| 1. |
- Green, Torbjörn M., et al.
(författare)
-
A new method to visualize grease flow in a double restriction seal using microparticle image velocimetry
- 2011
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 54, s. 784-792
-
Tidskriftsartikel (refereegranskat)abstract
- A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.
|
|
| 2. |
- Li, Jinxia, et al.
(författare)
-
µPIV measurement of grease velocity profiles in channels with two different types of flow restrictions
- 2012
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 54, s. 94-99
-
Tidskriftsartikel (refereegranskat)abstract
- Grease is commonly used to lubricate various machine components such as rolling bearings and seals. In this paper the flow of lubricating grease passing restrictions is described. Such flow occurs in rolling bearings during relubrication events where the grease is flowing in the transverse (axial) direction through the bearing and is hindered by guide rings, flanges et cetera, as well as in seals where transverse flow occurs, for example during so-called breathing caused by temperature fluctuations in the bearing. This study uses a 2D flow model geometry consisting of a wide channel with rectangular cross-section and two different types of restrictions to measure the grease velocity vector field, using the method of Micro Particle Image Velocimetry. In the case of a single restriction, the horizontal distance required for the velocity profile to fully develop is approximately the same as the height of the channel. In the corner before and after the restriction, the velocities are very low and part of the grease is stationary. For the channel with two flow restrictions, this effect is even more pronounced in the “pocket” between the restrictions. Clearly, a large part of the grease is not moving. This condition particularly applies to the cases with a low-pressure drop and where high consistency grease is used. In practice this means that grease is not replaced in such “corners” and that some aged/contaminated grease will remain in seal pockets.
|
|
| 3. |
- Baart, Pieter, et al.
(författare)
-
On the Normal Stress Effect in Grease-Lubricated Bearing Seals
- 2015
-
Ingår i: Tribology & Lubrication Technology. - 1545-858X. ; 71:9, s. 52-58
-
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.
|
|
| 4. |
- Dittes, Nicholas, et al.
(författare)
-
Dielectric Thermoscopy Characterization of Water Contaminated Grease
- 2018
-
Ingår i: Tribology and Lubrication Technology. - : Society of Tribologists and Lubrication Engineers (STLE). - 1545-858X. ; 61:3, s. 393-402
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this article. The purpose of this investigation was to identify the dielectric properties that could be measured to differentiate varying levels of water contamination in calcium sulfonate complex (CaS-X) grease with three different test cells with the purpose of eventually developing a grease condition sensor. Measuring the change in dielectric constant over a small temperature change yielded useful estimations of water content and amount of grease where the added water content ranged from 0.22% to about 5.5%. Additionally, other parameters such as incomplete fill/coverage of the sensors were investigated as a prestudy. The results from this set of experiments show that the measurement has potential to be developed into a condition monitoring sensor in the future.
|
|
| 5. |
- Dittes, Nicholas, 1987-, et al.
(författare)
-
Optical Attenuation Characterization of Water Contaminated Lubricating Grease
- 2018
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 61:4, s. 726-732
-
Tidskriftsartikel (refereegranskat)abstract
- Water-contaminated grease samples are investigated with attenuation spectra in the visible and near-infrared (NIR) regions in this article. The purpose of this investigation was to identify a model with optical attenuation spectra such that the water content of grease samples could be characterized with a simple measurement setup using common methodology from the field of instrumental chemistry. The ratio between two chosen wavelengths of light appears to approximate the water content of grease samples with an acceptable coefficient of determination using a methodology to show what can potentially be done to develop condition monitoring tools. To illustrate the outlined method, a prestudy of grease aging and oxidation levels is also investigated to show that other variables do not significantly change the measurement.
|
|
| 6. |
|
|
| 7. |
- Li, Jinxia, et al.
(författare)
-
Lubricating grease shear flow and boundary layers in a concentric cylinder configuration
- 2014
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 57:6, s. 1106-1115
-
Tidskriftsartikel (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 microparticle 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.
|
|
| 8. |
- Sahlin, Fredrik, et al.
(författare)
-
A mixed lubrication model incorporating measured surface topography. Part 1: Theory of flow factors
- 2010
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 224:4, s. 335-351
-
Tidskriftsartikel (refereegranskat)abstract
- A mixed lubrication model that permits real three-dimensional surface topography as input is developed. The theory of computing flow factors within the model is presented, and with a following paper (Part 2) the method of measuring and adapting the surface roughness, and model validation through flow measurements and application to a bearing is shown. A contact mechanics model is used to calculate the elastoplastic displacement of a periodic topography signal. A method based on homogenization is used to calculate flow factors for all lubrication regimes. The flow factors are compared with the Patir and Cheng method. Results indicate that the two methods compare well for longitudinal roughness lay, but differ significantly for a cross-patterned surface roughness due to the more complete flow description of the current model.
|
|
| 9. |
- Sahlin, Fredrik, et al.
(författare)
-
A mixed lubrication model incorporating measured surface topography. Part 2: Roughness treatment, model validation, and simulation
- 2010
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 224:4, s. 353-365
-
Tidskriftsartikel (refereegranskat)abstract
- A mixed lubrication flow factor model that permits real three-dimensional surface topography as input has been developed. Part 1 gives the theory of computing flow factors within the model. In this article, a method of adapting the measured surface topography signal to suit the numerical models is developed and presented in detail. The mixed lubrication model is validated through flow measurements for three different rough surface test specimens. Simulation of a hydrodynamic bearing was conducted and the results are presented in terms of pressure distributions and Stribeck curves covering all lubrication regimes. The results indicate that the model may be an efficient and accurate engineering design and research tool for tribological devices operating in all lubrication regimes.
|
|
| 10. |
- Westerberg, Lars-Göran, et al.
(författare)
-
Free-surface grease flow: influence of surface roughness and temperature
- 2015
-
Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 59, s. 18-
-
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.
|
|
