U.S. patent application number 10/265309 was filed with the patent office on 2003-07-31 for fluorescent grease and bearings having the same therein.
Invention is credited to Akiyama, Motoharu, Sugimura, Joichi.
Application Number | 20030144159 10/265309 |
Document ID | / |
Family ID | 27615074 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030144159 |
Kind Code |
A1 |
Akiyama, Motoharu ; et
al. |
July 31, 2003 |
Fluorescent grease and bearings having the same therein
Abstract
The invention provides a fluorescent grease which enables
monitoring of behaviors of the grease for elucidation of the
mechanism of grease lubrication, and a rolling element bearing or a
condition monitoring rolling element bearing, both charged with the
fluorescent grease. The fluorescent grease contains, as its
essential components, a base oil, a thickener agent, and a
fluorescent substance.
Inventors: |
Akiyama, Motoharu;
(Nagano-ken, JP) ; Sugimura, Joichi; (Fukuoka-shi,
JP) |
Correspondence
Address: |
FLYNN THIEL BOUTELL & TANIS, P.C.
2026 RAMBLING ROAD
KALAMAZOO
MI
49008-1699
US
|
Family ID: |
27615074 |
Appl. No.: |
10/265309 |
Filed: |
September 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10265309 |
Sep 26, 2002 |
|
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09755318 |
Jan 5, 2001 |
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Current U.S.
Class: |
508/462 ;
508/247; 508/539 |
Current CPC
Class: |
C10M 2203/022 20130101;
C10M 2207/1285 20130101; C10M 2207/186 20130101; C10M 2203/04
20130101; C10M 2207/125 20130101; C10M 2203/02 20130101; C10N
2040/02 20130101; C10N 2010/02 20130101; C10M 2207/246 20130101;
C10M 2203/024 20130101; C10M 2207/206 20130101; C10M 2207/1245
20130101; C10M 2203/00 20130101; C10M 2207/1225 20130101; C10M
2207/1265 20130101; C10M 171/007 20130101; C10M 2207/32 20130101;
C10M 2207/129 20130101; C10M 169/00 20130101; C10M 2207/166
20130101; C10M 2207/325 20130101 |
Class at
Publication: |
508/462 ;
508/247; 508/539 |
International
Class: |
C10M 169/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2000 |
JP |
2000-171823 |
Claims
What is claimed:
1. A fluorescent grease comprising, as essential components, a base
oil consisting of a synthetic carbonate ester, a thickener agent
consisting of a lithium soap and a fluorescent substance consisting
of at least one member selected from the group consisting of
pyrene, perylene, 1,6-diphenyl-1,3,5-hexatriene,
1,8-diphenyl-1,3,5,7-octatetraene and coumarine 6.
2. The fluorescent grease of claim 1, wherein the fluorescent
substance is at least one member selected from the group consisting
of pyrene, perylene, 1,6-diphenyl-1,3,5-hexatriene and
1,8-diphenyl-1,3,5,7-octatetr- aene.
3. A rolling element bearing charged with the fluorescent grease of
claim 1.
4. A condition monitoring rolling element bearing charged with the
fluorescent grease of claim 1.
5. A method of testing grease characteristics using the fluorescent
grease of claim 1, comprising the steps of: adhering the
fluorescent grease to a ball; rotating the ball while pressing the
ball onto a glass substrate; irradiating the ball with light
through the glass substrate; and observing behavior of the
fluorescent grease with a CCD camera while the ball is being
rotated.
6. The method of claim 5, wherein the fluorescent grease is made of
at least two fluorescent substances, the ball is irradiated with
light of multiple wavelengths and plural images of the fluorescent
substances appearing on the CCD are compared with one another.
7. The method of claim 6, wherein at least one of the fluorescent
substances has an affinity for the base oil and another fluorescent
substance has an affinity for the thickening agent.
8. A method of testing bearings characteristics comprising the
steps of: charging a bearing with the fluorescent grease of claim
1; rotating the bearing at a specified temperature for a specified
time and at a specified speed; receiving fluorescent grease
dispersed from the bearing by a test piece; irradiating the test
piece with light; and examining a grease spot on the test
piece.
9. The method of claim 8, wherein the bearing is a mechanically
sealed bearing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a grease, which is able to realize
a low torque of a rolling element bearing and improve wear
resistance as a result of visual observation of a grease lubricant
film wherein the formation of the grease lubricant film and the
behavior of its break-down that have never been satisfactorily
elucidated up to now, i.e. the action of a base oil and a thickener
agent under non-steady state operating conditions, are made clear.
