1、BSI Standards PublicationBS ISO 18766:2014Rubber, vulcanized orthermoplastic Lowtemperature testing Generalintroduction and guideBS ISO 18766:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 18766:2014.The UK participation in its preparation was entrusted t
2、o TechnicalCommittee PRI/22, Physical testing of rubber.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The Briti
3、sh Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 85096 7ICS 83.060Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 July 2014.A
4、mendments issued since publicationDate Text affectedBS ISO 18766:2014 ISO 2014Rubber, vulcanized or thermoplastic Low temperature testing General introduction and guideCaoutchouc vulcanis ou thermoplastique Essais basse temprature Introduction gnrale et lignes directricesINTERNATIONAL STANDARDISO187
5、66First edition2014-07-15Reference numberISO 18766:2014(E)BS ISO 18766:2014ISO 18766:2014(E)ii ISO 2014 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2014All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any m
6、eans, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva
7、 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 18766:2014ISO 18766:2014(E) ISO 2014 All rights reserved iiiContents PageForeword iv1 Scope . 12 Terms and definitions . 13 Types of low temperature test 13.1 General . 13.2 Change in s
8、tiffness . 13.3 Brittleness point 23.4 Recovery tests 23.5 Crystallization 24 Significance of low temperature tests 35 Comparison of tests . 3Bibliography 4BS ISO 18766:2014ISO 18766:2014(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standar
9、ds bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organi
10、zations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended for its fu
11、rther maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/direct
12、ives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the I
13、ntroduction and/or on the ISO list of patent declarations received (see www.iso.org/patents). Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related
14、to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 45, Rubber and rubber products, Subcommittee SC 2, Tes
15、ting and analysis.iv ISO 2014 All rights reservedBS ISO 18766:2014INTERNATIONAL STANDARD ISO 18766:2014(E)Rubber, vulcanized or thermoplastic Low temperature testing General introduction and guide1 ScopeThis International Standard provides a general introduction to, and guidance on, the methods of t
16、est for low temperature properties of vulcanized and thermoplastic rubbers.It is intended to provide an understanding of the significance of the various low temperature properties and to assist in the selection of an appropriate test method.2 Terms and definitionsFor the purposes of this document, t
17、he following terms and definitions apply.2.1low temperature testtest to measure any property at a temperature below standard laboratory temperature3 Types of low temperature test3.1 GeneralWith reduction of temperature, rubbers become stiffer, until finally becoming hard and brittle, and also recove
18、ry from an applied deformation becomes more sluggish. The point of becoming hard and brittle is the glass transition. Any physical test can be made at sub-normal temperatures and, for particular purposes, it might be desirable to follow changes in, for example, tensile strength, dynamic modulus, res
19、ilience, or electrical resistivity as the temperature is lowered, depending on what is relevant to service. The glass transition temperature (Tg) is most commonly determined from differential scanning calorimetry (DSC) or dynamic thermal mechanical analysis (DTMA) testing. In this respect, it should
20、 be noted that the measured Tgwill depend on the frequency of the test used, a “fast” test yielding a higher Tgthan a “slow” one. Further information can be found in Reference 6.Largely for practical convenience, a number of specific low temperature test procedures have evolved for measuring these g
21、eneral trends in behaviour and have been widely standardized.These low temperature tests can be grouped as follows: change in stiffness; brittleness point; rate of recovery (set and retraction).In addition, some rubbers, for example natural rubber and polychloroprene, stiffen at low temperatures by
22、partial crystallization. This is a gradual process continuing over many days or weeks and is most rapid at a particular temperature characteristic of each polymer, for example 25 C for natural rubber. Hence, tests intended to measure the effect of crystallization have to detect changes in stiffness
23、or recovery after periods of “ageing” at a low temperature.3.2 Change in stiffnessHistorically, before the introduction of thermal analysers, it was relatively difficult and expensive to measure tensile or compressive modulus at sub-ambient temperatures. Torsion tests, although rarely ISO 2014 All r
24、ights reserved 1BS ISO 18766:2014ISO 18766:2014(E)used to measure stiffness at ambient temperature, were found to be very convenient for measuring change of stiffness as temperature is lowered. The system standardized for rubber as the Gehman test in ISO 1432 uses a torsion wire to provide the torqu
25、e to twist a strip test piece. The stiffness is measured as a function of rising temperature. The measurements may be made in a liquid or gaseous environment, either at intervals or with continuous rise of temperature. In principle, these alternatives yield equivalent results.The normal expression o
26、f results is to give the temperatures at which the relative modulus (calculated with respect to that at 23 C) is 2, 5, 10, and 100. If required, the apparent torsional modulus at any temperature may be calculated but, because it depends on the test conditions, should not be taken as an absolute valu
27、e.With modern universal test machines with environmental cabinets and, in particular, dynamic thermal mechanical analysers, it can be argued that essentially the same data could be better obtained using the more commonly used modes of deformation, and which would match data obtained at ambient and e
