Kiln

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Image:Charcoal Kilns, California.JPG Image:Kiln.jpg Image:Hop kiln.png A kiln is a thermally insulated chambers or oven in which a controlled temperature regime is produced. Kilns are used for hardening, burning, or drying materials. Kilns have been used for converting wood into charcoal or to dry green lumber so that the lumber can be used immediately. A variety of wood dry kilns exist today. Some modern lumber kilns are also partially depressurized to speed the drying process and reduce fuel usage. Kilns are also used for cremation (at high temperature) and drying of tobacco leaves (at low temperature).

A kiln is required to come to a controlled temperature, often very high, and so the design of the ovens normally focuses on insulation, and the ability to add fuel over a course of time. Care must be taken not to heat the kiln too rapidly or to too high a temperature.

Ceramic or Pottery kilns

Pottery, clay that is chemically altered and permanently hardened by firing in a kiln. The nature and type of pottery, or ceramics (Greek keramos, “potter's clay”), is determined by the composition of the clay and the way it is prepared; the temperature at which it is fired; and the glazes used.

Kilns are used to transform a clay based article into a ceramic material. Satisfactory firing converts a relatively weak and porous material consisting of innumerable particles into a strong, single mass composed on a glassy phase interspersed with pores and crystalline material. This crystalline material is a matrix of silica and alumina forms, and results in a materials that is hard and durable. This process is simply referred to as "firing." Clays contain aluminium and magnesium silicates which will change under high temperatures leaving oxides of aluminium, magnesium and silica.

Clay kiln technology is very old. The development of the kiln from a simple earthen trench filled with pots and fuel (pit firing) happened in several simple stages. Heat was conserved more efficiently around pots by building a firing chamber, baffles and a stoking hole. A chimney stack improves the draw of the kiln, and uses fuel more completely. Early examples of kilns found in the United Kingdom include those made for the making of roof-tiles during the Roman occupation. These kilns were built up the side of a slope, such that a fire could be lit at the bottom and the heat would rise up into the kiln. The Asian anagama kiln has been used since medieval times and is the oldest style of kiln in Japan. This kiln usually consists of one long firing chamber, pierced with smaller stacking ports on one side, with a firebox at one end and a flue at the other. Firing time can vary from one day to several weeks. Traditional anagama kilns are also built on a slope to allow for a better draft.

Oval Design

The oval kiln design allows for a more effective heating and a larger volume. The design was invented by Alan Williams of Dayton, Ohio. Popularized by Vulcan Kilns, it is now widely used by most manufacturers.

See also : Limekiln

Reference

• Hamer, Frank and Janet. The Potter's Dictionary of Materials and Techniques. A & C Black Publishers, Limited, London, England, Third Edition 1991. ISBN 0-8122-3112-0.de:Brennofen