Methods for forming powders of ceramic raw materials into complex shapes are desirable in many areas of technology.
For example, such methods are required for producing advanced, high-temperature structural parts such as heat engine components, recuperators and the like from powders of ceramic raw materials.
The water in the slip is drawn out into the walls of the plaster mould, leaving an inside layer of solid clay, which hardens quickly.
This forms a dense cast removing deleterious air gaps and minimizing shrinkage in the final sintering process.
For the production of complex shapes in small quantities, additive manufacturing (AM) represents an effective approach, and is the subject of significant research and development.
However, the difficulties in machining ceramic articles means that AM techniques can be attractive in situations where production volumes are too low to viably produce molds for slip casting methods.
The technique involves a successive wet dipping and dry powder coating or stucco to build up the mould shell layer.
Other techniques involve threading animal or artificial wool fiber through paperclay slip, to build up layers of material.
This involves pouring the slip (which contains a polymer "binder" to give it strength) onto a moving carrier belt, and then passing it under a stationary "doctor blade" to adjust the thickness.
The moving slip is then air dried, and the "tape" thus formed is peeled off the carrier belt, cut into rectangular shapes, and processed further.