In order for the core to emit a gas there must be uncured binder in the core/mold, and these core/mold materials must reach high temperatures. A comparison of the core temperature at the start of the filling cycle with the core temperature at the end of the cycle showed that the cores are severely overheated. This and the evaluation of a sectioned core with uncured binder reveal that the core possesses all the required conditions to produce gas.
The second condition that must exist for core gas related porosity is an entry point for the gas to get into the casting. The Fraction Solid results were used to identify the locations of the casting that formed a skin last and thus identified the entry point of the gas into the casting and the amount of time it was able to do so. The evaluation of the solidification progress shows that the defect prone region of the casting takes 140 seconds, after filling, to completely form a skin.
The match of the real areas of gas defects of the sample casting with the simulation results showed a good correlation. Now that the true defect had been identified, Custom Casting’s engineering department reduced the binder content of the sand, which yielded a slight improvement in the defect severity. During their investigation of the cores, they also discovered that the core molds were not heating the core evenly causing the uncured binder issue.