1、Designation: D4684 08D4684 12Standard Test Method forDetermination of Yield Stress and Apparent Viscosity ofEngine Oils at Low Temperature1This standard is issued under the fixed designation D4684; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test
3、 method covers the measurement of the yield stress and viscosity of engine oils after cooling at controlled rates overa period exceeding 45 h to a final test temperature between 10 and 40C. The precision is stated for test temperatures from 40to 15C. The viscosity measurements are made at a shear st
4、ress of 525 Pa over a shear rate of 0.4 to 15 s1. The viscosity asmeasured at this shear stress was found to produce the best correlation between the temperature at which the viscosity reached acritical value and borderline pumping failure temperature in engines.1.2 This test method contain two proc
5、edures: Procedure A incorporates several equipment and procedural modifications fromTest Method D468402 that have shown to improve the precision of the test, while Procedure B is unchanged from Test MethodD468402. Additionally, Procedure A applies to those instruments that utilize thermoelectric coo
6、ling technology or directrefrigeration technology of recent manufacture for instrument temperature control. Procedure B can use the same instruments usedin Procedure A or those cooled by circulating methanol.1.3 Procedure A of this test method has precision stated for a yield range from less than 35
7、 Pa to 210 Pa and apparent viscosityrange from 4300 to 270 000 mPas. The test procedure can determine higher yield stress and viscosity levels.1.4 This test method is applicable for unused oils, sometimes referred to as fresh oils, designed for both light duty and heavyduty engine applications. It a
8、lso has been shown to be suitable for used diesel and gasoline engine oils. The applicability topetroleum products other than engine oils has not been determined.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5.1 Except
9、ionThis test method uses the SI based unit of milliPascal second (mPas) as the unit of viscosity. For information,the equivalent unit, centiPoise (cP), is shown in parentheses.for viscosity which is equivalent to, centiPoise (cP).1.6 This standard does not purport to address all of the safety concer
10、ns, 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.2. Referenced Documents2.1 ASTM Standards:2D3829 Test Method for Predicting the Borderl
11、ine Pumping Temperature of Engine OilE1137 Specification for Industrial Platinum Resistance Thermometers2.2 ISO Standard:3ISO 17025 General Requirements for the Competence of Testing and Calibration LaboratoriesISO Guide 34 General Requirements for the Competence of Reference Material ProducersISO G
12、uide 35 Certification of Reference Materials1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricants and is the direct responsibility of Subcommittee D02.07 onFlow Properties.Current edition approved Dec. 1, 2008Dec. 1, 2012. Published January 2009April
13、 2013. Originally approved in 1987. Last previous edition approved in 20072008 asD46840708.1. DOI: 10.1520/D4684-08.10.1520/D4684-12.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume inform
14、ation, refer to the standards Document Summary page on the ASTM website.3 Available from International Organization for Standardization (ISO), 1 rue de Varemb, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.This document is not an ASTM standard and is intended only to provide the
15、 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 standar
16、d 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 viscosityvi
17、scosity, 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 instru
18、ment; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output or display,or both, of the temperature. The temperature sensing probe is in contact with the material whose temperature is being measure
19、d.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 shear stresses.3.1.4 non-Newtonian oil or fluidfluid, nan oil or fluid that at a given temperature exhibi
20、ts 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 which the shear stress is measured at the inner cylinder surface (such as this apparatus, described in 6.1
21、), 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, s1, = angular velocity, rad/s,Rs = stator radius, mm,Rr = rotor radius, mm, andt = time in seconds for one revolutio
22、n of the rotor.For the specific apparatus being described in 6.1.1,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 surface is the area under shear or the shear area.Tr 59.81 M Ro1Rt!31026 (4)Sr 5 Tr2pi!Rr2
23、h 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 dimensions given in 6.1.1,Tr 531.7 M 31026 (6)Sr 53.5 M (7)3.1.7 viscosityviscosity, nthe
24、 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 Pascal secondPas. A centipoise (cP) is one milliPascal second mPas.3.2 Definitions of
25、 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 are determined. Calibration oils, which are essentially Newtonian fluids, shall beD4684 122o
26、btained from suppliers complying with ISO Guide 34, ISO Guide 35, and ISO 17025 with traceability to a national metrologyinstitute (NMI). These calibration oils will have an approximate viscosity of 30 Pas (30 000 cP) at 20C or 60 Pas (60 000 cP)at 25C.3.2.2 cell constantconstant, nthe ratio of the
27、calibration fluid viscosity to the time required to complete the first threemeasured revolutions of the rotor.3.2.3 test oiloil, nany oil for which the apparent viscosity and yield stress are to be determined by this test method.3.2.4 unused oiloil, nan oil which has not been used in an operating en
