| 1. |
- Li, Jinxia, et al.
(författare)
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Lubricating Grease Shear Flow and Boundary Layers in a Concentric Cylinder Configuration
- 2015
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Konferensbidrag (refereegranskat)abstract
- Grease is extensively used to lubricate various machine elements such as rolling bearings, seals, and gears. Understanding the flow dynamics of grease is relevant for the prediction of grease distribution for optimum lubrication and for the migration of wear and contaminant particles. In this study, grease flow is visualized using micro Particle Image Velocimetry (μPIV). The experimental setup includes a concentric cylinder configuration with a rotating shaft to simulate the grease flow in a double restriction seal geometry with two different grease pocket sizes. It is shown that the grease is partially yielded in the large grease pocket geometry and fully yielded in the small grease pocket. For the small grease pocket, it is shown that three distinct grease flow layers are present: a high shear rate region close to the stationary wall, a bulk flow layer, and a high shear rate boundary region near the rotating shaft. The grease shear thinning behavior and its wall slip effects have been identified. The μPIV experimental results have been compared with a numerical model for both the large and small gap size. It is shown that the flow is close to one-dimensional in the center of the small pocket. A one-dimensional analytical model based on the Herschel-Bulkley rheology model has been developed, showing good agreement with the measured velocity profiles in the small grease pocket. Furthermore, wall slip effects and shear banding are observed, where the latter imply that using the assumption of uniform shear in conventional concentric cylinder rheometers may result in erroneous rheological results.
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| 2. |
- Li, Jinxia, et al.
(författare)
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Rheology of Lubricating Grease
- 2015
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Ingår i: Lube Magazine. - 1744-5418. ; 126, s. 12-18
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Westerberg, Lars-Göran, et al.
(författare)
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Free-Surface Flow of Lubricating Greases
- 2016
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Konferensbidrag (refereegranskat)abstract
- Grease lubrication is traditionally used in a great variety of mechanicalsystems such as rolling bearings, seals, and gears where it has beenshown more advantageous than oil, mainly due to its consistencyallowing the grease to stay inside the system and not leak out. Freesurface effects play an important role in rolling bearings and opengears as the configuration normally is filled with about 30% grease toavoid heavy churning. In this study an analytical model of thestationary uniform flow on a rotating disc is developed and validatedwith experiments. The model results in the velocity profile for the flowin the thin fully yielded viscous layer in connection to the surface aswell as an expression for the plug flow region on top of the viscouslayer. Experiments with two different greases having NLGI grade 1 and2 respectively shows it is possible to obtain a good fit with theanalytically obtained thickness using the rheological parameters foractual greases.
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| 4. |
- Westerberg, Lars-Göran, et al.
(författare)
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Free-surface grease flow: influence of surface roughness and temperature
- 2015
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 59, s. 18-
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Tidskriftsartikel (refereegranskat)abstract
- Grease flow in grease lubricated systems can often be qualified as free-surface flow. It occurs for example in rolling bearings after the churning phase or on open gears. Here only a fraction of the bearing or gearbox volume is filled with grease. Part of the grease is flowing in relatively thin layers induced by centrifugal forces caused by rotation of the various components. In this paper a model problem is investigated in the form of a free-surface flow of grease on a rotating disc. Experiments have been performed where the onset of flow and remaining grease have been studied varying the surface roughness, temperature and the centrifugal forces. The experiments have been coupled to analytical models describing the flow and temperature distribution in the grease. It was found that the impact of surface roughness could be neglected. The flow is determined by the centrifugal forces and rheology of the grease. Temperature effects the rheology but also the oil separation creating low shear strength/low viscosity layers at the surface.
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| 5. |
- Westerberg, Lars-Göran, et al.
(författare)
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Grease flow in an elbow channel
- 2015
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 57:3
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Tidskriftsartikel (refereegranskat)abstract
- The flow of lubricating greases in an elbow channel has been modeled and validated with velocity profiles from flow visualizations using micro-particle image velocimetry. The elbow geometry induces a nonsymmetric distribution of shear stress throughout its cross section, as well as varying shear rates through the transition from the elbow inlet to the outlet. The flow has been modeled both for higher flow rates and for creep flow. The influence of the grease rheology and flow conditions to wall slip, shear banding and an observed stick–slip type of motion observed for low flow rates are presented. The effect on the flow of the applied pressure is also modeled showing that the flow is sensitive to the pressure in the angular ( ϕ ) direction of the elbow. For high pressures, it is shown that the flow is reversed adjacent to the elbow walls.
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