Residual stresses that evolve in the casting process during solidification and cooling may cause problems during subsequent machining or component use. In one particular case, dimensional changes of a ductile iron main bearing cap for marine applications had been observed after storing of the part. For this reason, the typical practice was therefore to apply an annealing heat treatment to release residual stresses after casting.
The Finnish foundry group Componenta and the marine and energy component manufacturer Wärtsilä jointly investigated whether it would be possible to omit the annealing step for cast iron main bearing caps. The parts are typically exposed to a heat treatment at around 550-600 °C for about a day. Being able to skip this annealing process would advantageously shorten foundry lead times and allow for significant cost saving potentials.
Both partners are used to using information generated from MAGMASOFT® during casting processes. Several simulations and mold cooling rate measurements were performed to find suitable simulation parameters for accurate cooling conditions from solidification up to shake out, which are the basis for reliable residual stress results. The simulated stresses were compared to measurements on the produced castings to fully understand the residual stress state of the main bearing caps. Finally, dimensional measurements of main bearing caps without heat treatment before and after storing them were carried out to verify the robustness of the castings against dimensional changes during storage.
In order to measure the cooling curves, sensors were placed in the mold cavity, and the mold was closed and poured under normal production conditions. The casting was shaken out after 24 hours of cooling, and the temperatures at that point of time were about 290 °C.