Cold shuts

T.O. 33B-1-1 6-101 6.8.15.7 Cold shuts. Cold shuts appear as a distinct darkened line of variable length and definite smooth, (Heavier than Casting) outline. Cold shuts are formed when two bodies of molten metal flowing from different directions fail to unite and form homogeneous metal. Cold shuts may be produced by interrupted pouring, slow pouring or pouring the metal at too low temperature. 6.8.15.8 Misruns. Misruns appear as prominent darkened areas of variable dimensions with a definite smooth outline. Misruns are produced by failure of the molten metal to completely fill a section of a casting, leaving the region void. This condition may be produced by lack of fluidity or pouring at too low temperature. 6.8.15.9 Dendritics. Dendritics appear as a series of irregular sharp lines usually in a parallel pattern. 6.8.15.10 Unfused Chaplets. Unfused chaplets may appear as a dark smooth line conforming to the shape of the chaplet and casting. In light alloy castings unfused chaplets may also appear as light lines. This condition is caused by cold or coated chaplets or by pouring the metal at too low temperature to fuse properly with the chaplet. 6.8.15.11 Core shift. Core shift may be detected when it is possible to angle the radiation or rotate the piece in a manner that would make it possible to measure the deviation of a specified wall thickness. Core shifts may be caused by jarring the mold, insecure anchorage or omission of chaplets. 6.8.15.12 Surface Irregularities. Surface irregularities may cause an image corresponding to any irregularity visible on the surface. These irregularities frequently show on a radiograph and may resemble or are confused with a flaw in the metal. It is, therefore, good practice to have the casting conveniently at hand when making an accurate interpretation of a radiograph. 6.8.16 Welds. Metal may be joined together by welding to form many shapes and structures required in an aircraft. This fabrication procedure, when carefully controlled, will provide a joint that is equal in strength to the parent materials. There must be just enough heat to produce fusion and adequate penetration, but not too much, which would cause porosity, cracks or undercutting. Most weld discontinuities can be readily detected by radiographic inspection since they consist of a change in material homogeneity. Cracks in welds are often detectable since they will usually occur in the direction of the thickness of the plate and will be parallel to the X-ray beam. Stresses created in the metal by welding and not accompanied by a physical separation of material will not be detected by radiography and cracks not properly oriented may also be missed. Oxides created by the molten metal may be trapped in the weld. This condition results in reduced strength and is subject to review to determine possible implication as a result of the service the weld is expected to yield. In tungsten inert gas (TIG) welding, tungsten electrode inclusions can occur. These appear as nearly clear specks in a radiograph due to the very high absorption of the radiation by tungsten. These inclusions usually appear in clusters of 2 or more. A single tungsten inclusion is unusual. Foreign material whose density is approximately the same as the weld metal may not be detected. In the inspection of weldments, radiography is an indispensable tool for the location of internal discontinuities. It is the oldest and best known nondestructive means for this purpose. It is used to establish welding procedures, to qualify welders, to inspect welded fabrications in process, and for quality control of welded parts. For routine inspection, test welds made periodically on production welding may be inspected by X-ray to supplement destructive tests where results are in doubt. When quality has been established, an occasional X-ray exposure can be made on routine work. All X-ray shadow images are geometric projections of the actual size of conditions in or on the weld. There may be some slight distortion depending on angle of X-ray beam and distance of the weld from the film. Density, in general, is some indication of the depth magnitude of the weld discontinuity.