1、Designation: D 4684 08An American National StandardStandard Test Method forDetermination of Yield Stress and Apparent Viscosity ofEngine Oils at Low Temperature1This standard is issued under the fixed designation D 4684; the number immediately following the designation indicates the year oforiginal
2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense
3、.1. Scope*1.1 This test method covers the measurement of the yieldstress and viscosity of engine oils after cooling at controlledrates over a period exceeding 45 h to a final test temperaturebetween 10 and 40C. The viscosity measurements are madeat a shear stress of 525 Pa over a shear rate of 0.4 t
4、o 15 s1. Theviscosity as measured at this shear stress was found to producethe best correlation between the temperature at which theviscosity reached a critical value and borderline pumpingfailure temperature in engines.1.2 This test method contain two procedures: Procedure Aincorporates several equ
5、ipment and procedural modificationsfrom Test Method D 468402 that have shown to improve theprecision of the test, while Procedure B is unchanged from TestMethod D 468402.Additionally, ProcedureAapplies to thoseinstruments that utilize thermoelectric cooling technology ordirect refrigeration technolo
6、gy of recent manufacture for in-strument temperature control. Procedure B can use the sameinstruments used in Procedure A or those cooled by circulatingmethanol.1.3 Procedure A of this test method has precision stated fora yield range from less than 35 Pa to 210 Pa and apparentviscosity range from 4
7、300 to 270 000 mPas. The test proce-dure can determine higher yield stress and viscosity levels.1.4 This test method is applicable for unused oils, some-times referred to as fresh oils, designed for both light duty andheavy duty engine applications. It also has been shown to besuitable for used dies
8、el and gasoline engine oils. The applica-bility to petroleum products other than engine oils has not beendetermined.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5.1 ExceptionThis test method uses the milliPascalsecond (
9、mPas) as the unit of viscosity. For information, theequivalent unit, centiPoise (cP), is shown in parentheses.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safet
10、y and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3829 Test Method for Predicting the Borderline PumpingTemperature of Engine Oil2.2 ISO Standard:3ISO 17025 General Requirements for the Competence ofTesting and
11、 Calibration LaboratoriesISO Guide 34 General Requirements for the Competence ofReference Material ProducersISO Guide 35 Certification of Reference Materials3. Terminology3.1 Definitions:3.1.1 apparent viscositythe determined viscosity obtainedby use of this test method.3.1.2 Newtonian oil or fluida
12、n oil or fluid that at a giventemperature exhibits a constant viscosity at all shear rates orshear stresses.3.1.3 non-Newtonian oil or fluidan oil or fluid that at agiven temperature exhibits a viscosity that varies with chang-ing shear stress or shear rate.3.1.4 shear ratethe velocity gradient in f
13、luid flow. For aNewtonian fluid in a concentric cylinder rotary viscometer inwhich the shear stress is measured at the inner cylinder surface(such as this apparatus, described in 6.1), and ignoring any endeffects, the shear rate is given as follows:Gr52V!Rs2Rs22 Rr2(1)1This test method is under the
14、jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.07 on Flow Properties.Current edition approved Dec. 1, 2008. Published January 2009. Originallyapproved in 1987. Last previous edition approved in 2007 as D 4684071.2For referen
15、ced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Organization for Standardization (ISO), 1 r
16、ue deVaremb, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.54p! Rs2t Rs22 Rr2!(2)where:Gr= shear r
17、ate at the surface of the rotor in reciprocalseconds, s1,V = angular velocity, rad/s,Rs= stator radius, mm,Rr= rotor radius, mm, andt = time in seconds for one revolution of the rotor.For the specific apparatus being described in 6.1.1,Gr5 63/t (3)3.1.5 shear stressthe motivating force per unit area
18、 forfluid flow. For the rotary viscometer being described, the rotorsurface is the area under shear or the shear area.Tr5 9.81 M Ro1 Rt! 3 1026(4)Sr5Tr2 p!Rr2h3 109(5)where:Tr= torque applied to rotor, Nm,M = applied mass, g,Ro= radius of the shaft, mm,Rt= radius of the string, mm,Sr= shear stress a
19、t the rotor surface, Pa, andh = height of the rotor, mm.For the dimensions given in 6.1.1,Tr5 31.7 M 3 1026(6)Sr5 3.5 M (7)3.1.6 viscositythe ratio between the applied shear stressand rate of shear, sometimes called the coefficient of dynamicviscosity. This value is thus a measure of the resistance
