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thermal conductivity didn’t change much over the elevated tempera- ture range. Thermal Properties From


Laser Flash The thermal conductivity and


specific heat capacity values mea- sured from laser flash are listed in Fig. 4. Shell 7 (rapid shelling technique) was highly porous and broke apart when being ground during laser flash sample prepara- tion. Effective density calculated from sample surface topolography was used to calculate these values. Laser flash showed a similar trend to the inverse method on both thermal conductivity and heat capacity values. Comparing Inverse Method,


Laser Flash and Teoretical Values The thermal conductivity


values were fairly close between the inverse method and laser flash. However, the inverse method pre- sented higher specific heat capac- ity values. In the inverse method, the shell was heated rapidly when metal was poured and cooled at a relatively slower rate during solidification.


The laser flash method showed similar total reaction enthalpy (i.e., defined thermodynamic potential) to the theoretically calculated values, because the thin specimen used in the laser flash method was under partially ther- mally stabilized condition which was closer to thermal equilibrium. Nevertheless, the shell in reality was hardly in thermal equilibrium conditions. Therefore, the inverse method provided more realistic effective heat capacity values for modeling. However, thermal property data measured from laser flash could be used as starting points in the automatic optimiza- tion process, which greatly reduces the number of simulation cases needed and decreases the potential error in iteration step estimates. The theoretical thermal con-


ductivity of shell 1, shell 3 and pure silica with 33% porosity are shown in Fig. 5. The shells’ measured and theoretical values of


January 2015 MODERN CASTING | 43


thermal conductivity were simi- lar at a lower temperature (<752F [<400C]), but were more heat con- ductive at a higher temperature.


Tis article is based on a paper (14-023) that was presented at the 2014 AFS Metalcasting Congress.


ONLINE RESOURCE


Read the original research paper in its entirety at: www.moderncasting.com


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