1、Designation: D6896 14D6896 17Standard 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 th
2、e 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*1.1 This test method covers the measurement of the yield stress and viscosity of engine o
3、ils after cooling at controlled rates overa period of 43 h or 45 h to a final test temperature of 20 C or 25 C. The precision is stated for test temperatures 20 C and25 C. The viscosity measurements are made at a shear stress of 525 Pa over a shear rate of 0.4 s-1 to 15 s-1. This test methodis suita
4、ble for measurement of viscosities ranging from 4000 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. The applicability and precision to other used or unused engine oils orto petroleum products other than en
5、gine oils has not been determined.1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in 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
6、This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.5 This internationa
7、l standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2
8、. Referenced Documents2.1 ASTM Standards:2D3829 Test Method for Predicting the Borderline Pumping Temperature of Engine OilD4684 Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low TemperatureD5133 Test Method for Low Temperature, Low Shear Rate, Viscosity/Temp
9、erature Dependence of Lubricating Oils Using aTemperature-Scanning TechniqueE563 Practice for Preparation and Use of an Ice-Point Bath as a Reference TemperatureE644 Test Methods for Testing Industrial Resistance ThermometersE1137 Specification for Industrial Platinum Resistance ThermometersE2877 Gu
10、ide for Digital Contact Thermometers2.2 ISO Standards:3ISO 17025 General Requirements for the Competence of Testing and Calibration LaboratoriesISO Guide 34 General Requirements for the Competence of Reference Material Producers3. Terminology3.1 Definitions:3.1.1 apparent viscosity, nthe determined
11、viscosity obtained by use of this test method.1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.07 on Flow Properties.Current edition approved July 1, 2014May 1, 2017. Published Au
12、gust 2014May 2017. Originally approved in 2003. Last previous edition approved in 20122014 asD6896 12.D6896 14. DOI: 10.1520/D6896-14.10.1520/D6896-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Stan
13、dardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.This document is not an ASTM standard and is intended only to provide the user of
14、 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 the current versionof the standard as pub
15、lished 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 States13.1.2 Digital Contact Thermometerdigital contact thermometer (DC
16、T), nan electronic device consisting of a digital displayand associated temperature sensing probe.3.1.2.1 DiscussionThis device consists of a temperature sensor connected to a measuring instrument; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature fr
17、om the measured quantity, and provides a digital output or displayof the temperature, or both. The temperature sensing probe is in contact with the material whose temperature is being measured.This device is output. This digital output goes to a digital display and/or recording device that may be in
18、ternal or external to thedevice. These devices are sometimes referred to as a“digital digital thermometer.thermometers.”NOTE 1Portable electronic thermometers (PET) is an acronym sometimes used to refer to a subset of the devices covered by this definition.3.1.2.2 DiscussionPET is an acronym for por
19、table electronic thermometers, a subset of digital contact thermometers (DCT).3.1.3 Newtonian oil or fluid, nan oil or fluid that at a given temperature exhibits a constant viscosity at all shear rates or shearstresses.3.1.4 non-Newtonian oil or fluid, nan oil or fluid that at a given temperature ex
20、hibits a viscosity that varies with changingshear stress or shear rate.3.1.5 shear rate, nthe velocity gradient in fluid flow. For a Newtonian fluid in a concentric cylinder rotary viscometer in whichthe shear stress is measured at the inner cylinder surface (such as the apparatus described in 6.1),
21、 and ignoring any end effects,the shear rate is given as follows: 5 2!Rs2Rs22Rr2 (1)5 4pi!Rs2t Rs22Rr2! (2)where: = shear rate at the surface of the rotor in reciprocal seconds, s-1, = angular velocity, rad/s,Rs = stator radius, mm,Rr = rotor radius, mm, andt = time for one revolution of the rotor,
22、s.For the specific apparatus described in 6.1, 563/t (3)3.1.6 shear stress, nthe motivating force per unit area for fluid flow. For the rotary viscometer being described, the rotorsurface is the area under shear or the shear area.Tr 59.81 M Ro1Rt!31026 (4) 5 Tr2pi!Rr2h 3109 (5)where:Tr = torque appl
23、ied 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,Tr 531.7 M 31026 (6) 53.5 M (7)3.1.7 viscosity, nthe ratio between the applied shear stress and r
24、ate of shear, sometimes called the coefficient of dynamicviscosity. This value is thus a measure of the resistance to flow of the liquid. The SI unit of viscosity is the pascal second (Pas).3.2 Definitions of Terms Specific to This Standard:D6896 1723.2.1 calibration oils, nthose oils that establish
25、 the instruments reference framework of apparent viscosity versus speed, fromwhich the apparent viscosities of test oils are determined.3.2.2 test oil, nany oil for which the apparent viscosity and yield stress are to be determined by this test method.3.2.3 used oil, nan oil which has been used in a
26、n operating engine.3.2.4 yield stress, 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 cooling rate, soak time, and temperature. Yie
27、ld 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.4. Summary of Test Method4.1 A used engine oil sample is heated at 80 C and then vigorously agitated. The s
28、ample is then cooled at a programmedcooling rate to a final test temperature. A low torque is applied to the rotor shaft to measure the yield stress. A higher torque isthen applied to determine the apparent viscosity of the sample.5. Significance and Use5.1 When an engine oil is cooled, the rate and
29、 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 temperature. As in other low temperature rheological
30、 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 diesel engine oils can experience a sootagglome
31、rization 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 measured in this test method have been correlate
32、d to pressurization times in a motored engine test (1).45.2 Cooling Profiles:5.2.1 For oils to be tested at 20 C and 25 C, Table X1.1 applies. The cooling profile described in Table X1.1 is based onthe viscosity properties of the ASTM Pumpability Reference Oils (PRO). This series of oils includes oi
33、ls with normallow-temperature flow properties and oils that have been associated with low-temperature pumpability problems (2-7).6. Apparatus6.1 Mini-Rotary Viscometer5,an apparatus that consists of one or more viscometric cells in a temperature-controlled aluminumblock. Each cell contains a calibra
34、ted rotor-stator set. The rotor shall have a crossbar near the top of the shaft extending in bothdirections far enough to allow the locking pin (6.6) to stop rotation at successive half turns. Rotation of the rotor is achieved byan applied load acting through a string wound around the rotor shaft.6.
