Clay firing Strength

Plastic fire clays have a composition similar to china and ball clays, except for the elevated Fe203 and Ti02 contents. Because of their composition, plastic fire clays have similar plasticity, dried strength, and fired strength when compared with china clays. Plastic fire clays range in color from gray to red or even black in the raw state. Like other fire clays, plastic fire clays produce buff-colored bodies when fired. 

Ball Clay Traditional ceramics Plasticity, fired strength... 

After drying, the bricks ate put into a kiln where the temperature is raised slowly to between 870 and 1316°C or higher depending on the temperature needed to fuse the clay. With the clay particles pattiaHy melted and fused together, the brick is a ceramic material with exceHent strength and fire resistance. 

Clays have plate-like molecules with charges on their surfaces (Chapter 16). The charges draw water into the clay as a thin lubricating layer between the plates. With the right moisture content, clays are plastie they can be moulded, extruded, turned or carved. But when they are dried, they have sufficient strength to be handled and stacked in kilns for firing. 

In slip easting a thin slurry, or suspension, of clay in water is poured into a porous mould. Water is absorbed into the mould wall, causing a layer of clay to form and adhere to it. The excess slurry is tipped out of the mould and the slip-cast shell, now dry enough to have strength, is taken out and fired. The process allows intricate shapes (like plates, cups, vases) to be made quickly and accurately. 

This depends very largely on the composition of the body and the temperature to which it is fired. The addition of a clay grog will normally reduce the tensile strength but the degree of reduction depends on the proportion used, the grain-size distribution of the grog, and the particle shape. The... 

Clays used in foundries include hydrous alumina silicates, known as bentonites. Their properties provide cohesion and plasticity in the green state and also high strength when dried. There are three clays that are commonly used in foundries western bentonite [sodium bentonite, burnout point 1290°C (2350°F)], southern bentonite [calcium bentonite, burnout point 1065°C (1950°F)], and fire clay [kaolinite, burnout point 1425°C (2600°F)]. 

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