IS 13360-6-22: Plastics - Methods of testing, Part 6: Thermal properties, Section 22: Determination of time-temperature limits after prolonged exposure to hear

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IS 13360-6-22 (2006): Plastics - Methods of testing, Part
6: Thermal properties, Section 22: Determination of
time-temperature limits after prolonged exposure to hear
[PCD 12: Plastics]
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IS 13360 (Part 6/See 22): 2006
ISO 2578:1993

Indian Standard
PLASTICS — METHODS OF TESTING
PART 6 THERMAL PROPERTIES
Section 22 Determination of Time-Temperature Limits After Prolonged Exposure to Heat
ICS 83.080.01

@ BIS 2006
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

September 2006 Price Group 7
Plastics Sectional Committee, PCD 12
NATIONAL FOREWORD
This Indian Standard (Part 6/See 22) which is identical with ISO 2578:1993 ‘Plastics — Determination
oftime-temperature limits after prolonged exposure to heat’ issued bythe International Organization for
Standardization (ISO) was adopted by the Bureau of Indian Standards on the recommendation of the
Plastics Sectional Committee and approval ofthe Petroleum, Coal and Related Products Division Council.
The text of ISO Standard has been approved as suitable for publication as an Indian Standard without
deviations. Certain conventions are, however, not-identical to those used in Indian Standards. Attention
is particularly drawn to the following:
a) Wherever the words ‘International Standard’ appear referring to this standard, they should be
read as ‘Indian Standard’.
b) Comma ( ,) has been used as adecimal marker while in Indian Standards, the current practice
is to use apoint ( .) as the decimal marker.
Inthis adopted standard, reference appears to certain International Standards-for which Indian Standards
also exist. The corresponding Indian Standards which are to be substituted in their places are given
below along with their degree of equivalence for the editions indicated:
International Standard Corresponding Indian Standard Degree of Equivalence
ISO 291 : 1997 Plastics — IS 196 : 1966 Atmospheric Technically Equivalent
Standard atmospheres for conditions for testing (revised)
conditioning and testing
IEC 60216-1 (1990)1) Guide for IS 8504 (Part 1) :1994 Guide for Identical
determination of thermal endurance determination of thermal ‘endurance
properties of electrical insulating properties of electrical insulating
materials — Part 1 : General materials: Part 1General guidelines
guidelines for ageing procedures for ageing procedures and evaluation
and evaluation of test results of test results (first revision)

IEC 60216-2 (1990)2) Guide for IS 8504 (Part 2) :1983 Guide for Technically Equivalent
determlnation of thermal endurance determination of thermal endurance
properties of electrical insulating properties of electrical insulating
materials — Part 2: Choice of the materials: Part 2 List of materials
test criteria and available tests
IEC 6021-6-3-1 (1990)3) Guide for IS 8504 (Part 3) :1994 Guide for &
determination of thermal endurance determination of thermal endurance
properties of electrical insulating properties of electrical insulating
materials — Part 3: Instructions materials: Part 3 Statistical methods
for calculating thermal endurance
characteristics — Section 1 :
Calculations using mean values of
normally distributed complete data
,
l}Revisedin2001.
2)Revisedin2005.
3)Revisedin2002.
( Continuedon thiticover)
IS 13360 (Part 8/Sac 22): 2008
ISO 2578:1993
Indian Standard
PLASTICS — METHODS OF TESTING
PART 6 THERMAL PROPERTIES
Section 22 Determination of Thne-Temperature Limits After Prolonged Exposure to Heat
1 scope cation, the editions indicated were valid. All standards
are subject to revision, and parties to agtiements
-based on this International Standard are encouraged
1.1 This International Standard specifies the princi-
to investigate the possibility of applyhg the most re-
ples and procedures for evaluating the thermal en-
cent editions of the standards indicated below.
durance propetiies of plastics exposed to elevated
Members of IEC and ISO maintain registers of cur-
temperature for long periods.
rently valid International -Standards.
1.2 The term thermal endurance is used here to re- ISO 291:1977, i%3tiCS — Standard atmospheres for
fer to tests made in air, excluding any other influence conditioning and testing.
or stress applied to the test specimens. Thermal en-
durance properties evaluated in different environ- IEC216-1:1990, Guide for the determination of ther-
ments and/or with different stresses applied to the mal +ndurance properties of eiectrkal insulating me-
test specimens require d“tierent test procedures. terials — Part 1: General guidelines for ageing
procedures and evaluation of test results.
1.3 In this International Standard, the study of the
thermal ageing of pfastics is based solely on the IEC216-2:1990, Guide for the determination of ther-
change in certain properties resulting from a period mal endurance properties of electrical insulating ma-
of exposure to elevated temperature. The properties terials — Part 2: Choice of the test criteria.
studied are always measured after the temperature
has returned to ambient. IEC216-3-1:1990, Guide for the determination of
thermal endurance properties of electrica/ insulating

