1、Designation: D 4684 07An 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 (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defens
3、e.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
4、to 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 Procedure A of this test method has precision stated fora yield range from
5、less than 35 Pa to 210 Pa and apparentviscosity range from 4300 to 270 000 mPas. The test proce-dure can determine higher yield stress and viscosity levels.1.3 This test method is applicable for unused oils, some-times referred to as fresh oils, designed for both light duty andheavy duty engine appl
6、ications. It also has been shown to besuitable for used diesel and gasoline engine oils. The applica-bility to petroleum products other than engine oils has not beendetermined.1.4 This test method uses the milliPascal second (mPas) asthe unit of viscosity. For information, the equivalent unit,centiP
7、oise (cP), is shown in parentheses.1.5 This test method contain two procedures: Procedure Aincorporates several equipment 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, P
8、rocedureAapplies to thoseinstruments that utilize thermoelectric cooling technology andthose that use indirect refrigeration technology of recentmanufacture for instrument temperature control. Procedure Bcan use the same instruments used in Procedure A or thosecooled by circulating methanol.1.6 This
9、 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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents
10、2.1 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 Calibration Laboratories3. Terminology3.1 Definitions:3.1.1 apparent viscositythe determined viscosity obtainedby use
11、 of this test method.3.1.2 Newtonian oil or fluidan 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 she
12、ar rate.3.1.4 shear ratethe velocity gradient in fluid 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:G
13、r52V!Rs2Rs22 Rr2(1)54p! Rs2t Rs22 Rr2!(2)where:Gr= shear rate at the surface of the rotor in reciprocalseconds, s1,1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.07 on Flow Properties.Current e
14、dition approved Jan. 15, 2007. Published March 2007. Originallyapproved in 1987. Last previous edition approved in 2002 as D 468402a.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume infor
15、mation, refer to the standards Document Summary page onthe ASTM website.3Available from International Organization for Standardization (ISO), 1 rue 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.Copyrigh
16、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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
17、.5 shear stressthe motivating force per unit area 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, m
18、m,Rt= radius of the string, mm,Sr= shear stress at 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
19、. This value is thus a measure of the resistance 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 fram
20、ework of apparent viscosity versusspeed, from which the apparent viscosities of test oils aredetermined. Calibration oils, which are essentially Newtonianfluids, are available commercially from suppliers complyingwith ISO 17025 and traceable to a national metrology institute(NMI), and have an approx
21、imate viscosity of 30 Pas (30 000cP) at 20C or 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 be
22、 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
23、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
24、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, t
25、he 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 resu
26、lts 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
27、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 oi
28、ls 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” conducte
29、d 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 te
30、mperatureprofile 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 Viscometer6An apparatus that consists ofone or more
31、 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 shallhave a crossbar near the top of the shaft extending in bothdirections far enough to allow the locking pin (6.6) to stoprotat
32、ion 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 viscometric cell has the followingtypical dimensions:4Pumpability Reference Oils (PRO) 21 through 29.5The boldface numbers in parentheses refer
33、 to the references at the end of thisstandard.6The sole source of supply of the apparatus known to the committee at this timeis Cannon Instrument Co., P.O. Box 16, State College, PA 16804. If you are awareof alternative suppliers, please provide this information to ASTM InternationalHeadquarters. Yo
34、ur comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.D4684072Diameter of rotor 17.0 6 0.05 mmLength of rotor 20.0 6 0.14 mmInside diameter of cell 19.0 6 0.05 mmRadius of shaft 3.18 6 0.13 mmRadius of string 0.1 mm6.1.2 Cell CapA cov
35、er inserted into the top of theviscometer cell to minimize room air circulation into the cells.The cell cap is a stepped cylinder 38 6 1 mm (1.5 6 0.05 in.)in length made of a low thermal conductivity material such asan acetyl copolymer like Delrint. The top half is 28 6 1mm(1.10 6 0.05 in.) in diam
36、eter 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 contact rotor shaft. Thepiece has a center bore of 11 6 1 mm (0.438 6 0.05 in.). Thecap is made i
37、n two halves to facilitate placement in the top ofthe cell.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 SystemRegula
38、tes the mini-rotaryviscometer block 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
39、.2 Temperature ProfileThe temperature profile is fullydescribed in Table X1.1 and Table X1.2.6.4 Thermometers6For 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
40、0.2C subdivisions.Other thermometric 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
41、does not create a biasedtemperature 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 dr
42、y gas tominimize moisture condensation 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
43、 Locking PinA device to keep the rotor 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 00
44、0 cP) at 25C for Procedure A for calibration 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
45、a residue is suitable.(WarningFlammable.)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 vali
46、d viscositymeasurements. If the sample 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
47、not permanently attached to thetemperature 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
48、.2 During the calibration all the cells are to contain 10mL of a typical fluid with the rotor and cell caps in place.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
49、sensor and controller. Make at least two tempera-ture measurements at every calibration temperature with atleast 10 min between observations. For instruments using anindependent temperature controller, see X2.1 for calibrationguidance.NOTE 1All temperatures in this test method refer to the actualtemperature and not necessarily the indicated temperature.9.2 The calibration constant of each rotor/stator combina-tion is determined by conducting two tests at 25C using aviscometric standard as a te
