Film thickness in grease lubricated slow rotating rolling bearings

Morales-Espejel, Guillermo E.; Lugt, Piet M.; Pasaribu, H.R.; Cen, Hui

doi:10.1016/j.triboint.2014.01.023

Cited by 79 publications

(58 citation statements)

References 34 publications

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“…At ultra-low speed, the film thickness may increase with decreasing speed [13]. This was modelled using an effective viscosity that is much higher than that of the base oil and is a function of the speed [22]. The higher film thickness may be ascribed to the large increase in viscosity when the shear rate approaches zero and/or to the formation of boundary layers.…”

Section: Discussionmentioning

confidence: 99%

Effect of Thickener Particle Geometry and Concentration on the Grease EHL Film Thickness at Medium Speeds

et al. 2016

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The aim of this paper was to understand the parameters influencing the grease film thickness in a rolling elastohydrodynamically lubricated contact under fully flooded conditions at medium speeds. Film thickness measurements were taken under pure rolling for six commercial greases and their bled oils. The grease film thickness was found to be higher than corresponding bled oil, suggesting the presence of thickener in the contact. No rheological properties (characterized by steady and dynamic shear) showed any direct relation to the film thickness of the studied greases. AFM measurements of the thickener microstructure, from which the dimensional properties of the thickener particles (fibers/platelets/ spheres) were estimated, showed that the relative increase in the film thickness due to entrainment of the thickener was proportional to the ratio of thickener volume fraction to the size of the fibers/platelets/spheres. Hence, with the same concentration, smaller thickener particles lead to the generation of thicker films than larger thickener particles. Next, this relation was used to establish the percentage of the thickener particles passing through the contact. Depending on the grease type, between about 1 and 70 % of the thickener particles were found to travel through the contact.Keywords EHL Á Grease lubrication Á Rheology Á Microstructure List of symbols DAverage diameter of the thickener particle (m) E 0

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Section: Discussionmentioning

confidence: 99%

Effect of Thickener Particle Geometry and Concentration on the Grease EHL Film Thickness at Medium Speeds

et al. 2016

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“…Tribological test conditions are collected in Table 3. 9 samples obtained after applying different pre-heating temperatures and times. As can be observed, there are significant microstructural similarities between the same samples as long as the applied temperature was well below the dropping point of the grease and the heating time was not longer than typically 15-30 s. However, the time-temperature combination which produces significant changes in the microstructure depends on grease consistency and thickener type.…”

Section: Tribological Measurementsmentioning

confidence: 99%

“…Apart from the main lubrication role, which is mainly performed by the lubricating oil, the rest of differential and characteristic performance properties of lubricating greases are due to the microstructure. Several authors have highlighted the role of the thickener in film thickness [7][8][9][10], some of them emphasizing the thickener microstructure [11]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 grease microstructure on the lubrication film thickness, demonstrating that the smaller thickener structural units, the thicker films were obtained.…”

Section: Introductionmentioning

confidence: 99%

AFM and SEM Assessment of Lubricating Grease Microstructures: Influence of Sample Preparation Protocol, Frictional Working Conditions and Composition

2016

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The microstructure of lubricating greases greatly conditions their in-service performance. In that sense, optimal testing protocols are required in order to accomplish their correct morphological characterization. This study explores and compares the suitability of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) techniques for imaging six different commercial metallic soap-based greases and two novel biopolymer-based formulations. Pros and cons of both techniques as well as the effect of sample preparation protocol were analyzed. The results revealed a wide variety of morphological characteristics depending on composition. Thus, the four anhydrous calcium-based greases demonstrated two clearly distinct microstructures (fibrous and granular) determined by the type of base oil employed. With regard to the lithium complex greases, the typically reported microstructure characterized by welldefined entangled and fibrous network was observed in both AFM and SEM techniques.As for the two biopolymer-based greases, fiber networks were also encountered.Besides this, selected greases were subjected to different tribological tests, and the effect of high-shear frictional working treatments on their microstructure was also analyzed. As a result of the friction and internal wear, the AFM results evidenced microstructural changes which depended on grease composition. Overall, the combined use of AFM and SEM techniques was demonstrated to be a powerful approach to microstructurally characterize lubricating greases.

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“…A similar phenomenon has also been observed by other researchers. Morales-Espejel et al [11] developed an empirical model to predict the film thickness of grease at low speed based on extensive experimental work by Cen et al [12]. Cyriac et al [13] investigated the influence of rheology and grease formulation (thickener microstructure and concentration) on the greaselubricated film formation under fully flooded conditions at medium speeds.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of EHD grease lubrication in finite line contacts

et al. 2018

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Abstract:The objective of this study was to investigate the grease-lubricated film-forming mechanisms in the finite line contact and to improve the grease-lubricated finite line contact's film-forming capacity. An elastohydrodynamic lubrication (EHL) test rig with two interferometry microscopes, which could simultaneously monitor two different contact locations in the finite line contact, was constructed in order to study the influences of the grease thickener formulation on the film thickness and lubrication condition. By using the relative light intensity method, the thickness maps of the grease-lubricated film were calculated from the interferometer images captured by the two microscopes. The test results revealed that the grease thickener's formulation had remarkable effects on film formation and the perturbation of film thickness. For the lithium-based grease, the film's thickness near the two ends of the roller was prone to severe perturbation caused by the conglomeration of clumps that were hard to shear. For the aluminum-complex-based grease, the fibers tended to accumulate in the middle of the roller rather than at the two ends. The urea-based grease could be easily sheared into smaller particles. In addition to the straight-line profile rollers, the logarithmic profile rollers were tested and found to effectively enhance the axial grease flow, increase the axial shear stress, and thus shear more fibers into particles within the contact area.

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Film thickness in grease lubricated slow rotating rolling bearings

Cited by 79 publications

References 34 publications

Effect of Thickener Particle Geometry and Concentration on the Grease EHL Film Thickness at Medium Speeds

Effect of Thickener Particle Geometry and Concentration on the Grease EHL Film Thickness at Medium Speeds

AFM and SEM Assessment of Lubricating Grease Microstructures: Influence of Sample Preparation Protocol, Frictional Working Conditions and Composition

Experimental investigation of EHD grease lubrication in finite line contacts

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