The invention also relates to a bearing or condition monitoring
rolling element bearing charged with such a grease as mentioned
above.
[0003] 2. Description of the Prior Art
[0004] For the observation or measurement of a lubricant film,
there have been used a number of methods including, aside from a
fluorescence method, a light interference method, a micro
displacement transducer method, an X-ray transmission method, an
electric capacitance method, an electric resistance method, a
method using an ultrasonic wave, and the like. Of these observation
or measurement methods, the most widely employed method of directly
measuring a film thickness is the light interference method or its
extension of ultra thin film interferometry.
[0005] For the indirect measurement of a film thickness of the
order of size of molecules, the micro displacement transducer
method has been used. However, with the light interference method,
it is necessary that a specific type of coating film be formed on a
test piece. On the other hand, the micro displacement transducer
method is disadvantageous in that this method is applicable only to
conditions where the elastic deformation of sliding surfaces is
negligible.
[0006] Moreover, it is not only oil but greases that are used as a
lubricant in rolling element bearings. The fluorescence method has
been applied only in the studies of oil lubrication, and the use of
a fluorescent grease as a grease in these methods has never been
known.
SUMMARY OF THE INVENTION
[0007] It is accordingly an object of the invention to provide a
fluorescent grease which enables monitoring of behaviors of a
grease for elucidation of the mechanism of grease lubrication.
[0008] It is another object of the invention to provide a rolling
element bearing or condition monitoring rolling element bearing
charged with the fluorescent grease.
[0009] Based on the very simple principle that when a proper amount
of a fluorescent substance exists, it can be observed as it shines
bright, fluorescent substances have been applied to many aspects of
tribology. The best known application is directed to the
measurement of an oil film thickness between a piston ring and a
cylinder liner of an automotive vehicle, for which a measuring
method using a laser induced fluorescence technique has been
established in recent years. Fluorescent substances have also been
applied to studies of oil flow between an oil seal and a rotary
shaft or spindle. With an ordinary light interference method, a
film thickness can be measured down to a level as small as about
1/4 of the wavelength of visible light, i.e. about 100 nm. In
contrast, when using the fluorescence method, the limitation of the
measurement can be decreased to the order of nanometers provided
that the fluorescent intensity and measuring sensitivity can be
increased.
[0010] The lubricating mechanism of a grease is more complicated
than that of ordinary oil lubrication because the grease consists
of a thickener agent and a base oil, and thus, any theory of
accurately predicting a lubricant film thickness for a given set of
operating conditions has not been established yet.
[0011] According to the invention, there is provided a fluorescent
grease which comprises a base oil dissolving a fluorescent
substance therein, and a thickener agent added to the base oil.
[0012] The base oil used is a synthetic carbonate ester of the
following general formula (1) 1
[0013] wherein R and R' may be the same or different and
independently represent a branched alkyl group having from 13 to 15
carbon atoms. More specifically, in the general formula (1), R and
R' may be the same or different and independently represent a
branched alkyl group of the following general formula (2) 2
[0014] wherein n=13 to 15 and m=0 to 6.
[0015] There are listed, as the thickener agents, an alkali metal
salt and/or an alkaline earth metal salt, which is prepared from an
alkali metal or alkaline earth metal hydroxide and a higher fatty
acid having 10 or more carbon atoms or a higher hydroxy-fatty acid
having one or more hydroxyl group and 10 or more carbon atoms.
Typical examples include lithium soaps such as lithium stearate,
lithium 12-hydroxystearate, and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic drawing of a fluorescence microscope
used in the Examples of the invention; and
[0017] FIGS. 2(A) to 2(I) are, respectively, fluorescence images of
a lubricant film of a fluorescent grease according to the
invention.
PREFERRED EMBODIMENTS OF THE INVENTION
[0018] In the practice of the invention, any fluorescent
substances, which are likely to be dissolved in a base oil, may be
usable.
