Kilns

Posted in Uncategorized on 10/13/2009 01:09 pm by admin

Kilns are thermally insulated chambers or ovens that are controlled to very high temperatures. They are used to harden, burn or dry materials. Specific uses include:

Brick Oven Kiln
Drying green lumber
Drying firewood
Cremation
Firing materials like clay to form ceramics
Heating limestone with clay to make cement
Tobacco leave drying
Drying malted barley for brewing
Drying hops for brewing (known as a hop kiln or oast house)
Smelting ore to extract metal
Heating wood to produce charcoal
Fusing metallic oxide paints to the surface of glass

Kilns for Ceramics
Kilns are a vital part of the manufacturing process of all ceramics. During the heating process, chemical and physical reactions occur which cause the material to be permanently altered.

In the case of pottery, clay is shaped, dried and then fired in a kiln. The final characteristics are determined by the composition and preparation of the clay body, the temperature at which it is fired, and by the glazes used.

New kilns
Modern kilns often have sophisticated electrical systems to control the firing temperatures. Pyrometric devices have been used since 1000 AD to provide visual indication of the firing regime.

Clay is combined with other minerals to create a clay body that is workable. Part of the firing process includes sintering. This process heats the clay until the particles partially melt and flow together. Through firing, the pores are reduced in size, causing the material to shrink slightly. This crystalline material is a comprised of predominantly silicon and aluminium oxides, which makes it very hard and strong, but also brittle.