1083ch4_4-cones, crayons, labels, paints, and pellets.pdf

7/22/2019 1083ch4_4-Cones, Crayons, Labels, Paints, and Pellets.pdf

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4.4 Cones, Crayons, Labels, Paints, and Pellets

T. J. CLAGGETT, R. W. WORRALL (1969, 1982) B. G. LIPTK (1995)

S. EDVI, J. E. JAMISON (2003)

Temperature Settings: Cones are numbered as inTable 4.4bwith each number corresponding to an approx-

imate setting. Crayons and paints are usually rated with a combination of temperature

and time, meaning that a color change is expected to occur if a particular temperature

is held for a particular time period.

Phase Change Types: Reversible and nonreversible temperature-indicating labels, strips, and buttons

Multi-temperature and Mylar liquid crystal strips and sheetsCrayons

Pellets

Paints or lacquers

Temperature Ranges: Cones cover a range between 1100 and 3650F (593 and 2010C)Reversible liquid crystal strips: range between 20 and 194F (30 and 90C)Nonreversible labels with 4 temperatures on each label: range between 100 and 500F

(38 and 260C)Reversible liquid crystal Mylar sheets: range between 68 and 113F (20 and 45C)Crayons, pellets, and paints: range between 100 and 2500F (39 and 1371C)

Costs: $3 to $6 for a box of 50 cones, $0.50 to $1.50 per plug

Reversible liquid crystal strips (seven temperature ranges): package of 10 is $12;package of 30 is $33

Nonreversible labels, monitors, and buttons: package of 10 is $13 to $55; package of

30 is $37 to $55

Reversible liquid crystal Mylar sheets: 12 in. 12 in. sheets =$22, 6 sheets of 6 in. 12 in. sheets is $76; 6 sheets, one of each temperature range is $52

Crayons: $9 each to $55 for a 10-crayon set

Pellets: $11 per tube of 20 pellets

Paints/lacquers: 2 oz bottle is $11, 1 pt is $60; thinners: 2 oz bottle is $4, 1 pt is $13

Applications: Labels: machinery, equipment, electrical parts, electronic assemblies, aeronautical,

heating, ventilation, and air conditioning (HVAC), and appliances

Crayons: welding, forging, heat-treating, and accessible work pieces

Pellets: furnace temperaturePaints: smooth glass, polished metals, rubber, and fabrics

Inaccuracy: Indication is affected by speed of heat-up and by time spent at target temperature;

usual error is about 5F (3C) for cones and about 10 to 20F (5 to 10C) for crayons,pellets, and paints. The error of most crayons, pellets, and paints is 1% of their rating.

Liquid crystal strips can detect skin temperatures within 1F (0.5C).

Partial List of Suppliers: Biosynergy Inc., a Div. of American Clinical Laboratory (ACL) (freeze-thaw indicator)

(www.iscpubs.com/pubs/prodhilite)

Electronic Development Labs Inc. (EDL) (cones and crayons) (www.edl-inc.com)

Orton Ceramic Foundation (cones) (www.ortonceramic.com)

Hub Material Co. Inc. (cones and crayons) (www.hubmaterial.com)

Korthals (www.korthals.nl)

2003 by Bla Liptk
http://www.iscpubs.com/http://www.edl-inc.com/http://www.ortonceramic.com/http://www.hubmaterial.com/http://www.korthals.nl/http://www.korthals.nl/http://www.hubmaterial.com/http://www.ortonceramic.com/http://www.edl-inc.com/http://www.iscpubs.com/


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600 Temperature Measurement

LA-Co/Markal Co. (stick-ons) (www.laco.com)

Omega Engineering, Inc. (crayons, pellets, labels, paints) (www.omega.com)

Tempil, a Div. of Illinois Tool Works Inc. (ITW) (crayons, paints)

(www.tempil.com)

INTRODUCTION

A number of temperature-related physical changes have been

used to produce simple thermometers. Crayons, pellets, and

paint marks on heated work-pieces, cones, or pellets placed in

furnaces change from solid to liquid when their melting point

is reached. Paints and heat-sensitive labels change their color,

while luminescent materials change their brightness. Liquid cho-

lesteric crystals detect skin temperature, and liquid crystal strips

are ideal for motors, transformers, relays, and electronic parts.

