1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 2921:2011Rubber, vulcanized Determination of low-temperature retraction (TR test)BS ISO 2921:2011 BRITISH STANDARDNational forewordThis British Standard is the UK implemen
2、tation of ISO 2921:2011. Itsupersedes BS ISO 2921:2005 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee PRI/22, Physical testing of rubber.A list of organizations represented on this committee can beobtained on request to its secretary.This publication d
3、oes not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 66376 5ICS 83.060Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of t
4、heStandards Policy and Strategy Committee on 30 November 2011.Amendments issued since publicationDate Text affectedBS ISO 2921:2011Rubber, vulcanized Determination of low-temperature retraction (TR test)Caoutchouc vulcanis Dtermination du retrait basse temprature (essai TR) ISO 2011Reference numberI
5、SO 2921:2011(E)Fifth edition2011-10-15ISO2921INTERNATIONAL STANDARDBS ISO 2921:2011ISO 2921:2011(E)COPYRIGHT PROTECTED DOCUMENT ISO 2011All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, in
6、cluding photocopying and microfilm, without permission in writing 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 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished i
7、n Switzerlandii ISO 2011 All rights reservedBS ISO 2921:2011ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committ
8、ees. 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 organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Int
9、ernational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft International St
10、andards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subj
11、ect of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 2921 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee SC 2, Testing and analysis.This fifth edition cancels and replaces the fourth edition (ISO 2921:2005)
12、, which has been technically revised, mainly to include an annex specifying a calibration schedule for the apparatus used.ISO 2921:2011(E) ISO 2011 All rights reserved iiiBS ISO 2921:2011BS ISO 2921:2011INTERNATIONAL STANDARD ISO 2921:2011(E)Rubber, vulcanized Determination of low-temperature retrac
13、tion (TR test)WARNING Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health p
14、ractices and to ensure compliance with any national regulatory conditions.IMPORTANT Certain procedures specified in this International Standard might involve the use or generation of substances, or the generation of waste, that could constitute a local environmental hazard. Reference should be made
15、to appropriate documentation on safe handling and disposal after use.1 ScopeThis International Standard specifies a method for the determination of the temperature-retraction characteristics of stretched vulcanized rubber.This International Standard does not cover thermoplastic rubbers, as many ther
16、moplastic elastomers have a yield point in the range of 5 % to 20 % elongation. This fact might affect the result when carrying out TR tests on thermoplastic rubbers, and the results obtained from such tests should be analysed with caution.2 Normative referencesThe following referenced documents are
17、 indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 18899:2004, Rubber Guide to the calibration of test equipmentISO 23529, Rubber Gener
18、al procedures for preparing and conditioning test pieces for physical test methods3 PrincipleA test piece is stretched at standard laboratory temperature and then cooled to a sufficiently low temperature such that retraction does not occur upon removal of the stretching force. The stretching force i
19、s removed and the temperature increased at a uniform rate. The temperatures at which specified percentage retractions occur are determined.4 Apparatus4.1 Retraction apparatus, comprising the components specified in 4.2 to 4.8 (see also Figure 1).4.2 Heat-transfer medium, liquid or gaseous, which rem
20、ains fluid at the test temperature and which does not appreciably affect the material being tested, as prescribed in ISO 23529.Gases may be employed as the heat-transfer medium provided the design of the apparatus is such that results obtained using them will duplicate those obtained with liquids. I
21、SO 2011 All rights reserved 1BS ISO 2921:2011The following fluids have been used satisfactorily:a) for temperatures down to 60 C, silicone fluids of kinematic viscosity of about 5 mm2/s at ambient temperature, which are usually suitable owing to their chemical inertness towards rubbers, their non-fl
22、ammability and their non-toxicity;b) for temperatures down to 73 C, ethanol;c) for temperatures down to 120 C, methylcyclohexane cooled by liquid nitrogen (found to be satisfactory with the use of suitable apparatus).4.3 Temperature-measuring device, capable of measuring the temperature to within 0,
23、5 C over the whole range of temperatures over which the apparatus is to be used.The temperature sensor shall be positioned near the test pieces.4.4 Temperature control, capable of maintaining the temperature of the heat-transfer medium to within 1 C.4.5 Container for the heat-transfer medium: A bath
24、 for a liquid medium or a test chamber for a gaseous medium, with means of heating the heat-transfer medium.4.6 Means of agitating the heat-transfer medium: A stirrer for liquids or a fan or blower for gases, which ensures thorough circulation of the heat-transfer medium. It is important that the st
25、irrer also moves the liquid vertically to ensure a uniform temperature in the liquid.4.7 Stopwatch or other timing device, calibrated in seconds.4.8 Rack with test piece holders, equipped with a loading device, holders for one or more test pieces and a locking device for the upper (movable) test pie
26、ce holders (see Figure 1).The rack shall be designed to maintain a slight tension (10 kPa to 20 kPa in air) on each test piece and to permit them to be stretched up to a maximum of 350 %; the design shall permit the upper test piece holder to be locked into position at the chosen elongation and subs
27、equently released. Means shall be provided to enable the length of each test piece to be read, at any time during the test, with an accuracy of 0,25 mm or better.Alternatively, a series of removable scales graduated to allow the retraction to be read directly as a percentage of the elongation of the
28、 frozen rubber with an accuracy of 0,5 % may be used.The movable parts of the apparatus shall be constructed so that the lowest possible friction occurs.5 CalibrationThe test apparatus shall be calibrated in accordance with the schedule given in Annex A.6 Test pieces6.1 PreparationTest pieces shall
