ASTM D6896-03(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6896 − 03(Reapproved 2007)
Standard Test Method for
Determination of Yield Stress and Apparent Viscosity of
Used Engine Oils at Low Temperature
This standard is issued under the fixed designation D6896; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method covers the measurement of the yield 3.1 Definitions:
stress and viscosity of engine oils after cooling at controlled
3.1.1 apparent viscosity—the determined viscosity obtained
rates over a period of 43 or 45 h to a final test temperature of
by use of this test method.
-20 or -25°C. The viscosity measurements are made at a shear
3.1.2 Newtonian oil or fluid—an oil or fluid that at a given
-1
stress of 525 Pa over a shear rate of 0.4 to 15 s . This test
temperature exhibits a constant viscosity at all shear rates or
method is suitable for measurement of viscosities ranging from
shear stresses.
4000 mPa·s to >400 000 mPa·s, and is suitable for yield stress
3.1.3 non-Newtonian oil or fluid—an oil or fluid that at a
measurements of 7 Pa to >350 Pa.
given temperature exhibits a viscosity that varies with chang-
1.2 This test method is applicable for used diesel oils. The
ing shear stress or shear rate.
applicability and precision to other used or unused engine oils
3.1.4 shear rate—the velocity gradient in fluid flow. For a
or to petroleum products other than engine oils has not been
Newtonian fluid in a concentric cylinder rotary viscometer in
determined.
which the shear stress is measured at the inner cylinder surface
1.3 This test method uses the millipascal second (mPa·s) as
(such as the apparatus described in 6.1), and ignoring any end
the unit of viscosity. For information, the equivalent centipoise
effects, the shear rate is given as follows:
unit is shown in parentheses.
2 Ω R
~ !
s
1.4 This standard does not purport to address all of the G 5 (1)
r 2 2
R 2 R
s r
safety concerns, if any, associated with its use. It is the
4 π R
~ !
s
responsibility of the user of this standard to establish appro-
5 (2)
2 2
t R 2 R
~ !
s r
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
where:
G = shear rate at the surface of the rotor in reciprocal
r
2. Referenced Documents
-1
seconds, s ,
2.1 ASTM Standards: Ω = angular velocity, rad/s,
R = stator radius, mm,
D3829 Test Method for Predicting the Borderline Pumping
s
R = rotor radius, mm, and
Temperature of Engine Oil r
t = time for one revolution of the rotor, s.
D4684 Test Method for Determination of Yield Stress and
Apparent Viscosity of Engine Oils at Low Temperature
For the specific apparatus described in 6.1,
D5133 Test Method for Low Temperature, Low Shear Rate,
G 5 63/t (3)
r
Viscosity/Temperature Dependence of Lubricating Oils
3.1.5 shear stress—the motivating force per unit area for
Using a Temperature-Scanning Technique
fluid flow. For the rotary viscometer being described, the rotor
surface is the area under shear or the shear area.
1 T 5 9.81 M ~R 1R ! 310 (4)
This test method is under the jurisdiction of ASTM Committee D02 on r o t
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
TT
r
D02.07 on Flow Properties.
S 5 310 (5)
r 2
2 π R h
~ !
r
Current edition approved Nov. 1, 2007. Published January 2008. Originally
ϵ1
approved in 2003. Last previous edition approved in 2003 as D6896–03 . DOI:
where:
10.1520/D6896-03R07.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
T = torque applied to rotor, N·m,
r
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
M = applied mass, g,
Standards volume information, refer to the standard’s Document Summary page on
R = radius of the shaft, mm,
o
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6896 − 03 (2007)
in this test method have been correlated to pressurization times
R = radius of the string, mm,
t
in a motored engine test (1).
S = shear stress at the rotor surface, Pa, and
r
h = height of the rotor, mm.
5.2 Cooling Profiles:
For the dimensions given in 6.1.1, 5.2.1 For oils to be tested at -20°C and -25°C, Table X1.1
applies.ThecoolingprofiledescribedinTableX1.1isbasedon
T 5 31.7 M 310 (6)
r
the viscosity properties of the ASTM Pumpability Reference
S 5 3.5 M (7)
r
Oils (PRO). This series of oils includes oils with normal
3.1.6 viscosity—the ratio between the applied shear stress
low-temperature flow properties and oils that have been
and rate of shear, sometimes called the coefficient of dynamic
associated with low-temperature pumpability problems (2-7).
viscosity. This value is thus a measure of the resistance to flow
of the liquid. The SI unit of viscosity is the pascal second Pa·s. 6. Apparatus
A centipoise (cP) is one millipascal second mPa·s. 4
6.1 Mini-Rotary Viscometer , an apparatus that consists of
3.2 Definitions of Terms Specific to This Standard: one or more viscometric cells in a temperature-controlled
3.2.1 calibration oils—those oils that establish the instru- aluminum block. Each cell contains a calibrated rotor-stator
set. Rotation of the rotor is achieved by an applied load acting
ment’s reference framework of apparent viscosity versus
speed, from which the apparent viscosities of test oils are through a string wound around the rotor shaft.
