1、Designation: D 6896 03 (Reapproved 2007)An American National StandardStandard Test Method forDetermination of Yield Stress and Apparent Viscosity ofUsed Engine Oils at Low Temperature1This standard is issued under the fixed designation D 6896; the number immediately following the designation indicat
2、es the year oforiginal 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.1. Scope1.1 This test method covers the measurement of t
3、he yieldstress and viscosity of engine oils after cooling at controlledrates over a period of 43 or 45 h to a final test temperature of-20 or -25C. The viscosity measurements are made at a shearstress of 525 Pa over a shear rate of 0.4 to 15 s-1. This testmethod is suitable for measurement of viscos
4、ities ranging from4000 mPas to 400 000 mPas, and is suitable for yield stressmeasurements of 7 Pa to 350 Pa.1.2 This test method is applicable for used diesel oils. Theapplicability and precision to other used or unused engine oilsor to petroleum products other than engine oils has not beendetermine
5、d.1.3 This test method uses the millipascal second (mPas) asthe unit of viscosity. For information, the equivalent centipoiseunit is shown in parentheses.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of t
6、his standard to establish appro-priate safety 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 OilD 4684 Test Method for Determination
7、of Yield Stress andApparent Viscosity of Engine Oils at Low TemperatureD 5133 Test Method for Low Temperature, Low ShearRate, Viscosity/Temperature Dependence of LubricatingOils Using a Temperature-Scanning Technique3. Terminology3.1 Definitions:3.1.1 apparent viscositythe determined viscosity obtai
8、nedby use 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 stre
9、ss or shear 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 the apparatus described in 6.1), and ignoring any endeffects, the shear rate is given as fo
10、llows:Gr52V!Rs2Rs22 Rr2(1)54p!Rs2t Rs22 Rr2!(2)where:Gr= shear rate at the surface of the rotor in reciprocalseconds, s-1,V = angular velocity, rad/s,Rs= stator radius, mm,Rr= rotor radius, mm, andt = time for one revolution of the rotor, s.For the specific apparatus described in 6.1,Gr5 63/t (3)3.1
11、.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)Sr5TTr2p!Rr2h3 109(5)where:Tr= torque applied to rotor, Nm,M = applied mass, g,Ro= radius of the shaft, m
12、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 6.1.1,1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.07 on F
13、low Properties.Current edition approved Nov. 1, 2007. Published January 2008. Originallyapproved in 2003. Last previous edition approved in 2003 as D 689603e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of
14、ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Copyright by ASTM Intl (all rights reserved); Thu Jan 15 01:35:08 EST 2009Downloaded/pr
15、inted byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions authorized.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 resistanc
16、e to flowof the liquid. The SI unit of viscosity is the pascal second Pas.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 w
17、hich the apparent viscosities of test oils aredetermined. Calibration oils, which are essentially Newtonianfluids, are available commercially and have an approximateviscosity of 30 Pas (30 000 cP) at -20C.3.2.2 test oilany oil for which the apparent viscosity andyield stress are to be determined by
18、this test method.3.2.3 used oilan oil which has been used in an operatingengine.3.2.4 yield stressthe shear stress required to initiate flow.3.2.4.1 DiscussionFor all Newtonian fluids and somenon-Newtonian fluids, the yield stress is zero. An oil can havea yield stress that is a function of its low-
19、temperature coolingrate, soak time, and temperature. Yield stress measurement bythis test method determines only whether the test oil has a yieldstress of at least 35 Pa; a yield stress below 35 Pa is consideredto be insignificant for engine oils.4. Summary of Test Method4.1 A used engine oil sample
20、 is heated at 80C and thenvigorously agitated. The sample is then cooled at a pro-grammed cooling rate to a final test temperature. A low torqueis applied to the rotor shaft to measure the yield stress.Ahighertorque is then applied to determine the apparent viscosity of thesample.5. Significance and