29、be prepared in general accordance with ISO 23529.ISO 2921:2011(E)2 ISO 2011 All rights reservedBS ISO 2921:2011Key1 pulley 8 upper part of upper test piece holder2 cord 9 locking device for upper test piece holder3 counterweight 10 thermal insulation4 stirrer 11 bath for heat-transfer medium5 heatin
30、g device (immersion heater) for heat-transfer medium 12 upper test piece holder6 rack 13 test piece7 removable graduated scales 14 lower test piece holderFigure 1 Retraction apparatusISO 2921:2011(E) ISO 2011 All rights reserved 3BS ISO 2921:20116.2 Types6.2.1 Standard test pieceThe standard test pi
31、ece shall be a strip with enlarged ends for clamping, with dimensions in accordance with Figure 2. The reference length shall be either 100 mm 0,2 mm or 50 mm 0,2 mm. The test piece with a reference length of 100 mm 0,2 mm is preferred for tests with small elongations and the test piece with a refer
32、ence length of 50 mm 0,2 mm for tests with larger elongations. Test pieces shall be cut with a sharp die from a flat sheet 2 mm 0,2 mm thick. The sheets may be prepared by moulding or from finished products by cutting and buffing.The 50 mm test piece may be used also with 50 % elongation if the read
33、ing accuracy of the measurement system is 0,125 mm or better.6.2.2 Test pieces cut from productsAlternatively, other types of test piece cut from finished rubber products may be used (for example an O-ring with a cross-sectional diameter between 1,5 mm and 4 mm).Note that such test pieces do not nec
34、essarily give the same values of retraction temperature as do the two sizes of standard test piece specified in 6.2.1, and comparison between the values obtained using different types of test piece should be avoided.6.3 NumberAt least three test pieces shall be used for each test.Dimensions in milli
35、metresFigure 2 Test piece6.4 Conditioning6.4.1 Unless otherwise specified for technical reasons, the procedure in 6.4.2 to 6.4.5 shall be followed.6.4.2 The time-interval between vulcanization and testing shall be in accordance with ISO 23529.6.4.3 Samples and test pieces shall be protected from lig
36、ht as completely as possible during the interval between vulcanization and testing.6.4.4 Test pieces shall be conditioned, immediately before testing, at one of the standard laboratory temperatures specified in ISO 23529.ISO 2921:2011(E)4 ISO 2011 All rights reservedBS ISO 2921:20116.4.5 If samples
37、that are apt to crystallize are exposed to low storage temperatures before testing, crystallization can occur that significantly affects the TR values measured. If values for the material in the uncrystallized condition are desired, the test pieces shall be decrystallized before testing by heating t
38、hem in an oven at 70 C for 30 min. They shall then be conditioned at a standard laboratory temperature for at least 30 min, but not more than 60 min.7 ProcedureThe bath shall contain enough heat-transfer medium (4.2) to cover the test pieces with at least 25 mm of liquid during testing.Cool the heat
39、-transfer medium, whilst stirring, to below 70 C as described in ISO 23529.While the liquid is cooling, insert the test pieces in the rack (4.8) and, at the standard laboratory temperature being used, stretch each test piece from the reference length to the chosen elongation and lock it in position.
40、 Ensure that the test pieces are only kept stretched at the standard temperature for the minimum time.The elongation shall be chosen in the light of the following criteria:a) provided technical reasons do not dictate otherwise, and to reduce the effect of crystallization, an elongation of 50 % shall
41、 be used;b) one of the following elongations shall be used to study the combined effect of crystallization and low temperature:1) 250 %,2) half the elongation at break if 250 % is unobtainable,3) 350 %, if the elongation at break is greater than 600 %.When the heat-transfer medium has reached an equ
42、ilibrium temperature between 70 C and 73 C, place the rack with the test pieces in the bath. Allow to stand for 10 min 2 min in the bath between 70 C and 73 C. Release the locking device for the upper holder and allow the test pieces to retract freely. At the same time, raise the temperature of the
43、liquid at the rate of 1 C/min, the tolerance being such that the temperature rise during any 10 min interval is within 10 C 2 C.If an elongated test piece retracts to its original length at 70 C, cool to a lower temperature, using, if necessary, another heat-transfer medium.Take the first reading at
44、 70 C and continue to read the temperature and the corresponding retracted length or percentage retraction every 2 min until retraction has reached 75 %.For the study of crystallization effects or the effect of long-term exposure, longer times of exposure under strain at one or more selected low tem
45、peratures may be used, depending on the purpose of the test and the material under investigation.NOTE Different elongations do not necessarily give the same results.ISO 2921:2011(E) ISO 2011 All rights reserved 5BS ISO 2921:20118 Expression of resultsThe percentage retraction r may be read from the
46、graduated scales or calculated from the following equation:rl ll l=s rs 0100wherelsis the stretched length in the locked position;lris the retracted length at the temperature concerned;l0is the reference length.Plot r against the corresponding temperature on a graph.From the graph, read the temperat
47、ures which correspond to retractions of 10 %, 30 %, 50 % and 70 %. These temperatures are designated TR10, TR30, TR50 and TR70.Calculate the median value of three determinations of the temperature for TR10, TR30, TR50 and TR70.9 Test reportThe test report shall include the following information:a) s
48、ample details:1) a full description of the sample and its origin,2) compound details and cure details, where appropriate,3) the method of preparation of the test pieces from the sample, for example moulded or cut;b) test method:1) a reference to the test method used, i.e. the number of this Internat
49、ional Standard,2) the type of test piece used;c) test details:1) the standard laboratory temperature used,2) the time and temperature of conditioning prior to test,3) the elongation at freezing,4) the heat-transfer medium used,5) details of any procedures not specified in this International Standard;d) test results:1) the number of test pieces used,2) the median values of TR10, TR30, TR50 and TR70,3) the individual values of TR10, TR30, TR50 and TR70 for each test piece;e) the date of the tes
