1、Designation: D6896 03 (Reapproved 2007)D6896 12Standard 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
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.1. Scope Scope*1.1 This test method covers the measurement of the yield stress a
3、nd viscosity of engine oils after cooling at controlled rates overa period of 43 or 45 h to a final test temperature of -20 or -25C. The precision is stated for test temperatures -20 and -25C. Theviscosity measurements are made at a shear stress of 525 Pa over a shear rate of 0.4 to 15 s-1. This tes
4、t method is suitable formeasurement of viscosities ranging from 4000 mPas to 400 000 mPas, and is suitable for yield stress measurements of 7 Pa to350 Pa.1.2 This test method is applicable for used diesel oils. The applicability and precision to other used or unused engine oils orto petroleum produc
5、ts other than engine oils has not been determined.1.3 This test method uses the millipascal second (mPas) as the unit of viscosity. For information, the equivalent centipoise unitis shown in parentheses.The values stated in SI units are to be regarded as standard. No other units of measurement are i
6、ncludedin this standard.1.3.1 ExceptionThis test method uses the SI based unit of milliPascal second (mPas) for viscosity which is equivalent tocentiPoise (cP).1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the us
7、er of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D3829 Test Method for Predicting the Borderline Pumping Temperature of Engine OilD4684 Test Method for Determinati
8、on of Yield Stress and Apparent Viscosity of Engine Oils at Low TemperatureD5133 Test Method for Low Temperature, Low Shear Rate, Viscosity/Temperature Dependence of Lubricating Oils Using aTemperature-Scanning TechniqueE1137 Specification for Industrial Platinum Resistance Thermometers3. Terminolog
9、y3.1 Definitions:3.1.1 apparent viscosityviscosity, nthe determined viscosity obtained by use of this test method.3.1.2 Digital Contact Thermometer (DCT), nan electronic device consisting of a digital display and associated temperaturesensing probe.3.1.2.1 DiscussionThis device consists of a tempera
10、ture sensor connected to a measuring instrument; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output or display1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Pro
11、ducts and Lubricants and is the direct responsibility of Subcommittee D02.07 onFlow Properties.Current edition approved Nov. 1, 2007Nov. 1, 2012. Published January 2008April 2013. Originally approved in 2003. Last previous edition approved in 20032007 asD6896D689603(2007).03 1. DOI: 10.1520/D6896-03
12、R07.10.1520/D6896-12.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard an
13、d is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only
14、the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1of the temperature, or
15、both. The temperature sensing probe is in contact with the material whose temperature is being measured.This device is sometimes referred to as a digital thermometer.3.1.3 Newtonian oil or fluidfluid, nan oil or fluid that at a given temperature exhibits a constant viscosity at all shear ratesor she
16、ar stresses.3.1.4 non-Newtonian oil or fluidfluid, nan oil or fluid that at a given temperature exhibits a viscosity that varies withchanging shear stress or shear rate.3.1.5 shear raterate, nthe velocity gradient in fluid flow. For a Newtonian fluid in a concentric cylinder rotary viscometerin whic
17、h 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 follows:Gr 5 2!Rs2Rs22Rr2 (1)5 4pi!Rs2t Rs22Rr2! (2)where:Gr = shear rate at the surface of the rotor in reciprocal seconds, s-1, = angular v
18、elocity, 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,Gr 563/t (3)3.1.6 shear stressstress, nthe motivating force per unit area for fluid flow. For the rotary viscometer being described, therotor surfac
19、e is the area under shear or the shear area.Tr 59.81 M Ro1Rt!31026 (4)Sr 5 TTr2pi!Rr2h 3109 (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 at the rotor surface, Pa, andh = height of the rotor, mm.For the dime
20、nsions given in 6.1.1,Tr 531.7 M 31026 (6)Sr 53.5 M (7)3.1.7 viscosityviscosity, nthe ratio between the applied shear stress and rate of shear, sometimes called the coefficient ofdynamic viscosity. This value is thus a measure of the resistance to flow of the liquid. The SI unit of viscosity is the
