外文翻译--对铸件缺陷位置和尺寸的无损检测方法的评价(编辑修改稿)

外文翻译--对铸件缺陷位置和尺寸的无损检测方法的评价(编辑修改稿)内容摘要：

e test coil to the test surface is critical. This means that for any ponent (other than flat plate), special probes are usually designed to follow specific ponent contours. A small eddy current machine can cost as little as $2020, but a large automated machine can cost up to $20 000 RT 一 Short wavelength, electromagic radiation will pass through many materials, depending upon density and thickness, and then create a range of exposures on either film or a fluoroscopic screen, to present a visual image of the internal position of the item. Differences in absorption within the material due to such things as gas holes, cracks and bursts will create photographic density differences on the film or detector, which can be interpreted by trained personnel. The source of radiation can be an Xray tube or a gamma source (such as Iridium or Cobalt) and the images can be generated on either film or as realtime images on fluoroscopic screens. Defect orientation is a vital factor in radiography since it is thickness differences, which the process detects. Hence, a lamination type defect, parallel to the film would be almost impossible to detect. On the other hand, a crack perpendicular to the film would almost certainly be detected. It is therefore often the case that a single ponent would have to be radio graphed from more than one direction, in order to detect most defects. Finally, the radiation used is highly hazardous and therefore any environment in which it is used, must suitably shielded, to prevent exposure of the operator. As well as shielding the use of X or gamma rays will also require, monitors, alarms, interlocks and personal dosimetry systems, which along with the film itself, adds to the cost. A basic Xray set up would cost around $10000 and with ancillary equipment and film could cost $3000 per year to run. UT— At an interface between materials of differing acoustic impedance, a sound wave will have a proportion reflected and the remainder transmitted. Thus a gas hole or crack in a forging will reflect a sound beam because of their large difference in acoustic impedance with the metal structure containing them. Since ultrasound travels in a given material at a known (predictable) velocity, then the distance to a reflector will be a direct function of this time of flight of the pulse of sound. Its location can therefore be estimated .Since the amplitude of the returning signal is also related to the size of the reflector, then an approximation can be made of the extent of the reflector, in terms of length throughwall thickness and width. The data can be presented as an „A‟ scan, on a cathode ray tube (requiring skilled interpretation) or as a „B‟ or „C‟ scan, where the data are plotted on printers or strip charts as a permanent record. Depths of peration can be adjusted (by calibration and probe selection) from 10mm to 3 meters in suitable, finegrained material. However cast, or large grained forged material, could be attenuate signals to the extent that they are untestable. A typical portable flaw detector and probes would cost around $5000, a fully automated „C‟ scan immersion system could cost $2020. c) The variables associated with the forging condition For VT and PT surfaces better than Ra would yield the best results. For MT a similar situation exists, where a confusing background could result from rough surfaces. ET also requires a。