1、Designation: D6896 17D6896 18Standard 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 safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior
7、 to use.1.5 This international 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 Barrie
8、rs to Trade (TBT) Committee.2. 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, L
9、ow Shear Rate, Viscosity/Temperature 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 Re
10、sistance ThermometersE2877 Guide for Digital Contact Thermometers2.2 ISO Standards:3ISO 17025 General Requirementsrequirements for the Competencecompetence of Testingtesting and Calibration Laboratories-calibration laboratoriesISO Guide 34 General Requirementsrequirements for the Competence of Refer
11、ence Material Producerscompetence of referencematerial producers1 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 May 1, 2017June 1,
12、2018. Published May 2017July 2018. Originally approved in 2003. Last previous edition approved in 20142017 asD6896 14.D6896 17. DOI: 10.1520/D6896-17.10.1520/D6896-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual B
13、ook of ASTM Standardsvolume 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 pro
14、vide 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 the current versionof the
15、 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 States13. Terminology3.1 Definitions:3.1.1 apparent vis
16、cosity, 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 temperature sensor connected to a measuring instrum
17、ent; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output. This digitaloutput goes to a digital display and/or recording device that may be internal or external to the device. These devices are s
18、ometimesreferred to as “digital thermometers.”3.1.2.2 DiscussionPET is an acronym for portable 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 shears
19、tresses.3.1.4 non-Newtonian oil or fluid, nan oil or fluid that at a given temperature exhibits a viscosity that varies with changingshear stress or shear rate.3.1.5 viscosity, nthe ratio between the applied shear stress and rate of shear, sometimes called the coefficient of dynamicviscosity. This v
20、alue 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:Definitions of Terms Specific to This Standard:3.2.1 apparent viscosity,calibration oils, nthe determined viscosity obtained by use of this test method.those oils that
21、establishthe instruments reference framework of apparent viscosity versus speed, from which the apparent viscosities of test oils aredetermined.3.1.2 digital contact thermometer (DCT), nan electronic device consisting of a digital display and associated temperaturesensing probe.3.1.2.1 DiscussionThi
22、s device consists of a temperature 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. This digitaloutput goes to a digital display and/or recording
23、device that may be internal or external to the device. These devices are sometimesreferred to as “digital thermometers.”3.1.2.2 DiscussionPET is an acronym for portable electronic thermometers, a subset of digital contact thermometers (DCT).3.1.3 Newtonian oil or fluid, nan oil or fluid that at a gi
24、ven 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 exhibits a viscosity that varies with changingshear stress or shear rate.3.2.2 shear rate, nthe velocity gradient in fluid flow. For a Newt
25、onian 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), 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 sur
26、face of the rotor in reciprocal seconds, s-1, = angular velocity, rad/s,D6896 182Rs = stator radius, mm,Rr = rotor radius, mm, andt = time for one revolution of the rotor, s.For the specific apparatus described in 6.1, 563/t (3)3.2.2.1 DiscussionFor a Newtonian fluid in a concentric cylinder rotary
27、viscometer in which the shear stress is measured at the inner cylinder surface(such as the apparatus described in 6.1), and ignoring any end effects, the shear rate is given as follows: 5 2Rs2Rs22Rr2 (1)5 4piRs2t Rs22Rr2! (2)where: = shear rate at the surface of the rotor in reciprocal seconds, s-1,
28、 = 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, 563t (3)3.2.3 shear stress, nthe motivating force per unit area for fluid flow. For the rotary viscometer being described, the rotorsur
29、face is the area under shear or the shear area.Tr 59.81 M Ro1Rt!31026 (4) 5 Tr2pi!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, = shear stress at the rotor surface, Pa, andh = height of the rotor, mm.For the dimens
30、ions given in 6.1.1,Tr 531.7 M 31026 (6) 53.5 M (7)3.2.3.1 DiscussionFor the rotary viscometer described in 6.1, the rotor surface is the area under shear or the shear area. For this test method, endeffects are not considered.Tr59.81 M Ro1Rt!31026 (4) 5 Tr2piRr2h 3109 (5)where:Tr = torque applied to
31、 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, andD6896 183h = height of the rotor, mm.For the dimensions given in 6.1.1,Tr531.7 M 31026 (6) 53.5 M (7)3.2.4 test oil, nany oil for which the apparent viscosity and yi
32、eld stress are to be determined by this test method.3.2.5 used oil, nan oil which has been used in an operating engine.3.2.6 viscosity, yield stress, nthe ratio between the applied shear stress and rate of shear, sometimes called the coefficient ofdynamic viscosity. This value is thus a measure of t
33、he resistance to flow of the liquid. The SI unit of viscosity is the pascal second(Pas).shear stress required to initiate flow.3.2.6.1 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 c
34、ooling 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.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibr
35、ation oils, nthose oils that establish 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
36、 oil, nan oil which has been used in an 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
37、 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.4. Summary of Test Method4.1 A used engine oil sample is heated at 80
38、 C and then vigorously agitated. The sample 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
39、 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 temperature. A
40、s 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 diesel en
41、gine 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 measured i
42、n this test method have been correlated 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
43、(PRO). This series of oils includes oils 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 alumi
44、numblock. Each cell contains a calibrated rotor-stator set. The rotor shall have a crossbar near the top of the shaft extending in both4 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
45、 at this time is Cannon Instrument Co., P.O. Box 16, State College, PA 16804. If you are aware ofalternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee,1 which you
46、may attend.D6896 184directions 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.6.1.1 The mini-rotary viscometric cell has the following typical dimensions:Dia
47、meter 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 cell to minimize room air circulation into the cells is requiredfor thermometric
48、ally 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 suitablefor use between the temperature ranges of this test method. The top
49、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 contact 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 airin
