Lubricating grease is commonly used for lubricating “sealed and greased for life” rolling element bearings. This grease also provides an additional sealing function to protect the bearing against ingress of contaminants. In this work the sealing function of lubricating grease in the vicinity of the seal lip contact has been studied experimentally by measuring the migration of spherical fluorescent contaminant particles in the vicinity of the contact, as a function of shaft speed and lubricant type. The experimental results reveal that in some greases contaminant particles migrate towards the sealing contact where the shear rate reaches its highest value. However, for other greases, Newtonian base oils, and elastic fluids, this is not necessarily the case and contaminant particles consistently migrate away from the sealing contact. Various physical phenomena have been investigated to explain the difference in migration behavior. It is concluded that migration towards the sealing contact is driven by the viscosity gradient and migration away from the sealing contact is related to the Weissenberg number. The sealing function of grease in the vicinity of the sealing contact is due to the migration of contaminant particles. The migration reduces the probability of particles to reach the sealing and bearing contacts.

References

References
1.
Baart
,
P.
,
Lugt
,
P. M.
, and
Prakash
,
B.
, 2009, “
Review of the Lubrication, Sealing and Pumping Mechanisms in Oil and Grease Lubricated Radial Lip Seals
,”
J. Eng. Tribol.
,
223
(
3
), pp.
347
358
.
2.
Haycock
,
R. F.
,
Caines
,
A. J.
, and
Hillier
,
J. E.
, 2004,
Automotive Lubricants Reference Book
,
Society of Automotive Engineers, Inc.
,
Warrendale
,
2nd ed.
3.
Boner
,
C. J.
, 1976
Modern Lubricating Greases
,
Scientific Publications Ltd
,
Brosely, Shropshire
, Sec. 11.15.
4.
Miller
,
R. W.
, 1993,
Lubricants and Their Applications
,
McGraw-Hill
,
NewYork
, p.
68
.
5.
1996,
Lubricating Grease Guide
,
4th ed.
,
National Lubricating Grease Institute
,
Kansas City
.
6.
Lansdown
,
A. R.
,
Lubrication and Lubricant Selection, A Practical Guide
,
3rd ed.
,
Professional Engineering Publishing Limited
,
London
, pp.
132
140
.
7.
Green
,
T. M.
,
Baart
,
P.
,
Westerberg
,
L. G.
,
Lundström
,
T. S.
,
Höglund
,
E.
,
Lugt
,
P. M.
, and
Li
,
J.
, 2011, “
A New Method to Visualize Grease Flow in a Double Restriction Seal using Micro Particle Image Velocimetry
,”
Tribol. Trans.
,
54
(
5
), pp.
784
792
.
8.
Baart
,
P.
,
Green
,
T. M.
,
Li
,
J.
,
Lundström
,
T. S. L.
,
Westerberg
,
L. G.
,
Höglund
,
E.
, and
Lugt
,
P. M.
, “
The Influence of Speed, Grease Type, and Temperature on Radial Contaminant Particle Migration in a Double Restriction Seal
,”
Tribol. Trans., in press
.
9.
Baart
,
P.
,
Lugt
,
P. M.
, and
Prakash
,
B.
, 2010, “
The Sealing Function of Grease: Contaminant Migration in Grease Lubricated Radial Lip Seals
,”
Proceedings of the STLE/ASME International Joint Tribology Conference
, IJTC2010-41032.
10.
Karnis
,
A.
, and
Mason
,
G.
,1966, “
Particle Motion in Sheared Suspensions. XIX. Viscoelastic Media
,”
Trans. Soc. Rheol.
,
10
, pp.
571
592
.
11.
Gauthier
,
F.
,
Goldsmith
,
H. L.
, and
Mason
,
S. G.
, 1971, “
Particle Motions in Non-Newtonian Media I: Couette flow
,”
Rheol. Acta
,
10
, pp.
344
364
.
12.
Gauthier
,
F.
,
Goldsmith
,
H. L.
, and
Mason
,
S. G.
, 1971, “
Particle Motions in Non-Newtonian Media II: Poiseuille flow
,”
Rheol. Acta
,
15
, pp.
297
330
.
13.
Husband
,
D. M.
,
Mondy
,
L. A.
,
Ganani
,
E.
, and
Graham
,
A. L.
, 1994, “
Direct Measurements of Shear-Induced Particle Migration in Suspensions of Bimodal Spheres
,”
Rheol. Acta
,
33
, pp.
185
192
.
14.
Yang
,
B. H.
,
Wang
,
J.
,
Joseph
,
D. D.
,
Hu
,
H. H.
,
Pan
,
T.-W.
, and
Glowinski
,
R.
, 2005, “
Migration of a Sphere in Tube Flow
,”
J. Fluid Mech.
,
540
, pp.
109
131
.
15.
Ho
,
B. P.
, and
Leal
,
L. G.
, 1976, “
Migration of Rigid Spheres in a Two-Dimensional Unidirectional Shear Flow of a Second-Order Fluid
,”
J. Fluid Mech.
,
76
(
4
), pp.
783
799
.
16.
Huang
,
P.Y.
, and
Joseph
,
D. D.
, 1999, “
Effects of Shear Thinning on Migration of Neutrally Buoyant Particles in Pressure Driven Flow of Newtonian and Viscoelastic Fluids
,”
J. Non-Newtonian Fluid Mech.
,
90
, pp.
159
185
.
17.
Baart
,
P.
,
Lugt
,
P. M.
, and
Prakash
,
B.
, 2010, “
Non-Newtonian Effects on Film Formation in Grease Lubricated Radial Lip Seals
,”
Tribol. Trans.
,
53
(
3
), pp.
308
318
.
18.
Horve
,
L. A.
, 1996,
The Effect of Operating Parameters Upon Radial Lip Seal Performance
,
Marcel Dekker
,
New York
.
19.
Kammuller
,
M.
, 1986, “
Zur Abdichting von Radial-Wellendichtringen
,”
Thesis
,
IMA University of Stuttgart
,
Germany
.
20.
Snijkers
,
F.
,
D’Avino
,
G.
,
Maffettone
,
P. L.
,
Greco
,
F.
,
Hulsen
,
M.
, and
Vermant
,
J.
, 2009, “
Rotation of a Sphere in a Viscoselastic Liquid Subjected to Shear Flow. Part II: Experimental Results
,”
J. Rheol.
,
53
, pp.
459
480
.
21.
Qu
,
J.
, 1993, “
Experimental Study on the Sealing Effect due to Rotational Oil Flow
,”
SAE 930528.
22.
Wennehorst
,
B.
, and
Poll
,
G.
, 2008, “
Optical Investigation into the Dynamic Sealing Gap of Radial Shaft Seals
,”
16th International Colloquium Tribology 2008 - Lubricants
,
Materials and Lubrication Engineering
,
Ostfildern
.
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