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To dry green lumber so that the lumber can be used immediately; Drying wood for use as firewood; Heating wood to the point of pyrolysis to produce charcoal; For annealing, fusing and deforming glass; For cremation (at high temperature); Drying of tobacco leaves; Firing of certain materials to form ceramic materials; Drying malted barley for brewing;
Ceramic kilnsKilns are an essential part of the manufacture of all ceramics, which, by definition, require heat treatment, often at high temperature. During this process, chemical and physical reactions occur which cause the material to be permanently altered. In the case of pottery, clay materials are 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 that may be used. While modern kilns often have sophisticated electrical systems to control the firing temperatures, pyrometric devices have been used to provide visual indication of the firing regime since around 1000 AD. Clay consists of fine-grained particles, that are relatively weak and porous. Part of the firing process includes sintering. This process heats the clay until the particles partially melt and flow together, creating a strong, single mass, composed of a glassy phase interspersed with pores and crystalline material. Through firing, the pores are reduced in size, causing the material to shrink slightly. This crystalline material is a matrix of predominantly silicon and aluminium oxides, and is very hard and strong, although usually somewhat brittle.
Types of KilnsIn the broadest terms there are two types of kiln, both sharing the same basic characteristics of being an insulated box with controlled inner temperature and atmosphere. Intermittent – The ware to be fired, is loaded into the kiln. The kiln is sealed and the internal temperature increased according to a schedule. After the firing process is complete, both the kiln and ware are cooled. Continuous, or sometimes called Tunnel. These are long structures in which only the central portion is directly heated. From the cool entrance, ware is slowly transported through the kiln, and its temperature is increased steadily as it approaches the central, hottest part of the kiln. From there, its transportation continues and the temperature is reduced until it exits the kiln at near room temperature. A specialty type of kiln, common in tableware and tile manufacture, is the Roller-hearth Kiln, in which ware placed on bats is carried through the kiln on rollers.
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