GB1005557A - Improvements in or relating to packing of test-pieces during tomography - Google Patents

Abstract

1,005,557. Radiography. ROLLS ROYCE Ltd. June 8, 1964, No. 23597/64. Heading H5R. An article to be tested for flaws by tomography is packed round with a material having a radiation absorption coefficient similar to that of the material of the article, the composite package being of circular cross-section in the plane to be tested. When this method of packing is applied to tomography as described in Specification 961,868, it is possible to avoid the effects due to variation of absorption of the radiation as the cross-sectional width of the article in the radiation beam alters, as occurs with such articles as turbine blades. The article 1 (Fig. 1) and packing 2 form a cylindrical package which is mounted on a turntable 3 on support 4. The X-ray source 5 directs rays through the article on to a photographic plate 7 on a rotatable support 8. When the test article is of irregular size or if several articles are to be tested, the packing material used is a liquid, e.g. zinc bromide solution, or powder 10 (Fig. 2) which is contained around the article 1 in a cylindrical box 9. Since small air spaces are liable to form in it, the packing powder is not of the same material as the test article and a material with a greater absorption coefficient is best used, for example, granules of molybdenum or tin, or a mixture of either with iron granules. A solid packing material may be formed (Fig. 4) of two pieces 11, 12 complementary with the shape of the article 1 and of similar absorption coefficient. A clear record of the boundary line between article and packing material is ensured by covering the article with a thin layer 13 of tape formed of rubber, synthetic resin &c. of a substantially different absorption coefficient to compensate for the reduced attenuation of rays passing through the edges of the cylinder 2, compared with those passing through the centre, further packing 14, 15, (Fig. 4), is provided around the cylinder, composed of the same material as the pieces 11, 12. The extra packing may not completely enclose the cylinder (Fig. 5, not shown) as long as equal attenuation is obtained over the plane to be investigated. Besides the tomographic method used in Specification 961,868, methods may be used comprising rotating both the turntable 3 and the film about their own axes, with a stationary source, or rotating the source and film about the stationary article as the centre of radius.