1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA
2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any
3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ICS 83.060 ISBN 0-626-14412-4 SANS 11432:2003Edition 1ISO 1432:1988Edition 3SOUTH AFRICAN NATIONAL STANDARD Rubber, vulcanized or thermoplastic Determina
4、tion of low temperature stiffening (Gehman test) Published by Standards South Africa 1 dr lategan road groenkloof ! private bag x191 pretoria 0001 tel: 012 428 7911 fax: 012 344 1568 international code + 27 12 www.stansa.co.za Standards South Africa 2003 This national standard is the identical imple
5、mentation of ISO 1432:1988 and is adopted with the permission of the International Organization for Standardization SANS 11432:2003 Edition 1 ISO 1432:1988 Edition 3 Table of changes Change No. Date Scope National Foreword This South African standard was approved by National Committee STANSA TC 5140
6、.17, Rubber and rubber products, in accordance with procedures of Standards South Africa, in compliance with annex 3 of the WTO/TBT agreement. INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOflHAR OPTAHM3AMR fl0 CTAHflAPTM3A
7、L/MM Rubber, vulcanized or thermoplastic - Determination of low temperature stiffening (Gehman test) Caoutchouc vulcanis6 ou thermoplastique - Essai Gehman) Mtermination de Ia rigidit6 2 basse tempkrature ISO 1432 Third edition 1988-12-15 Reference numl 3er ISO 1432: 1988 CE) Iso 1432 : 1988 (EI For
8、eword ISO (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 committees. Esch member body interested in a subject for which a tech
9、nical committee has been established has the right to be represented on that committee. International organizations, govern- mental 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
10、of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % a
11、pproval by the member bodies voting. International Standard ISO 1432 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products. This third edition cancels and replaces the second edition (ISO 1432 : 1982), of which it constitutes a minor revision. 0 International Organkation for Stan
12、dardkation, 1988 Printed in Switzerland INTERNATIONAL STANDARD ISO 1432 : 1988 (E) Rubber, vulcanized or thermoplastic - Determination of low temperature stiffening (Gehman test) 1 Scope This International Standard specifies a static procedure, known as the Gehman test, for determining the relative
13、stiffness characteristics of vulcanized or thermoplastic rubbers over a temperature range from room temperature to approximately -150 OC. 2 Apparatud) 2.1 Torsion apparatus, one possible form of which is shown in figure 1. lt consists of a torsion head (A), capable of being turned 180 in a plane nor
14、mal to the torsion wire (B). The top of the wire is fastened to the torsion head through a loosely fitting sleeve (C). The bottom sf the wire is fastened to the test piece clamp stud (D) by means of a screw connector (E). A device for “friction-free” indication or recording sf angle by mechanical or
15、 electrical means shall be provided permitting convenient and exact adjustment sf the zero Point; the ap- paratus shown in the figure has a pointer (F) and a movable protractor (G) which perform these functions. The indicating or recording System shall allow reading or recording of the angle of twis
16、t to the nearest degree. The torsion apparatus is clamped to a supporting stand (H). lt is advantageous to make the vertical Portion of the stand from material of poor thermal conductivity. The base of the stand shall be of stainless steel or other corrosion-resistant material. 2.2 Torsional wires (
17、B), made of tempered spring wire, of length 65 mm + 8 mm, and having torsional constants of 0,7 mN.m, 2,81 mN.m and l1,24 mN.m. In cases of dispute, the 2,81 mN.m wire shall be used. 2.3 Test piece rack (l), made of material of poor thermal conductivity, for holding the test piece (J) in a vertical
18、Position in the heat transfer medium. The rack may be constructed to hold several test pieces. 2) The rack is clamped to the stand (H). Two clamps shall be provided for holding each test piece. The bottom clamp (K) shall be a fixed part of the test piece rack. Tbc sha (D) top clamp (L) acts as an ex
19、tension of the test piece and I not tauch the rack.3) The top clamp is secured to a stud which in turn is connected to the screw connector (E). 2.4 the Temperature-measuring device, capable of measuring temperature to within 1 OC over the whole range of temperature over which the apparatus is to be
