Pyrometric cone
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Pyrometric cones are
pyrometric device Pyrometric devices gauge heatwork (the combined effect of both time and temperature) when firing materials inside a kiln. Pyrometric devices do not measure temperature, but can report ''temperature equivalents''. In principle, a pyrometric device r ...
s that are used to gauge
heatwork Heatwork is the combined effect of temperature and time. It is important to several industries: *Ceramics *Glass and metal annealing *Metal heat treating Pyrometric devices can be used to gauge heat work as they deform or contract due to heatwork ...
during the firing of
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
materials. The cones, often used in sets of three, are positioned in a
kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...
with the wares to be fired and provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature. Thus, pyrometric cones give a ''temperature equivalent''; they are not simple temperature-measuring devices.


Definition

The pyrometric cone is "A pyramid with a triangular base and of a defined shape and size; the "cone" is shaped from a carefully proportioned and uniformly mixed batch of ceramic materials so that when it is heated under stated conditions, it will bend due to softening, the tip of the cone becoming level with the base at a definitive temperature. Pyrometric cones are made in series, the temperature interval between the successive cones usually being 20 degrees Celsius. The best known series are Seger Cones (Germany), Orton Cones (USA) and Staffordshire Cones (UK)."


Usage

For some products, such as porcelain and lead-free glazes, it can be advantageous to fire within a two-cone range. The three-cone system can be used to determine temperature uniformity and to check the performance of an electronic controller. The three-cone system consists of three consecutively numbered cones: * Guide cone – one cone number cooler than firing cone. * Firing cone – the cone recommended by manufacturer of glaze, slip, etc. * Guard cone – one cone number hotter than firing cone. Additionally, most kilns have temperature differences from top to bottom. The amount of difference depends on the design of the kiln, the age of the heating elements, the load distribution in the kiln, and the cone number to which the kiln is fired. Usually, kilns have a greater temperature difference at cooler cone numbers. Cones should be used on the lower, middle and top shelves to determine how much difference exists during firing. This will aid in the way the kiln is loaded and fired to reduce the difference. Downdraft venting will also even out temperatures variance. Both temperature and time and sometimes atmosphere affect the final bending position of a cone. Temperature is the predominant variable. The temperature is referred to as an equivalent temperature, since actual firing conditions may vary somewhat from those in which the cones were originally standardized. Observation of cone bending is used to determine when a kiln has reached a desired state. Additionally, small cones or bars can be arranged to mechanically trigger kiln controls when the temperature rises enough for them to deform. Precise, consistent placement of large and small cones must be followed to ensure the proper temperature equivalent is being reached. Every effort needs to be made to always have the cone inclined at 8° from the vertical. Large cones must be mounted 2 inches above the plaque and small cones mounted 15/16 inches. With the cones having their own base, "self-supporting cones" eliminate errors with their mounting.


Temperature ranges

The following temperature equivalents for pyrometric cones were retrieved from references in the
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section.


Control of variability

Pyrometric cones are sensitive measuring devices and it is important to users that they should remain consistent in the way that they react to heating. Cone manufacturers follow procedures to control variability (within batches and between batches) to ensure that cones of a given grade remain consistent in their properties over long periods. A number of national standards and an
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
standard have been published regarding pyrometric cones. Even though cones from different manufacturers can have relatively similar numbering systems, they are not identical in their characteristics. If a change is made from one manufacturer to another, then allowances for the differences can sometimes be necessary.


History

In 1782,
Josiah Wedgwood Josiah Wedgwood (12 July 1730 – 3 January 1795) was an English potter, entrepreneur and abolitionist. Founding the Wedgwood company in 1759, he developed improved pottery bodies by systematic experimentation, and was the leader in the indus ...
created accurately scaled pyrometric beads, which led him to be elected a fellow of the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
. The modern form of the pyrometric cone was developed by Hermann Seger and first used to control the firing of porcelain wares at the
Royal Porcelain Factory, Berlin The Royal Porcelain Factory in Berlin (german: Königliche Porzellan-Manufaktur Berlin, abbreviated as KPM), also known as the Royal Porcelain Manufactory Berlin and whose products are generally called Berlin porcelain, was founded in 1763 by Kin ...
(''Königliche Porzellanmanufaktur'', in 1886, where Seger was director. ''Seger cones'' are to this day made by a small number of companies and the term is often used as a synonym for ''pyrometric cones''. The ''Standard Pyrometric Cone Company'' was founded in Columbus, Ohio, by Edward J. Orton, Jr. in 1896 to manufacture pyrometric cones, and following his death a charitable trust established to operate the company, which is known Edward Orton Jr. Ceramic Foundation, or
Orton Ceramic Foundation The roots of the Orton Ceramic Foundation date back to the establishment of the "Standard Pyrometric Cone Company" in 1896 by Edward J. Orton, Jr. In 1894, he was appointed the first Chairman of the Ceramic Engineering Department at Ohio State Un ...
.


Ceramic art

A biennial ceramic art exhibition for small work, the Orton Cone Box Show, takes the Orton Cone company's pyrometric cone box as the size constraint for submissions.


Notes


References

* Hamer, Frank and Hamer, Janet (1991). ''The Potter's Dictionary of Materials and Techniques.'' Third edition. A & C Black Publishers, Limited, London, England. .


External links


Temperature equivalents table Nimra



Temperature equivalents table Orton Celsius

Temperature Equivalents and Description of Orton Cones up to Cone 14


{{DEFAULTSORT:Pyrometric Cone Pottery Temperature