonly used methods of radiography when the focus has been difficult to adapt to the needs of the ball through the lens. The special bracket focusing method is a new improvement based on the original focusing method, which is more suitable for the radiographic inspection of large spherical pressure vessels.