For centuries, manually operated furnaces have been

temperature-controlled by the operators placing a heat-sen-

sitive object inside the furnace and observing the status of

that indicator through a peephole. The most easily observedphysical changes were found to be changes in color or melt-

ing. Pyrometric cones have been used as temperature indica-

tors and are still used as endpoint indicators in such batch

processes as firing in pottery furnaces. They can be small,

expendable, plugs, chips, or geometrically shaped objects

whose purpose is to accompany the products through a heat-

ing cycle. The physical or metallurgical changes that occur

indicate the temperature reached in the process.

COLOR INDICATORS

Color indicators are a class of sensors that have the property

of changing their original color when a certain temperature

is reached. The change is distinct, not just an alteration in

shade. For instance, an indicator may change from yellow to

gray or from light blue to light brown. Some can go through

several color changes at different temperatures.

Paints and Pellets

Paints and pellets are familiar forms of these indicators that

are applied directly to a solid object either when it is cold and

about to be heated, or when it is already hot. Some indicatorscan determine the temperature of solid objects immersed in

oil. They are not recommended for use in hot gases.

Temperature is indicated by a chemical reaction, where

a molecule of a gas such as ammonia, carbon dioxide, or

water vapor is driven off the basic stock (colorful salts of

metals like nickel, cobalt, or chromium), changing its color.

The change is usually permanent after the object cools down.

An exception occurs when the gas is water vapor; the indi-

cator may slowly reabsorb this gas from the air and revert to

the original color.

Change in color of these types of indicators is not only

a function of temperature but also of time. For this reason,

the immediate past temperature history of the indicator will

influence the exact point at which it will change color. Theindicators are usually rated for a specific temperature over a

certain time period, for instance, 140F (60C) in 30 min.This means that if held at a constant 140F the color changewill occur in 30 min. If the color change occurs in less than

30 min, the average temperature is higher than 140F, andvice versa. On such an indicator, if the temperature does not

exceed 130F (54C), the change will never occur becausethe indicator is stable below this temperature.

Crayons

Figure 4.4a shows typical time-temperature relationshipsfor two different crayons. In the examples shown, the tem-

perature at which color change occurs is quite critical when

exposure time is short. For lower soakout temperatures, thechangeover will occur in a longer time.

Flatter curves than those shown are possible where

changeover will occur within a few seconds after operatingtemperature is reached, or it will not occur at all.

Many different temperature ratings are available. They

can be obtained in a series for every few degrees to themaximum offered (about 2500F, or 1371C). This class ofindicators is quite inexpensive and is used in industry where

only an endpoint is needed and someone can be present towatch for or interpret the results. A disadvantage of these

sensors is that the material adheres tightly to the object onwhich it is placed and presents a problem if it must be

removed later.

FIG. 4.4a

Time-temperature relationship for color indicators.

With Temperature Held ConstantColor Change Takes Place inTime Shown by Curve

Crayon#1

Crayon#2

Time

F

ahrenheit(Celsius)

1Sec

10Sec

1Min

10Min

1Hr

10Hr

1Day

250(121)

300(149)

350(177)

400

(204)

450(232)

2003 by Bla Liptk
http://www.laco.com/http://www.laco.com/http://www.omega.com/http://www.tempil.com/http://www.tempil.com/http://www.omega.com/http://www.laco.com/


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4.4 Cones, Crayons, Labels, Paints, and Pellets 601

PYROMETRIC CONES

The German ceramist Herman Seger invented the first pyro-

metric cone in 1886.1The individual cones look like truncated

pyramids. The numbering of the different cones available on

the market and the temperatures at which they melt are givenin Table 4.4b. The cone melting temperatures listed in the

table are based on a heat-up rate of 170C/h. If the heat-uprate is slower, the cones bend at slightly lower temperatures;

if it is faster, it will take a little higher temperature to bend

the cones as shown in Table 4.4c.Because the pyrometric cone measures the effects of both

temperature and the length of firing time, it acts as a heat

integratora function that cannot be easily reproduced by

thermocouples or other electronic-type pyrometers. For thisreason, the ceramic industry continues to use cones, in addi-

tion to recording pyrometers, even in its most modern kilns.

