temperatures are just below the melting
point, the strength and toughness are
A casting simulation program developed
by Magma Foundry Technologies of
Schaumburg, IL was used to study the
technique that produced these castings.
The program models the filling of the
mold, showing metal velocity, metal
temperature, cooling, progressive solidification and other parameters. This
helps predict the location of hot spots
and shrinkage defects.
Analysis of the mold-filling technique
used for the original castings revealed a
deficiency in the feeding or rigging
method. The mold was filled through
two feed paths into the flanges (Figures
6 and 7). The lower half of the flanges
filled first, then the center section of the
body, and finally the neck and foot area.
A high level of turbulence was created as the metal flowed into the neck and
foot. The turbulence produced reoxida-tion of the metal, which introduced
oxide defects. The metal was also rela-
tively cold when it reached this area,
which created excessive tensile stress in
the neck from the highly constrained
foot as the solidification progressed
back toward the main body.
Casting simulation using a three-feeder system (Figures 6 and 7) demonstrated a less turbulent fill that promoted a desirable directional solidification
from the body out towards the foot. This
change minimized the highly constrained situation where the foot solidified first.
The three-feeder rigging system the
simulation identified was then put to the
test as 24 new castings were produced
and subjected to extensive evaluation.
Radiographic testing revealed no significant defects.
Six of the new castings were LP
tested, which found multiple surface
indications that all appeared to be
shallow. The castings were then sec-
tioned and mechanically deformed.
Grinding was performed to remove the
defects. None of the defects on the inte-
rior and exterior surfaces were found
to be connected. No internal casting
defects were revealed within the vol-