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IS0
I NT ERN AT I ON A L O R G A N I Z AT 1 ON FOR STAN DARD I Z AT 1 ON
IS0 RECOMMENDATION
R 188
ACCELERATED AGEING OR SIMULATED SERVICE TESTS
ON VULCANIZED NATURAL OR SYNTHETIC RUBBERS
1st EDITION
February 1961
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations
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BRIEF HISTORY
The IS0 Recommendation R 188, Accelerated Ageing or Simulated Service Tests on
Vulcanized Natural or Synthetic Rubbers, was drawn up by Technical Committee ISO/TC 45,
Rubber, the Secretariat of which is held by the British Standards Institution (B.S.I.).
Work on this matter which the Technical Committee had begun since 1948, came to an
end in 1957, with the adoption of a proposal as a Draft IS0 Recommendation.
On 17 July 1957, the Draft IS0 Recommendation (No. 171) was distributed to all the
IS0 Member Bodies and was approved by the following Member Bodies:
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Australia Hung a r y Romania
Spain
Austria India
Ireland Sweden
Burma
Italy Switzerland
Canada
Czechoslovakia Japan Union of South Africa
Denmark New Zealand United Kingdom
Finland Pakistan U.S.A.
Poland U.S.S.R.
Germany
Greece Portugal
One Member Body opposed the approval of the Draft: France.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in February 1961, to accept it as an IS0 RECOMMENDATION.
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ISO/R 188 - 1961 (E)
IS0 Recommendation R 188 February 1961
ACCELERATED AGEING OR SIMULATED SERVICE TESTS
ON VULCANIZED NATURAL OR SYNTHETIC RUBBERS
1. INTRODUCTION
Accelerated ageing tests are designed to estimate the relative resistance of rubber vulcanizates
to deterioration with the passage of time. For this purpose, the rubber is subjected to controlled
deteriorating influences for definite periods, after which its properties are measured and compared
with the corresponding properties of the untreated rubber.
The purpose of the test may be to assess the deterioration of the rubber either
(U) during prolonged periods at normal temperatures, or
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(b) during use at high temperatures or at elevated oxygen pressure.
Three ageing tests are given in the following sections:
......... section 2, page 6,
Cell type oven method
Oven method . section 3, page 7,
Oxygen pressure method . section 4, page 9.
The selection of the conditioning time and temperature will depend on the purpose of the test
and the type of polymer. This selection decides whether an accelerated ageing or simulated
service (heat) test is to be used.
The number of tests pieces used for each ageing period and the method of expressing the results
obtained on them are as stated in the appropriate standard for the property under test.
In the two first forms of ageing test specified above, deterioration is accelerated by raising the
L temperature and, in the third form of test, by increasing the oxygen concentration. The degree of
acceleration thus produced varies from one vulcanizate to another and from one quality to
another. Consequences of this are:
(a) Accelerated tests do not truly reproduce the changes produced by natural ageing.
(b) They do not indicate accurately the relative natural or service life of different rubbers;
thus, raising the temperature may tend to equalize the apparent life of rubbers which
deteriorate at different rates under natural ageing conditions.
(c) Different accelerated tests do not agree in assessing the relative life of different rubbers
and may even arrange them in different orders of merit.
(d) Ageing should be measured by the changes in the property or properties which are
of practical importance, provided these can be measured accurately, since no one
property can be used as a general index of degree of deterioration.
Attention is drawn to the fact that oven and bomb ageing tests should not be used to simulate
natural ageing which occurs in the presence of either light or ozone when the rubbers are
stretched.
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ISO/R 188 - 1961 (E)
2. CELL TYPE OVEN METHOD
Summary and explanatory note. This ageing test of rubber consists in subjecting test pieces
2.1
to controlled deterioration by air at an elevated temperature and at atmospheric pressure,
after which the physical properties are measured and compared with those of unaged test
pieces. The physical properties concerned in the service application are used to measure
the deterioration, but in the absence of any statement of these, it is recommended that tensile
strength, modulus, breaking elongation and hardness should be measured. In this test, the
oxygen concentration is low, and if oxidation is rapid, oxygen may not diffuse into the
rubber quickly enough to maintain uniform oxidation. The test is therefore liable to give
misleading results with poor-ageing rubbers, unless the test pieces are very thin.