6.1.1 The mini-rotary viscometric cell has the following
determined. Calibration oils, which are essentially Newtonian
typical dimensions:
fluids, are available commercially and have an approximate
viscosity of 30 Pa·s (30 000 cP) at -20°C.
millimetres
Diameter of rotor 17.0
3.2.2 test oil—any oil for which the apparent viscosity and
Length of rotor 20.0
yield stress are to be determined by this test method. Inside diameter of cell 19.0
Radius of shaft 3.18
3.2.3 used oil—an oil which has been used in an operating
Radius of string 0.10
engine.
6.2 Weights:
3.2.4 yield stress—the shear stress required to initiate flow. 6.2.1 Yield Stress, weight set consists of ten 10 g units with
a tolerance of 1 % for each unit.
3.2.4.1 Discussion—For all Newtonian fluids and some
6.2.2 Viscosity, 150 g weight with a 1 % tolerance.
non-Newtonian fluids, the yield stress is zero.An oil can have
a yield stress that is a function of its low-temperature cooling
6.3 Temperature Control System, that will regulate the
rate, soak time, and temperature. Yield stress measurement by
mini-rotary viscometer block temperature in accordance with
thistestmethoddeterminesonlywhetherthetestoilhasayield
the temperature limits described in Table X1.1.
stress of at least 35 Pa; a yield stress below 35 Pa is considered
6.3.1 Temperature Controller is the most critical part of this
to be insignificant for engine oils.
procedure.Adescription of the requirements that the controller
shall meet are included in Appendix X2.
4. Summary of Test Method
6.3.2 Temperature Profile—The temperature profile is fully
described in Table X1.1.
4.1 A used engine oil sample is heated at 80°C and then
vigorously agitated. The sample is then cooled at a pro-
6.4 Thermometers, for measuring the temperature of the
grammed cooling rate to a final test temperature.Alow torque
block. Two ranges are required, one graduated from at least
isappliedtotherotorshafttomeasuretheyieldstress.Ahigher
+70 to 90°C in 1°C subdivisions, the other with a range from
torqueisthenappliedtodeterminetheapparentviscosityofthe
at least -36 to +5°C or -45 to +5°C, in 0.2°C subdivisions.
sample.
Other thermometric devices of equal accuracy and resolution
may be used to calibrate the temperature sensor.
5. Significance and Use
6.5 Refrigeration Device, consisting of a means of remov-
ing heat from the instrument such that the cell temperature is
5.1 When an engine oil is cooled, the rate and duration of
controlled in accordance with the program described in Table
cooling can affect its yield stress and viscosity. In this
X1.1.
laboratory test, used engine oil is slowly cooled through a
temperaturerangewherewaxcrystallizationisknowntooccur,
6.6 Circulating System, that will circulate the liquid coolant
followed by relatively rapid cooling to the final test tempera-
to the instrument as needed. Methanol is a suitable coolant if
ture.As in other low temperature rheological tests such as Test
the circulating coolant is below -10°C. One should observe
Methods D3829, D4684, and D5133, a preheating condition is
toxicity and flammability precautions that apply to the use of
required to ensure that all residual waxes are solubilized in the
oil prior to the cooldown (that is, remove thermal memory).
However,itisalsoknownthathighlysooteduseddieselengine 3
The boldface numbers in parentheses refer to the list of references at the end of
oils can experience a soot agglomerization phenomenon when
this standard.
The sole source of supply of the apparatus known to the committee at this time
heated under quiescent conditions. The current method uses a
is Cannon Instrument Co., P.O. Box 16, State College, PA 16804. If you are aware
separate preheat and agitation step to break up any soot
of alternative suppliers, please provide this information to ASTM International
agglomerization that may have occurred prior to cooldown.
Headquarters.Your comments will receive careful consideration at a meeting of the
The viscosity of highly sooted diesel engine oils as measured responsible technical committee, which you may attend.
D6896 − 03 (2007)
methanol. The circulating system shall be capable of maintain- 9.2.6 Repeat9.2.5foreachoftheremainingcells,takingthe
ingtesttemperatureduringthetest.Ifmethanolisleakingfrom cells in order from left to right.
the system, discontinue the test and repair the leak.
