CAN/CGSB-48.5-95 Part III: Chap. 10

10.1 Introduction Several metal-shaping processes are in use in modern manufacturing industries. Industrial radiographers may be called upon to examine parts either during the manufacturing process, or at the assembly stage, as well as when the parts are used in service. Some aspects of the "casting" and "forging" processes that are necessary for the routine functions of industrial radiographers are discussed here. Other metal-shaping processes to name a few more recent ones, are extrusion, drawing, rolling, forming (hot or cold), explosive forming, high-energy rate forming, and sintered metal (powder metallurgy) techniques. As can be appreciated, the details are far too many to include in this manual. Radiographers who become associated with these processes during the course of their work will be able to find the process details in the Tool and Manufacturing Engineers Handbook published by the Society of Manufacturing Engineers. A "Casting" is a metal object shaped by pouring molten metal into a die or a mould having the desired shape. The term "casting" is used not only to describe the end-product, but also very loosely all of the "processes" that contribute to achieve the end result. A "Forging" is a metal object shaped by hammering or pressing the metal in a semi-soft condition, in a pair of dies having the desired shape. The term "forging" is also used to describe the "processes" of achieving the end product. Generally speaking, the radiography of "castings" is carried out on a much wider scale than the radiography of "forgings". This is due to the fact that there are several different casting processes, and that there are innumerable applications where castings are employed compared to the number of forgings, as well the fact that the cast material does not have the mechanical strength or fibrous flow of the forged part. Radiography can be used for inspecting castings of any of the common metals including cast iron, steel, aluminium, magnesium, copper, zinc and their alloys. Practically all sizes and shapes of castings can be radiographed. However, there are limitations as to the section thickness that can be inspected with the sources of radiation that are available in a particular industrial radiographic facility. Additionally, the geometric construction of the part should be such as to make it accessible to the radiation source and that a film can be placed against it on the side remote from the source. The thickness of the most complex shaped light alloy casting generally does not restrict its inspection be radiography. Most aluminium and magnesium castings can be satisfactorily X-rayed with commonly available X-ray equipment. X-ray equipment in the 140 kV (peak) range seems to be most widely applicable. For steel castings, 220, 400 and 1 000 kV (peak) units are most suitable and will permit inspection of steel thicknesses from about 50 to 125 mm (2 to 5 inches). Certain radioactive isotopes or high-energy X-ray equipment, such as linear accelerators and betatrons, permit inspection of heavier metal sections, in some instances a maximum of up to 450 mm (18.0 inches) of steel, or the equivalent thickness of other materials of different density. Thus, Cobalt 60 may be used for the inspection of steel up to approximately 200 mm (8.0 inches) in thickness. There are two ways in which radiography serves the casting industry. First, it can be used in the development work at the initial stages of casting design. It can also be used to improve the foundry techniques. Prototype castings can be examined in order to determine the position of runners, risers, gates, chills, and to study and control shrinkage, cooling rates, segregation of impurities, and porosity. Secondly, radiography can be employed as an on-going inspectioin method to control the quality and to meet specifications in a production environment. By revealing subsurface discontinuities, it can detect unacceptable castings before costly machining operations are performed. Also, it can detect discontinuities that would not be uncovere