28、levated temperatures. However, the traditional ISO 1432 method continues to be widely used.3.3 Brittleness pointA somewhat arbitrary method for determining the point at which the material becomes brittle is described in ISO 812. It operates on the basis of striking a test piece in the form of a simp
29、le cantilever with the striker moving at 2 m/s. The result is either pass or fail, failure being any crack or complete separation of the test piece. Various forms of apparatus are possible and the test may be conducted in a liquid or gaseous medium but, in principle, the results are equivalent.Two p
30、rocedures are specified: determination of brittleness temperature and determination of 50 % brittleness temperature. The former gives the lowest temperature at which there are no failures, while the latter finds the temperature at which 50 % of test pieces fail. It has been suggested that the 50 % m
31、ethod is more reproducible but might use more test pieces. For specification purposes, the test may be used as a go/no go procedure at one given temperature.3.4 Recovery testsThe most straightforward way to measure recovery from a deformation at a low temperature would be to use an adaptation of the
32、 normal compression set or tension set tests. A test in compression is given in ISO 815-2. Essentially, it is the usual compression set procedure but with the deformed test piece being released and the recovery taking place at the specified low test temperature.Although simple in principle, the test
33、 is practically rather difficult because of the need to unload the test piece and measure its recovery within a low temperature enclosure. Variability can be large and the test is best made with specially designed apparatus.Traditionally, an alternative approach based on recovery in tension and know
34、n as the low temperature retraction test (TR test) has been widely used and is described in ISO 2921. The stretched test pieces are put into the heat transfer medium at a low temperature below the glass transition temperature. The test pieces are then allowed to recover as the temperature is raised.
35、 From a graph of percentage retraction against temperature, the temperatures corresponding to 10 %, 30 %, 50 %, and 70 % retraction are noted. This way of expressing the results is similar in principle to the results of the Gehman test for stiffness.3.5 CrystallizationIn principle, any of the low te
36、mperature tests can be used to study crystallization effects by holding the test piece at the low temperature for much longer than in the standard tests. A clause suggesting that this can be done is included in, for example, the TR test standard. However, a procedure based on hardness measurement ha
37、s been standardized as ISO 3387. The hardness of a test piece is measured soon after being place in the low temperature cabinet and after it has been held at the low temperature for a period of time, usually 24 h and 168 h. This procedure has a similar practical difficulty, of making a measurement a
38、t low temperature inside an enclosure, as for determining low temperature compression 2 ISO 2014 All rights reservedBS ISO 18766:2014ISO 18766:2014(E)set. One reason for introducing the hardness procedure was because it can be used with unvulcanized compound as well as vulcanized rubber. This would
39、not be feasible with the other standard low temperature tests.4 Significance of low temperature testsNone of the standard low temperature tests yields absolute values, as the results depend on the particular test conditions. Different conditions can give different results. Consequently, the results
40、can be used as guidance as to performance at low temperature but might not precisely equate to the performance of a particular product. However, in the Gehman and TR tests, the results are essentially a measure of the change in a property, which is less dependent on the conditions.It is obvious that
41、 the different tests measure different aspects of low temperature behaviour and are, hence, complementary. Which test is preferable in a given situation will depend on which aspect or aspects are relevant to service. For example, if remaining ductile is the only consideration then the brittleness te
42、st is appropriate. If recovery from deformation, as in a seal, is important then set or TR tests are more relevant. As mentioned earlier, a property other than those in the standardized low temperature tests might be the most appropriate for a particular circumstance.5 Comparison of testsNotwithstan
43、ding the fact that the various tests measure different aspects of behaviour, the question is often asked as to how the results compare. Published reports on comparisons of methods are discussed in Reference 6. The indications are that the ranking of compounds is not always the same for all the tests
44、 but reasonable correlations can be expected between similar measures (hardness and Gehman modulus) or between measures at the same degree of stiffening for example brittleness and TR10 or T10 (Gehman). ISO 2014 All rights reserved 3BS ISO 18766:2014ISO 18766:2014(E)Bibliography1 ISO 812, Rubber, vu
45、lcanized or thermoplastic Determination of low-temperature brittleness2 ISO 815-2, Rubber, vulcanized or thermoplastic Determination of compression set Part 2: At low temperatures3 ISO 1432, Rubber, vulcanized or thermoplastic Determination of low-temperature stiffening (Gehman test)4 ISO 2921, Rubb
46、er, vulcanized Determination of low-temperature retraction (TR test)5 ISO 3387, Rubber Determination of crystallization effects by hardness measurements6 Brown R .P. Physical Testing of Rubber. Springer, 20064 ISO 2014 All rights reservedBS ISO 18766:2014BS ISO 18766:2014ISO 18766:2014(E) ISO 2014 A
47、ll rights reservedICS 83.060Price based on 4 pagesThis page deliberately left blankBSI is the national body responsible for preparing British Standards and other standards-related publications, information and services.BSI is incorporated by Royal Charter. British Standards and other standardization
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