| 1. |
- Almqvist, Andreas, et al.
(författare)
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Selected papers from those presented at the 3rd International Tribology Symposium of IFToMM
- 2014
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Ingår i: Lubrication Science. - : Wiley. - 0954-0075 .- 1557-6833. ; 26:5, s. 273-275
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Selected papers presented at the 3rd International Tribology Symposium of the International Federation for the Promotion of Mechanism and Machine Science (IFToMM) are discussed. The 3rd International Tribology Symposium of IFToMM was organized by the Division of Machine Elements of Luleå University of Technology in Sweden from March 19 21, 2013. The symposium was held in the university campus, providing a perfect forum for the tribologists for presenting their latest research and exchange of ideas. The participants were also given the opportunity to experience the snowy landscape during a memorable outdoor dinner. The symposium attracted 146 participants from 26 countries along with 92 papers spread over 32 sessions. These papers covered the fundamental and applied aspects of wide ranging topics such as friction, wear, lubrication, lubricants, tribology in hostile environment, tribomaterials, solid lubricants, surface engineering, and tribotesting.
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| 2. |
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| 3. |
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| 4. |
- Baart, Pieter, et al.
(författare)
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Contaminant migration in the vicinity of a grease lubricated bearing seal contact
- 2011
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 133:4
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 5. |
- Baart, Pieter, et al.
(författare)
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Non-newtonian effects on film formation in grease-lubricated radial lip seals
- 2010
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 53:3, s. 308-318
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Tidskriftsartikel (refereegranskat)abstract
- In existing models, the only lubricant property used for predicting film thickness in radial lip seals is the (base) oil viscosity. Lubricating greases show non-Newtonian behavior, and additional normal stress components develop that may contribute to the load-carrying capacity. This study investigates the shear rheology of greases and determines whether this "normal stress effect" in grease can significantly contribute to film formation in radial lip seals. First, the rheological behavior of grease is studied in a rotary plate-plate rheometer at small gaps of 25-500 μ m up to shear rates of 5 · 104 s-1. The rheology measurements are used for a rheology model that predicts the first normal stress difference in the grease. Second, a seal lip model was developed to predict the lift force generated by the normal stress effect that separates the seal from the shaft. The model results show that the load-carrying capacity depends very much on the operating conditions: lip geometry, speed, and temperature. The model predicts a lift force that is over 50% of the seal specific lip force for low-contact pressure-bearing seals. The model can easily be used in existing oil seal models and makes it possible to optimize seal design by utilizing the normal stress effect.
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| 6. |
- Baart, Pieter, et al.
(författare)
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Non-Newtonian effects on film formation in grease lubricated radial lip seals
- 2009
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Ingår i: Society of Tribologists and Lubrication Engineers annual meeting & exhibition 2009. - Red Hook, NY : Curran Associates, Inc.. - 9781615674374 ; , s. 140-142
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Konferensbidrag (refereegranskat)abstract
- This study investigates the high shear rheology of grease and determines whether the "normal stress effect" can significantly contribute to film formation in radial lip seal applications. Rheology measurements and a rheology model for the grease have been developed to model the normal stress at high shear rates. Subsequently, a seal lip model is developed to predict lift forces, generated by the normal stress effect. The model predicts lift forces over 50% of the seals specific lip force for low contact pressure bearing seals.
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| 7. |
- Baart, Pieter, et al.
(författare)
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On the Normal Stress Effect in Grease-Lubricated Bearing Seals
- 2015
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Ingår i: Tribology & Lubrication Technology. - 1545-858X. ; 71:9, s. 52-58
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Tidskriftsartikel (refereegranskat)abstract
- The film formation in lip seals, due to non-Newtonian rheology of the lubricant, has been a topic of speculation. Earlier work suggests that normal stresses in grease would be favorable for the film build-up between the seal lip and shaft or bearing ring. In the current paper we evaluate this earlier work and our earlier theoretical seal lip model with a series of experiments. We use a modified concentric cylinder geometry and a model fluid to study the fluid pressure distribution in the seal type geometry. The results are then related to grease lubricated seals and our earlier theoretical predictions. The present analysis shows that this earlier work and our earlier predictions are not correct and indicate that normal stresses in the grease pull the seal lip towards the shaft, increasing the contact pressure. However, normal stresses also ensure the presence of grease on the shaft or bearing inner ring which enhances replenishment of the sealing contact.
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| 8. |
- Baart, Pieter, et al.
(författare)
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On the Normal Stress Effect in Grease-Lubricated Bearing Seals
- 2014
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 57:5, s. 939-943
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Tidskriftsartikel (refereegranskat)abstract
- The film formation in lip seals, due to non-Newtonian rheology of the lubricant, has been a topic of speculation. Earlier work suggests that normal stresses in grease would be favorable for the film build-up between the seal lip and shaft or bearing ring. In the current paper we evaluate this earlier work and our earlier theoretical seal lip model with a series of experiments. We use a modified concentric cylinder geometry and a model fluid to study the fluid pressure distribution in the seal type geometry. The results are then related to grease lubricated seals and our earlier theoretical predictions. The present analysis shows that this earlier work and our earlier predictions are not correct and indicate that normal stresses in the grease pull the seal lip towards the shaft, increasing the contact pressure. However, normal stresses also ensure the presence of grease on the shaft or bearing inner ring which enhances replenishment of the sealing contact.
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| 9. |
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| 10. |
- Baart, Pieter, et al.
(författare)
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Review of the lubrication, sealing, and pumping mechanisms in oil- and grease-lubricated radial lip seals
- 2009
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 223:3, s. 347-358
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Tidskriftsartikel (refereegranskat)abstract
- Radial lip seals are successfully used since the 1940s to seal lubricated systems. Despite extensive experimental and theoretical research in the field, it is still not fully clear how these seals function. Experimental studies, found in the public literature, show that the relatively high surface roughness of the seal lip is very important for good and reliable performance. In addition, the pressure distribution under the lip seems to be a critical factor. Six fundamental hypotheses are presented on the lubrication, pumping, and sealing mechanisms to explain the working principles of these seals. It is generally accepted that lubrication results from micro-elastohydrodynamic film build up between the rough seal surface and the shaft. Non-symmetrical tangential deformations of the lip surface are observed during experiments and assumed to act like spiral groove bearings that generate a pumping action and lubricant film. Another hypothesis suggests that the lubricant will behave non-Newtonian under the very high shear rates experienced in operating conditions. This will reduce friction because of shear-thinning and enhances sealing. Macroscopic aids, like hydrodynamic pumping aids and engineered asperity patterns on the shaft, do improve seal performance. Almost all public literature discusses oil-lubricated radial lip seals while many seals are grease lubricated, especially in certain technical fields. Due to the non-Newtonian behaviour of grease, the lubrication, sealing, and pumping mechanisms are assumed to differ from the oil-lubricated seals. Lower friction and improved protection against contamination are measured, and it is expected that the interest in grease lubrication will rapidly grow in future.
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