The Ceramics Industry

The indicator material is generally quite similar to the sub-

stance of the work under test. Pyrometric cones are actually

composed of ceramic materials very carefully blended to

soften at a certain temperature. The slender cone is slightly

tilted from the vertical; when its softening point is reached,

the tip bends over and may actually touch the base. This

action can be watched through the window of the firing

furnace, or its condition can be studied after cooling. Obser-

vation of a fired cone will show the experienced operator if

the furnace atmosphere was oxidizing, reducing, or carbur-

izing. If the latter has taken place, the cone will have formed

a shell less dense than the interior. Presumably the work will

have taken on the same characteristic.

The cones are set in a plaque of fire-clay (called a cone pat)close together and tipped at about 8 degrees from the vertical

toward the cone that is expected to bend first. The cone pat

is located in front of the peephole where the operator (or

a closed-circuit TV camera) can observe its status. Usually

three cones are placed on a pat: (1) the controlling target

cone is in the center, (2) a cone that melts at a lower

temperature is in front of it, and (3) one that melts at a

higher temperature is behind it. Figure 4.4dillustrates the

visual appearance of a cone pat throughout a batch that

was fired to a #4 cone target, corresponding to 2174F(1190C). The softening points can be selected very accu-

rately, and accuracies of 2 to 5F (1 to 3C) can be obtained.

TABLE 4.4b

The Numbering of Pyrometric Cones2,3

Cone Centigrade Fahrenheit

Color

of Fire Cone Centigrade Fahrenheit

Color

of Fire

15 1435 2615 07 990 1814

14 1400 2552 08 950 1742

13 1350 2462 09 930 1706 orange

12 1335 2435 010 905 1661

11 1325 2417 white 011 895 1643 cherryred

10 1305 2381 012 875 1607

9 1285 2345 013 860 1580

8 1260 2300 014 830 1526

7 1250 2282 015 805 1481

6 1230 2246 016 795 1463

5 1205 2201 017 770 1418

4 1190 2174 018 720 1328 dull

red3 1170 2138 019 660 1220

2 1165 2129 020 650 1202

1 1160 2120 021 615 1139

01 1145 2093 yellow 022 605 1121

02 1125 2057

03 1115 2039

04 1060 1940

05 1040 1904

06 1015 1859

2003 by Bla Liptk


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602 Temperature Measurement

Bar and Hole Indicators

As an alternate to cones, the indicator may take the shape of

a long cylindrical bar. The bars are supported at their ends

with axes horizontal. On temperature rise they soften and sag

at the middle under gravity. The deformation serves as ameasure of temperature.

Another group of indicators operates by shrinkage rather

than deformation. After removal from the furnace the diameter

of a hole in the indicator, or perhaps the indicators length, ismeasured and compared with the original dimension.

Like color indicators, pyrometric ceramics should not

be considered exact temperature measuring devices. Thefusion, bending, and/or shrinking that they undergo is a time-

temperature relationship and, as such, it is only useful to

determine the end point of the specific job. This property is

frequently more important than an exact measurement of theinstantaneous temperature. The use of this type of indicator

may almost be considered an art.

While pyrometer cones are not well suited automatic

process control, they are inexpensive and valuable quality

TABLE 4.4c

The Melting Temperatures of Various Cone Types and Cone Numbers That Can

Be Expected at Different Heating Rates4

Cone Type: Heating

Rate: Cone Number

Large

108F/hRegular

270F/h

Self-Supporting Reg.Small Reg.