[0019] Examples of such substances include condensed ring-type
hydrocarbons such as pyrene, perylene, anthracene, naphthacene,
chrysene, triphenylene, pentaphene, 1,2-benzpyrene, hexaphene,
trinaphthylene, coronene, tetracene, dibenzcoronene, rubrene and
the like, diphenylpolyenes such as p-diphenylbenzene (p-t-phenyl),
1,6-diphenyl-1,3,5-hexatriene, 1,8-diphenyl-1,3,5,7-octatetraene
and the like, polycyclic hydrocarbons such as
tetraphenyl-p-quinodimethane, asy-phenyl-o-tolyl-p-quinodimethane,
p-distyrylbenzene and the like, benzene derivatives such as
hydroquinone dimethyl ether, polycyclic compounds such as
derivatives of benzidine, stilbene and the like, condensed
ring-type compounds such as naphthylamine and derivatives thereof,
and heterocyclic derivatives such as thiadiazole derivatives,
pyridine derivatives, benzoxazole derivatives, flavone derivatives,
coumarin derivatives, quinoline derivatives, acridine derivatives
and the like.
[0020] Moreover, dyes may be used in combination, including
fluoresein, acridine orange, methylene blue, rosamine, trypaflavin,
thionine, pyronin G, resorcinol, eosin, erythrosin, rhodamine B,
chlorophyll a, chlorophyll b, benzoflavin, phenosafranine and the
like.
[0021] Preferred fluorescent substances include one or more of
those substances selected from pyrene, perylene,
1,6-diphenyl-1,3,5-hexatriene, 1,8-diphenyl-1,3,5,7-octatetraene,
and coumarine 6.
[0022] Most preferably, mention is made of pyrene, which exhibits
the highest fluorescent intensity with little bleaching phenomenon
(attenuation of fluorescent intensity) being recognized when a CCD
camera and a high pressure mercury lamp as a light source are
employed. The saturation concentration in a mineral hydrocarbon,
PAO or a carbonate is at a level of about 2 mass %.
[0023] Pyrene has a peak wavelength of absorbed light at 336 nm and
a peak wavelength of eximer emission at 480 nm (when dissolved in
cyclohexane). Accordingly, bluish green fluorescence is emitted on
irradiation of UV light in the vicinity of the peak wavelength. It
will be noted that the absorption wavelength depends on the type of
fluorescent substance, and perylene has an absorption peak in the
visible light region, so that fluorescence can be observed without
use of any specific type of light source such as a mercury
lamp.
[0024] The grease of the invention may further comprise additives
ordinarily employed in greases, such as an antioxidant, a rust
inhibitor, an extreme pressure agent and the like.
[0025] The embodiments of the invention may be summarized as
follows.
[0026] (1) A fluorescent grease, which comprises, as essential
components, a base oil, a thickener agent, and a fluorescent
substance.
[0027] (2) A fluorescent grease as recited in (1) above, wherein
the fluorescent substance is at least one member selected from
pyrene, perylene, 1,6-diphenyl-1,3,5-hexatriene,
1,8-diphenyl-1,3,5,7-octatetraen- e, and coumarine 6.
[0028] (3) A fluorescent grease as recited in (1) or (2) above,
wherein the base oil consists of a synthetic carbonate ester, and
the thickener agent consists of a lithium soap.
[0029] (4) A rolling element bearing having a fluorescent grease
recited in any one of (1) to (3) above filled therein.
[0030] (5) A condition monitoring rolling element bearing having a
fluorescent grease recited in any one of (1) to (3) above filled
therein.
[0031] (6) In another embodiment of the present invention, the
fluorescent grease contains at least two different fluorescent
substances. The fluorescent grease is then charged to the rolling
element bearing or condition monitoring rolling element bearing and
the bearing irradiated with light of multiple wavelengths. The
bearing is then rotated and the behavior of the fluorescent grease
observed by a CCD camera. Plural images of the fluorescent
substances appearing on the CCD are then compared with each other
to help determine the characteristics of the grease.
[0032] The invention is more particularly described by way of
example.
[0033] FIG. 1 shows a fluorescence microscope for observing the
behavior of a grease lubricant film between a steel ball and a flat
glass disk by use of fluorescent grease.
[0034] A fluorescence microscope has an exciter filter 2 for
passing a light ray with a wavelength band capable of exciting a
fluorescent substance from light rays emitted from a light source 1
(mercury lamp), a barrier filter 6 and a dichroic mirror 5 capable
of cutting reflected light and passing a fluorescence alone, a
glass disk 3, a ball (steel ball) 4, and a CCD camera 7.
