ASTM_D_395-18.pdf

D395-183.2 The residual deformation of a test specimen is measured 30 min after removal from a suitable compression device in whichthe specimen had been subjected for a definite time to compressive deformation under specified conditions.3.3 After the measurement of the residual deformation,the compression set,as specified in the appropriate test method,iscalculated according to Eq 1 and Eq 2.4.Significance and Use4.1 Compression set tests are intended to measure the ability of rubber compounds to retain elastic properties after prolongedaction of compressive stresses.The actual stressing service may involve the maintenance of a definite deflection,the constantapplication of a known force,or the rapidly repeated deformation and recovery resulting from intermittent compressive forces.Though the latter dynamic stressing,like the others,produces compression set,its effects as a whole are simulated more closelyby compression flexing or hysteresis tests.Therefore,compression set tests are considered to be mainly applicable to serviceconditions involving static stresses.Tests are frequently conducted at elevated temperatures.5.Test Specimens5.1 Specimens from each sample may be tested in duplicate(Option 1)or triplicate(Option 2).The compression set of thesample in Option 1 shall be the average of the two specimens expressed as a percentage.The compression set of the sample inOption 2 shall be the median(middle most value)of the three specimens expressed as a percentage.5.2 The standard test specimen shall be a cylindrical disk cut from a laboratory prepared slab.5.2.1 The dimensions of the standard specimens shall be:Type12Thickness,mm(in.)12.50.56.00.2(0.490.02)(0.240.01)Diameter,mm(in.)29.00.513.00.2(1.140.02)(0.510.01)Type 1 specimen is used in Test Methods A,B,and C.Type 2 specimen is used in Test Method B and C.5.2.2 When cutting the standard specimen,the circular die having the required inside dimensions specified in 5.2.1 shall berotated in a drill press or similar device and lubricated by means of a soap solution.A minimum distance of 13 mm(0.51 in.)shallbe maintained between the cutting edge of the die and the edge of the slab.The cutting pressure shall be as light as possible tominimize cupping of the cut edges.The dies shall be maintained carefully so that the cutting edges are sharp and free of nicks.5.3 An optional method of preparing the standard specimen may be the direct molding of a circular disk having the dimensionsrequired for the test method used and specified in 5.2.1.NoTE 1-It should be recognized that an equal time and temperature,if used for both the slab and molded specimen,will not produce an equivalentstate of cure in the two types of specimen.A higher degree of cure will be obtained in the molded specimen.Adjustments,preferably in the time of cure,must be taken into consideration if comparisons between the specimens prepared by different methods are to be considered valid.NorE 2-It is suggested,for the purpose of uniformity and closer tolerances in the molded specimen,that the dimensions of the mold be specified andshrinkage compensated for therein.A two-plate mold with a cavity 13.00.1 mm(0.5100.004 in.)in thickness and 29.200.05 mm(1.1480.002in.)in diameter,with overflow grooves,will provide Type I specimens for Test Method A and Test Method B.A similar mold but having a cavity of 6.3 0.3 mm(0.250.012 in.)in thickness and 13.30.1 mm(0.520.004 in.)in diameter will provide Type 2 specimens for Test Method B.5.4 When the standard test specimen is to be replaced by a specimen taken from a vulcanized rubber part of greater thicknessthan the one indicated in 5.2.1,the sample thickness shall be reduced first by cutting transversely with a sharp knife and thenfollowed by buffing to the required thickness in accordance with Practice D3183.5.5 An alternative method of preparing specimens is by plying up cylindrical disks cut from a standard sheet prepared inaccordance with Practice D3182 using the specimen sizes specified in 5.2.1 and cutting as described in 5.2.2,or where a drill pressis not available cutting the specimens with a single stroke from a cutting die.5.5.1 The disks shall be plied,without cementing,to the thickness required.Such plies shall be smooth,flat,of uniformthickness,and shall not exceed seven in number for Type 1 specimens and four in number for Type 2 specimens.5.5.2 Care shall be taken during handling and placing of the plied test specimen in the test fixture by keeping the circular facesparallel and at right angles to the axis of the cylinder.5.5.3 The results obtained on plied specimens may be different from those obtained using solid specimens and the results maybe variable,particularly if air is trapped between disks.5.5.4 The results obtained on the specimens prepared by one of the methods may be compared only to those prepared by thesame method.5.6 For routine or product specification testing,it is sometimes more convenient to prepare specimens of a different size orshape,or both.When such specimens are used,the results should be compared only with those obtained from specimens of similarsize and shape and not with those obtained with standard specimen.For such cases,the product specification should define the24D395-18specimen as to the size and shape.If suitable specimens cannot be prepared from the product,the test method and allowable limitsmust be agreed upon between the producer and the purchaser.6.Conditioning6.1 Store all vulcanized test specimens or product samples to be tested