1、Designation: D4684 14Standard 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 case of rev
2、ision, 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 U.S. Department of Defense.1. Scope*1.1 This test me
3、thod covers the measurement of the yieldstress and viscosity of engine oils after cooling at controlledrates over a period exceeding 45 h to a final test temperaturebetween 10 C and 40 C. The precision is stated for testtemperatures from 40 C to 15 C. The viscosity measure-ments are made at a shear
4、stress of 525 Pa over a shear rate of0.4 s1to 15 s1. The viscosity as measured at this shear stresswas found to produce the best correlation between the tem-perature at which the viscosity reached a critical value andborderline pumping failure temperature in engines.1.2 This test method contain two
5、procedures: Procedure Aincorporates several equipment and procedural modificationsfrom Test Method D468402 that have shown to improve theprecision of the test, while Procedure B is unchanged from TestMethod D468402. Additionally, Procedure A applies to thoseinstruments that utilize thermoelectric co
6、oling technology ordirect refrigeration technology of recent manufacture for in-strument temperature control. Procedure B can use the sameinstruments used in Procedure A or those cooled by circulatingmethanol.1.3 Procedure A of this test method has precision stated fora yield range from less than 35
7、 Pa to 210 Pa and apparentviscosity range from 4300 mPas to 270 000 mPas. The testprocedure can determine higher yield stress and viscositylevels.1.4 This test method is applicable for unused oils, some-times referred to as fresh oils, designed for both light duty andheavy duty engine applications.
8、It also has been shown to besuitable for used diesel and gasoline engine oils. The applica-bility to petroleum products other than engine oils has not beendetermined.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5.1 Exce
9、ptionThis test method uses the SI based unit ofmilliPascal second (mPas) for viscosity which is equivalent to,centiPoise (cP).1.6 This standard does 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 ap
10、pro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D3829 Test Method for Predicting the Borderline PumpingTemperature of Engine OilE563 Practice for Preparation and Use of an Ice-Point Bathas a Ref
11、erence TemperatureE644 Test Methods for Testing Industrial Resistance Ther-mometersE1137 Specification for Industrial Platinum Resistance Ther-mometersE2877 Guide for Digital Contact Thermometers2.2 ISO Standard:3ISO 17025 General Requirements for the Competence ofTesting and Calibration Laboratorie
12、sISO 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 method.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fu
13、els, and Lubricants and is the direct responsibility ofSubcommittee D02.07 on Flow Properties.Current edition approved July 1, 2014. Published August 2014. Originallyapproved in 1987. Last previous edition approved in 2012 as D4684 12. DOI:10.1520/D4684-14.2For referenced ASTM standards, visit the A
14、STM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Organization for Standardization (ISO), 1 rue deVaremb, Case postale 56, C
15、H-1211, Geneva 20, Switzerland, http:/www.iso.ch.*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 Thermometer (DCT), nan electronicdevice consisting
16、 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 of the sensor,computes the temperature from the measured quantity, andprovides
17、 a digital output or display, or both, of the temperature.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.NOTE 1Portable electronic thermometers (PET) is an acronym some-times used to ref
18、er 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 or fluid, nan oil or fluid that at agiven temperature exhibits a viscosity that
19、 varies with chang-ing shear stress or shear rate.3.1.5 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 cylinder surface(such as this apparatus, described in 6.1), and ignoring any end
20、effects, 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, s1, = angular velocity, rad/s,Rs= stator radius, mm,Rr= rotor radius, mm, andt = time in seconds for one revolution of the rotor.For the specific a
21、pparatus being described in 6.1.1, 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(4) 5Tr2 !Rr2h3109(5)where:Tr= torque applied to rotor, Nm,
22、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 between the applied shear stressand rate of shear, someti
23、mes 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 secondPas.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration oils, nthose oils that establish an instru-ments reference framew
24、ork of apparent viscosity versusspeed, from which the apparent viscosities of test oils aredetermined.3.2.2 cell constant, nthe ratio of the calibration fluidviscosity to the time required to complete the first threemeasured revolutions of the rotor.3.2.3 test oil, nany oil for which the apparent vi
25、scosityand yield stress are to be determined by this test method.3.2.4 unused oil, nan oil which has not been used in anoperating engine.3.2.5 used oil, nan oil which has been used in an operatingengine.3.2.6 yield stress, nthe shear stress required to initiateflow. For all Newtonian fluids and many
26、 non-Newtonian fluids,the yield stress is zero. An engine oil can have a yield stressthat is a function of its low-temperature cooling rate, soak time,and temperature.4. Summary of Test Method4.1 An engine oil sample is held at 80 C and then cooled ata programmed cooling rate to a final test tempera