[0035] The fluorescent wavelength of a fluorescent substance
generally has a wavelength longer than an absorption wavelength, so
that a cutoff wavelength or a transmitted wavelength band is
selected by means of the filters so as to allow irradiation of
light of a shorter wavelength and observation of light of a longer
wavelength.
[0036] With pyrene, there were used the exciter filter 2 with a
transmitted wavelength band of 330 to 380 nm, and the dichroic
mirror 5 and the barrier filter 6 having cut-off wavelengths of 400
nm and 420 nm, respectively.
[0037] A testing device was so designed that the contact portion of
the glass disk and the steel ball was provided below an objective
and a fluorescence of a lubricant film was taken with the CCD
camera. The glass disk was made of a non-fluorescent synthetic
quartz glass having a thickness of 3 to 8 mm, and its drive shaft
was driven with an AC servo motor via a timing belt. The ball
(steel ball) 4 was freely supported by means of two tapered
rollers, and was in rolling contact with the glass disk 3 by
traction with the glass disk 3. The ball 4 could also be rigidly
supported to a loading arm so as to afford pure sliding contact
between the ball and the glass disk 3. The motor could permit
several driving modes such as of a constant speed motion,
acceleration and deceleration, reciprocating motion and the
like.
EXAMPLE 1
[0038] A grease was prepared and had a formulation of 80 mass % of
a synthetic carbonate ester of the following chemical formula used
as a base oil, and 20 mass % of a lithium stearate soap used as a
thickener agent. 3
[0039] The base oil had a viscosity of 18 mm.sup.2/s (40.degree.
C.), and the grease had a worked consistency of 198 (25.degree. C.)
and a dropping point of 197.degree. C.
[0040] The thus prepared grease was applied between the steel ball
and the glass disk, each cleaned with heptane, followed by
uni-directional and reciprocating sliding contact to observe the
behavior thereof.
[0041] The load applied was 4.9 N, and the speed was set at 10
levels ranging from 23 mm/s to 230 mm/s for the uni-directional
contact and also at 10 levels ranging from 23 mm/s to 230 mm/s for
the reciprocating contact. The reciprocating contact was performed
for 20 reciprocating cycles wherein an amplitude was 34.5 mm and an
acceleration was 3.46 m/s.sup.2 at the time of acceleration or
deceleration. When the test was performed, the room temperature was
at 15.degree. C.
[0042] The fluorescence images of the lubricant films of the
greases are shown in FIGS. 2(A) to 2(I).
[0043] FIG. 2(A) shows a fluorescence image of a grease at a
standstill. The contact area at the center is dark, and it is
brighter outside the contact. The brightness is proportional to the
amount of fluorescent substance, from which it will be seen that
the gap between the ball and the glass disk increases with the
distance from the contact center.
[0044] FIG. 2(B) shows a fluorescence image in the uni-directional
motion. A dark portion is observed at the outlet of the contact and
is considered as a cavity created through the formation of a
hydrodynamic lubricating film.
[0045] FIG. 2(C) shows a fluorescence image at the tenth cycle of
the uni-directional motion. Something like a cavity starts to
appear near the inlet of the contact. This is considered to be an
air cavity formed in the previous cycles remaining within the soap
fibers overrolled on the track, or a cavity formed by hydrodynamic
action at a dam of the grease piled up at the inlet and side of the
contact.
[0046] FIGS. 2(D), 2(E) and 2(F), respectively, show fluorescence
images at the first cycle of the reciprocating test wherein FIG.
2(D) is taken at the middle of the reciprocating stroke, FIG. 2(E)
is taken during deceleration, and FIG. 2(F) is taken just after the
reversal of motion.
[0047] It will be seen that at the reversal of motion, the
re-supply of the base oil is insufficient to cause the base oil
starvation at the inlet.
[0048] FIGS. 2(G), 2(H) and 2(I), respectively, show fluorescence
images at the tenth cycle of the reciprocating test wherein FIG.
2(G) is taken at the middle of the reciprocating stroke, FIG. 2(H)
is taken during deceleration, and FIG. 2(I) is taken just after the
reversal of motion. Comparison of these images reveals that the
inlet starvation of the base oil becomes more significant at the
tenth cycle than at the first cycle. More particularly, it will be
noted that in the grease lubrication, the base oil is squeezed out
from the track, and the re-supply of the base oil onto the track is
retarded, especially after the reversal of motion.