9.2.7 Calculate the viscometer constant for each cell (rotor/
(Warning—Methanol is flammable.)
stator combination) with the following equation:
6.7 Chart Recorder, to verify that the correct cooling curve
C 5η /t (8)
o
is being followed, it is recommended that a chart recorder be
where:
used to monitor the block temperature.
η = viscosity of the standard oil, cP (mPa·s) at -20°C,
o
6.8 Sample Pre-treatment Oven, an oven capable of main-
C = cell constant with 150 g mass, Pa, and
taining a temperature of 80 6 1°C for a minimum of 2 h.
T = time for three complete revolutions, s.
9.2.8 If any cell has a calibration constant more than 10 %
7. Reagents and Materials
higher or lower than the average for the other cells, the fault
7.1 Newtonian Oil, a low cloud-point of approximately 30
may be a problem with rotor operation. Examine rotor for
Pa·s (30 000 cP) viscosity at -20°C for calibration of the
damage and recalibrate instrument.
viscometric cells.
9.3 If corrected values for controller temperature and ther-
7.2 Methanol—Commercial or technical grade of dry
mometer deviate by more than the tolerance, use X2.2 to assist
methanol is suitable for the cooling bath.
in determining the fault.
7.3 Oil Solvent, commercial heptanes or similar solvent that
9.4 Oven—Check the calibration of the temperature sensing
evaporates without leaving a residue is suitable. (Warning—
device by appropriate methods. The temperature should be
Flammable.)
constant at 80 6 1°C.
7.4 Acetone—A technical grade of acetone is suitable pro-
vided it does not leave a residue upon evaporation.
10. Procedure
(Warning—Flammable.)
10.1 Select the cooling profile for the desired test tempera-
8. Sampling
ture. Table X1.2 lists the nominal times to reach a particular
test temperature.
8.1 A representative sample of test oil free from suspended
10.1.1 Choose the preprogrammed temperature profile. If
granular material and water is necessary to obtain valid
theprofileisnotavailable,enteritusingthecustomprofilepart
viscosity measurements. If the sample in its container is
of the software program. The instrument manual provides
received below the dew-point temperature of the room, allow
instructions on adding custom profiles. The entries for a
the sample to warm to room temperature before opening the
custom program will be found in Table X1.3.
container.
10.1.2 If the instrument temperature is controlled by an
9. Calibration and Standardization
external controller, it will need to be programmed to follow the
cooling program in Table X1.1 with adjustment for the
9.1 Calibrate the temperature sensor in place while attached
temperature difference found in 9.1, if any.
to the temperature controller. The sensed temperature shall be
verified using a reference thermometer specified in 6.4 at a
10.2 Test Sample and Viscometric Cell Preparation:
minimum of three temperatures. Make these temperature
10.2.1 Using suitable closed container, preheat the samples
measurementsatleast5°Caparttoestablishacalibrationcurve
in an oven to 80 6 1°C for 2.25 h. At the end of this time,
for this combination of temperature sensor and controller. For
removethesamplesfromtheovenandallowtocoolfor15min
instruments using an independent temperature controller, see
at room temperature.
X2.1 for calibration guidance.
10.2.2 Agitate each sample using vigorous mechanical or
NOTE 1—All temperatures in this test method refer to the actual
manual shaking for 60 s. Allow the samples to stand for a
temperature as measured in the left thermowell and not necessarily the
minimum of 10 min to allow for settling.
indicated temperature.
10.2.3 Remove the nine rotors from the viscometric cells
9.2 The calibration of each viscometric cell (viscometer
and ensure that both the cells and rotors are clean. See 10.6 for
constants) can be determined with the viscosity standard and
the cleaning procedure.
the following procedure at -20°C.
10.2.4 Place a 10 6 1.0 mL oil sample in each cell.
9.2.1 Use steps 10.2.3-10.6.
10.2.5 Install the rotors in the proper stators and install the
9.2.2 Program the temperature controller to cool the mini-
upper pivots.
rotary viscometer block to -20°C within1hor less, then start
the program. 10.2.6 Place the loop of the 700-mm long string over the
9.2.3 Allow the oil in the cells to soak at -20 6 0.2°C for at crossarm at the top of the rotor shaft and wind all but 200 mm
least 1 h, making small temperature control adjustments, if of the length of the string around the shaft. Do not overlap
necessary, to maintain the test temperature. strings. Loop the remaining end of the string over the top
9.2.4 At the end of the soak period, record the temperature bearing cover. Orient the rotor such that an end of the cros
...