20、to flowof the liquid. The SI unit of viscosity is the Pascal secondPas. A centipoise (cP) is one milliPascal second mPas.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration oilsthose oils that establish the instru-ments reference framework of apparent viscosity versusspeed, from whi
21、ch the apparent viscosities of test oils aredetermined. Calibration oils, which are essentially Newtonianfluids, shall be obtained from suppliers complying with ISOGuide 34, ISO Guide 35, and ISO 17025 with traceability to anational metrology institute (NMI). These calibration oils willhave an appro
22、ximate viscosity of 30 Pas (30 000 cP) at 20Cor 60 Pas (60 000 cP) at 25C.3.2.2 cell constantthe ratio of the calibration fluid viscos-ity to the time required to complete the first three measuredrevolutions of the rotor.3.2.3 test oilany oil for which the apparent viscosity andyield stress are to b
23、e determined by this test method.3.2.4 unused oilan oil which has not been used in anoperating engine.3.2.5 used oilan oil which has been used in an operatingengine.3.2.6 yield stressthe shear stress required to initiate flow.For all Newtonian fluids and many non-Newtonian fluids, theyield stress is
24、 zero.An engine oil can have a yield stress that isa function of its low-temperature cooling rate, soak time, andtemperature.4. Summary of Test Method4.1 An engine oil sample is held at 80C and then cooled ata programmed cooling rate to a final test temperature and heldfor a specified time period.At
25、 the end of this period, a series ofincreasing low torques are applied to the rotor shaft untilrotation occurs to determine the yield stress, if any is exhibited.A higher torque is then applied to determine the apparentviscosity of the sample.5. Significance and Use5.1 When an engine oil is cooled,
26、the rate and duration ofcooling can affect its yield stress and viscosity. In thislaboratory test, a fresh engine oil is slowly cooled through atemperature range where wax crystallization is known to occur,followed by relatively rapid cooling to the final test tempera-ture. These laboratory test res
27、ults have predicted as failures theknown engine oils that have failed in the field because of lackof oil pumpability.4These documented field failing oils haveall consisted of oils normally tested at 25C. These fieldfailures are believed to be the result of the oil forming a gelstructure that results
28、 in either excessive yield stress or viscosityof the engine oil, or both.5.2 Cooling Profiles:5.2.1 For oils to be tested at 20C or colder, Table X1.1applies. The cooling profile described in Table X1.1 is based onthe viscosity properties of the ASTM Pumpability ReferenceOils (PRO). This series of o
29、ils includes oils with normallow-temperature flow properties and oils that have beenassociated with low-temperature pumpability problems (1-5).5Significance for the 35 and 40C temperature profiles isbased on the data collected from the “Cold Starting andPumpability Studies in Modern Engines” conduct
30、ed by ASTM(6,7).5.2.2 For oils to be tested at 15 or 10C, Table X1.2applies. No significance has been determined for this tempera-ture profile because of the absence of appropriate referenceoils. Similarly, precision of the test method using this profilefor the 10C test temperature is unknown. The t
31、emperatureprofile of Table X1.2 is derived from the one in Table X1.1 andhas been moved up in temperature, relative to Table X1.1,inconsideration of the expected higher cloud points of theviscous oils tested at 15 and 10C.6. Apparatus6.1 Mini-Rotary ViscometerAn apparatus that consists ofone or more
32、 viscometric cells in a temperature-controlled blockmade of a metallic material with high thermal conductivity.Each cell contains a calibrated rotor-stator set. The rotor shall4Pumpability Reference Oils (PRO) 21 through 29.5The boldface numbers in parentheses refer to the references at the end of t
33、hisstandard.D4684082have a crossbar near the top of the shaft extending in bothdirections far enough to allow the locking pin (6.6) to stoprotation at successive half turns. Rotation of the rotor isachieved by an applied force acting through a string woundaround the rotor shaft.6.1.1 The mini-rotary
34、 viscometric cell has the followingdimensions:Diameter of rotor 17.06 6 0.08 mmLength of rotor 20.0 6 0.14 mmInside diameter of cell 19.07 6 0.08 mmRadius of shaft 3.18 6 0.13 mmRadius of string 0.1 mm6.1.2 Cell CapA cover inserted into the top of theviscometer cell to minimize room air circulation
