Copyright: Unregistered evaluation copy of HELLLP!


yesyesyesyesyesPyrometric Conespyroconeyesyes21/02/95


Table of Contents
Pyrometric Cones

Table of Contents

About Pyrometric Cones

°F Cone Chart

°C Cone Chart

Limits of Accuracy

Warner Instruments


Firing

Seger

Limit

Kiln

Orton

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About Pyrometric Cones
PYROMETRIC CONES

Firing instructions provided with ceramic materials, or in ceramics texts and magazine articles, frequently refer to cone numbers rather than temperatures, because the heat treating process involves both time and temperature.  Pyrometric cones are special formulations of ceramic material which are designed to mature at different extremes of applied heat, are therefore useful in gauging the progress of a firing.  The 'time vs temperature' relationship is reflected in the tables furnished herein.  As you can see, a "cone 6" firing can result from a variety of schedules ...

to 2194°F (1201°C) in 20.5 hours,

to 2232°F (1222°C) in 8.27 hours,

to 2291°F (1255°C) in 4.24 hours, ... etc.

    When firing with electronic temperature controllers, you must establish the LIMIT setting on the basis of the terminal firing rate (i.e., the rate of temperature change at the end of the firing), using the data presented in this table as a guide.

Example:  Firing to cone 6, you intend to approach the limit temperature at

a rate of 270°F (150°C) per hour.  So you turn to the cone charts,

find "Cone Number" 6 in the first column, then move your finger

across the page to the "270°F/HR" (or "150°C/HR") column, to

find the suggested LIMIT setting ... which is 2232°F (or 1222°C).

    This matter of rate vs limit setting naturally applies to the final few hundred degrees of the firing, and you must also consider the nature of the load ...  is the rate slow enough to assure a reasonable degree of temperature uniformity throughout just prior to shut-off?  On the other hand, if you're firing to a high temperature ...  say, over 2100°F ...  you might well expect that your kiln will not have enough heating capacity to keep up with the controller's 270°F/Hr ramp, so the "final approach" will occur at some slower, kiln dependent, rate.  Experience will help you decide how much to "fudge" on the limit setting to compensate for this "kiln lag".

OVERTIME OR OVER-TEMPERATURE - OVER-FIRED WARE!

    This is a simple, but often overlooked point ...  its important that you remember it.  You can see from the cone charts that firing is a matter of (1) temperature and (2) time.  Too much, or not enough, of either ...  and the results will be poor; perhaps a complete loss.

    Keep this in the back of your mind: if you come up with an over-fired load, it can just as well be the result of too much time, as too much temperature.


Limits of Accuracy
ACCURACY - TEMPERATURE STANDARDS

     Contrary to popular belief, pyrometric cones are not the last word in temperature-measuring

accuracy, and must not be used as standards.  As previously mentioned, cones mature as a

result of heat treating time and temperature.

     For example, a cone rated at 1850F will actually bend a few hundred degrees lower than that

point if held at the lower temperature for a sufficiently long period of time.

     Pyrometric cones are also subject to other factors which influence their maturity temperature.

Besides normal manufacturing tolerances, the mounting method used, the mounting position (angle)

and the moisture content of the cone (resulting from relative humidity unless special precautions are

taken) all effect the bending point. According to studies done several years ago by the National Bureau

of Standards, these factors introduce uncertainties as large as 54°F.  The accuracy of any other

measuring device should never be judged on the basis of pyrometric cones.


°F Cone Chart
TEMPERATURE EQUIVALENTS FOR ORTON STANDARD PYROMETRIC CONES

 (As Determined at the National Bureau of Standards)

	LARGE CONES	small
CONE NUMBER	Heating Rate in F/Hr	Color	Firing Stage	Customary Firing Application
	108F/Hr	270F/Hr	540F/Hr
		302		"black	free water boils out
		437		heat"	alpha to beta cristobalite inversion
		1022			alpha to beta quartz inversion
		1067
022	1085	1112	1165		dehydration
021	1116	1137	1189		90% complete
020	1157	1175	1231
019	1234	1261	1333	dull		overglaze colors
018	1285	1323	1386	red		enamels and gold
017	1341	1377	1443			ceramic decals
016	1407	1458	1517
015	1454	1479	1549			glass sagging
014	1533	1540	1596			chrome & red glaze
013	1596	1566	1615
012	1591	1623	1650	cherry
011	1627	1641	1680	red	most of	lustre glaze
010	1629	1641	1686		organic matter
09	1679	1693	1751		now burnt
08	1733	1751	1801	cherry	away	low firing lead &
07	1783	1803	1846	red to		fritted glazes
06	1816	1830	1873	orange	teracottas	porous biscuit-low
05	1888	1915	1944		mature	fire earthenware
04	1922	1940	2008	orange
03	1987	2014	2068	changing
02	2014	2048	2098	to
01	2043	2079	2152	yellow/	earthenware	industrial earthen
1	2077	2109	2154	orange	matures	ware, bisque and
2	2088	2124	2154			bone china glost
3	2106	2134	2185	yellow/
4	2134	2167	2208	orange	teracottas
5	2151	2185	2230	yellow to	melt, increasing
6	2194	2232	2291	lt. yellow	formation	semi-porcelain
7	2219	2264	2307		of beta type	salt glaze
8	2257	2305	2372	yellow	cristobalite	stoneware
9	2300	2336	2403	with white		bone china bisque
10	2345	2381	2426	tinge		& some porcelain
11	2361	2399	2437	intense		porcelain
12	2383	2419	2471	yellow-
13		2455		white
14		2491
15		2608

