RUBBER PROPERTY-COMPRESSION SET'

¶Thls standard is issued under the fixed designation D 395; the number immedlately following the designation indicates the year of original adoption or. in the case of revision, the ywr of last revision. A number in parentheses indicate the year of last reappmval. A supersfript epsilon (6) indicates an editorial change s i n a the last revision or reapproval. Theremethod,dshave been approvedlor use by agenctesof the Deoortrnenr o f Deknse andlilr lrsrinn in (he DoD Index of Spe~~Jicu~rons und Stondurds

scope ments for Standards Related to Rubber and

¶1.1 These test methods cover the testing of Rubber Testing' rubber intended for use in applications in which D 3 182 Practice for Rubber-Materials, the rubber will be subjected to compressive Equipment, and Procedures for Mixing stresses in air or liquid media. They are applica- Standard Conipounds and Preparing Stand- ble particularly to the rubber used in machinery ard Vulcanized Sheets) mountings, vibration dampers, and seals. Two D 3 183 Practice for Rubber-Preparation of methods are covered as follows: Pieces for Test Purposes from Products'

sec- D 3767 Pfactice for Rubber-Measurement of Method tion Dimensions3

¶A-Compression Set Under Constant Force 7-10 E 145 Specification for Gravity-Convection in Air and Forced-Ventilation Ovens' B-Compression Set Under Constant Deflec- 11-14 NOTE I-The specific dated edition of Practice tion in Air D 3040 that prevalls in this document is referenced in

¶1.2 The choice of method is optional, but the Precision section. consideration should be given to the nature of 3. Summary of Methods the service for which correlation of test results may be sought. Unless otherwise stated in a 3. I A test specimen is compressed to either a detailed specification, Method B shall be used. deflection or by a specified force and maintained

¶1.3 Method B is not suitable for vulcanizates under this condition for a specified time and at harder than 9 0 IRHD. a specified temperature.

¶1.4 The values stated in SI units are to be 3.2 The residual deformation of a test speci- regarded as the standard. men is measured 30 min after removal from a

¶I .5 This standard may involve hazardous ma- suitable compression device in which the speci- terials. operations. and equipment. This standard men had been subjected for a definite time to does not purport t o address all of the safety prob- compressive deformation under specified condi- lems associated with its use. It is the responsibil- tions. ity of whoever uses this standard to consult and 3.3 After the measurement of the residual de- e.stahlish appropriate safely and health practices formation, the compression set as specified in the unddeterminethe applicability of regulatory limi- tutions prior to use. 2. Applicable Documents ' Thew test methods are under the junsdlctmn of ASTM

¶Committee D-l I on Rubber and are the dtrect responsibility of

I ASTM Standards: Sukommlttee DI I .¹⁰¹⁰ bid. 1 ' Ibid. - Readiness 1 2 Robert Lindstrom. NASA. Marshall Soace Flight Center. "Shuttle Proiect Flight Review,i'~SOP~8000.1,~&cemb& 29, 1983, p 2. See Xppendix VIII-C. l 3 William Lucas, NASA, Marshall Space Flight Center, "MSFC Flight Readiness Review (FRR) Board for MSFC Elements for Mission 51-L," January 7, 1986, pp. 1-2. See Appendix ._*- vm-n I. I4 Discussion with Mr. McDonald, September 4, 1986. Ibid. on Physlcal Testing.

¶Current edltton approved Sept 27. 1985. Puhllshed Novem-D I349 Practice for Rubber-Standard Tem- her IY85. Onglnally published as D 395 - 34. Last previous

peratures and Atmospheres for Testing and edition D 395 - 84. Annual B o d o1ASI'M Standard. Vols 09.01 and 09.02 Conditioning' ' .4nnuol Booh o/ ASTM Siandardr, Vol 09.01

¶D 3040 Practice for Preparing Precision State- ' 4nnrioI Boo!, oIASTM Siandurdr. VoI 14.02

¶I

¶4Snl D 395 appropriate method, is calculated according to 5.3 An optional method of preparing the Eqs ( I ) and (2). standard specimen may be the direct molding of a circular disk having the dimensions required 4. Significance and Use for the method used and specified in 5.2.1.