28、gine.3.2.5 used oiloil, nan oil which has been used in an operating engine.3.2.6 yield stressstress, nthe shear stress required to initiate flow. For all Newtonian fluids and many non-Newtonian fluids,the yield stress is zero. An engine oil can have a yield stress that is a function of its low-tempe
29、rature cooling rate, soak time, andtemperature.4. Summary of Test Method4.1 An engine oil sample is held at 80C and then cooled at a programmed cooling rate to a final test temperature and held fora specified time period. At the end of this period, a series of increasing low torques are applied to t
30、he rotor shaft until rotationoccurs to determine the yield stress, if any is exhibited. A higher torque 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 of cooling can affect its yield stress and viscosity
31、. In this laboratory test,a fresh 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. These laboratory test results have predicted as failures the known engine oils that havefailed in
32、the field because of lack of oil pumpability.4 These documented field failing oils have all consisted of oils normally testedat 25C. These field failures are believed to be the result of the oil forming a gel structure that results in either excessive yieldstress or viscosity of the engine oil, or b
33、oth.5.2 Cooling Profiles:5.2.1 For oils to be tested at 20C or colder, Table X1.1 applies. The cooling profile described in Table X1.1 is based on theviscosity properties of theASTM Pumpability Reference Oils (PRO). This series of oils includes oils with normal low-temperatureflow properties and oil
34、s that have been associated with low-temperature pumpability problems (1-5).5 Significance for the 35 and40C temperature profiles is based on the data collected from the “Cold Starting and Pumpability Studies in Modern Engines”conducted by ASTM (6,7).5.2.2 For oils to be tested at 15 or 10C, Table X
35、1.2 applies. No significance has been determined for this temperature profilebecause of the absence of appropriate reference oils. Similarly, precision of the test method using this profile for the 10C testtemperature is unknown. The temperature profile of Table X1.2 is derived from the one in Table
36、 X1.1 and has been moved up intemperature, relative to Table X1.1, in consideration of the expected higher cloud points of the viscous oils tested at 15and 10C.6. Apparatus6.1 Mini-Rotary ViscometerAn apparatus that consists of one or more viscometric cells in a temperature-controlled blockmade of a
37、 metallic material with high thermal conductivity. Each cell contains a calibrated rotor-stator set. The rotor shall havea crossbar near the top of the shaft extending in both directions far enough to allow the locking pin (6.6) to stop rotation atsuccessive half turns. Rotation of the rotor is achi
38、eved by an applied force acting through a string wound around the rotor shaft.6.1.1 The mini-rotary viscometric cell has the following dimensions:Diameter of rotor 17.06 0.08 mmLength of rotor 20.0 0.14 mmInside diameter of cell 19.07 0.08 mmRadius of shaft 3.18 0.13 mmRadius of string 0.1 mm6.1.2 C
39、ell CapA cover inserted into the top of the viscometer cell to minimize room air circulation into the cells is requiredfor thermometrically cooled instruments. The cell cap is a stepped cylinder 38 6 1 mm (1.5 6 0.05 in.) in length made of a lowthermal conductivity material, for example, thermoplast
40、ic such as acetyl copolymers that have known solvent resistivity and aresuitable for use between the temperature ranges of this test method. The top half is 28 6 1 mm (1.10 6 0.05 in.) in diameter andthe bottom half is 19 mm (0.745 in.) in diameter with a tolerance consistent with the cell diameter.
41、 The tolerance on the bottom4 Pumpability Reference Oils (PRO) 21 through 29.5 The boldface numbers in parentheses refer to the references at the end of this standard.D4684 123half is such that it will easily fit into cell but not allow cap to contact rotor shaft. The piece has a center bore of 11 6
42、 1 mm (0.4386 0.05 in.). mm. The cap is made in two halves to 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 frost-free.6.2 Weights:6.2.1 Yield
43、Stress MeasurementA set of ten weights, each with a mass of 10 6 0.1 g. One of the weights is a holder for theother weights.6.2.2 Viscosity MeasurementWeight with mass of 150 6 1.0 g.6.3 Temperature Control System Regulates the mini-rotary viscometer block temperature in accordance with the temperat
44、urerequirements described in Table X1.1 or Table X1.2.6.3.1 Temperature ControllerAs a very critical part of this procedure, a description of the requirements that the controller shallmeet are included in Appendix X2.6.3.2 Temperature ProfileThe temperature profile is fully described in Table X1.1 a
45、nd Table X1.2.6.4 ThermometersTemperature Measuring Device For measuring the temperature of the block. Two are required, onegraduated from at least +70 to 90C in 1CUse either a calibrated DCT described in 6.4.1 subdivisions, the other with a scale fromabove +5C down to at least 41C or lower, or liqu
46、id-in-glass thermometers described in 6.4.20.2C subdivisions. Otherthermometric devices of equal accuracy and resolution may be used to measure the temperature, such as digital meters using aresistance temperature detector (RTD) or a thermistor sensor The DCT or the calibrated low temperature liquid
47、-in-glassthermometer shall be used as the thermometer for temperature measurement independent of the instruments 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 an
48、d possiblyirreversible damage to the electronics of the display.6.4.1 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
49、 thermistor that are either glass or metal sheathed.(3) For metal sheathed probe, use a 3 mm diameter probe with a sensing element that is less than 30 mm in length; a metalsheathed 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
