On the Problems of a Migrating Hot Spot
In this work the meaning of a migrating hot spot during solidification will be discussed. Initially, just after mould filling, global as well as local thermal centres, or hot spots, are established. This occurs at mass concentrations and heavy sections as the mould wall initially is at ambient temperature. However, these hot spots are found to be migrating during solidification. This migration influences any temperature measurement and subsequent thermal analysis, introducing uncertainties. It has also been found that common casting defects such as shrinkage porosity and metal expansion penetration can be associated with a migrating hot spot. In these cases the final position of the hot spot is located across the interface between the casting and the mould. The solidification starts at the mould walls and it was found that the columnar zone is affected by the migrating hot spot. The macrostructure was preserved using DAAS technique and it was revealed that an otherwise normal columnar zone because of the migrating hot spot had been affected. Based on these findings it is suggested that the migrating hot spot is making the columnar zone weaker and more susceptible for pressure differences arising during solidification.
A. Roósz, V. Mertinger, P. Barkóczy and Cs. Hoó
L. Elmquist and A. Diószegi, "On the Problems of a Migrating Hot Spot", Materials Science Forum, Vol. 649, pp. 443-448, 2010