21、 Use5.1 When an engine oil is cooled, the rate and duration ofcooling can affect its yield stress and viscosity. In thislaboratory test, used engine oil is slowly cooled through atemperature range where wax crystallization is known to occur,followed by relatively rapid cooling to the final test temp
22、era-ture. As in other low temperature rheological tests such as TestMethods D 3829, D 4684, and D 5133, a preheating conditionis required to ensure that all residual waxes are solubilized inthe oil prior to the cooldown (that is, remove thermal memory).However, it is also known that highly sooted us
23、ed diesel engineoils can experience a soot agglomerization phenomenon whenheated under quiescent conditions. The current method uses aseparate preheat and agitation step to break up any sootagglomerization that may have occurred prior to cooldown.The viscosity of highly sooted diesel engine oils as
24、measuredin this test method have been correlated to pressurization timesin a motored engine test (1).35.2 Cooling Profiles:5.2.1 For oils to be tested at -20C and -25C, Table X1.1applies. The cooling profile described in Table X1.1 is based onthe viscosity properties of the ASTM Pumpability Referenc
25、eOils (PRO). This series of oils includes oils with normallow-temperature flow properties and oils that have beenassociated with low-temperature pumpability problems (2-7).6. Apparatus6.1 Mini-Rotary Viscometer4, an apparatus that consists ofone or more viscometric cells in a temperature-controlleda
26、luminum block. Each cell contains a calibrated rotor-statorset. Rotation of the rotor is achieved by an applied load actingthrough a string wound around the rotor shaft.6.1.1 The mini-rotary viscometric cell has the followingtypical dimensions:millimetresDiameter of rotor 17.0Length of rotor 20.0Ins
27、ide diameter of cell 19.0Radius of shaft 3.18Radius of string 0.106.2 Weights:6.2.1 Yield Stress, weight set consists of ten 10 g units witha tolerance of 1 % for each unit.6.2.2 Viscosity, 150 g weight with a 1 % tolerance.6.3 Temperature Control System, that will regulate themini-rotary viscometer
28、 block temperature in accordance withthe temperature limits described in Table X1.1.6.3.1 Temperature Controller is the most critical part of thisprocedure. A description of the requirements that the controllershall meet are included in Appendix X2.6.3.2 Temperature ProfileThe temperature profile is
29、 fullydescribed in Table X1.1.6.4 Thermometers, for measuring the temperature of theblock. Two ranges are required, one graduated from at least+70 to 90C in 1C subdivisions, the other with a range fromat least -36 to +5C or -45 to +5C, in 0.2C subdivisions.Other thermometric devices of equal accurac
30、y and resolutionmay be used to calibrate the temperature sensor.6.5 Refrigeration Device, consisting of a means of remov-ing heat from the instrument such that the cell temperature iscontrolled in accordance with the program described in TableX1.1.6.6 Circulating System, that will circulate the liqu
31、id coolantto the instrument as needed. Methanol is a suitable coolant ifthe circulating coolant is below -10C. One should observetoxicity and flammability precautions that apply to the use ofmethanol. The circulating system shall be capable of maintain-ing test temperature during the test. If methan
32、ol is leaking fromthe system, discontinue the test and repair the leak.(WarningMethanol is flammable.)6.7 Chart Recorder, to verify that the correct cooling curveis being followed, it is recommended that a chart recorder beused to monitor the block temperature.3The boldface numbers in parentheses re
33、fer to the list of references at the end ofthis standard.4The 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 InternationalHeadq
34、uarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.D 6896 03 (2007)2Copyright by ASTM Intl (all rights reserved); Thu Jan 15 01:35:08 EST 2009Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No furthe
35、r reproductions authorized.6.8 Sample Pre-treatment Oven, an oven capable of main-taining a temperature of 80 6 1C for a minimum of 2 h.7. Reagents and Materials7.1 Newtonian Oil, a low cloud-point of approximately 30Pas (30 000 cP) viscosity at -20C for calibration of theviscometric cells.7.2 Metha
