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| 2. |
- 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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| 3. |
- Baart, Pieter, et al.
(författare)
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Oil-bleeding model for lubricating grease based on viscous flow through a porous microstructure
- 2010
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 53:3, s. 340-348
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Tidskriftsartikel (refereegranskat)abstract
- One of the criteria in selecting lubricating grease for rolling-element bearing applications is its ability to bleed oil, sometimes called ogrease bleeding.o Oil bleeding is assumed to be the dominating mechanism supplying new oil to the rolling track for lubrication. In this study, a physical model has been developed to understand the relation between parameters that control oil bleeding. In the model, lubricating grease is described as a porous network, formed by the thickener fibers, that contains the base oil. This type of structure is confirmed by SEM and AFM images of a lithium complex grease showing a matrix of rigid fibers with random orientation. A relatively simple flow model based on Darcy's law for viscous flow in porous media and an anisotropic microstructure deformation model was developed. The model relates the pressure gradient, oil viscosity, thickener structure deformations, and permeability to the volumetric oil flow out of the thickener network. The permeability depends strongly on the thickener microstructure. The model was verified with experiments at a wide variety of temperatures and rotational speeds.
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| 4. |
- Baart, Pieter, et al.
(författare)
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The sealing function of grease : contamination migration in grease lubricated radial lip seals
- 2010
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Ingår i: Proceedings of the STLE/ASME International Joint Tribology Conference 2010. - New York : American Society of Mechanical Engineers. - 9780791844199 ; , s. 81-83
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Konferensbidrag (refereegranskat)abstract
- Lubricating grease is commonly used for lubricating `sealed and greased for life' bearings. This grease lubricates the rolling contacts. It also provides an additional sealing function to protect the bearing against ingress of contamination. The sealing function of lubricating grease in the vicinity of the seal lip contact has been studied experimentally. The effects of the lubricant rheology on the migration of ingress particles has been examined. In grease, experimental results reveal that contaminant particles consistently migrate towards the sealing contact where the shear rate reaches its highest value. In contrast, for a Newtonian base oil and a non shear thinning elastic fluid, it has been observed that the migration effect takes place in the opposite direction, and brings particles away from the sealing contact. It is concluded that the sealing function of grease in the vicinity of the sealing contact is due to the fluid rheology and more specifically to the shear thinning behaviour of the lubricant
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| 5. |
- Li, Jinxia, et al.
(författare)
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Measurements of grease flow in channels with restrictions using μPIV
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- Grease is commonly used to lubricate various machine components such as rolling element bearings, open gears etc. Better understanding of the flow properties of grease will contribute to understanding the lubrication mechanism in bearings and flow in lubrication systems. In an earlier paper Micro Particle Image Velocimetry (μPIV) techniques were used to study the flow in a rectangular channel. The present paper is an extension of this work where restrictions were applied in such a channel, which creates a much more complex velocity field. The grease is seeded with fluorescent particles, which are illuminated by a double-pulsed laser. The test geometries that are used in this study are a channel with one flat restriction and one with two flow restrictions in a similar channel. The stationary grease mass-flow and the two dimensional velocity fields have been monitored for different pressure drops. For the channel with one flat restriction, the flow was measured to be symmetric at the inlet and outlet, and the distance for the flow to fully develop is comparable with the height of the channel; Slow motion was followed near the step corner at the inlet. For the channel with two flow restrictions, the vector profiles show that the maximum velocity appears at the restrictions; In-between the two restrictions, a part of the grease is not moving. This particularly applies to cases with low-pressure drop and where high consistency grease was used.
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