ASTM D4425-24 用离心法（科伯斯法）测定润滑脂分油量的标准试验方法

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Designation: D4425 −24
Standard Test Method for
Oil Separation from Lubricating Grease by Centrifuging
(Koppers Method)
1
This standard is issued under the ﬁxed designation D4425; 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*
1.1 This test method covers a procedure for determining the
tendency of lubricating grease to separate oil when subjected to
high centrifugal forces.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
standard.
1.3 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 appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
D4057 Practice for Manual Sampling of Petroleum and
Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid
Fuels, and Lubricants
3. Terminology
3.1 Deﬁnitions:
3.1.1 For deﬁnitions of terms used in this test method, refer
to Terminology D4175.
3.1.2 lubricating grease, n—a semi-ﬂuid to solid product of
a dispersion of a thickener in a liquid lubricant.
3.1.2.1 Discussion—The dispersion of the thickener forms a
two-phase system and immobilizes the liquid lubricant by
surface tension and other physical forces. Other ingredients are
commonly included to impart special properties.
3.1.3 thickener, n—in lubricating grease, a substance com-
posed of ﬁnely-divided particles dispersed in a liquid to form
the products’s structure.
3.1.3.1 Discussion—Thickeners can be ﬁbers (such as vari-
ous metallic soaps) or plates or spheres (such as certain
non-soap thickeners), which are insoluble or, at most, only very
slightly soluble in the liquid lubricant. The general require-
ments are that the solid particles be extremely small, uniformly
dispersed, and capable of forming a relatively stable, gel-like
structure with the liquid lubricant.
3.2 Symbols:
a= distance from top of grease surface to tube mouth
(mm).
b= height of liquid column in an inverted test tube (mm).
d= test tube inside diameter (mm).
H= accumulated test time at a given reading (h).
K36 = resistance to centrifugal separation (V/H).
r= measured at the maximum radius of rotation (mm).
rpm = rotational speed (r/min).
V= volume of separated oil, as a percentage of the
original grease volume (%).
V
g
= grease volume in a test tube (cm
3
).
V
o
= volume of separated oil (cm
3
).
V
t
= test tube total volume (cm
3
).
A= angle of rotor, between the test tube axis and axis of
rotation (degrees).
ω= rotational speed (rad/s).
G= relative centrifugal acceleration.
3.3 The relative effect of centrifugal forces, when related to
the gravitational standard acceleration (9.81 m ⁄s
2
), is noted
with the symbol G. It can be calculated as follows:
G51.02 ×10
24
×r× ω
2
(1)
or
G51.12 ×10
26
×r×rpm
¯
2
(2)
4. Summary of Test Method
4.1 Pairs of centrifuge tubes are charged with grease
samples and are placed in the centrifuge. The grease samples
1
This test method is under the jurisdiction of Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
mittee D02.G0.03 on Physical Tests.
Current edition approved Nov. 1, 2024. Published November 2024. Originally
approved in 1984. Last previous edition approved in 2019 as D4425 – 19. DOI:
10.1520/D4425-24.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at www.astm.org/contact. For Annual Book of
ASTM Standards volume information, refer to the standard’s Document Summary
page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
1

are subjected to a centrifugal force equivalent to a Gvalue of

36 000, at 50 °C 61 °C, for speciﬁc periods of time. The

resistance of the grease to separate the oil is then deﬁned as a

ratio of the percent of oil separated to the total number of hours

of testing.

5. Signiﬁcance and Use

5.1 This test method is useful in evaluating the degree to

which a grease would separate into ﬂuid and solid components

when subjected to high centrifugal forces. Flexible shaft

couplings, universal joints, and rolling element thrust bearings

are examples of machinery which subject lubricating greases to

large and prolonged centrifugal forces. This test method has

been found to give results that correlate well with results from

actual service. The test method may be run at other conditions

with agreement between parties but the precision noted in this

test method will no longer apply.

6. Apparatus

6.1 High-Speed Centrifuge, capable of developing a Gvalue

of 36 000. Mount the unit on a ﬂat level surface to allow

unrestricted air ﬂow to the motor. This is essential for long

motor life. The centrifuge should be equipped with:

6.1.1 Fixed Angle Rotor, multiple place, which can sustain a

Gvalue of 36 000.

