This report summarises the results of the NPL Studio project DISIC in which the dimensional stability of ceramic shell investment casting moulds has been investigated using a suite of laboratory tests as well as plant casting trials. Shell moulds of ‘generic’ types were manufactured by the University of Birmingham, and industrially employed mould types were supplied by four industrial partners. Different behaviours of different types of shell systems have been identified. The full silica system has been shown to be the most dimensionally stable except in a low temperature regime between 800 °C and 1000 °C during initial firing. A full aluminosilicate system was the least dimensionally stable at higher temperatures during casting. Zircon/molochite and zircon alumina systems have intermediate behaviour. The dimensional deviation obtained from the initial wax shape to the cast metal shape was investigated using a plate casting test. The results of these trials broadly paralleled the laboratory tests.
The complex temperature and stress distributions during casting cannot be directly modelled in laboratory tests, and success in casting is related also to the size and shape of the casting, as well as the thickness of the mould created around the wax precursor. Nevertheless it is believed that the results of the project enable users to rank the shell systems according to risk of deformation and dimension change during the various stages of pre-firing and casting.