ASTM D5481-96(2001)
(Test Method)Standard Test Method for Measuring Apparent Viscosity at High-Temperature and High-Shear Rate by Multicell Capillary Viscometer
Standard Test Method for Measuring Apparent Viscosity at High-Temperature and High-Shear Rate by Multicell Capillary Viscometer
SCOPE
1.1 This test method covers the laboratory determination of high-temperature high-shear (HTHS) viscosity of engine oils at a temperature of 150°C using a multicell capillary viscometer containing pressure, temperature, and timing instrumentation. The shear rate for this test method corresponds to an apparent shear rate at the wall of 1.4 million reciprocal seconds (1.4 10 6 s1). This shear rate has been found to decrease the discrepancy between this test method and other high-temperature high-shear test methods3 used for engine oil specifications. Viscosities are determined directly from calibrations that have been established with Newtonian oils with viscosities from 2 to 5 mPa·s at 150°C.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation: D 5481 – 96 (Reapproved 2001)
Standard Test Method for
Measuring Apparent Viscosity at High-Temperature and
High-Shear Rate by Multicell Capillary Viscometer
This standard is issued under the fixed designation D 5481; 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 (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Several different configurations of capillary viscometers have been successfully used for measuring
the viscosity of engine oils at the high shear rates and high temperatures that occur in engines. See Test
Method D 4624. This test method covers the use of a single apparatus at a single temperature and
single shear rate to achieve greater uniformity and improved precision.
1. Scope D 4683 Test Method for Measuring Viscosity at High Shear
Rate and High Temperature by Tapered Bearing Simula-
1.1 This test method covers the laboratory determination of
tor
high-temperature high-shear (HTHS) viscosity of engine oils at
D 4741 Test Method for Measuring Viscosity at High Tem-
a temperature of 150°C using a multicell capillary viscometer
perature and High Shear Rate by Tapered Plug Viscom-
containing pressure, temperature, and timing instrumentation.
eter
The shear rate for this test method corresponds to an apparent
shear rate at the wall of 1.4 million reciprocal seconds
3. Terminology
6 −1 3
(1.4 3 10 s ). This shear rate has been found to decrease the
3.1 Definitions:
discrepancy between this test method and other high-
3 3.1.1 apparent shear rate at the wall—shear rate at the wall
temperature high-shear test methods used for engine oil
of the capillary calculated for a Newtonian fluid, as follows:
specifications. Viscosities are determined directly from calibra-
tions that have been established with Newtonian oils with
S 5 4V/pR t (1)
a
viscosities from 2 to 5 mPa·s at 150°C.
where:
1.2 This standard does not purport to address all of the
−1
S = apparent shear rate at the wall, s ,
a
safety concerns, if any, associated with its use. It is the
V = volume, mm ,
responsibility of the user of this standard to establish appro-
R = capillary radius, mm, and
priate safety and health practices and determine the applica-
t = measured flow time, s.
bility of regulatory limitations prior to use.
3.1.1.1 Discussion—The actual shear rate at the wall will
differ for a non-Newtonian fluid.
2. Referenced Documents
3.1.2 apparent viscosity—the determined viscosity obtained
2.1 ASTM Standards:
by this test method.
D 4624 Test Method for Measuring Apparent Viscosity by
3.1.3 density—mass per unit volume.
Capillary Viscometer at High Shear Rate and High Tem-
3.1.3.1 Discussion—In the SI, the unit of density is the
perature
kilogram per metre cubed (kg/m ); the gram per cubic centi-
3 3 −3 3
metre (g/cm ) is often used. One kg/m is 10 g/cm .
3.1.4 kinematic viscosity—the ratio of the viscosity to the
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
density of the fluid.
D02.07.0B on High Temperature Rheology of Non-Newtonian Fluids.
3.1.4.1 Discussion—Kinematic viscosity is a measure of a
Current edition approved Apr. 10, 1996. Published June 1996. Originally
fluid’s resistance to flow under the force of gravity. In the SI,
published as D 5481 – 93. Last previous edition D 5481 – 93.
the unit of kinematic viscosity is the metre squared per second
Manning, R. E., and Lloyd, W. A., “Multicell High Temperature High-Shear
Capillary Viscometer,” SAE Paper 861562. Available from Society of Automotive
(m /s); for practical use, a submultiple (millimetre squared per
Engineers, 400 Commonwealth Dr., Warrendale, PA 15096. 2
second, mm /s) is more convenient. The centistoke (cSt) is 1
Girshick, F., “Non-Newtonian Fluid Dynamics in High Temperature High
mm /s and is often used.
Shear Capillary Viscometers,” SAE Paper 922288. Available from Society of
Automotive Engineers, 400 Commonwealth Dr., Warrendale, PA 15096.