The various properties of plastics change at various materials — Part3: Instructions for calculating thermal
rates on thermal ageing. To enable comparisons to be endurance characteristics — Section 1: Calculations
made of the thermal ageing of dfierent plastics, the using mean values of normally distributed comp/ete
criteria for judgement depend on the type of property data.
to be studied and its acceptable limiting value.
IEC 2-16-3-3:-, ‘~Guide for the determination of ther-
1.4 In the application of this standard it is assumed mal endurance properties of electrical insulating ma-
that apractically linear relationship exists between the terials — Part 3: Instructions for calculating thermal
logarithm of the time required to cause the predeter- endurance characteristics — Section 3: Calculations
mined property change and the reciprocal of the cor- for incomplete data.
responding absolute temperature (Arrhenius Law).
IEC21641:1990, Guide for the determir!ation of
F-orthe plastics tested, no transition, in particular a thermal endurance propetiies of electrhal nsulating
first-order transition, should occur in the temperature materials — Part 4: Ageing ovens — S~ction ?:
range under study. Single-chamber ovens.
2 Normative references IEC216-5:1990, Guide for the determination~of ther-
mal endurance propeflies of electrical iwwting me-
terials — Part 5: Guidelines for the apphcation of
The following standards contain provisions which,
thermal endurance characteristics.
through reference in this text, constitute provisions
of this International Standard. At the time of publi-
1) Tobepublished.[15B(B.C.)82]

1
IS 13360 (Part 6/See 22): 2006
ISO 2578: ~993
3 Definitions a mechanical, optical or electrical property) are deter-
mined as afunction of time.
For the purposes of this International Standard, the
The procedure is continued until the relevant thresh-
following definitions apply.
old value of that characteristic has been reached, re-
. sulting in the time to failure at that particular
3.I temperature index (lI): Number corresponding
temperature.
to the temperature, in degrees Celsius, derived from
the thermal endurance relationship at a given time Futiher specimens are exposed at at least two other
(normally 20000 h). temperatures and the variations in the relevant char-
acteristic determined. It is raoommended to heat-age
3.2 reiative temperature index (Rllh Temperature test specimens at three to four temperatures, and
index of a test material, obtained at the time which determine the time to failure for each of the tem-
corresponds to the known temperature index of a peratures.
reference material when both materials are subjected
to the same ageing and diagnostic procedures in a
comparative test.
4.2 Datarmindon of 11
3.3 halving intervai (HiC): Number corresponding
The times to failure are plotted versus the reciprocal
to the temperature interval, in degrees Celsius, which
expresses the halving of the time to end-point taken values of the exposure temperatures. The intersection
at the temperature of the TI or the RTI. of this curve with the chosen time limit (in general
20000 h)gives the temperature index sought.
HIC is a measure of the slope of the thermal endur-
ance graph. It is not constant, but varies with tem-
perature even when the thermal endurance
4.3 Useof correlationoodfkht
relationship is linear, In many practical cases, the error
arising from the use of MC in the temperature range
The reliability of the extrapolation of. the graph de
of interest remains within acceptable limits.
pends on obtaining an acoeptabia Arrhenius plot,
which may not be possible with materials showing
3.4 thermai enduranoe graph (Arrhenius graph):
behaviour related to a transition phenomenon in the
Graph in which the logarithm of time to reach a
chosen temperature range.
specified end-point in a thermal endurance test is
plotted versus the reciprocal thermodynamic (abso-
For this purpose the correlation coefficient r is csicu-
lute) test temperature.
Iated in accordance with annex B. If this calculation
results in a value smaller than 0,95 (for three test
3.5 threshoid vaiuo Value, corresponding to a per-
tem~eratwes; see also IEC216), an additional test at
centage of the initial value of the property under in- adifferent test temperature may improve the linearity