 199  1994  FireRight Controls/Warner Instruments                                                               ™The Edward Orton Jr Ceramic Foundation


°C Cone Chart
TEMPERATURE EQUIVALENTS FOR ORTON STANDARD PYROMETRIC CONES

 (As Determined at the National Bureau of Standards)

	LARGE CONES	small
CONE NUMBER	Heating Rate in C/Hr	Color	Firing Stage	Customary Firing Application
	60C/Hr	150C/Hr	300C/Hr
		150		"black	free water boils out
		225		heat"	alpha to beta cristobalite inversion
		550			alpha to beta quartz inversion
		575
022	585	600	630		dehydration
021	602	614	643		90% complete
020	625	635	666
019	668	683	723	dull		overglaze colors
018	696	717	752	red		enamels and gold
017	727	747	784			ceramic decals
016	764	792	825
015	790	804	843			glass sagging
014	834	838	870			chrome & red glaze
013	869	852	880
012	866	884	900	cherry
011	886	894	915	red	most of	lustre glaze
010	887	894	919		organic matter
09	915	923	955		now burnt
08	945	955	983	cherry	away	low firing lead &
07	973	984	1008	red to		fritted glazes
06	991	999	1023	orange	teracottas	porous biscuit-low
05	1031	1046	1062		mature	fire earthenware
04	1050	1060	1098	orange
03	1086	1101	1131	changing
02	1101	1120	1148	to
01	1117	1137	1178	yellow/	earthenware	industrial earthen
1	1136	1154	1179	orange	matures	ware, bisque and
2	1142	1162	1179			bone china glost
3	1152	1168	1196	yellow/
4	1168	1186	1209	orange	teracottas
5	1177	1196	1221	yellow to	melt, increasing
6	1201	1222	1255	lt yellow	formation	semi-porcelain
7	1215	1240	1264		of beta type	salt glaze
8	1236	1263	1300	yellow	cristobalite	stoneware
9	1260	1280	1317	with white		bone china bisque
10	1285	1305	1330	tinge		& some porcelain
11	1294	1315	1336	intense		porcelain
12	1306	1326	1355	yellow-
13		1346		white
14		1366
15		1431

 199  1994  FireRight Controls/Warner Instruments                                                                       ™The Edward Orton Jr Ceramic Foundation


Warner Instruments

FireRight Controls/Warner Instruments

1320 Fulton Street   Box 604

Grand Haven, Michigan 49417-0604   USA

Phone:  (616) 842-7658

FAX/BBS: (616) 842-1471

Warner Instruments manufactures FireRight   electronic temperature

control systems, for ceramic kilns and glass annealing furnaces (lehrs).

The FireRight bbs is available 24-hours every day, and offers a variety of

customer support information, in addition to a wide variety of general interest

conference areas and files.

If you have files or information related to the ceramics and glass arts which

you wish to share with your colleagues, please upload them here.  If you are

looking for information related to these activities, we invite you to call.

FireRight bbs is FREE.  All callers are given full access on the first call.


Firing
Firing, refers to the heat-treating process used in

ceramic work to convert soft clay shapes to a hardened

glass-like form, or to process glazes which are used to

provide the desired surface texture or color.  This usually

involves heating the piece up to a temperature somewhere

within the range of 1500°F to 2500°F over a specified

period of time.


Seger
The concept of monitoring the process of heat-treating ceramics by using small specially-

formulated cone-shaped clay pieces, originated in Germany.  Known abroad as Seger

Temperature Cones (named for their developer), and also sometimes referred to as the

sentinel pyrometer outside of the U.S., these devices have not changed much over several

decades of use.  Cones are actually shaped in the form of triangular pyramids (about 3-inches

high), and are composed of metallic and mineral substances which fuse at certain temperatures.

They are made in a series, each successive cone having a fusing temperture that differs slightly

from the one above or below it in the scale; that is, if the series were placed in a furnace and the temperature gradually raised, one cone after another would melt as its melting point was reached.

These cones are usually used in threes to determine the minimum and maximum exposure for a

given firing process, the lower cone giving warning that process is about to approach completion,

the middle cone being watched as the indicator of the desired firing results, and the upper cone

guarding the process from over-firing.


Limit
The firing process for ceramics is usually a simple

matter of increasing the temperature at a given rate

to a specified maximum value, known as the Limit

Temperature, then simply turning the kiln off, allowing

it to cool on its own.


Kiln
Ceramic kilns (pronounced kills - the n is silent), are

special purpose gas or electric furnaces specially designed

for firing ceramics.  Kilns range in size from, small enough

to contain only a tea cup, to large enough to accomodate

a train car.


Orton
The Edward Orton Jr Ceramics Foundation has always been

the recognized authority on,and premere producer of, pyrometric

cones in the United States, and sponsors continuing research

and development activities in this field.  If you would like to know

more about Orton Cones, write them at 6991 Old 3C Highway,

Westerville, OH 43081  Phone: (614) 895-2663  FAX: 895-5610.


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