Annual Book of ASTM Standards, Vol 05.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5481
3.1.5 Newtonian oil or fluid—an oil or fluid that exhibits a achieve a flow rate corresponding to an apparent shear rate at
6 −1
constant viscosity at all shear rates or shear stresses. the wall of 1.4 3 10 s . The calibration of each cell is used
3.1.6 non-Newtonian oil or fluid—an oil or fluid that exhib- to determine the viscosity corresponding to the measured
its a viscosity that varies with changing shear rate or shear pressure.
stress. 4.2 Each viscometric cell is calibrated by establishing the
3.1.7 shear rate—the spatial gradient of velocity in laminar relationship between pressure and flow rate for a series of
flow; the derivative of velocity with respect to distance in a Newtonian oils of known viscosity.
direction perpendicular to the direction of flow.
5. Significance and Use
3.1.7.1 Discussion—The derived unit of shear rate is veloc-
ity divided by length. With the time in seconds and with
5.1 Viscosity is an important property of fluid lubricants.
consistent units of length, shear rate becomes reciprocal
The viscosity of all fluids varies with temperature. Many
−1
seconds, or s . common petroleum lubricants are non-Newtonian: their vis-
3.1.8 shear stress—force per area of fluid in the direction of
cosity also varies with shear rate. The usefulness of the
flow. viscosity of lubricants is greatest when the viscosity is mea-
3.1.8.1 Discussion—In a capillary viscometer, the signifi-
sured at or near the conditions of shear rate and temperature
cant shear stress is the shear stress at the wall, that is, the total
that the lubricants will experience in service.
force acting on the cross section of the capillary divided by the
5.2 The conditions of shear rate and temperature of this test
area of the inside surface of the capillary. The shear stress at the
method are thought to be representative of those in the bearing
wall does not depend on the fluid properties (that is, Newtonian
of automotive engines in severe service.
or non-Newtonian). The SI unit for shear stress is the pascal
5.3 Many equipment manufacturers and lubricant specifica-
(Pa). Mathematically, the shear stress at the wall of a capillary
tions require a minimum high-temperature high-shear viscosity
6 −1
viscometer is as follows:
at 150°C and 10 s . The shear rate in capillary viscometers
varies across the radius of the capillary. The apparent shear rate
Z 5 PR/2L (2)
at the wall for this test method is increased to compensate for
where:
the variable shear rate.
Z = shear stress, Pa,
5.4 This test was evaluated in an ASTM cooperative pro-
P = pressure drop, Pa, 6
gram.
R = capillary radius, and
L = capillary length in consistent units.
6. Apparatus
3.1.9 viscosity—the ratio between shear stress and shear rate
6.1 High-Temperature High-Shear (HTHS)
at the same location.
Viscomete, consisting of several viscometer cells in a
3.1.9.1 Discussion—Viscosity is sometimes called the coef-
temperature-controlled block and including means for control-
ficient of viscosity, or the dynamic viscosity. It is a measure of
ling and measuring temperature and applied pressure and for
a fluid’s resistance to flow. In the SI, the unit of viscosity is a
timing the flow of a predetermined volume of test oil. Each
pascal second (Pa·s); for practical use a submultiple (millipas-
viscometric cell contains a precision glass capillary and means
cal second, mPa·s) is more convenient. The centipoise (cP) is
for adjusting the test oil volume to the predetermined value.
1 mPa·s and is often used.
6.1.1 The HTHS viscometer has the following typical di-
3.2 Definitions of Terms Specific to This Standard:
mensions and specifications:
3.2.1 calibrations oils—those oils used for establishing the
Diameter of capillary 0.15 mm
instrument’s reference framework of apparent viscosity versus
Length of capillary 15 to 18 mm
pressure drop from which the apparent viscosities of the test Temperature control 150 6 0.1°C
Pressure range 350 to 3500 KPa (50 to 500 psi)
oils are determined.
Pressure control 61%
3.2.1.1 Discussion—Calibration oils, which are Newtonian
Sample volume 7 6 1mL
fluids, are available commercially or can be blended by the
6.1.2 The thermometer for measuring the temperature of the
user.
block is a pre-set digital resistance thermometer. The accuracy
3.2.2 test oil—any oil for which the apparent viscosity is to
of this thermometer may be checked by means of a special
be determined by the test method.
thermowell and calibrated thermometer whose accuracy is
3.2.3 viscometric cell—that part of the viscometer compris-
60.1°C or better. See manufacturer’s recommendations for
ing all parts which may be wet by the test sample, including
procedure.
exit tube, working capillary, fill tube, pressure/exhaust connec-
tion, plug valve, and fill reservoir.
7. Reagents and Materials
7.1 Newtonian Oils, having certified viscosities of 2 to 7
4. Summary of Test Method
mPa·s at 150°C. See Table 1.
4.1 The viscosity of the test oil in any of the viscometric
cells is obtained by determining the pressure required to
Report is available from ASTM International Headquarters. Request RR:D02-
1378.
5 7
Calibration oils, suitable for this purpose, are available from Cannon Instru- A source of supply is Cannon Instrument Co., P.O. Box 16, State College, PA
ment Co., P. O. Box 16, State College, PA 16804. 16804.