¶4.1 Compression set tests are intended to mea- NOTE 2-11 should be recognized that an equal time sure the ability of rubber compounds to retain and temperature. if used for both the slab and molded elastic properties after prolonged action of com- specimen, will not produce an equivalent state of cure in the two types of specimen. A higher degree of cure pressive stresses. The actual stressing service may will be obtained in the molded specimen. Adjustments, involve the maintenance of a definite deflection, preferably in the time of cure, must be taken into the constant applicatiotl of a known force, or the consideration if comparisons between the specimens rapidly repeated deformation and recovery re- prepared by different methods are to be considered valid. sulting from intermittent compressive forces. NOTE 3-It is suggested, for the purpose of uniform- Though the latter dynamic stressing, like the ity and closer tolerances in the molded specimen, that others, produces compression set, its effects as a the dimensions of the mold be specified and shrinkage whole are simulated more closely by compression compensated for therein. A two-plate mold with a flexing or hystersis tests. Therefore, compression cavity 13.0 i 0.1 mm (0.510 i 0.004 in.) in thickness and 29.20 k 0.05 mm ( I . 148 k 0.002 in.) in diameter, set tests are considered to be mainly applicable with overflow grooves will provide Type I specimens to service conditions involving static stresses. for Method A and Method B. A similar mold but having Tests are frequently conducted at elevated tem- a cavity of 6.3 f 0.3 mm (0.25 Z! 0.012 in.) in thickness peratures. *

and 13.2 i 0.1 mm (0.52 0.004 in.) in diameter will provide Type 2 specimens for Method B.

Test Specimens 5.4 When the standard test specimen is to be

¶5.1 Specimens from each sample may be replaced by a specimen taken from a vulcanized tested in duplicate (Option I ) or triplicate ( O p rubber part of greater thickness than the one tion 2). The compression set of the sample in indicated in 5.2. I , the sample thicknesr shall be Option I shall be the average of the two speci- reduced first by cutting transversely with a sharp mens, expressed as a percentage. The compres- knife and then followed by buffing to the required sion set of the sample in Option 2 shall be the thickness in accordance with Practic' D 3183. median (middle most value) of the three speci- 5.5 An alternative method of preparing spec- mens expressed as a percentage. imens is by plying up cylindrical disks cut from

¶5.2 The standard test specimen shall be a cy- a standard sheet prepared in accordance with lindrical disk cut from a laboratory prepared slab. Practice D 3 I82 using the specimen sizes speci5.2. I The dimensions of the standard speci- fied in 5.2.1 and cutting as described in 5.2.2. mens shall be: 5.5.1 The disks shall be plied, without ce-Type I* 2. menting, to the thickness required. Such plies Thicknesg m m (in.) 12.5 t 0.5 (0.49 6.0 f 0.2 (0.24 shall be smooth, flat, of uniform thickness, and f 0.02) f 0.01) shall not exceed seven in number for Type 1 Diamclcr.mm(in.) 29.0fO.S(1.14 13.0f0.2(0.~1 specimens and four in number for Type 2 speci-A 0.02) *0.01) _____ mens.

¶A Type I specimen is used in Methods A and B. 5.5.2 Care shall be taken during handling and

¶'Type 2 specimen is used in Method 8. placing of the plied test specimen in the test

¶5.2.2 When cutting the standard specimen, fixture by keeping the circular faces parallel and the circular die having the required inside dimen- at right angles to the axis of the cylinder. sions specified in 5.2.1 shall be rotated in a drill 5.5.3 The results obtained on plied specimens press or similar device and lubricated by means may be different from those obtained using solid of a soap solution. A minimum distance of I3 specimens and the results may be variable, par- mm (0.51 in.) shall be maintained between the ticularly if air is trapped between disks. cutting edge of the die and the edge of the slab. 5.5.4 The results obtained on the specimens The cutting pressure shall be as light as possible prepared hy one of the methods may be com- to minimize cupping of the put edges. The dies pared only to those prepared by the same shall be maintained carefully so that the cutting method. edges are sharp and free of nicks. 5.6 For routine or product specification test37 1