21、pascal secondPas. A centipoise (cP) is one millipascal second mPas.(Pas).3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration oilsoils, nthose oils that establish the instruments reference framework of apparent viscosity versus speed,from which the apparent viscosities of test oils a
22、re determined. Calibration oils, which are essentially Newtonian fluids, areavailable commercially and have an approximate viscosity of 30 Pas (30 000 cP) at -20C.3.2.2 test oiloil, nany oil for which the apparent viscosity and yield stress are to be determined by this test method.3.2.3 used oiloil,
23、 nan oil which has been used in an operating engine.3.2.4 yield stressstress, nthe shear stress required to initiate flow.3.2.4.1 DiscussionFor all Newtonian fluids and some non-Newtonian fluids, the yield stress is zero. An oil can have a yield stress that is a functionof its low-temperature coolin
24、g rate, soak time, and temperature. Yield stress measurement by this test method determines onlywhether the test oil has a yield stress of at least 35 Pa; a yield stress below 35 Pa is considered to be insignificant for engine oils.D6896 1224. Summary of Test Method4.1 Aused engine oil sample is hea
25、ted at 80C and then vigorously agitated. The sample is then cooled at a programmed coolingrate to a final test temperature.Alow torque is applied to the rotor shaft to measure the yield stress.Ahigher torque is then appliedto determine the apparent viscosity of the sample.5. Significance and Use5.1
26、When an engine oil is cooled, the rate and duration of cooling can affect its yield stress and viscosity. In this laboratory test,used engine oil is slowly cooled through a temperature range where wax crystallization is known to occur, followed by relativelyrapid cooling to the final test temperatur
27、e. As in other low temperature rheological tests such as Test Methods D3829, D4684, andD5133, a preheating condition is required to ensure that all residual waxes are solubilized in the oil prior to the cooldown (thatis, remove thermal memory). However, it is also known that highly sooted used diese
28、l engine oils can experience a sootagglomerization phenomenon when heated under quiescent conditions. The current method uses a separate preheat and agitationstep to break up any soot agglomerization that may have occurred prior to cooldown. The viscosity of highly sooted diesel engineoils as measur
29、ed in this test method have been correlated to pressurization times in a motored engine test (1).35.2 Cooling Profiles:5.2.1 For oils to be tested at -20C and -25C, Table X1.1 applies. The cooling profile described in Table X1.1 is based on theviscosity properties of theASTM Pumpability Reference Oi
30、ls (PRO). This series of oils includes oils with normal low-temperatureflow properties and oils that have been associated with low-temperature pumpability problems (2-7).6. Apparatus6.1 Mini-Rotary Viscometer4,an apparatus that consists of one or more viscometric cells in a temperature-controlled al
31、uminumblock. Each cell contains a calibrated rotor-stator set. Rotation of the rotor is achieved by an applied load acting through a stringwound around the rotor shaft.6.1.1 The mini-rotary viscometric cell has the following typical dimensions:millimetresDiameter of rotor 17.0Length of rotor 20.0Ins
32、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 with a 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 the mini-rotary viscomet
33、er block temperature in accordance with thetemperature limits described in Table X1.1.6.3.1 Temperature Controller is the most critical part of this procedure.Adescription of the requirements that the controller shallmeet are included in Appendix X2.6.3.2 Temperature ProfileThe temperature profile i
34、s fully described in Table X1.1.6.4 Thermometers, Temperature Measuring Devicefor measuring the temperature of the block. TwoUse either a calibratedDCT described in 6.4.1 ranges are required, one graduatedor liquid-in-glass thermometers described in 6.4.2from at least +70 to90C in 1C subdivisions, t
35、he other with a range from at least -36 to +5C or -45 to +5C, in 0.2C subdivisions. Otherthermometric devices of equal accuracy and resolution may be used to calibrate the temperature sensor A DCT or a calibratedlow temperature liquid-in-glass thermometer shall be used as the thermometer for tempera
