Film thickness decay and replenishment in point contact lubricated with different greases: A study into oil bleeding and the evolution of lubricant reservoir

Huang, Lu; Guo, Dan; Wen, Shizhu

doi:10.1016/j.triboint.2014.11.005

Cited by 44 publications

(18 citation statements)

References 21 publications

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“…Thus, the minimum time that is necessary for a reflow ensuring a sufficient lubricant supply, such that no starvation occurs, can be determined from Figure 13 to be >2.0 s. These results are in accordance with results for oil lubricated contacts under starved lubrication presented in [29]. However, since the replenishment time is dependent on the lubricant flow, it varies with different lubricants and lubricant properties [21,30,41]. Moreover, some studies [33,41,42] show that the replenishment time does not only depend on the over rolling frequencies, but additionally on operating conditions, such as vibrations or centrifugal forces in radial bearings as well as the wettability of the lubricant on different surfaces, e.g., in the presence of deposited thickener layers on the surfaces.…”

Section: Discussionsupporting

confidence: 81%

“…Thus, the lubricant supply decreases with higher over rolling frequency, which results in a lower film thickness than under fully flooded lubrication [21,[24][25][26]. In further studies [26][27][28][29][30], the effect of oil replenishment on the film formation of oil lubricated EHD contacts under starved conditions was investigated using a ball-on-disc tribometer. According to the results of [28,29], replenishment time has a significant effect on the regeneration of the oil film in the rolling track, and thus on the lubricant supply, respectively the film formation.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

et al. 2019

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The service life of rolling bearings is significantly affected by the lubricating film formation in elastohydrodynamic (EHD) contacts. Grease lubricated EHD contacts show a film thickness decay from a characteristic rotational speed, which is referred to as starvation. Thus, the film thickness of grease lubricated contacts differs from that of oil lubricated contacts. However, the base oil properties under fully flooded conditions are commonly assumed to estimate the operating lifetime of grease lubricated bearings, which are usually not fully flooded. Hence, this assumption results in an overestimation of the film thickness for rotational speeds in the range of starvation, which can lead to uncertainties in the bearing design. At high rotational speeds, i.e., high over rolling frequencies, starvation is likely to occur, due to insufficient lubricant supply by replenishment behind the rolling element. Therefore, the focus of this contribution is to investigate the effect of over rolling frequency, and thus replenishment time, on the lubricating film formation in starved, grease lubricated EHD contacts. The film thickness measurements were performed on a ball-on-disc tribometer, which was extended by adding a second ball specimen in front of the measuring ball. By varying the angular distance between the two contacts, the lubricant displacement can be controlled, such that the effect of replenishment time on the film formation can be determined. These investigations should help to establish an advanced understanding of the mechanisms of grease lubrication, and encourage future work with a focus on developing a method to predict the film formation in grease lubricated EHD contacts.

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Section: Discussionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

et al. 2019

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“…The photographs of grease reservoir were recorded after 500 revolutions' operation. As was reported in the previous study [13], the re-formed lubricant reservoir during operation was mainly due to oil bleeding. It is clearly seen that the maximum radium "a" of the lubricant reservoir was much larger for aged LiP8 and UP8 than that of the corresponding fresh samples, which indicated that aged greases bled more oil to replenish the contact during the operation than fresh greases.…”

Section: Film Thickness Of Thermally Aged Lip8 and Up8 Under Starved supporting

confidence: 73%

“…Bled oil was considered as a very important factor that contributing to replenishment, especially under starved and boundary lubrication condition [10][11][12]. Huang et al [13] observed that the bled oil contributed to forming lubricant reservoir, and different grease formulation lead to different oil bleeding ratio under same operation condition. However, it was also reported that grease failed to further lubricate the contact when losing 50 % of its base oil [14].…”

Section: Introductionmentioning

confidence: 99%

Thermal Oxidation Mechanism of Polyalphaolefin Greases with Lithium Soap and Diurea Thickeners: Effects of the Thickener

Huang

Guo

Cann

et al. 2016

Tribology Transactions

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In this work, lithium and diurea greases formulated by poly-alpha-olefin were aged up to 1200 hours in an oven at 120 °C and periodically taken out for testing. SEM and IR spectrum proved that both physical and chemical degradation happened during thermal aging process such as apparent viscosity decreasing, thickener destruction and chemical species changing. Diurea grease showed much better anti-oxidation performance during thermal aging process than Lithium grease. Dual effect of thermal aging on the grease lubricity was observed and analyzed.Results showed that early oxidation might reduce grease lubricity due to the formation of ketones and aldehydes while the decrease of grease viscosity and oil bleeding due to thickener destruction would contribute to better replenishment.

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“…Most of the grease was pushed outside the contact and hardly reflowed back. However, as proposed in our earlier work [19], a reformed lubricant reservoir consisting mostly of base oil and a small fraction of thickener debris appeared under the effect of shearing. The mobile lubricant was called bled oil, which meant that it was bled out of grease.…”

Section: Lubricant Reflowsupporting

confidence: 64%

Effects of nano thickener deposited film on the behaviour of starvation and replenishment of lubricating greases

et al. 2016

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Abstract:The mechanism of grease replenishment in and around a starved point contact was studied in this work. Greases made of different thickeners and same base oil were tested and compared. Disappearing and re-formation of a dynamic grease reservoir during operation revealed that grease bled oil to replenish contact. However, the replenishment process was slow because of the presence of grease fingers along the track and thickener-deposited film inside the track. The contact angles of base oil on the chromium-coated surface and thickener-deposited surfaces were measured. Results proved that the contact angle on the deposited film remarkably increased compared with that on the chromium-coated surface from 25° to more than 40°. However, the deposited film could be consumed with continuous rolling, and replenishment was then enhanced.

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Film thickness decay and replenishment in point contact lubricated with different greases: A study into oil bleeding and the evolution of lubricant reservoir

Cited by 44 publications

References 21 publications

Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

Thermal Oxidation Mechanism of Polyalphaolefin Greases with Lithium Soap and Diurea Thickeners: Effects of the Thickener

Effects of nano thickener deposited film on the behaviour of starvation and replenishment of lubricating greases

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