20、used. The sensitive element shall be positioned near a test piece equidistant from the top and bottom. 2.5 Heat-transfer medium, which may be liquid or gaseous. Any material which remains fluid at the test temperature and which will not affect materials being tested may be used. Among the liquids th
21、at have been found suitable for use at low temperatures are acetone, methanol, ethanol, butanol, Silicone fluid and n-hexane. Air, carbon dioxide or nitrogen are commonly used gaseous media. Vapours of liquid nitrogen are useful for testing at very low temperatures. lt should be noted that stiffness
22、 measurements in gaseous media may not give in each case the same results as the measurements made in liquid media. 2.6 Temperature control, capable of maintaining the temperature sf the heat-transfer medium to within + 1 OC. 2.7 Tank, for a liquid heat-transfer medium, or test chamber for a gaseous
23、 medium. 1) The apparatus and its use are described in GEHMAN, S. D., WOODFORD, D. E., and WILKINSON, C. S., LOW temperalure characteristics of elastomers, /nd. and Eng. Chem., 39 Sept. 1947: 1108. 2) Racks providing space for five or ten test pieces are commonly used. 3) Clearance between the top o
24、f the test piece rack and the test piece clamp stud is ensured by inserting thin spacers between the two. Slotted laminated plastics of thickness about 1,3 mm and width about 12 mm have been found satisfactory. At low temperatures the test pieces stiffen in Position and the spacers may be removed wi
25、thout losing the clearance. 1 ISO 1432 : 1988 (El 2.8 Stirrer, for liquids, or fan or blower, for gases, which ensures thorough circuiation of the heat-transfer medium. 2.9 Stopwatch, or seconds. 3 Test piece other timing 31 . Preparation of test piece device, calibrated in The dimensions of the tes
26、t piece shall be 40 mm -t 2,5 mm, 3 mm It: 02 mm and 2 mm + 0,2 mm. lt shall be moulded or tut with a suitable die from a vulcanized sheet of suitable thickness. 3.2 Conditioning of test piece 3.2.1 The minimum time between vulcanization and testing shall be 16 h. For non-product tests, the maximum
27、time between vulcaniza- tion and testing shall be 4 weeks and, for evaluations intended to be comparable, the tests should be carried out, as far as possible, after the same time interval. For product tests, whenever possible, the time between vulcanization and testing should not exceed 3 months. In
28、 other cases, tests shall be made within 2 months of the date of receipt by the customer of the product. 3.2.2 Samples and test pieces shall be protected from light as completely as possible during the interval between vulcanization and testing. 3.2.3 Prepared test pieces shall be conditioned immedi
29、ately before testing for a minimum of 3 h at a Standard temperature, the same temperature being used throughout any one test or series of tests intended to be comparable. ISO 1432 : 1988 (El l u I , I I I 0 A Torsion head 0 E Screw connector 0 I Rack 0 B Torsion wire 0 F Pointer 0 J Test piece 0 C S
30、leeve 0 G Movable protractor 0 K Bottom clamp 0 D Clamp stud 0 H Supporting stand 0 L Top clamp Figure 1 - Apparatus for determination of stiffness characteristics 3 ISO 1432 : 1988 (El 4 Procedure 4.1 Calibration of torsion wire Insert one end of the torsion wire (B) in a vertical Position, in the
31、fixed clamp, and attach the lower end of the wire at the ex- act longitudinal centre of a rod of known dimensions and mass. (lt is suggested that the length of the rod be 200 mm to 250 mm and the diameter about 6,4 mm.) Twist the rod through an angle of not more than 90 and then release it. Allow it
32、 to oscillate freely in a horizontal plane and note the time, in seconds, for 20 oscillations. (An oscillation includes the Swing from one extreme to the other and return.) The mass moment of inertia, 1, ex squared, is given by the equation mL2 1 - = 12 where m L pressed in kilogram metres is the ma
33、ss, in kilograms, of the rod; is the length, in metres, of the rod. The torsional constant of the wire (i.e. the restoring torque per radian), K, expressed in newton metres, is given by the equation I K=4712- T2 where T is the period, in seconds, of one oscillation. The torsion wires sha torsional c
34、onstants. ll calibrate within + 3 % of their specif ied 4.2 Mounting of test piece Clamp each test piece used in such a manner that 25 mm b) increase the temperature continuously with a heating rate of 1 OC/min. Make the stiffness measurement in the stepwise case after con- ditioning of the test pie
35、ce for 5 min at each temperature and in the continuous case at 5 min intervals. Continue the tests until a temperature is reached at which the angular twist is within 5O to IO0 of the twist at 23 OC. 4.4 Stiffness measurement in gaseous media Procedures with air, carbon dioxide or nitrogen differ fr
