1、Designation: D 6896 03e1An 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 indicates the year ofor
2、iginal 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.e1NOTETable X1.3 was corrected editorially in August 2004.1. Scope1.1 Th
3、is test method covers the measurement of the 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 testme
4、thod is suitable for measurement of viscosities 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 ot
5、her than engine oils has not beendetermined.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
6、. 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 Documents2.1 ASTM Standards:D 3829 Test Method for Predicting the Borderline PumpingTemperature of Engine
7、 Oil2D 4684 Test Method for Determination of Yield Stress andApparent Viscosity of Engine Oils at Low Temperature2D 5133 Test Method for Low Temperature, Low ShearRate, Viscosity/Temperature Dependence of LubricatingOils Using a Temperature-Scanning Technique23. Terminology3.1 Definitions:3.1.1 appa
8、rent viscositythe determined viscosity obtainedby 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 vis
9、cosity that varies with chang-ing shear stress 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 a
10、ny endeffects, the shear rate is given as follows: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 specifi
11、c apparatus described in 6.1,Gr5 63/t (3)3.1.5 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
12、= applied mass, g,Ro= radius of the shaft, mm,Rt= radius of the string, mm,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 edition approved March 10, 2003. Publishe
13、d May 2003.2Annual Book of ASTM Standards, Vol 05.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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
14、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 to flowof the liquid. The SI unit of viscosity is the pascal second Pas.A centipoise (cP) is one millipascal secon
15、d 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 which the apparent viscosities of test oils aredetermined. Calibration oils, which are essentially Newtonianfluids, a
16、re 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 this test method.3.2.3 used oilan oil which has been used in an operatingengine.3.2.4 yield stressthe shear stress r
17、equired 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-temperature coolingrate, soak time, and temperature. Yield stress measurement bythis test method determines only whe
18、ther 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 is heated at 80C and thenvigorously agitated. The sample is then cooled at a pro-grammed cooling rate to a final te
19、st 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 Use5.1 When an engine oil is cooled, the rate and duration ofcooling can affect its yield stress and viscosity. In
20、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 tempera-ture. As in other low temperature rheological tests such as TestMethods D 3829, D 4684, and D 5133, a preheating
21、 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 used diesel engineoils can experience a soot agglomerization phenomenon whenheated under quiescent conditions. The cur
22、rent 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 measuredin this test method have been correlated to pressurization timesin a motored engine test (1).35.2 Cooling Pr
23、ofiles: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 ReferenceOils (PRO). This series of oils includes oils with normallow-temperature flow properties and oils that have beenass
24、ociated 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-controlledaluminum block. Each cell contains a calibrated rotor-statorset. Rotation of the rotor is achieved by an applied load
25、 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 20.0Inside diameter of cell 19.0Radius of shaft 3.18Radius of string 0.106.2 Weights:6.2.1 Yield Stress, weight set consist
26、s 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 block temperature in accordance withthe temperature limits described in Table X1.1.6.3.1 Temperature Controller is
27、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 fullydescribed in Table X1.1.6.4 Thermometers, for measuring the temperature of theblock. Two ranges are required,
28、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 accuracy and resolutionmay be used to calibrate the temperature sensor.6.5 Refrigeration Device, consisting of a means of r
29、emov-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 liquid coolantto the instrument as needed. Methanol is a suitable coolant ifthe circulating coolant is below -10C. One s
30、hould 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 methanol is leaking from3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.4T
31、he 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. Your comments will receive careful consideration a
32、t a meeting of theresponsible technical committee1, which you may attend.D689603e12the 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 moni
33、tor the block temperature.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 Methan
34、olCommercial 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 u
35、pon 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 r
36、oom 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 thes
37、e 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 actualtemperatur
38、e 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 t
39、o 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 te
40、mperaturereading 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 cel
41、l (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 aver
42、age 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 calibration
43、 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
44、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 c
45、ontroller, 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 the
46、 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 viscometri
47、c 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
48、 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 of the rotor shaft is pointing directly forward. Ifavailable, secur
49、e crossarm with locking pin. If the rotations aremanually timed, it is helpful to color one end of the crossarm.10.2.6.1 The string may be prewound around the shaftbefore installation of the rotor in 10.2.5.10.2.7 Place the housing cover over the viscometric cells tominimize the formation of frost on the cold metal parts exposedto air. In some climates it may be necessary to flush the coverwith a dry gas (for example, dry air or nitrogen) to minimizethe frost formation.D689603e1310.2.8 Start the programmed temperature profile.10.2.9