EXAMPLE 2
[0049] The grease characteristics have been tested using a device
shown in FIG. 1 by adding "rhodamine B" to the fluorescent grease
consisting of the base oil, the thickener agent and the fluorescent
substance which is the same as that shown in Example 1.
[0050] The fluorescent grease was irradiated with light with
wavelengths of 340 nm and light with wavelengths of 550 nm, on
which light the fluorescent substance reacts, and the fluorescent
grease was observed by a CCD camera. An image of the fluorescent
substance irradiated with the light with wavelengths of 340 nm and
that irradiated with the light with wavelengths of 550 nm were
substantially the same, and confirmed that the base oil and the
thickener agent coexisted with each other and did not separate from
each other. Further, fluorescent grease was irradiated with light
with a wavelength of 340 nm and light with a wavelength of 550 nm,
and the fluorescent grease was observed by a CCD camera using
"calcium stearate" instead of the thickener agent. Images of the
fluorescent substance irradiated with the light with a wavelength
of 340 nm and that irradiated with the light with a wavelength of
550 nm were different from each other, and revealed that the base
oil and the thickener were separated from each other.
EXAMPLE 3
[0051] Fluorescent grease comprising the base oil and the thickener
agent, which is the same as that used in Example 1, was tested by
an acceleration testing device, and it deteriorated.
[0052] The fluorescent grease was tested for 100 hours, 500 hours
and 1,000 hours and respectively collected, and the fluorescent
substance and "rhodamine B" was added to the fluorescent grease in
the same manner as Example 2, and the grease characteristics were
tested by the device shown in FIG. 1 wherein an image of the
fluorescent substance irradiated with the light with a wavelength
of 340 nm was compared with that irradiated with the light with a
wavelength of 550 nm. As time passed, the base oil separated from
the thickener agent.
EXAMPLE 4
[0053] 30% of a bearing space of a mechanically sealed bearing was
charged with the fluorescent grease comprising the base oil, the
thickener agent and the fluorescent substance, then the same
bearing was rotated at 140.degree. C. for 100 hours at 20,000 rpm,
and fluorescent grease dispersed from the bearing was received by a
test piece (paper) while the circumfluence of the bearing was
surrounded by the test piece.
[0054] When the test piece was irradiated with light and a grease
spot on the test piece was examined, it was revealed that many fine
spots were distributed.
[0055] Further, 30% of a bearing space of a mechanically sealed
bearing was charged with the fluorescent grease comprising the base
oil, the thickener agent and the fluorescent substance, then the
same bearing was rotated at 100.degree. C. for 100 hours at 20,000
rpm and fluorescent grease dispersed from the bearing was received
by a test piece (paper) while the circumfluence of the bearing was
surrounded by the test piece.
[0056] When the test piece was irradiated with light and a grease
spot on the test piece was examined, fine spots were hardly
found.
[0057] Still further, 10% of a bearing space of a mechanically
sealed bearing was charged with the fluorescent grease comprising
the base oil, the thickener agent and the fluorescent substance,
then the same bearing was rotated at 100.degree. C. for 100 hours
at 20,000 rpm and fluorescent grease dispersed from the bearing was
received by a test piece (paper) while the circumfluence of the
bearing was surrounded by the test piece.
[0058] When the test piece was irradiated with light and a grease
spot on the test piece was examined, fine spots were hardly
found.
[0059] It was verified by the test that the bearing charged with
the fluorescent grease, which was charged in the bearing space by
30% or 10%, was durable to a rotation of 20,000 rpm in the case of
the testing temperature of 100.degree. C.
[0060] It has generally been considered that ability of the grease
to re-supply the base oil onto the overrolled track influences the
degree of oil starvation at the contact. As will be apparent from
the above, this can be confirmed by the direct observation of
behaviors of the fluorescent grease of the invention. This means
that when a fluorescent grease is charged to a bearing, condition
monitoring becomes possible.
[0061] Analysis of the intensity of fluorescence enables one to
quantitatively determine an amount of a residual base oil and an
amount of re-supplied or a returned base oil.
[0062] In the reciprocating sliding contact, it has been
appreciably confirmed that the inlet starvation of a base oil
caused by a residual cavity becomes remarkable at the reversal of
motion. In order to reduce the traction at the reversal of motion.,
it will be necessary to develop a proper combination of a thickener
agent and a base oil that allows better oil release and
anti-foaming properties.
* * * * *