vestigation, at which the ageing tes t is stopped and
of data.

the time to failure is calculated.
NOTES
4.4 Determinationof Ml
1 The level of 50% is often used to determine the
thresholdvalue. For determination of RTI, the chosen reference plas-
tic, its thermal endurance and the method of deter-
2 If a minimum valueis requiredafter ageing,it maybe
mination are of central importance.
agreedbetweentheinterestedpartiesto usethisminimum
valueasthethresholdvalue,insteadof apercentageof the
The reference plastic shall be of the sametype asthe
initialvalue.
tested plastic, and have a history of satisfactory ser-
vice. It shall have a known temperature index for the
3.6 test-specimen faiiure timo Time required at
property and a-threshold value which are the same,
the exposure temperature for aspecimen to either fail
or at least reasonably similar to, those to be employed
the proof test or reach the threshold value of the
in the RTItest. The TI and HtC of the reference ma-
characteristic under investigation, whichever is
tefial should also be approximately the same as the
shorter.
values expected for the tested plastic.
Since processing conditions may significantly affect
4 Principle
the ageing characteristics of some materials, the
sampling, cutting of sheet from the supply roll, cutting
4.4 Determinationoftime to faiiure of anisotropic material in the same direction, mould-
ing, curing, preconditioning, -etc. shall be performed in
At a chosen temperature, the variations in the nu- the same manner for both materials, and the speci-