36、nolCommercial or technical grade of drymethanol is suitable for the cooling bath.7.3 Oil Solvent, commercial heptanes or similar solvent thatevaporates without leaving a residue is suitable. (WarningFlammable.)7.4 AcetoneA technical grade of acetone is suitable pro-vided it does not leave a residue
37、upon evaporation.(WarningFlammable.)8. Sampling8.1 A representative sample of test oil free from suspendedgranular material and water is necessary to obtain validviscosity measurements. If the sample in its container isreceived below the dew-point temperature of the room, allowthe sample to warm to
38、room temperature before opening thecontainer.9. Calibration and Standardization9.1 Calibrate the temperature sensor in place while attachedto the temperature controller. The sensed temperature shall beverified using a reference thermometer specified in 6.4 at aminimum of three temperatures. Make the
39、se temperaturemeasurements at least 5C apart to establish a calibration curvefor this combination of temperature sensor and controller. Forinstruments using an independent temperature controller, seeX2.1 for calibration guidance.NOTE 1All temperatures in this test method refer to the actualtemperatu
40、re as measured in the left thermowell and not necessarily theindicated temperature.9.2 The calibration of each viscometric cell (viscometerconstants) can be determined with the viscosity standard andthe following procedure at -20C.9.2.1 Use steps 10.2.3-10.6.9.2.2 Program the temperature controller
41、to cool the mini-rotary viscometer block to -20C within1horless, then startthe program.9.2.3 Allow the oil in the cells to soak at -20 6 0.2C for atleast 1 h, making small temperature control adjustments, ifnecessary, to maintain the test temperature.9.2.4 At the end of the soak period, record the t
42、emperaturereading of the measuring device in the left thermowell (testtemperature) and remove the cover of the viscometer cell.9.2.5 Perform step 10.4.1.9.2.6 Repeat 9.2.5 for each of the remaining cells, taking thecells in order from left to right.9.2.7 Calculate the viscometer constant for each ce
43、ll (rotor/stator combination) with the following equation:C 5ho/t (8)where:ho= viscosity of the standard oil, cP (mPas) at -20C,C = cell constant with 150 g mass, Pa, andT = time for three complete revolutions, s.9.2.8 If any cell has a calibration constant more than 10 %higher or lower than the ave
44、rage for the other cells, the faultmay be a problem with rotor operation. Examine rotor fordamage and recalibrate instrument.9.3 If corrected values for controller temperature and ther-mometer deviate by more than the tolerance, use X2.2 to assistin determining the fault.9.4 OvenCheck the calibratio
45、n of the temperature sensingdevice by appropriate methods. The temperature should beconstant at 80 6 1C.10. Procedure10.1 Select the cooling profile for the desired test tempera-ture. Table X1.2 lists the nominal times to reach a particulartest temperature.10.1.1 Choose the preprogrammed temperature
46、 profile. Ifthe profile is not available, enter it using the custom profile partof the software program. The instrument manual providesinstructions on adding custom profiles. The entries for acustom program will be found in Table X1.3.10.1.2 If the instrument temperature is controlled by anexternal
47、controller, it will need to be programmed to follow thecooling program in Table X1.1 with adjustment for thetemperature difference found in 9.1, if any.10.2 Test Sample and Viscometric Cell Preparation:10.2.1 Using suitable closed container, preheat the samplesin an oven to 80 6 1C for 2.25 h. At th
48、e end of this time,remove the samples from the oven and allow to cool for 15 minat room temperature.10.2.2 Agitate each sample using vigorous mechanical ormanual shaking for 60 s. Allow the samples to stand for aminimum of 10 min to allow for settling.10.2.3 Remove the nine rotors from the viscometr
49、ic cellsand ensure that both the cells and rotors are clean. See 10.6 forthe cleaning procedure.10.2.4 Place a 10 6 1.0 mL oil sample in each cell.10.2.5 Install the rotors in the proper stators and install theupper pivots.10.2.6 Place the loop of the 700-mm long string over thecrossarm at the top of the rotor shaft and wind all but 200 mmof the length of the string around the shaft. Do not overlapstrings. Loop the remaining end of the string over the topbearing cover. Orient the rotor such that an end of the crossarmat the top o
