ASTM D4425-97(2002)

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An American National Standard
Designation:D4425–97 (Reapproved 2002)
Standard Test Method for
Oil Separation from Lubricating Grease by Centrifuging
(Koppers Method)
This standard is issued under the fixed designation D 4425; 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.
1. Scope 3.2 Symbols:
1.1 This test method describes a procedure for determining
the tendency of lubricating grease to separate oil when sub-
a = distance from top of grease surface to tube mouth
jected to high centrifugal forces.
(mm).
1.2 This standard does not purport to address all of the
b = height of liquid column in an inverted test tube
safety concerns, if any, associated with its use. It is the
(mm).
responsibility of the user of this standard to establish appro-
d = test tube inside diameter (mm).
priate safety and health practices and determine the applica-
H = accumulated test time at a given reading (h).
bility of regulatory limitations prior to use.
K36 = resistance to centrifugal separation (V/H).
1.3 The values stated in SI units are to be regarded as the
r = measured at the maximum radius of rotation (mm).
rpm = rotational speed (r/min).
standard.
V = volume of separated oil, as a percentage of the
2. Referenced Documents
original grease volume (%).
V = grease volume in a test tube (cm ).
2.1 ASTM Standards:
g
V = volume of separated oil (cm ).
D 217 Test Methods for Cone Penetration of Lubricating o
V = test tube total volume (cm ).
t
Grease
A = angle of rotor, between the test tube axis and axis of
3. Terminology rotation (degrees).
v = rotational speed (rad/s).
3.1 Definitions:
G = relative centrifugal acceleration.
3.1.1 lubricating grease, n—a semi-fluid to solid product of
a thickener in a liquid lubricant.
The relative effect of centrifugal forces, when related to the
3.1.1.1 Discussion—Thedispersionofthethickenerformsa
gravitational standard acceleration (9.81 m/s ), is noted with
two-phase system and immobilizes the liquid lubricant by
the symbol G. It can be calculated as follows:
surface tension and other physical forces. Other ingredients are
24 2
commonly included to impart special properties. D 217
G 5 1.02 3 10 3 r3v , (1)
3.1.2 thickener, n—in lubricating grease, a substance com-
or
posed of finely-divided particles dispersed in a liquid to form
26 2
G 5 1.12 3 10 3 r 3 rpm¯ (2)
the products’s structure.
3.1.2.1 Discussion—Thickeners can be fibers (such as vari-
4. Summary of Test Method
ous metallic soaps) or plates or spheres (such as certain
4.1 Pairs of centrifuge tubes are charged with grease
non-soapthickeners),whichareinsolubleor,atmost,onlyvery
samples and are placed in the centrifuge. The grease samples
slightly soluble in the liquid lubricant. The general require-
are subjected to a centrifugal force equivalent to a G value of
ments are that the solid particles be extremely small, uniformly
36 000, at 50°C 6 1°C, for specific periods of time. The
dispersed, and capable of forming a relatively stable, gel-like
resistance of the grease to separate the oil is then defined as a
structure with the liquid lubricant.
ratio of the percent of oil separated to the total number of hours
of testing.
5. Significance and Use
This test method is under the jurisdiction of Committee D02 on Petroleum
Products and is the direct responsibility of Subcommittee D02.G on Lubricating
5.1 This test method is useful in evaluating the degree to
Grease.
which a grease would separate into fluid and solid components
Current edition approved June 10, 1997. Published October 1997. Originally
when subjected to high centrifugal forces. Flexible shaft
published as D 4425 – 84. Last previous edition D 4425 – 90.
Annual Book of ASTM Standards, Vol 05.01. couplings, universal joints, and rolling element thrust bearings
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4425–97 (2002)
areexamplesofmachinerywhichsubjectlubricatinggreasesto 6.1.4 Centrifuge Tubes made of transparent material, ca-
large and prolonged centrifugal forces. This test method has pable of withstanding a G value of 36 000 for 100 h minimum
been found to give results that correlate well with results from (Note 1).
actual service. The test method may be run at other conditions
NOTE 1—Polypropylene tubes were found to be the most durable.
with agreement between parties but the precision noted in this
6.2 Balance, having a capacity of about 100 g with a
test method will no longer apply.
minimum sensitivity of 0.1 g.
6. Apparatus
7. Sampling
6.1 High-Speed Centrifuge capableofdevelopinga Gvalue
of 36 000. Mount the unit on a flat level surface to allow
7.1 The sample presented for analysis should be large
unrestricted air flow to the motor. This is essential for long
enough to make possible the selection of a representative
motor life. The centrifuge should be equipped with:
portion for testing. Each run will require approximately 0.5 g
6.1.1 Fixed Angle Rotor, multiple place, which can sustain
for each cubic centimetre of tube capacity . Examine for any
a G value of 36 000.
indication of non-homogeneity such as oil separation, phase
6.1.2 Thermometer, preferably of a dial type, installed so
changes, or gross contamination. If any abnormal conditions
that the temperature in the vicinity (5 to 15 mm) of the rotor
are found, obtain a new sample.
can be measured. (For Sorvall centrifuge, see Fig. 1.)
7.2 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 Determinethetotalvolume, V,incubiccentimetres,of
FIG. 1 Installation of Dial Thermometer (Sorvall Centrifuge)
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:7gof 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.
FIG. 2 Choking Air Inlet of Chamber (Sorvall Centrifuge)
9.6 Operate the centrifuge at a G value 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
6.1.3 Air Choke, installed at the air inlet of the centrifuge
the test tube to the closest point on the grease surface as shown
chamber(forSorvallcentrifuge,seeFig.2),andusedtocontrol
in Fig. 3, and calculate the grease volume as in 10.1.
the temperatu
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