D 5481
TABLE 1 Calibration Oils
than before each new series of runs and every twentieth run.
Approximate The non-Newtonian calibration oil should be run at least
Approximate Pressure for Test Method
A
Viscosity
Calibration Oil monthly. The calibration oil viscosity determined in this way
(mPa·s) psi kPa
must not differ from the standard value by more than the
HT39 2.0 225 1500 repeatability of the test (see 12.1). If it is out of limits, and if
HT75 2.7 290 2000
the result is confirmed by a repeat run, look for the source of
HT150 3.7 375 2500
the trouble, rectify it, and repeat the entire calibration proce-
HT240 5.0 480 3300
HT390 7.0 645 4500 dure, if necessary. Some possible steps to find the source of the
A
trouble are to check the system thoroughly for faults, including
Consult the supplier for specific values.
foreign material in the capillary, verify the fidelity of the
operating procedure, and accuracy of temperature control, and
7.2 Non-Newtonian Reference Sample, having a certified
readout.
6 −1
viscosity at 150°C and 10 s .
9.3 Stability of Temperature Calibration—Check the cali-
7.3 Carbon Dioxide or Nitrogen Cylinder, with reducer
bration of the temperature sensor at least once a year using a
valve having a maximum pressure of at least 500 psi (3500 Pa).
standardized thermometer inserted in the thermowell in the
aluminum block.
8. Sampling
8.1 A representative sample of test oil, free from suspended
10. Procedure
solid material and water, is necessary to obtain valid results.
10.1 Bring the viscometer to the test temperature and allow
When the sample is suspected to contain suspended material,
test temperature to stabilize for at least 30 min. Because the
filter with about 10-μm filter paper.
viscometer uses only a small amount of electrical power, it may
9. Calibration and Standardization
be desirable to leave the viscometer at test temperature unless
use is not anticipated for an extended period of time.
9.1 Calibration:
10.2 Flush the previous sample with 4 to 6 mL of the new
9.1.1 The volume and capillary diameter of each viscomet-
test sample. Open the plug valve. Warning: Always keep the
ric cell is provided by the manufacturer, and the flow time, t ,
o
plug valve closed except when charging or adjusting the
corresponding to an apparent shear rate at the wall of 1.4 3 10
−1
volume of sample; NEVER turn on the pressure with the plug
s is calculated by the manufacturer using the following
valve open. Inserta4to 6-mL test sample, and close the plug
equation:
valve. Turn on the pressure (it is not necessary to adjust the
6 3
t 5 4V/1.4*10 pR (3)
o
pressure from the previous run) until the flush sample has
where symbols are defined as in 3.1.1.
passed through the capillary to waste. It is not necessary to
9.1.2 Using a minimum of four Newtonian calibration oils
achieve temperature equilibrium since no time measurement is
covering the viscosity range from 2 to 5 mPa·s (cP) at 150°C,
being made. Turn off the pressure.
determine the relationship between pressure and flow rate. The
10.3 Chargea9to11-mL test sample into the viscometric
pressure should be adjusted for each calibration oil such that
cell by opening the plug valve, inserting the test sample, and
the flow time is within 620 % of the nominal flow time, t .
then closing the plug valve.
o
Make three determinations for each oil in each cell.
10.4 Repeat 10.2 and 10.3 for each of the viscometric cells.
9.1.2.1 The following relationship can be used to express
10.5 Allow 15 min for the test sample to attain 150 6 0.1°C.
the data:
10.6 After temperature equilibrium has been established,
ensure that the plug valve is closed on each cell and make
C t
h5 C ·t·P 2 · 1 1 C · 1 2 (4)
F G F S DG
1 3
measurement of efflux time and pressure as follows:
t t
o
10.6.1 From the calibration of the viscometric cell and the
where:
expected viscosity of the sample (if known), estimate the
h = viscosity, mPa·s,
required pressure to achieve the nominal flow time, t (see
o
t = flow time, s,
9.1.1). Table 2 provides a guide for setting pressure if the SAE
P = pressure, kPa or psi, and
viscosity grade is known. Adjust the pressure in the ballast tank
C ,C ,C = coefficients specific to each viscometer cell.
1 2 3
to this value within 61 %; allow approximately 10 s for this
9.1.2.2 Coefficient C is specific to the units in which
pressure to stabilize.
pressure is expressed, as well as to each cell. Coefficient C
10.6.2 Reset the timer to zero.
will be essentially constant over the relatively narrow range of
shear rates and viscosities of interest in measurement of the
high-temperature viscosity of automotive engine oil. In more
TABLE 2 Approximate Pressure for Test Method
general applications, C may not be constant for all values of
Pressure
Reynolds Number.
SAE Grade
psi kPa
9.1.2.3 Annex A1 describes the procedure for determining
coefficients C , C , and C . 20 225 1500
1 2 3
30 250 1750
9.2 Stability of Viscosity Calibration—Check the stability of
40 300 210
...
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