merical value of a chosen characteristic (for example, mens shall-betested in the same thickness.
2
IS 13360 (Part 6/Sac 22): 2006
ISO 2578:1993
5 Choice of test the relevant test specifications and to reduce this number.
However, it must be recognized that the precision of the
test result depends to a large extent on the number of
The test chosen shall relate to a characteristic which
specimens tested.
is likely to be of significance in practice and, wherever
. possible, use shall be made of test methods specified 5 Incontrast, whentheindividualresultsaretooscattered,
in International Standards. If the dimensions and/or anincreaseinthe numberof specimensmaybenecessary
form of the test specimens are altered by the heat inorder to obtain satisfacto~ precision.
treatment, then only test methods which are inde-
pendent of these effects maybe used. 6 It is advisable to make an approximate assessment, @y
means of preliminary tests, of the number and duration of
the ageing tests required.
6 Choice of end-point
8 Exposure temperatures
For the selection of the end-point, two factors shall
be agreed upon:
8.1 Test specimens shall be exposed at not less
a) the periid of time for which a time-temperature than three temperatures, covering a range adequate
limit shall be estimated; for general purposes, a to establish the time-temperature limit by extrap~
period of 20000 h is recommended; Iation with the required d=gree of accuracy. The low-
est exposure temperature shall be-chosen so that the
time taken to reach the threshold value is at least
NOTE3 Other times (shorteror longer than 20000 h) 5000 h. Similary, the highest temperature shall be
may be chosen if necessary. chosen sothat the time taken to reach the threshold
value is not shorter than 100 h. The lowest exposure
b) the acceptable threshold value of the chosen temperature shall not be more than .25 “C above the
characteristic; this threshold value depends on the anticipated T1.
conditions of use foreseen,
8.2 If the temperature limit sought is intended for a
time other than 20000 h (see clause 6, note 3), the
7 Test specimens
lowest exposure temperature shall be chosen so that
the time taken to reach the threshold value is at least
7.1 The dimensions and method of preparation of one-fourth of the time limit chosen for extrapolation.
the test specimens shall be in accordance with the
specifications given for the relevant test method. 8.3 Selection of adequate exposure temperatures
requires previously determined information on the
material under test. If such information is not avail-
7.2 For a criterion requiring a destructive test, the
able, exploratory tests may help in selecting exposure
minimum total number (n)of test specimens needed
depends on temperatures which are suitable for evaluating the
thermal endurance characteristics.
— the number a of test specimens required for one
test, according to the test specifications given for
9 Ageing ovens
the relevant test method;
For heat ageing, ovens shall be used that meet the
— the number b of tests necessary to determine the
requirements specified in IEC216-4, in particular with
end-point at one exposure temperature;
resDect to the temperature tolerances and ventilation
rates of air exchange.
— the number c of exposure temperatures;
— the number d of specimens needed for the initial 10 Procedure
test before heat ageing.
Thus the total number of specimens is: 10.1 In addition to the specimens to be exposed to
heat-ageing temperatures, an adequate number of
n=abc+d
test specimens shall be kept separately as a resewe
For a criterion requiring nondestructive testing, and
— for cases in which the accuracy requires heat
for each exposure temperature, in most cases agroup
of five test specimens is adequate. ageing at an additional temperature;
NOTES — as reference specimens,
4 When there is a large number of specimens to be They shall be stored in an appropriately controlled at-
tested, it maybe possibleincertaincasesto deviatefrom mosphere (see ISO 291).
3
IS 13360 (Part 6/See 22): 2006
ISO 2578:1993
10.2 Before the heat-egeing procedure is started, 10.5 Continue this procedure until the numerical
an initial test shall be made at room temperature with value of the characteristic under investigation reaches
the required number of specimens conditioned and the relevant threshold value.
tested in accordance with the chosen test method.
11 Evaluation of results
, Thermosetting materials shall be conditioned for 48 h
at the lowest exposure temperature of the range se-
11.1 For both destructive and nondestructive tests,
lected.
for each exposure temperature and for each heat-
NOTE7 If necessary, thermoplastic materials should be ageing period, the value of the chosen property is
annealed for 48 h at the lowest exposure temperature of plotted as afunction of the logarithm of the time (see
the range selected. figure 1).The point at which this graph intersects the
horizontal line representing the end-point criterion is
taken as the time tofailure.
10.3 Place the required number of specimens in
When applying a proof test, the times to failure shall
each of the ovens maintained at the selected tem-
be calculated as the mean values.~
peratures.
If there is a risk of cross-contamination between test 11.2 The calculation of the thermal endurance curve
specimens originating from different plastics, use is based on these times to failures and the respective
exposure temperatures. If mean values are used, the
separate ovens for each material.
logarithmic mean represents the time to failure.
11.3 Calculate a first-order regression line in ac-
10.4 At the end of each heat-egeing period (see
cordance with annex A,
note8), the required number of test specimens is re-
moved from the oven and conditioned, if necessa~,
11.4 Plot the times to failure versus exposure tem-
under the appropriately controlled atmosphere (see
peratures on graph paper having a logarithmic time
ISO 291). The test, in accordance with the selected
scale as the ordinate and an abscissa based on the
test criterion, shall be carried out at room tempera-
reciprocal of the absolute temperature but showing
ture.
the correlated values in degrees Celsius. The first-
order regression line is drawn through the points
NOTE8 After the first week, during which the number
plotted on the graph, which thus represents the ther-
of determinations of the characteristic under investigation
can vary depending on the material under test, the test du- mal endurance of the material under test. An example
rations are generally selected in accordance with annex C. is given in figure 2.

2) See IEC216-1:1990, subclause 11.1.
4
IS 13360 (Patt 6/See 22): 2006
ISO 2578:1993

0-++
0 I 2I0 1 I 5I0 1 I 1 11I00 I 20I0 I I 50I0 I I I 110I00 1 20I00 1 150I00I I I 1I00I00
Agelngtime,h
Figure 1 — Determination of the time to reach the end-point at each temperature — Property variation
(According to IEC216-1)

5