540F/h108F/h 270F/h

022021

020

10741105

1148

10921132

1173

10871112

1159

10941143

1180

11571195

1227

019

018

017

1240

1306

1348

1265

1337

1386

1243

1314

1353

1267

1341

1391

1314

1391

1445

016

015

014

1407

1449

1485

1443

1485

1528

1411

1452

1488

1445

1488

1531

1517

1549

1616

013

012

011

1539

1571

1603

1578

1587

1623

1542

1575

1607

1582

1591

1627

1638

1652

1684

01009

08

16291679

1733

16411693

1751

16321683

1737

16451597

1755

16861751

1801

07

06

05

1783

1816

1888

1803

1830

1915

1787

1819

1891

1807

1834

1918

1846

1873

1944

04

03

02

1922

1987

2014

1940

2014

2048

1926

1990

2017

1944

2017

2052

2008

2068

2098

01

1

2

2043

2077

2088

2079

2109

2124

2046

2080

2091

2082

2113

2127

2152

2154

2154

3

4

5

2106

2134

2151

2134

2167

2185

2109

2142

2165

2138

2169

2199

2185

2208

2230

6

7

8

2194

2219

2257

2232

2264

2305

2199

2228

2273

2232

2273

2314

2291

2307

2372

9

10

11

2300

2345

2351

2335

2381

2399

2300

2345

2361

2336

2381

2399

2403

2426

2437

12

13

2383

2410

2419

2455

2383

2428

2419

2458

2471

2471

2003 by Bla Liptk


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4.4 Cones, Crayons, Labels, Paints, and Pellets 603

control tools in guaranteeing repeatable qualities of ceramic

and similar batch products from kilns and furnaces.

ENGINE TEST RESEARCH

An entirely different material, used in a similar manner, isthe metal test plug. This small device can tell temperature bya change in hardness that results from the heat treatment it

has received. One use is to have it located carefully in an

operating engine, in an otherwise inaccessible spot, where it

will respond to the temperatures that occur during operation.

When the test is over the plug is removed and carefullyanalyzed to determine the change in hardness along the hor-

izontal axis.

Time is again a factor, but metal responds much faster

than ceramic material. Exposures of less than 1 s duration

can be detected. Advantages of this class of temperature

sensors are their relative economy and being able to bedesigned for very specific purposes. Their shortcomings are

self evident.

References

1. Rhodes, D., Kilns Design, Construction and Operation,Radnor, PA:

Chilton, 1968.

2. Kenny, J.B., Pottery Making, Radnor, PA: Chilton, 1974.

3. Temperature-Sensitive Paints, Crayons,Measurements and Control,

December 1991.

4. Orton Ceramic Foundation, Cone Chart, Westerville, OH, 2001.

Bibliography

Adler, C.B., Reliability Aspects of Temperature Measurement, Instrumen-

tation, Systems, and Automation Society Conference, Chicago, 2002.

Bluestein, I., Understanding Contact Temperature Sensors, Sensors,Octo-

ber 2001.

Hormuth, G.A., Ways to Measure Temperature, Control Engineering,

Reprint No. 948, 1971.

Plumb, H. H., Temperature: Its Measure and Control in Science and Indus-

try, Vol. 4, 5th Symposium on Temperature, National Bureau of Stan-

dards, American Institute of Physics, Instrumentation, Systems, and

Automation Society, Pittsburgh, PA, 1972.Temperature-Sensitive Paints, Crayons, Measurements and Control,

December 1991.

Weiss, M., Color Analysis for Process Control, Control,June 1998.

FIG. 4.4d

This is the appearance of the cones at different times during a batch which has a target temperature set by Cone #4.2,3

Start Nearing Setpoint Done

5 4 35 4 3

5 4

2003 by Bla Liptk

1083ch4_4-cones, crayons, labels, paints, and pellets.pdf

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