In the industrial foundry Livarna Gorica. d. o. o, cracks were always occurring in the
same place during the final manipulation of the cast "pipe part". The casting is made
from gray cast iron with lamellar graphite. Our task was to eliminate this defect. We
assumed that residual internal stresses were to blame for the formation of cracks. First,
we performed an experimental casting of the problematic casting and measured the
boundary conditions. Then, we performed a computer simulation of the casting
process, measured internal stresses at the critical point of the casting, and analysed
the microstructure with a metallurgical light microscope near the crack. The computer
simulation showed us that the critical point is filled with the melt last, so it is already
very cold at that time and this point cools down significantly faster compared to other
parts of the casting. Uneven cooling and shrinkage of the casting onto the core cause
residual internal stresses, which were also confirmed by measurements. In addition,
high cooling rates at the critical point of the casting cause a hard and brittle white
solidified microstructure, which was shown by metallographic analysis. This, together
with the residual stresses, creates ideal conditions for the initiation and propagation of
cracks. We solved the problem by turning the casting so that the critical point is no
longer filled last during casting. As a result, the melt there is much warmer and the
cooling is more uniform, which reduces the development of internal stresses. In
addition, the mould and the core overheat more due to the greater flow of melt around
the critical point. As a result, the cooling rate there is also lower, which avoids hard and
brittle white solidification. Since the core is more overheated, it becomes less rigid,
which further reduces residual internal stresses. With this measure, we have thus
eliminated both causes of crack initiation and propagation.
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