1、Designation: D6896 14Standard Test Method forDetermination of Yield Stress and Apparent Viscosity ofUsed Engine Oils at Low Temperature1This standard is issued under the fixed designation D6896; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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.1. Scope*1.1 This test method covers the measurement of the yieldstress and viscosity of engine oils after
3、 cooling at controlledrates over a period of 43 h or 45 h to a final test temperature of20 C or 25 C. The precision is stated for test temperatures20 C and 25 C. The viscosity measurements are made at ashear stress of 525 Pa over a shear rate of 0.4 s-1to 15 s-1. Thistest method is suitable for meas
4、urement of viscosities rangingfrom 4000 mPas to 400 000 mPas, and is suitable for yieldstress measurements 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
5、not beendetermined.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3.1 ExceptionThis test method uses the SI based unit ofmilliPascal second (mPas) for viscosity which is equivalent tocentiPoise (cP).1.4 This standard does
6、 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 Documents2.1 ASTM Stand
7、ards:2D3829 Test Method for Predicting the Borderline PumpingTemperature of Engine OilD4684 Test Method for Determination of Yield Stress andApparent Viscosity of Engine Oils at Low TemperatureD5133 Test Method for Low Temperature, Low Shear Rate,Viscosity/Temperature Dependence of Lubricating OilsU
8、sing a Temperature-Scanning TechniqueE563 Practice for Preparation and Use of an Ice-Point Bathas a Reference TemperatureE644 Test Methods for Testing Industrial Resistance Ther-mometersE1137 Specification for Industrial Platinum Resistance Ther-mometersE2877 Guide for Digital Contact Thermometers2.
9、2 ISO Standards:3ISO 17025 General Requirements for the Competence ofTesting and Calibration LaboratoriesISO Guide 34 General Requirements for the Competence ofReference Material Producers3. Terminology3.1 Definitions:3.1.1 apparent viscosity, nthe determined viscosity ob-tained by use of this test
10、method.3.1.2 Digital Contact Thermometer (DCT), nan electronicdevice consisting of a digital display and associated tempera-ture sensing probe.3.1.2.1 DiscussionThis device consists of a temperaturesensor connected to a measuring instrument; this instrumentmeasures the temperature-dependent quantity
11、 of the sensor,computes the temperature from the measured quantity, andprovides a digital output or display of the temperature, or both.The temperature sensing probe is in contact with the materialwhose temperature is being measured. This device is some-times referred to as a digital thermometer.NOT
12、E 1Portable electronic thermometers (PET) is an acronym some-times used to refer to a subset of the devices covered by this definition.3.1.3 Newtonian oil or fluid, nan oil or fluid that at a giventemperature exhibits a constant viscosity at all shear rates orshear stresses.3.1.4 non-Newtonian oil o
13、r fluid, nan oil or fluid that at agiven temperature exhibits a viscosity that varies with chang-ing shear stress or shear rate.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.07
14、on Flow Properties.Current edition approved July 1, 2014. Published August 2014. Originallyapproved in 2003. Last previous edition approved in 2012 as D6896 12. DOI:10.1520/D6896-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.o
15、rg. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.*A Summary of Changes section appears at the end of
16、this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.5 shear rate, nthe velocity gradient in fluid flow. Fora Newtonian fluid in a concentric cylinder rotary viscometer inwhich the shear stress is measured at the inner cyl
17、inder surface(such as the apparatus described in 6.1), and ignoring any endeffects, the shear rate is given as follows: 52!Rs2Rs22 Rr2(1)54!Rs2t Rs22 Rr2!(2)where: = shear rate at the surface of the rotor in reciprocalseconds, s-1, = angular velocity, rad/s,Rs= stator radius, mm,Rr= rotor radius, mm
18、, andt = time for one revolution of the rotor, s.For the specific apparatus described in 6.1, 5 63/t (3)3.1.6 shear stress, nthe 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 Ro1Rt! 31026
19、(4) 5Tr2!Rr2h3109(5)where:Tr= torque applied to rotor, Nm,M = applied mass, g,Ro= radius of the shaft, mm,Rt= radius of the string, mm, = 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 31026(6) 5 3.5 M (7)3.1.7 viscosity, nthe ratio
20、 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).3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration oils,
21、 nthose oils that establish the instru-ments reference framework of apparent viscosity versusspeed, from which the apparent viscosities of test oils aredetermined.3.2.2 test oil, nany oil for which the apparent viscosityand yield stress are to be determined by this test method.3.2.3 used oil, nan oi
22、l which has been used in an operatingengine.3.2.4 yield stress, nthe shear stress required to initiateflow.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
23、, 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 is heated at 80 C and thenvigorou
24、sly 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 Use5.1 When an engine oil is coo
25、led, 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 tempera-ture. As in other low tempera
26、ture rheological tests such as TestMethods D3829, D4684, and D5133, a preheating condition isrequired to ensure that all residual waxes are solubilized in theoil prior to the cooldown (that is, remove thermal memory).However, it is also known that highly sooted used diesel engineoils can experience
27、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 measuredin this test method have bee
28、n correlated to pressurization timesin a motored engine test (1).45.2 Cooling Profiles:5.2.1 For oils to be tested at 20 C and 25 C, 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 inc