2.2 Test pieces. It is recommended that the ageing should be carried out on the test pieces
prepared and conditioned as required for the appropriate tests, and not on complete articles
or sample sheets, and their form should be such that no mechanical, chemical or heat treat-
ment will be required after ageing.
Only test pieces of similar dimensions and having approximately the same exposed areas
are compared with each other. The test pieces should be measured before and marked
after ageing.
Care should be taken that the material used for identifying test pieces should not be applied
in any restricted area of the test piece and should be such as not to injure the rubber or
become destroyed during ageing. Care should be taken to ensure that the test pieces have
a good smooth finish and are free from blemishes and other flaws.
2.3 Apparatus. The apparatus should consist of one or more cylindrical vertical cells, having
a minimum height of 30 cm. The cells should be surrounded by a thermostatically controlled
good heat transfer medium (aluminium block, liquid bath, saturated vapour).
The design of the apparatus should be such that heated air will enter the bottom of the
cell and be exhausted out at the top of it without being recirculated. Air passing through
one cell should not enter other cells. Provision is made for a slow circulation of air
through the cells of not less than three changes per hour. The incoming air should be
within 1 "C of the specified temperature at the point of entry into the cell.
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The temperature of the test cells should be uniform in time and space within f 1.0 "C of
the specified ageing temperature. Suitable means should be provided for controlling and
measuring the temperature.
2.4 Procedure. When the test is not to be carried out within a few hours following vulcani-
zation, all test pieces are stored in the dark for a period not exceeding 14 days prior to
commencement of the ageing test. The maximum temperature of storage before subjection
to an accelerated ageing test should not exceed 30 OC.
The testing of unaged test pieces is carried out within 14 days from the commencement of
the ageing period; this will enable unaged test pieces and test pieces aged for periods of not
more than 14 days to be tested together.
The test pieces are placed in the oven after it has been pre-heated to the operating temperature.
The test pieces are stationary, free from strain, freely exposed to air on all sides and not
exposed to light. The test pieces should take up not more than 10 per cent in volume of the
space of each cell.
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ISO/R 188 - 1961 (E)
When the ageing period is complete, the test pieces are removed from the oven and condi-
tioned in accordance with the details given in the appropriate test method for the particular
property being studied.
2.5 Duration of test. The period required to obtain any given degree of deterioration of the
test pieces will depend upon the type of rubber under examination. It is recommended
that the ageing period should be 3, 7, 10 or some multiple of 7 days.
As 7 days is too short a period to produce a marked deterioration in most rubbers of good
quality, one of the longer periods is preferred. The ageing periods used, however, should be
such that deterioration of the test pieces will not be so great as to prevent determination
of final physical properties.
2.6 Temperature of oven. The oven should be at one of the following temperatures:
70 f 1 "C 175 f 2 "C
100 f 1 "C 200 f 2 "C
125 f 1 "C 250 f 2 "C
150 f 2 "C
The product specification should indicate the temperature to be used.
2.7 Expression of results. The number of test pieces and the method of expressing the results
are in accordance with the recommendations already made for the particular test being
carried out.
The properties of the test pieces aged for different periods are determined as the intervals
terminate in the process of ageing.
The test results of both the unaged (O) and the aged (A) test pieces are reported, as well as
the coefficient of deterioration as calculated from the following formula :
O-A
x 100
O
The properties determined should be stated.
3. OVEN METHOD
Summary and explanatory note. This ageing test of rubber consists in subjecting test pieces
3.1
to controlled deterioration by air at an elevated temperature and at atmospheric pressure,
after which the physical properties are measured and compared with those of unaged test
pieces. The physical properties concerned in the service application are used to measure the
deterioration, but in the absence of any statement of these, it is recommended that tensile
strength, modulus, breaking elongation and hardness should be measured. In this test, the
oxygen concentration is low, and if oxidation is rapid, oxygen may not diffuse into the rubber
quickly enough to maintain uniform oxidation. The test is therefore liable to give mis-
leading results with poor-ageing rubbers, unless the test pieces are very thin.
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ISO/R 188 - 1961 (E)
3.2 Test pieces. It is recommended that the ageing shoul
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