Published: Jan 1951
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The experience of the Naval Gun Factory in ultrasonic testing has been limited to the use of the Sperry Reflectoscope. The applications and findings with this instrument have, on the whole, been quite similar to those of many other users. The greatest value from the equipment has been obtained in the testing of forgings, particularly non-ferrous forgings to which other methods of examination are not well suited. for example, considerable use is made of aluminum bronze forgings containing from 8 to 12 per cent aluminum, heat treated to tensile strengths as high as 100,000 psi. From time to time, serious runs of defective forgings have occurred, forgings split down a central plane with the splits sometimes, but not always, extending to an outside surface. Fluorescent penetrant methods are, of course, of limited value in detecting such defects, and radiography frequently inapplicable because of the thicknesses involved and the directions of the defects. Since many of the forgings are of relatively uniform sections, in the range of 4 to 10 in. in thickness, they present an almost ideal application for the “Reflectoscope”, which has been used for checking them in this manner for over two years. Originally it was intended to use the instrument to determine the point in the manufacturing process at which major splits were formed, and with this in mind, the ingots were examined after casting and also the forgings made therefrom, both before and after heat treatment. Unfortunately, or perhaps fortunately, no major series of defects have occurred since the instrument was placed in use, possibly because the shops involved, knowing that this equipment was available and could point to specific operations, employed greater care in each step, such as watching melt composition, pouring temperature, forging temperature, etc., more closely. Out of the ingot examination has come one interesting application, that of determining the amount of cropping necessary to insure sound forging stock. Using a frequency of 1 mc., it is very simple to detect both the primary piping down the center of an ingot, which usually absorbs the signal completely, and secondary piping, which normally produces a reflection. The proper point for cropping can be located very accurately, permitting maximum utilization of material and eliminating exploratory cutting. At the same time, any other localized defective portions are also marked for removal from the ingot. Test forgings have been made from such localized defective portions, also proving defective in most cases, but not duplicating the serious splits we had encountered in the past. Although the cause of these defects has not yet been found, apparently a salutary effect has resulted.
Welding Engineer, U. S. Naval Gun Factory, Washington, D. C.