Investment casting waxes are injected or extruded into tooling cavities to form disposable patterns and related assemblies for subsequent processing in the precision investment casting (PIC) process. The flow characteristics, or rheology, of these waxy materials play a crucial part in determining dimensional and surface quality of the injected part.
Traditionally, wax flow has been characterised using a combination of simple viscosity measurement methods and injection trials. Such techniques do provide useful information but can be cumbersome and time consuming to run and tend to generate point data that typically fails to cover the full spectrum of temperatures and shear rates that waxes are subject to in the PIC process.
Today, the wax industry has access to powerful computer controlled rheometers that can quickly and accurately characterise the rheology of PIC waxes.
This paper examines the pros and cons of the traditional viscosity measurement methods mentioned above and goes on to demonstrate why the author believes a modern computer driven rheometer is the best option for the characterisation of wax rheology. Data is presented illustrating the many uses of such an instrument, including characterising the effect of filler morphology on wax flow, wax rheology at very high and low temperatures and the effect of shear rate on wax behaviour.