36、ture measurement independent of theinstruments temperature control, and shall be located in the thermowell.NOTE 1The display device and sensor must be correctly paired. Incorrect pairing will result in temperature measurement errors and possiblyirreversible damage to the electronics of the display.6
37、.4.1 A DCT shall meet the following:(1) A range from -45 to 100C with a display resolution to at least 0.01C.(2) The only acceptable sensors are a resistance temperature device (RTD), such as a platinum resistance thermometer (PRT)or a thermistor that are either glass or metal sheathed.3 The boldfac
38、e numbers in parentheses refer to the list of references at the end of this standard.4 The sole source of supply of the apparatus known to the committee at this time is Cannon Instrument Co., P.O. Box 16, State College, PA 16804. If you are aware ofalternative suppliers, please provide this informat
39、ion to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee,1 which you may attend.D6896 123(3) For metal sheathed probe, use a 3 mm diameter probe with a sensing element that is less than 30 mm in length; a metalsheathe
40、d probe requires a thermowell sleeve measuring 6 mm outside diameter by 58 mm long with a hole in the center toaccommodate the probe. For a glass sheathed probe, use a probe 6 mm in diameter containing a sensing element less than 12 mmin length.(4) A combined (display and probe) minimum accuracy of
41、650 mK (0.05C).(5) A response time of less than or equal to 25 s as defined in Specification E1137.(6) A drift of less than 50 mK (0.05C) per year.(7) Error of less than 50 mK (0.05C) over the range of intended use.(8) The DCT shall have a report of temperature calibration from a calibration laborat
42、ory with demonstrated competency intemperature calibration which is traceable to a national calibration laboratory or metrology standards body.(9) The DCT shall be calibrated over a range from -40 to 85C with at least 4 data points evenly distributed over the rangeof -40 to -1C. The test report shal
43、l include the calibration data.6.4.1.1 The DCT calibration shall be checked at least annually by either measuring the ice point or against a referencethermometer in a constant temperature bath at the prescribed immersion depth to ensure compliance with 6.4.1 (6 and 7).NOTE 2When a DCTs calibration d
44、rifts in one direction over several calibration checks, that is, ice point, it may be an indication of deteriorationof the DCT.6.4.2 Two liquid in glass thermometers are required. One shall be a calibrated 76 mm partial immersion thermometer with ascale from +5C to 1 degree less than the lowest test
45、 temperature in 0.2C subdivisions. The low temperature thermometer shallhave a report of calibration showing the temperature deviation at each calibrated test temperature. The second shall be a 76 mmpartial immersion thermometer graduated from at least +20 to 90C in 1C subdivisions.6.4.2.1 Calibrati
46、on CheckVerify the low temperature thermometer at least annually against a reference thermometer in aconstant temperature bath or in an ice bath. The thermometer is to be insert to its immersion depth. If using an ice bath, the icepoint reading is to be taken within 60 min after the thermometer has
47、been at test temperature for at least 3 min. If the correctedtemperature reading deviates from the reference thermometer or the ice point then repeat this calibration check. If the thermometerdeviates from the reference value on two successive checks then a full thermometer recalibration is needed.6
48、.4.2.2 RecalibrationA complete recalibration of the liquid-in-glass thermometer, while permitted, is not necessary in orderto meet the accuracy ascribed to liquid-in-glass thermometers design until the thermometers corrected measured temperaturedeviates from the reference thermometer or ice point by
49、 one scale division, or until five years has elapsed since the last fullcalibration.6.5 Refrigeration Device, consisting of a means of removing heat from the instrument such that the cell temperature iscontrolled in accordance with the program described in Table X1.1.6.6 Circulating System, that will circulate the liquid coolant to the instrument as needed. Methanol is a suitable coolant if thecirculating coolant is below -10C. One should observe toxicity and flammability precautions that apply to the use