6.1.2 Thermometer, preferably of a dial type, installed so

that the temperature in the vicinity (5 mm to 15 mm) of the

rotor can be measured.

6.1.3 Air Choke, installed at the air inlet of the centrifuge

chamber, and used to control the temperature if the unit lacks

an automatic temperature control. Some designs require outlet

choking as well.

6.1.4 Centrifuge Tubes, made of transparent material, ca-

pable of withstanding a Gvalue of 36 000 for 100 h minimum

(Note 1).

NOTE 1—Polypropylene tubes were found to be the most durable.

6.2 Balance, having a capacity of about 100 g with a

minimum sensitivity of 0.1 g.

7. Sampling

7.1 Samples should be taken in accordance with Practice

D4057.

7.2 The sample presented for analysis should be large

enough to make possible the selection of a representative

portion for testing. Each run will require approximately 0.5 g

for each cubic centimetre of tube capacity . Examine for any

indication of non-homogeneity such as oil separation, phase

changes, or gross contamination. If any abnormal conditions

are found, obtain a new sample.

7.3 The sample temperature at time of loading is to be

between 15 °C and 35 °C.

8. Preparation of Apparatus

8.1 Inspect the centrifuge unit paying particular attention to

the cleanliness of the rotor which will be unbalanced by any

surface deposits.

8.2 Examine the required number of tubes to be used for the

test, rejecting any with surface scratches or imperfections.

9. Procedure

9.1 For each grease, two centrifuge tubes are required. New

tubes must be used for each test and they must be handled with

care to avoid scratches.

9.1.1 Determine the total volume, V, in cubic centimetres, of

each tube by ﬁlling with water and then pouring into a

graduated cylinder and measuring.

9.1.2 Measure the inside diameter, d, in millimetres with a

vernier caliper.

9.2 Take grease samples from the container without includ-

ing any free oil found on the grease surface.

9.3 Charge each tube with approximately 0.5 g of grease for

each cubic centimeter of tube capacity (example: 7 g of grease

in a tube of 14 cm

) taking care that the difference in mass of

each does not exceed 0.3 g to minimize centrifuge imbalance.

9.4 Place the tubes in diametrically opposite compartments

if all rotor compartments are not used. Always use even

numbers of tubes.

9.5 The centrifuge lid must always be closed when the rotor

is turning. The rotor should never be touched while rotating.

9.6 Operate the centrifuge at a Gvalue of 1000 for 3 min to

eliminate any trapped air bubbles in the grease charge.

9.7 Measure the distance, a, in millimetres from the top of

the test tube to the closest point on the grease surface as shown

in Fig. 1, and calculate the grease volume as in 10.1.

9.8 Replace the tubes in the rotor head, close the lid, and

bring the speed up to a relative acceleration, G, of 36 000.

Consult manufacturer’s instructions for proper speed.