35、into the cellsis required for thermometrically cooled instruments. The cellcap is a stepped cylinder 38 6 1 mm (1.5 6 0.05 in.) in lengthmade of a low thermal conductivity material, for example,thermoplastic such as acetyl copolymers that have knownsolvent resistivity and are suitable for use betwee
36、n the tem-perature ranges of this test method. The top half is 28 6 1mm(1.10 6 0.05 in.) in diameter and the bottom half is 19 mm(0.745 in.) in diameter with a tolerance consistent with the celldiameter. The tolerance on the bottom half is such that it willeasily fit into cell but not allow cap to c
37、ontact rotor shaft. Thepiece has a center bore of 11 6 1 mm (0.438 6 0.05 in.). Thecap is made in two halves to facilitate placement in the top ofthe cell.6.1.2.1 Cell caps shall not be used in the direct refrigerationinstruments, since such use would block the flow of cold, dryair into the stators
38、to keep them frost-free.6.2 Weights:6.2.1 Yield Stress MeasurementA set of ten weights, eachwith a mass of 10 6 0.1 g. One of the weights is a holder forthe other weights.6.2.2 Viscosity MeasurementWeight with mass of 150 61.0 g.6.3 Temperature Control SystemRegulates the mini-rotaryviscometer block
39、 temperature in accordance with the tempera-ture requirements described in Table X1.1 or Table X1.2.6.3.1 Temperature ControllerAs a very critical part of thisprocedure, a description of the requirements that the controllershall meet are included in Appendix X2.6.3.2 Temperature ProfileThe temperatu
40、re profile is fullydescribed in Table X1.1 and Table X1.2.6.4 ThermometersFor measuring the temperature of theblock. Two are required, one graduated from at least +70 to90C in 1C subdivisions, the other with a scale from above+5C down to at least 41C or lower, in 0.2C subdivisions.Other thermometric
41、 devices of equal accuracy and resolutionmay be used to measure the temperature, such as digital metersusing a resistance temperature detector (RTD) or a thermistorsensor.6.4.1 When using metal encased thermometric devices, careshould be taken that the metal case does not create a biasedtemperature
42、reading. It has been observed that some metalsheathed devices indicate a higher than actual temperature ofthe sample. This is typically caused by heat conduction throughthe metal sheath but there can be other causes.6.5 Supply of Dry GasA supply of dry filtered dry gas tominimize moisture condensati
43、on on the upper portions of theinstrument.6.5.1 For thermoelectric cooled instruments, which use cellcaps, the dry gas supply is connected to the housing cover. Thesupply of dry gas is discontinued when the cover is removedfor the measurement phase of the test.6.6 Locking PinA device to keep the rot
44、or from turningprematurely and able to stop the rotor at the nearest halfrevolution by interaction with the rotor crossbar.7. Reagents and Materials7.1 Newtonian OilLow cloud-point of approximately 30Pas (30 000 cP) viscosity at 20C for Procedure B or 60 Pas(60 000 cP) at 25C for Procedure A for cal
45、ibration of theviscometric cells.7.2 MethanolCommercial or technical grade of drymethanol is suitable for the refrigerated cooling bath requiredfor some units. (WarningFlammable.)7.3 Oil SolventCommercial heptanes or similar solventthat evaporates without leaving a residue is suitable.(WarningFlamma
46、ble.)7.4 AcetoneA technical grade of acetone is suitable pro-vided it does not leave a residue upon evaporation.(WarningFlammable.)Procedure A8. Sampling8.1 A representative sample of test oil free from suspendedsolid material and water is necessary to obtain valid viscositymeasurements. If the samp
47、le in its container is received belowthe dew-point temperature of the room, allow the sample towarm to room temperature before opening the container.9. Calibration and Standardization9.1 Calibration ProcedureFor those instruments in whichthe temperature sensor is not permanently attached to thetempe
48、rature controller, calibrate the temperature sensor in theMRV block while the sensor is attached to the temperaturecontroller.9.1.1 The sensed temperature calibration shall be verifiedusing a reference thermometer noted in 6.4 at a minimum ofthree temperatures.9.1.2 During the calibration all the ce
49、lls are to contain10 mLof a typical fluid with the rotor and, if required, cell capsin place. Cell caps shall not be used for direct refrigerationinstruments (see 6.1.2).9.1.3 Make these temperature measurements at least 5Capart and include both 5C and the lowest test temperatureused to establish a calibration curve for this combination oftemperature sensor and controller. Make at least two tempera-ture measurements at every calibration temperature with atleast 10 min between observations. For
