T.O. 33B-1-1
Table 6-21 Deleted
6.8.12.1
The inspector reading radiographs should be acquainted with the exposure technique used, material
radiographed, conditions of processing, and the geometry of the exposure setup. In this way he can judge
more accurately the radiographs produced and interpret the discontinuities more accurately. To determine if
the part is rejectable or acceptable he will generally consult with the structural or design engineer unless
standards have been established. To properly apply information obtained through radiography, the material
inspected must also be accurately identified with respect to the object radiographed. Lead letters or numbers
are radiographed with the object to provide identification. This identification must be recorded and keyed to
the object.
6.8.13
Typical Radiographic Discontinuities.
The radiographic inspection process is comparatively expensive and should be used for evaluation of internal
discontinuities that cannot be evaluated by more economical methods. Therefore surface discontinuities of a
magnitude to be considered detrimental to the function of the part should be evaluated by visual inspection or
other NDI methods that are more economical than radiography. The major use of radiography is to reveal
internal discontinuities.
6.8.14
Castings.
The process of forming various shapes of metal by pouring molten metals into molds accounts for a
considerable share of the critical components of an aircraft. These castings are made by melting ferrous and
nonferrous alloys. The majority of the castings encountered requiring X-ray inspection are made of light
alloys; that is, aluminum and magnesium alloys. There are a number of inherent difficulties in this
manufacturing technique which plague the foundry. Since the molten metal occupies a larger space than the
same material after it freezes or cools, precautions must be taken to prevent the metal from shrinking too
rapidly and forming voids which are called shrinkage or from rupturing the metal to cause hot cracks. The
molten metal also traps considerable gases from the air. These may result in tiny regular shaped bubbles in
the solid metal casting. Some metals such as aluminum accumulate gas on the surface of the molten metal.
This may be trapped in the casting if adequate precautions are not taken to prevent pouring the gas into the
mold. In addition, sand may wash from the walls of the mold into the casting forming inclusions that reduce
the strength of the castings.
Change 3
6-97/(6-98 Blank)