Detailed discussion is found in Calistrat, M. M., Grease Separation under

Centrifugal Forces, ASME Paper 75-PTG-3. Presented at the Joint ASLE-ASME

Lubrication Conference, Oct. 21–23, 1975. FIG. 1 Measuring Grease Volume

D4425 − 24

9.9 At the end of the test interval, the rotor must come to a
complete stop before opening the lid.
9.10 Measure the amount of oil separated as follows:
9.10.1 Cover the mouth of the tube with a piece of hard
rubber or plastic material and invert for 1 min to 2 min or until
all the oil ﬂows to the top of the tube.
9.10.2 Measure the height, b, of the separated oil in
millimetres, as shown in Fig. 2.
9.11 Calculate the oil volume as indicated in 10.2.
9.12 Calculate the percent of oil separated from the grease
as indicated in 10.3.
9.13 If the test is to be continued, return the tubes to their
respective compartments in the centrifuge rotor. When the
covering over the tube mouth is removed all adhering oil must
be returned to the tubes.
9.14 Measure the amount of oil separation after one or more
of the following time periods: 6, 12, 24, 48, or 96 cumulative
hours of testing at a Gvalue of 36 000. No more than 72 h of
interruption is acceptable between two test periods.
9.15 The normal duration of a test is 24 cumulative hours.
9.15.1 The test can be extended to 48 h or 96 h if desired,
but special reporting conditions prevail (see 11.4.2).
10. Calculation
10.1 Calculate the grease volume to the nearest cm
3
as
follows:
V
g
5V
t
2
F
S
a1d
2 tan A
D
~
0.785 d
2
!
×10
23
G
(3)
where:
V
g
= grease volume, cm
3
,
V
t
= tube volume, cm
3
(see 9.1.1),
a= distance to grease surface, mm (see 9.7),
d= tube inside diameter, mm (see 9.1.2), and
A= angle of the rotor, in degrees. This angle is speciﬁed by
the rotor manufacturer.
10.2 Calculate the oil volume to the nearest cm
3
as follows:
V
o
50.785 d
2
b×10
23
(4)
where:
V
o
= separated oil volume, cm
3
, and
b= height of the separated oil, mm (see 9.10).
10.3 Calculate the amount of oil separated from the grease
to the nearest percent as follows:
V5V
o
V
g
×100 (5)
where:
V= oil separation, in volume percent.
11. Report
11.1 The amount of oil separated from a lubricating grease
subjected to centrifugal forces is a function of the Glevel, the
amount of time under test, and the test temperature. Thus, to
evaluate the resistance of a grease to separate the oil, the
following data are required:
11.1.1 The oil separation, in volume percent (see 10.3).
11.1.2 The level of centrifugal acceleration, in G(see 3.1).
11.1.3 The duration of the test, in hours.
11.1.4 The test temperature, in degrees Celsius.
11.2 In order to simplify the testing and reporting of the oil
separation from lubricating greases by centrifuging, the level
of centrifugal acceleration and the test temperature are main-
tained constant, at a Gvalue of 36 000 and 50 °C. Hence, the
resistance of a grease to separate the oil under centrifugal
forces is reported as the fraction K36.
K36 5V/H(6)
where:
V= oil separation, in volume percent (see 10.3), and
H=accumulated time of testing in hours (see 9.13).
The fraction K36 should not be reduced, and the values of
both Vand Hshould be reported.
11.3 The results of two tubes ﬁlled with the same grease
(see 9.3) are averaged for reporting purposes.
11.4 The values for Vand Hin Eq 6 are those at the time the
oil separation stabilizes. This is deﬁned as the time at which the
oil separation increases by less than 10 % between two
consecutive readings.
11.4.1 If the oil separation does not stabilize before the 24 h
test, the 24 h test results are used for reporting.
11.4.2 If the testing is extended beyond the 24 cumulative
hours, the same conditions in 11.4 apply, except more than 24 h
can be used. Examples of calculations can be found in
Appendix X1.
12. Precision and Bias
4
12.1 Precision—When run under the conditions stated in the
test method, the precision, as determined by statistical exami-
nation of interlaboratory results is as follows:
12.1.1 Repeatability—The difference between successive
test results, obtained by the same operator with the same
4
Supporting data have been ﬁled at ASTM International Headquarters and may
be obtained by requesting Research Report RR:D02-1185. Contact ASTM Customer
Service at www.astm.org/contact.
FIG. 2 Measuring Separated Oil
D4425 − 24
3

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标签： #标准试验 #试验方法 #标准试验方法

摘要：

本文详细解读ASTM D4425-24标准，即采用离心法（科伯斯法）测定润滑脂分油量的标准试验方法。该标准适用于评估润滑脂在储存、运输及使用过程中油与稠化剂的分离倾向，对润滑脂的质量控制和性能预测至关重要。通过科伯斯法离心分离技术，本方法能精准量化润滑脂在不同条件下的分油率，为航空航天、汽车及工业机械等关键领域提供可靠的润滑脂稳定性数据支持。阅读本文，您将全面了解ASTM D4425-24的试验原理、操作步骤及结果分析，以优化润滑脂配方与选型决策。

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