35、1.1 The mini-rotary viscometric cell has the following typical dimensions:Diameter of rotor 17.06 mm 0.08 mmLength of 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 viscometer cel
36、l to minimize room air circulation into the cells is requiredfor thermometrically cooled instruments. The cell cap is a stepped cylinder 38 mm 6 1 mm in length made of a low thermalconductivity material, for example, thermoplastic such as acetyl copolymers that have known solvent resistivity and are
37、 suitablefor use between the temperature ranges of this test method. The top half is 28 mm 6 1 mm in diameter and the bottom half is 19mm in diameter with a tolerance consistent with the cell diameter. The tolerance on the bottom half is such that it will easily fitinto cell but not allow cap to con
38、tact rotor shaft. The piece has a center bore of 11 mm 6 1 mm. The cap is made in two halvesto facilitate placement in the top of the cell.6.1.2.1 Cell caps shall not be used in the direct refrigeration instruments, since such use would block the flow of cold, dry airinto the stators to keep them fr
39、ost-free.6.2 Weights:4 The boldface numbers in parentheses refer to the list of references at the end of this standard.5 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 suppl
40、iers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee,1 which you may attend.D6896 1736.2.1 Yield Stress Measurement, a set of nine disks and a disk holder, each with a mass of 10
41、g 6 0.1 g.6.2.2 Viscosity Measurement, a mass of 150 g 6 1.0 g.6.3 Temperature Control System, that will regulate the mini-rotary viscometer block temperature in accordance with thetemperature limits described in Table X1.1.6.3.1 Temperature ProfileThe temperature profile is fully described in Table
42、 X1.1.6.4 Temperature Measuring DeviceUse either a DCT meeting the requirements described in 6.4.1 or liquid-in-glassthermometers described in 6.4.2. A DCT or a calibrated low temperature liquid-in-glass thermometer shall be used as thethermometer for temperature measurement independent of the instr
43、uments temperature control, and shall be located in thethermowell.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.6.4.1 Digital contact thermometer requirem
44、ents:Criteria Minimum 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 than 30 mm in length to be used with a thermowellsleeve, 6 mm O
45、.D. 58 mm long with a 3 mm hole in center.Sensor,glass sheathed6 mm O.D. with a sensing element less than 12 mm in lengthDisplay accuracy 50 mK (0.05 C) for combined probe and sensorResponse time less than or equal to 25 s as defined in Specification E1137Drift less than 50 mK (0.05 C) per yearCalib
46、ration Error less than 50 mK (0.05 C) over the range of intended use.Calibration Range 40 C to 85 CCalibration Data 4 data points evenly distributed over the range of 40 C to 1 C and included in calibrationreport.Calibration Report From a calibration laboratory with demonstrated competency in temper
47、ature calibration which istraceable to a national calibration laboratory or metrology standards bodyNOTE 2With respect to DCT probe immersion depth, a procedure to determine minimum depth can be found in Guide E2877, Section 5.3, or TestMethods E644, Section 7.6.4.1.1 The DCT calibration drift shall
48、 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. With respect toan ice bath, Practice E563 provides guidance on the preparation and use of an ice bath. H
49、owever, for this use, variance from thespecific steps, such as water source, is permitted provided preparation is consistent. The basis for the variance is due to thereference being used to track change in calibration not verification.NOTE 3When a DCTs calibration drifts in one direction over several calibration checks, that is, ice point, it may be an indication of deteriorationof the DCT.6.4.2 For liquid-in-glass thermometers, LiG, two are required. One LiG shall be a calibrated 76 mm par