at least 24 h but not more than 60 days.When the dateof vulcanization is not known,make tests within 60 days after delivery by the producer of the article represented by the specimen.6.2 Allow buffed specimens to rest at least 30 min before specimens are cut for testing.6.3 Condition all specimens before testing for a minimum of 3 h at 23 2C(73.4 3.6F).Specimens whose compressionset properties are affected by atmospheric moisture shall be conditioned for a minimum of 24 h in an atmosphere controlled to arelative humidity of 50 10%RH(40 to 60%RH).7.Precision and Bias7.1 These precision statements have been prepared in accordance with Practice D4483.Please refer to Practice D4483 forterminology and other testing and statistical concepts.7.2 Prepared test specimens of two rubbers for Test Methods A and B were supplied to five laboratories.These were tested induplicate each day on two separate testing days.A test result,therefore,is the average of two test specimens,for both Test MethodsA and B.7.3 One laboratory did not run the Test Method A testing:therefore,the precision for Test Method A is derived from fourlaboratories.7.4 The Type I precision results are given in Table I and Table 2.7.5 Bias-In test method statistical terminology,bias is the difference between an average test value and the reference or truetest property value.Reference values do not exist for these test methods since the value or level of the test property is exclusivelydefined by the test method.Bias,therefore,cannot be determined.TEST METHOD A-COMPRESSION SET UNDERCONSTANT FORCE IN AIR8.Apparatus8.1 Micrometer-A micrometer.analog or digital,for measuring specimen thickness,in accordance with Practice D3767.Method Al.8.2 Compression Device,consisting of a force application spring and two parallel compression plates assembled by means ofa frame or threaded bolt in such a manner that the device shall be portable and self-contained after the force has been applied andthat the parallelism of the plates shall be maintained.The force may be applied in accordance with either 8.2.1 or 8.2.2.8.2.1 Calibrated Spring Force Application-The required force shall be applied by a screw mechanism for compressing acalibrated spring the proper amount.The spring shall be of properly heat-treated spring steel with ends ground and perpendicularto the longitudinal axis of the spring.A suitable compression device is shown in Fig.1.The spring shall conform to the followingrequirements:8.2.1.1 The spring shall be calibrated at room temperature 235C(73.49F)by applying successive increments of forcenot exceeding 250 N(50 lbf)and measuring the corresponding deflection to the nearest 0.2 mm(0.01 in.).The curve obtained byTABLE 1 Type 1 Precision Results,Compression Set-TestMethod AMaterialMeanWithin LaboratoryBetween LaboratoryLevelS,(0SRR(R)11.73(%)0.0500.1428.20.1900.5431.1226.10.8982549.72376.7125.7S.within laboratory standard deviation.r=repeatability(in measurement units)(r)=repeatability(in percent).Sn=between laboratory standard deviation.R reproducibility(in measurement units).(R)=reproducibility(in percent).Supporting data have been filed at ASTM Intemational Headquarters and may be obtained by requesting Research Report RR:D11-1138.D395-18TABLE 2 Type 1 Precision Results,Compression Set-TestMethod BMaterialMeanWithin LaboratoryBetween LaboratoryLevelS.0Sa用(13.7(%)0.5911.6712.24.3631.8252.80.5671.603.05.9216831.7S.within laboratory standard deviation.r=repeatability(in measurement units).(r)=repeatability(in percent).SR=between laboratory standard deviation.R reproducibility(in measurement units).(R)=reproducibility(in percent).TestSpecimenFIG.1 Device for Compression Set Test,Using Calibrated Spring Loading,Test Method Aplotting the forces against the corresponding deflections shall have a slope of 70 3.5 kN/m(400 20 Ibf/in.)at 1.8 kN(400Ibf).The slope is obtained by dividing the two forces above and below 1.8 kN by the difference between the correspondingdeflections.8.2.1.2 The original dimensions of the spring shall not change due to fatigue by more than 0.3 mm(0.01 in.)after it has beenmounted in the compression device,compressed under a force of 1.8 kN(400 Ibf).and heated in the oven for one week at 702C(1583.6F).In ordinary use.a weekly check of the dimensions shall show no greater change than this over a period of Iyear.8.2.1.3 The minimum force required to close the spring(solid)shall be 2.4 kN(530 Ibf).8.2.2 External Force Application-The required force shall be applied to the compression plates and spring by external meansafter the test specimen is mounted in the apparatus.Either a calibrated compression machine or known masses may be used forforce application.Provision shall be made by the use of bolts and nuts or other devices to prevent the specimen and spring fromlosing their initial deflections when the external force is removed.The spring shall have essentially the same characteristics asdescribed in 8.2.1,but calibration is not required.A suitable compression device is shown in Fig.2.8.3 Plates-The plates between which the test specimen is compressed shall be made of steel of sufficient thickness to withstandthe compressive stresses without bending.8.3.I The surfaces against which the specimen is held shall have an industrial chrome(hard chrome)plated finish and shall becleaned thoroughly and wiped dry before each test.8.3.2 The steel surfaces contacting the rubber specimens shall be ground to a maximum roughness of 0.250 um(10 uin.).polished,and industrial chrome(hard chrome)plated.