4: Forming and Drying
There are a variety of forming methods commonly used for ceramic materials. The most traditional of these methods is the compaction of ceramic powders into shapes that can be subsequently fired to give the desired product.
Compaction usually involves the pressing of a dry granular powder, that has been combined with small amounts of water or an organic binder, into a die. This method is popular as it can be used to form a wide variety of shapes at a high rate.
Following forming the ceramic body will quite often need to be dried before it can be fired. Before drying commences particles are surrounded and separated from each other by water. Upon drying, water is removed and the distance between particles decreases. This causes significant shrinkage of the cast body.
The rate of drying is controlled through temperature, humidity and the rate of air flow. The rate of drying must not be too high as this can result in differential shrinkage in the body as the outside dries and shrinks faster than the inside.
Click on the graphic to see the shrinkage process.
Drying generally takes place just under 100°C and can take up to 24 hours.
Another common method of forming is slip casting. Slip casting involves a slip, which is a suspension of clay particles and other materials in water. The slip is made and poured into a porous mould. The mould walls absorbs water from the clay, leaving a solid layer behind. Eventually the mould cavity is solid clay and the mould can be removed. This technique is known as solid casting.
Click on the left image to see a demonstration of solid casting.
Another slip casting technique is drain casting. The thickness of the solid at the mould wall is dependent on time. In drain casting, the slip is poured out at a given time when the walls have the desired thickness.
Click on the right image to see a demonstration of drain casting.