¶D395 ing, it is sometimes more convenient to prepare 7.2. I . I The spring shall be calibrated at room specimens of a different size or shape, or both. * temperature 23 5'C (73.4 k 9°F) by applying When such specimens are used, the results should successive increments of force not exceeding 250 be compared only with those obtained from spec- N (50 Ibf) and measuring the corresponding de- imens of similar size and shape and not with flection to the nearest 0.2 mm (0.01 in.). The those obtained with standard specimen. For such curve obtained by plotting the forces against the cases, the product specification should define the corresponding deflections shall have a slope of specimen as to the size and shape. If suitable 70 f 3.5 kN/m (400 f 20 Ibf/in.) at 1.8 kN (400 specimens cannot be prepared from the product, Ibf). The slope is obtained by dividing the two the test method and allowable limits must be forces above and below I .8 kN by the difference agreed upon between the producer and the pur- between the corresponding deflections. chaser. 7.2. I .2 \The original dimensions of the spring shall not change due to fatigue by more than 0.3 6. Conditioning mm (0.01 in.) after it has been mounted in the

¶6.1 Store all vulcanized test specimens or compression device, compressed under a force of product samples to be tested at least 24 h but not 1.8 kN (400 lbf), and heated in the oven for one more than 60 days. When the date of vulcaniza- week at 70'C f 2'C ( I 58 z t 3.6'F). In ordinary tion is not known, make tests within 60 days use, a weekly check of the dimensions shall show after delivery by the producer of the article r e g no greater change than this over a period of 1 resented by the specimen. year.

¶6.2 Allow buffed specimens to rest at least 30 7.2. I .3 The minimum force required to close min before specimens are cut for testing. the spring (solid) shall be 2.4 kN (530 Ibf).

¶6.3 Condition all specimens before testing for 7.2.2 Exiernul Force Applicaiion-The re- a minimum of 3 h at 23 f 2'C (73.4 k 3.6'F). quired force shall be applied to the compression Specimens whose compression set properties are plates and spring by external means after the test affected by atmospheric moisture, shall be con- specimen is mounted in the apparatus. Either a ditioned fora minimum of24 h in an atmosphere calibrated compression machine or known

controlled to 50 5 ?6 relative humidity. masses may be used for force application. Pro-METHOD A-COMPRESSION SET UNDER vision shall be made by the use of bolts and nuts

CONSTANT FORCE IN AIR or other devices to prevent the specimen and spring from losing their initial deflections when

Apparatus the external force is removed. The spring shall
I Dial Micromeler-A dial micrometer, for have essentially the same characteristics as de- measuring specimen thickness, in accordance scribed in 7.2. I , but calibration is not required. with Practice 3767, Method A 1. A suitable compression device is shown in Fig. 7.2 Compression Device, consisting of a force 2. application spring and two parallel compression 7.3 flures-The plates between which the test platesassembled by means ofa frame or threaded specimen is compressed shall be made of steel of bolt in such a manner that the device shall be sufficient thickness to withstand the compressive portable and self-contained after the force has stresses without bending. The surfaces against been applied and that the parallelism ofthe plates which the specimen is held shall have a highly shall be maintained. The force may be applied in polished chromium-plated finish and shall be accordance with either 7.2. I or 7.2.2. cleaned thoroughly and wiped dry before each

¶7.2.1 Culibrured Spring Force Applicurion- test. The required force shall be applied by a screw 7.4 Oven, conforming to the specification for mechanism for compressing a calibrated spring a Type IIB laboratory oven given in Specification the proper amount. The spring shall be of E 145. properly heat-treated spring steel with ends ground and perpendicular to the longitudinal 8. Procedure axis of the spring. A suitable compression device 8.1 Original Thickness Measurement-Mea- is shown in Fig. I . The spring shall conform to sure the original thickness of the specimen to the the following requirements: nearest 0.02 mm (0.001 in.). Place the specimen

@I D395

¶on the anvil of the dial micrometer so that the 9. Calculation presser foot will indicate the thickness at the 9.1 Calculate the compression set as a per- central portion of the top and bottom faces. centage of the original thickness as follows:

