The application of the Rotary Air Diffuser to the drying of investment casting ceramic shells was developed and patented by drytech in 1979. The Rotary Air Diffuser is a device designed to provide a controlled velocity wipe of drying air across the surface of a product, producing a turbulent surface air pattern of direct and induced air streams. The Rotary Air Diffuser comprises of a speed controlled, directly driven, axial flow fan supplying air to a distribution cone mounted on support bearings and fitted with adjustable diffuser outlets. The distribution cone is rotated, via a torque limit coupling, by a double reduction, electric, motor gearbox unit. The overall air quantity handled by the device is carefully related to the overall surface area and moisture loading of the moulds to be dried. The outlet diffusers are selected to provide the correct air velocity at the required distance from the mould. The fan motor is controlled by an electronic speed controller to provide operating air velocities in the range of 2.0 to 1 0.0 meters per second. The size of the Rotary Diffuser installed in a system is matched to the configuration of the mould handling system, drying enclosure and the air conditioning system that is utilised to control the drier environment. The Diffuser draws its air as a mixture of air from the drier environment and air directly supplied from the air conditioning plant. Care is taken to ensure that good mixing of the air streams takes place prior to its distribution over the mould surface. Rotary diffusers and their associated conditioning systems are in use in both Manual and Robot production systems with many of the Worlds respected Investment Casting Foundries for the manufacture of Aerospace, Medical and Commercial cast parts. In the Drytech systems the mould handling conveyor, Rotary Diffuser air speed and the environmental systems are controlled by a programmable controller with the required communication links to provide an integrated system which allows the processing of each mould coat at the required Temperature, Moisture content and Air speed to give the optimum drying performance. To understand why the Rotary Diffuser provides improved mould drying it is necessary to consider the drying process itself. To avoid being tied by complex formulae and inconceivable coefficients it is reasonable to consider that the two main driving forces of the drying process are the air speed over the product surface and the difference in vapour pressure between the surface and the surrounding air. A continuous or laminar flow of air has the effect of removing the moisture from the product surface and the sustained removal produces a surface layer of lower vapour pressure. A wipe action of air however as it passes across the product removes the surface moisture and then during the period of lower air velocity allows the embedded moisture to migrate to the product surface. This ensures that the airflow striking the product always has the highest differential of vapour pressure possible and hence removes the moisture in the most efficient manner possible. High vapour pressure differences would be accompanied by high dry bulb temperature differences or corresponding lower wet bulb temperatures. When the mould is wet the wax, shell interface will respond to the wet bulb temperature and as it dries it will approach the dry bulb temperature. In order to maintain the wax, shell interface temperature within a narrow band it is therefore preferable to dry using a higher velocity air flow with the lower temperature differentials. Specific examples of the production of a water based shell with a one hour intercoat drying time are detailed in a technical paper presented in Europe and the United States. A copy of this paper is available upon request.