In all ceramic manufacturing factories the usual problem related to drying occurs due to differential drying and hence differential shrinkage. This happens because the drying speed at the surface becomes high and hence the water flowing through the capillaries can not keep up with loss from the surface by evaporation. This surface dries out completely […]

When drying takes place, water evaporates into the air leaving behind the dissolved salts and the finest clay particles carried to the surface. The rate of drying does not depend on the pressure of the ambient air but only on its capacity for taking up water vapour. Towards the end of drying the pressure of […]

Drying seems like a very simple process however it is not so, in reality it is more complex in nature. This is due to the capillary nature of clay bodies. Evaporation of water from the clay body is accompanied by a cooling effect. As long as there is water the clay feels cold however after […]

The three clear cut stages of drying:
1. Water leaves the pore first enabling the clay platelets to move closer together and the volume of mass is reduced by that of the water given up. The shrinkage is proportional to the water given up, the clay particles have come closer together but no air has yet […]

Controlling of shrinkage is one of the difficult tasks for clay technologists. This can be readily understood by assuming that the water present in clay exists in three different forms:
Water filling the spaces between the particles
Water envelops surrounding the individual particles
Water adsorbed over the whole external surface of the particles
During drying water leaves the clay […]

The surface tension of clay slips leads to an unpleasant de-mixing effect known as Casting Strike. While casting the stream of slip first strikes the mould and the stream of slip becomes surrounded with a water membrane containing the finest clay particles. Wherever this impinges on the mould water is removed and the fine clay […]

Longer casting time and higher slip density results in the reduction of water content in the cast piece. The water content of the cast produced is not affected by ageing the slip.
The formation of the cast in a plaster mould may be regarded as due to filtration of water out of the slip, the suctional […]

It is found that the casting rejections recycled hinder fluidization due to the presence of gypsum contamination arising out of plaster moulds which acts as the source of Ca2+ and SO42- ions. SO42- ions promotes flocculation. They also induce thixotropy in the slip which reduces casting time. But the cast is of flabby nature due […]

Thixotrophy can be measured by measuring the viscosity before and after standing. Thixotrophy for most of the clays and bodies normally will be very high when we use Na2CO3 and with Sodium Silicate it will be very less. To obtain better casts of the desired thickness and density, the casting process needs very steady conditions […]

Humus increases the surface tension of water and the mutual repulsion of the clay particles. The fluidization behaviour of clays cannot be judged only on their humus content. Clays with a low content of sodium and humus are difficult to fluidize.
The thickening of clay slips due to excess alkali is caused by the penetration of […]