Determination of thermal diffusivity for the correct design of iron castings

Abstract

A fuller understanding of the thermophysical characteristics of cast iron has been rendered necessary by recent changes in the design and manufacture of mechanical components, especially those employed in the automotive industry.

Thermal diffusivity is of particular importance in this respect. Its determination by means of a transient thermal step method is described in this paper. A thermal step is induced in test specimens by their rapid transfer from one thermostated environment to another at a higher temperature. Temperatures are then taken during the transient step at a point with known coordinates.

Simulation of this transient under different heat exchange conditions with a finite elements model (FEM), which can handle specimens of varying geometry, gives a grid formed of points representing Biot and Fourier numbers, and temperature values 9 standardised within the range zero to one.

Thermal diffusivity is determined by taking the Biot and Fourier numbers that minimise the difference between the values observed experimentally and those on the curve supplied by the model. This parameter is then correlated with the metallurgical characteristics.