¶8.2 Application of Compressive Force-As- semble the specimens in the compression device, C A = I(t. - ~,)/lol x 100 (1) using extreme care to place them exactly in the where: center between the plates to avoid tilting. If the C, = compression set (Method A) as a percent- calibrated spring device (Fig. 1) is used, apply the age of the original thickness, compressive force by tightening the screw until I, = original thickness (8. I), and the deflection as read from the scale is equivalent fi = final thickness (8.5). to that shown on the calibration curve for the spring corresponding to a force of 1.8 kN (400 10. Report lbf). With the external loading device (Fig. 2), 10.1 The report shall include the following: apply this force to the asembly in the compres- 10. I. I Original dimensions of the test speci- sion machine or by adding required masses, but men, including the original thickness, f, in the latter case, take care to add the mass 10.I .2 Actual compressive force on the speci- gradually without shock. Tighten the nuts and men as determined from the calibration curve of bolts just sufficiently to hold the initial deflec- the spring and spring deflection reading (7.2.1) tions of the specimen and spring. It is imperative or as applied by an external force (7.2.2), that no additional force be applied in tightening 10.I .3 Thickness of the test specimen 30 min the bolts. after removal from the clamp, f,,

¶8.3 Test Time and Test Temperature- 10.I .4 Type of test specimen used, together Choose a suitable temperature and time for the with the time and temperature of test, cornpression set, depending upon the conditions 10.1.5 Compression set, expressed as a per- of the expected service. In comparative tests, use centage of the original thickness, identical temperature and heating periods. It is 10.1.6 Method used (Method A), and suggested that the test temperature be chosen 10.1.7 Number of specimens tested. from those listed in Practice D 1349. Suggested test periods are 22 h and 70 h. The specimen METHOD 8-COMPRESSION SET UNDER shall be at room temperature when inserted in CONSTANT DEFLECTION IN AIR the compression device. Place the assembled

¶1 j. Apparatus compression device in the oven within 2 h after completion of the assembly and allow it to re- 1 I . I Dial Micrometer-A dial micrometer, main there for the required test period in dry air for measuring the specimen thickness, in accord- at the test temperature selected. At the end of the ance with Practice D 3767, Method A 1. test period, take the device from the oven and NOTE 4-FOr vulcanizates having a hardness below remove the specimens immediately and allow it 35 IRHD. the force on the presser fool should be to cool. reduced to 0.2 f 0.05 N (0.04 f 0.01 Ibf).

¶8.4 Cooling Period-While cooling, allow the 11.2 Spacer Bars, to maintain the constant specimens to rest on a poor thermally conducting deflection required under Method B. surface, such as wood, for 30 min before making 11.2.1 Spacer bars for Type 1 samples shall the measurement of the final thickness. Conduct have a thickness of 9.5 *

¶0.02 mm (0.375 f the cooling period at a standard laboratory tem- 0.001 in.). perature of 23 k 2°C (73.4 3.6'F). Specimens 11.2.2 Spacer ban for Type 2 samples shall whose compression set property is affected by have a thickness of 4.50 f 0.01 mm (0. I770 + atmospheric moisture shall be cooled in an at- 0.0005 in.).

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¶mosphere controlled to 50 5 % relative humid- 1 I .3 Compression Device, consisting of two or ity. more flat steel plates between the parallel faces

¶8.5 h i n d Thickness Measuremenl-After the of which the specimens may be compressed as rest period, measure the final thickness at the shown in Fig. 3. Steel spacers for the required center of the specimen in accordance with 8. I . percentage of compression given in 12.2 shall be

¶D395 placed on each side of the rubber specimens to 2 h after completion of the assembly and allow control their thickness while compressed. The it to remain there for the required test period in steel surfaces contacting the rubber specimens dry air at the test temperature selected. At the shall be ground to a maximum roughness of 250 end of the test period, take the device from the pm (10 pin.) and then chromium plated and oven and remove the test specimen immediately polished. and allow them to cool.

¶I 1.4 Oven, conforming to the specification for 12.4 Cooling Period-While cooling, allow a Type IIB laboratory oven given in Specification the test specimen to rest on a poor thermally E 145. conducting surface, such as wood, for 30 min

¶I 1.5 Plates-The plates between which the before making the measurement of the final test specimen is compressed shall be made of thickness. Maintain the conditions during the steel of suficient thickness to withstand the com- cooling period in accordance with 8.4. pressive stresses without bending. The surfaces 12.5 Final Thickness Measurement-After against which the specimen is held shall have a the rest period, measure the final thickness at the highly polished chromium-plated finish and shall center of the test specimen in accordance with be cleaned thoroughly and wiped dry before each 12.1. test.