Date of this Version
The author contributed a brief account of the radiographic practices necessary to comply with government specifications to a round table discussion on inspection methods at the last American Society for Metals Convention, and later was able to release for publication in Metal Progress a full set of the radiographic standards set up about a year ago to govern acceptance of structural castings for airplanes. Representaive negatives are reproduced in this article. Those eliminated are either of similar defects which did not register strong enough to appear on an engraving without retouching, or of defects readily observed by visual inspection without X-ray.
Towards the end of 1941 it became imperative that general standards for the acceptance of aircraft castings be established. At that time the commercial standards for the acceptance or rejection were largely intangible; castings rejected by one radiographic laboratory were later accepted by another. As a check on the validity of commercial X-ray inspection, rejected castings were subjected to breakdown or tensile tests conducted upon specimens machined from castings, and many were found to have strengths considerably in excess of design or specification values. Pressure of increased aircraft production made such a waste of material intolerable. As remarked at the outset it became necessary to establish an inspection procedure which would insure that:
1. No casting which might fail would find its way into an airplane structure.
2. A minimum number of usable parts would be discarded by unnecessarily rigid inspection standards, and
3. The inspection procedure be as economical of manpower and materials as was consistent with the first two aims.
To achieve these ends, a procedure for the X-ray examination of structural castings which attempted to resolve these principles was adopted by the Army Air Forces in February, 1942. An outline of the procedure and some representative radiographs will be given, principally applicable to sand and permanent mold castings of aluminum or magnesium alloys used in the airplane's structure. Castings for use in hydraulic systems need not be X-rayed if they are hydrostatically tested unless sections of these castings are also subject to structural loads, whereupon such sections are subject to the same requirements as structural castings.