27、ture and heldfor a specified time period.At the end of this period, a series ofincreasing low torques are applied to the rotor shaft untilrotation occurs to determine the yield stress, if any is exhibited.A higher torque is then applied to determine the apparentviscosity of the sample.5. Significanc
28、e and Use5.1 When an engine oil is cooled, the rate and duration ofcooling can affect its yield stress and viscosity. In thislaboratory test, a fresh engine oil is slowly cooled through atemperature range where wax crystallization is known to occur,followed by relatively rapid cooling to the final t
29、est tempera-ture. These laboratory test results have predicted as failures theknown engine oils that have failed in the field because of lackof oil pumpability.4These documented field failing oils allconsisted of oils normally tested at 25 C. These field failuresare believed to be the result of the
30、oil forming a gel structurethat results in either excessive yield stress or viscosity of theengine oil, or both.5.2 Cooling Profiles:5.2.1 For oils to be tested at 20 C or colder, Table X1.1applies. The cooling profile described in Table X1.1 is based onthe viscosity properties of the ASTM Pumpabili
31、ty ReferenceOils (PRO). This series of oils includes oils with normallow-temperature flow properties and oils that have been4Pumpability Reference Oils (PRO) 21 through 29.D4684 142associated with low-temperature pumpability problems (1-5).5Significance for the 35 C and 40 C temperature profiles isb
32、ased on the data collected from the “Cold Starting andPumpability Studies in Modern Engines” conducted by ASTM(6,7).5.2.2 For oils to be tested at 15 C or 10 C, Table X1.2applies. No significance has been determined for this tempera-ture profile because of the absence of appropriate referenceoils. S
33、imilarly, precision of the test method using this profilefor the 10 C test temperature is unknown. The temperatureprofile of Table X1.2 is derived from the one in Table X1.1 andhas been moved up in temperature, relative to Table X1.1,inconsideration of the expected higher cloud points of theviscous
34、oils tested at 15 C and 10 C.6. Apparatus6.1 Mini-Rotary ViscometerAn apparatus that consists ofone or more viscometric cells in a temperature-controlled blockmade of a metallic material with high thermal conductivity.Each cell contains a calibrated rotor-stator set. The rotor shallhave a crossbar n
35、ear the top of the shaft extending in bothdirections far enough to allow the locking pin (6.6) to stoprotation at successive half turns. Rotation of the rotor isachieved by an applied force acting through a string woundaround the rotor shaft.6.1.1 The mini-rotary viscometric cell has the followingdi
36、mensions: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 0.1 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
37、thermometrically cooled instruments. The cell capis 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.
38、 The top half is 28 mm 6 1 mm in diameter and thebottom 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 cap
39、is made in two halves to facilitate placement in the 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 MeasurementA set of nine disks a
40、nd adisk holder, each with a mass of 10 g 6 0.1 g.6.2.2 Viscosity MeasurementA mass of 150 g 6 1.0 g.6.3 Temperature Control SystemRegulates the mini-rotaryviscometer block temperature in accordance with the tempera-ture requirements described in Table X1.1 or Table X1.2.6.3.1 Temperature ProfileThe
41、 temperature profile is fullydescribed in Table X1.1 and Table X1.2.6.4 Temperature Measuring DeviceUse either a DCTmeeting the requirements described in 6.4.1 or liquid-in-glassthermometers described in 6.4.2. A calibrated DCT or cali-brated low temperature liquid-in-glass thermometer shall beused
42、as the thermometer for temperature measurement below25 C independent of the instruments temperature control, andshall be located in the thermowell.NOTE 2The display device and sensor must be correctly paired.Incorrect pairing will result in temperature measurement errors andpossibly irreversible dam
43、age to the electronics of the display.6.4.1 Digital contact thermometer requirements: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 sens
44、ing element less than30 mm in length to be used with a thermowellsleeve, 6 mm O.D. 58 mm long with 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 a
45、s defined inSpecification E1137Drift less than 50 mK (0.05 C) per yearCalibration Error less than 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
46、Report From a calibration laboratory with demon-strated competency in temperature calibrationwhich is traceable to a national calibrationlaboratory or metrology standards bodyNOTE 3With respect to DCT probe immersion depth, a procedure todetermine minimum immersion depth can be found in Guide E2877,
47、Section 5.3, or Test Methods E644, Section 7.6.4.1.1 The DCT calibration drift shall be checked at leastannually by either measuring the ice point or against areference thermometer in a constant temperature bath at theprescribed immersion depth to ensure compliance with6.4.1.With respect to an ice b
48、ath, Practice E563 providesguidance on the preparation and use of an ice bath. Howeverfor this use variance from the specific steps, such as watersource, is permitted provided preparation is consistent. Thebasis for the variance is due to the reference being used to trackchange in calibration not ve
49、rification.NOTE 4When a DCTs calibration drifts in one direction over severalcalibration checks, that is, 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 lowtemperature LiG thermometer shall have a report of calibrationshowin
