Experimental studies on equivalent thermal properties of particle-reinforced flexible mould materials

Abstract

The investment casting process uses wax patterns which may be produced using the soft tooling process where the common flexible (polymer) mould materials used are polyurethane rubber, silicone rubber, etc. of a typical kind. However, due to poor thermal conductivity of these materials, solidification time of (wax) patterns takes longer leading to reduced rapidity of the process to a great extent. This problem may be overcome by increasing thermal conductivity of mould material that can be achieved either by molecular orientation of polymer itself or by addition of conductive fillers into polymer. The method of controlled addition of thermal conductive (particulate) fillers into mould material may be adopted by realizing it as the simplest and easiest to implement technique in industry. In this article, an experimental study has been carried out to find the effects on equivalent thermal properties of flexible mould materials reinforced with conductive filler particles. Two different types of particles (aluminium and graphite) with different morphological characteristics are considered as fillers. The measurement of thermal properties is carried out by a transient plane heat source technique. As much as 10-fold increases in thermal conductivity and thermal diffusivity values of mould materials reinforced with conductive fillers are found. In explaining the experimental results by several empirical/semiempirical models, it is observed that the Lewis–Nielsen model provides a good estimation, while the Agari–Uno model (fitted with experimental data) shows better agreement than other models.