It is well known that the quality of casting shells is dependent on the viscosity of the shell-building slurry. This has two principal reasons. First, the viscosity is directly related to the solids content of the slurry, and reflects shifts in its composition through evaporation of the liquid component. Secondly, the performance of the slurry is directly related to its flow characteristics. The thicker the slurry – the higher its viscosity – the slower it runs off the form and the thicker the layer that it deposits. If the viscosity is too low – the slurry is too thin – it flows off the form too quickly, and the deposited layer is too thin. Since shells are formed from multiple layers, any deviations of slurry viscosity can contribute to failures of quality and performance of the shells, which can, in turn, lead to defects in the parts cast in the shells.

In order to control viscosity, it is necessary to measure it. The accuracy of control – how well the viscosity of a slurry can be set and maintained throughout the casting process – depends on the accuracy and repeatability, but also the ease of use, of the chosen measurement. The traditional measurement method is the flow cup, which measures viscosity as the number of seconds required by the slurry to run out of the cup. This measurement is not suited for continuous, repetitive monitoring of viscosity, nor is it particularly accurate. We will show how Rheonics’ SRV inline viscometer can be used for accurate, repeatable and continuous monitoring of slurry viscosity during shell building. We will then show how Rheonics’ SlurryTrack system can be used to apply the SRV’s measurements toward maintaining constant slurry viscosity during slurry preparation and shell building, despite evaporation losses, temperature changes and other influences that can cause unwanted changes to the shell quality. The SRV and SlurryTrack can, in addition, support the growing trend toward full shell-room automation, by reducing an important source of variability in the otherwise highly automated shell-building process.