36、om those with liquid media only in that cooling is done with the test pieces in the medium and the length of the conditioning period is different. 1) Apparatus is now in use in which the rack is stationary while the torsion head is movable and tan be positioned over each test piece in turn. 2) Movem
37、ent of the spacer may alter the setting of the angle indicating or recording device; therefore, adjust this device to zero after removing the spacer. 4 ISO 1432 : 1988 (El 4.4.1 Increase of temperature in Steps 6.3 Relative modulus With the test pieces in the test chamber, adjust the temperature of
38、the chamber to the lowest temperature desired in approximately 30 min. After this temperature has been main- tained constant for 10 min, make the measurements in a similar way as in the liquid media, each test piece being tested within 2 min. The relative modulus at any temperature is the ratio of t
39、he tor- sional modulus at that temperature to the torsional modulus at 23 OC. The value of the relative modulus for any temperature is readily determined from the angles of twist at that temperature and at 23 OC, as given by the twist versus temperature curve (6.1) and the ratio of the values of the
40、 factor (180 - a)la corresponding to those angles. Increase the temperature of the chamber by 5 OC intervals, each increase being made in approximately 10 min, and make stiffness measurements after conditioning of the test pieces for 10 min at each temperature. The temperatures at which the relative
41、 modulus is 2; 5; 10 and 100 respectively, are determined by the use of table 1 and the twist versus temperature curve for the test piece. The first column of table 1 lists each degree of twist in the range of 120 to 170, so that the value corresponding to the twist of the test piece at 23 OC tan be
42、 selected. 4.4.2 Continuous increase of temperature With the test pieces in the test chamber adjust the temperature of the chamber to the lowest temperature desired, by applica- tion of a linear time Programme, preferably with a rate of 3 OC/min. After this temperature has been reached, increase the
43、 temperature linearly at a rate of 1 OC/min. Successive columns give the twist angles which correspond to values 2; 5; 10 and 100 respectively, for the relative modulus. The temperatures corresponding to these angles are then read from the twist versus temperature curve for the test piece (6.1) and
44、are designated as t2, t5, t10 and tlm respectively. Carry out measurements of the twist angle at 5 OC intervals. 4.5 Crystallization When it is desired to study crystallization or plasticizer effects, the time of conditioning at the desired temperature should be increased. 64 . Apparent torsional mo
45、dulus of rigidity When it is desired to calculate the apparent torsional modulus of rigidity in pascalsl) at various temperatures, the free length of the test piece shall be accurately measured. 5 Number of tests At least three test pieces of each material shall be tested. lt is good practice to inc
46、lude a control rubber with known twist temperature characteristics. The apparen t torsional given by the equation modulus of rigidity, G, in Pascals, is 16 KL (180 - a) G= bd$a 6 Expression of results 61 . Twist versus temperature curve where Plot a graph of the pointer readings piece) against the t
47、emperature. (angles of twist of the test K is the torsional constant, in newton metres, of the wire; L is the measured free length, in metres, of the test piece; 6.2 Torsional modulus b is the width, in metres, of the test piece; The torsional modulus of the proportional to the qua ntity test piece
48、at any temperature is d is the thickness, in metres, of the test piece; 180 - a a P is the factor based on the ratio bld taken from table 2; where a is the angle of twist, in degrees, of the test piece. a is the angle of twist, in degrees, of the test piece. N/m* 1) lPa=l Iso 1432 : 1988 (El Table 1
49、 - Twist angles for designated values of the Table 2 - Valuesl) of factor p for various relative modulus (RM) ratios of bld Twist angle, a, in degrees at 23 OC 120 90 51 30 121 91 52 31 122 92 53 31 123 93 54 32 124 95 55 33 125 96 56 33 126 97 57 34 127 98 58 35 128 99 59 36 129 101 61 36 130 102 62 37 131 103 63 38 132 104 64 39 133 105 65 40 134 107 66 41 135 108 68 42 136 109 69 42 137 111 70 43 138 112 71 45 139 113 72 46 140 114 74 47 141 116 142 117 143 119 144 120 145 121 146 123 83 54 147 124 85 55 148 126 87 57 149 127 88 58 150 129 90 60 151 130 92 62 152 132 94 62 153 133
