Operating Manual

135
Casting radiography
For the interpretation of X-ray films of castings, thorough knowledge of the specific manu-
facturing process is required. The type of defects in castings varies for the different types of
materials and casting processes. Figures 15-1 and 15-2 show X-rays of complex castings.
These radiographs were made to check the overall shape and possible presence of casting
defects.
As it solidifies during the casting process, metal contracts and unless precautions are taken
shrinkage cavities can occur inside the casting.
These can take various forms, such as piping/worm-holes, (figure 15-3), sponginess or
filamentary cavities, depending on the rate at which the metal has solidified. When the
contracting spreads slowly through the metal, filamentary shrinkage (figure 15-4) or even
inter-crystalline shrinkage (figure 15-5) may occur, while if the solidification front shifts
rapidly, shrinkage cavities tend to occur (figure 15-6).
Gas cavities in the form of porosity or larger gas holes can occur either due to a damp mould
or release of gas from the molten metal, and can be particularly troublesome in cast light
alloys (figure 15-7). Cracks can also occur in castings.
If they are formed while the metal is still semi-solid they are usually called “hot tears” (figu-
re 15-8); if they occur when the metal has solidified, they are called “stress cracks” or “cold
tears” (figure 15-9).
A collection of radiographs of defects in iron/steel castings is provided in ASTM E446, and
for aluminium in ASTM E155.
Fig. 15-1. Radiograph of an aluminium casting
Longitudinal root crack.
Feathery, twisting lines of darker density along the edge of the
image of the root pass The “twisting” feature helps to distin-
guish the root crack from incomplete root penetration.
Tungsten inclusions.
Irregularly shaped lower density spots randomly located in the
weld image.
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