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Research Papers: Lubricants

Contaminant Migration in the Vicinity of a Grease Lubricated Bearing Seal Contact

[+] Author and Article Information
P. Baart, P. M. Lugt, B. Prakash

SKF Engineering and Research Centre, PO Box 2350, 3430 DT, Nieuwegein, The Netherlands, Division of Machine Elements,  Luleå University of Technology, SE-971 87, Luleå, Sweden, e-mail: pieter.baart@skf.comSKF Engineering and Research Centre, PO Box 2350, 3430 DT, Nieuwegein, The NetherlandsDivision of Machine Elements,  Luleå University of Technology, SE-971 87, Luleå, Sweden

J. Tribol 133(4), 041801 (Oct 06, 2011) (8 pages) doi:10.1115/1.4004958 History: Received May 27, 2011; Revised May 27, 2011; Published October 06, 2011; Online October 06, 2011

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.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Sealed and greased for life deep groove ball bearing (DGBB) with contacting seals, which are lubricated with grease

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Figure 2

Particle in a fluid velocity field in the vicinity of the sealing contact. Migration in the x direction is studied.

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Figure 3

Reynolds number in the vicinity of the sealing contact at a shaft speed of 233 rpm and a temperature of 70 °C

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Figure 4

Schematic top view of the setup with the digital microscope for observation of particles in the grease in the vicinity of the seal contact including a typical image of a particle distribution. The dashed line indicates the sealing contact.

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Figure 5

Setup with the digital microscope for observation of particles in the grease in the vicinity of the seal contact

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Figure 6

Rheological properties of greases in the vicinity of the sealing contact at 23 rpm: (a) apparent viscosity and (b) normal stress difference

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Figure 7

Contaminant particle migration in LG1 grease at 23 rpm; results from one experiment

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Figure 8

Particle migration in different types of lubricants at 23 rpm

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Figure 9

Particle migration in different greases at 23 rpm with fluorescent particles

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Figure 10

Particle migration in different greases at 233 rpm with fluorescent particles

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Figure 11

Particle migration images before and after the experiment at 233 rpm for LG1 and LG2 greases. The sealing contact is indicated with the dashed line; the arrow indicates the grease meniscus after grease loss.

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Figure 12

Weissenberg number for different lubricants at 23 rpm and 25 °C based on the shear rate dUy /dz from Fig. 2

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