29、ludes oils with normallow-temperature flow properties and oils that have beenassociated with low-temperature pumpability problems (2-7).6. Apparatus6.1 Mini-Rotary Viscometer5, an apparatus that consists ofone or more viscometric cells in a temperature-controlledaluminum block. Each cell contains a
30、calibrated rotor-statorset. The rotor shall have a crossbar near the top of the shaftextending in both directions far enough to allow the locking pin(6.6) to stop rotation at successive half turns. Rotation of therotor is achieved by an applied load acting through a stringwound around the rotor shaf
31、t.6.1.1 The mini-rotary viscometric cell has the followingtypical dimensions:4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.5The sole source of supply of the apparatus known to the committee at this timeis Cannon Instrument Co., P.O. Box 16, State Col
32、lege, PA 16804. If you are awareof alternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.D6896 142Diameter of rotor 17.06 mm 0.08 mmLength of
33、rotor 20.00 mm 0.14 mmInside diameter of cell 19.07 mm 0.08 mmRadius of shaft 3.18 mm 0.13 mmRadius of string 0.10 mm6.1.2 Cell CapA cover inserted into the top of the vis-cometer cell to minimize room air circulation into the cells isrequired for thermometrically cooled instruments. The cell capis
34、a stepped cylinder 38 mm 6 1 mm in length made of a lowthermal conductivity material, for example, thermoplastic suchas acetyl copolymers that have known solvent resistivity andare suitable for use between the temperature ranges of this testmethod. The top half is 28 mm 6 1 mm in diameter and thebot
35、tom half is 19 mm in diameter with a tolerance consistentwith the cell diameter. The tolerance on the bottom half is suchthat it will easily fit into cell but not allow cap to contact rotorshaft. The piece has a center bore of 11 mm 6 1 mm. The capis made in two halves to facilitate placement in the
36、 top of thecell.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 to keep them frost-free.6.2 Weights:6.2.1 Yield Stress Measurement, a set of nine disks and adisk holder, each with a mass of 10 g 6 0.1 g.
37、6.2.2 Viscosity Measurement, a mass of 150 g 6 1.0 g.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 ProfileThe temperature profile is fullydescribed in Table X1.1.6.4 Te
38、mperature Measuring DeviceUse either a DCTmeeting the requirements described in 6.4.1 or liquid-in-glassthermometers described in 6.4.2. A DCT or a calibrated lowtemperature liquid-in-glass thermometer shall be used as thethermometer for temperature measurement independent of theinstruments temperat
39、ure control, and shall be located in thethermowell.NOTE 2The display device and sensor must be correctly paired.Incorrect pairing will result in temperature measurement errors andpossibly irreversible damage to the electronics of the display.6.4.1 Digital contact thermometer requirements:Criteria Mi
40、nimum RequirementsDCT E2877 Class BTemperature range 45 C to 100 CDisplay resolution 0.1 C minimum, preferably 0.01 CSensor type RTD, such as a PRT or thermistorSensor,metal sheathed3 mm O.D. with an sensing element less than30 mm in length to be used with a thermowellsleeve, 6 mm O.D. 58 mm long wi
41、th a 3mm hole in center.Sensor,glass sheathed6 mm O.D. with a sensing element less than12 mm in lengthDisplay accuracy 50 mK (0.05 C) for combined probe andsensorResponse time less than or equal to 25 s as defined inSpecification E1137Drift less than 50 mK (0.05 C) per yearCalibration Error less tha
42、n 50 mK (0.05 C) over the range ofintended use.Calibration Range 40 C to 85 CCalibration Data 4 data points evenly distributed over therange of 40 C to 1 C and included in cali-bration report.Calibration Report From a calibration laboratory with demon-strated competency in temperature calibrationwhi
43、ch is traceable to a national calibrationlaboratory or metrology standards bodyNOTE 3With respect to DCT probe immersion depth, a procedure todetermine minimum depth can be found in Guide E2877, Section 5.3, orTest Methods E644, Section 7.6.4.1.1 The DCT calibration drift shall be checked at leastan
44、nually by either measuring the ice point or against areference thermometer in a constant temperature bath at theprescribed immersion depth to ensure compliance with 6.4.1.With respect to an ice bath, Practice E563 provides guidanceon the preparation and use of an ice bath. However, for this use,vari
45、ance from the specific steps, such as water source, ispermitted provided preparation is consistent. The basis for thevariance is due to the reference being used to track change incalibration not verification.NOTE 4When a DCTs calibration drifts in one direction over severalcalibration checks, that i
46、s, ice point, it may be an indication of deteriora-tion of the DCT.6.4.2 For liquid-in-glass thermometers, LiG, two are re-quired. One LiG shall be a calibrated 76 mm partial immersionthermometer with a scale from +5 C to 1 degree less than thelowest test temperature in 0.2 C subdivisions. This lowt
47、emperature LiG thermometer shall have a report of calibrationshowing the temperature deviation at each calibrated testtemperature. The second LiG thermometer shall be a 76 mmpartial immersion thermometer graduated from at least +20 Cto 90 C in 1 C subdivisions, which is used to verify thepreheat tem
48、perature.6.4.2.1 Calibration CheckVerify the low temperaturethermometer at least annually against a reference thermometerin a constant temperature bath or in an ice bath. The thermom-eter is to be insert to its immersion depth. If using an ice bath,the ice point reading is to be taken within 60 min
49、after thethermometer has been at test temperature for at least 3 min. Ifthe corrected temperature reading deviates from the referencethermometer or the ice point then repeat this calibration check.If the thermometer deviates from the reference value on twosuccessive checks then a full thermometer recalibration isneeded.6.4.2.2 RecalibrationA complete recalibration of theliquid-in-glass thermometer, while permitted, is not necessaryin order to meet the accuracy ascribed to liquid-in-glasst
