Shear-degradation of grease and base oil availability in starved EHL lubrication

Mérieux, J-S.; Hurley, S.; Lubrecht, Antonius; Cann, P. M.

doi:10.1016/s0167-8922(00)80162-5

Cited by 36 publications

(24 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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]. due to shear degradation of the grease [8,31,32] or due to centrifugal forces as proposed in [18]. If the increase is related to shear degradation, it would be dependent on the number of contacts by the rolling elements.…”

Section: Discussionsupporting

confidence: 82%

“…Figure 10 also shows the increase of film thickness at high rolling speeds >1000 mm/s in the range of starvation. As discussed in the introduction, this increase can either occur in a recovery phase due to shear degradation of the grease [8,31,32] or due to centrifugal forces as proposed in [18]. If the increase is related to shear degradation, it would be dependent on the number of contacts by the rolling elements.…”

Section: Discussionmentioning

confidence: 99%

“…As indicated in Figure 1, the measurement results of grease lubricated EHD contacts presented in [8] show an increase in lubricating film thickness within the range of starvation at rolling speeds >1000 mm/s. It is assumed, that the increase of film thickness occurs either due to a recovery phase with increasing shear degradation [8,31,32] or due to centrifugal forces at high disc revolution speeds, which push the grease towards the contact area, and thus increase the lubricant supply [18]. Therefore, in this contribution, both the effect of over rolling frequency on the film formation and the mechanism leading to the increase of film thickness at high rolling speeds >1000 mm/s in starved EHD contacts is studied.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2019

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Single contact measurements are very valuable but should ideally be combined with film thickness measurements in full bearings (Lugt (1)). M erieux et al (M erieux et al (11)) gave four types of grease film thickness evolutions based on film thickness measurements in a single contact running at a constant speed: fully flooded; starved; starved with stabilization; starved with recovery. They particularly studied the fourth situation and attributed the film recovery to an increased lubricant availability due to grease shear degradation.…”

Section: Introductionmentioning

confidence: 99%

An Experimental Study on Film Thickness in a Rolling Bearing for Fresh and Mechanically Aged Lubricating Greases

Zhou

Bosman

Lugt

2019

Tribology Transactions

View full text Add to dashboard Cite

The lubricating film formation of greases has been widely studied using single contact ball-on-disc configurations. However, other than for oil, the film formation with grease is governed by starvation, which in a full bearing is clearly different from that of the single contact. In this paper, film thickness measurements for various greases in a shielded deep groove ball bearing will be presented. The results were obtained using an in-house-made film thickness measurement rig based on the 'electric capacitance method'. It will be shown that the film thickness may deviate from the theoretical elastohydrodynamic film thickness calculated from the base oil and that the film thickness is not constant in time. It will also be shown that the film thickness for longer times is not only determined by the classical properties such as oil viscosity and grease bleed but also by shear degradation of its microstructure.

show abstract

“…17 They indicated that the displaced grease acts as reservoirs which replenish the track by bleeding the base oil. Merieux et al 18 showed experimentally that the shear degradation of the grease at the side of the track results in releasing base oil and film recovery. The effect of centrifugal forces on the mechanism of replenishment in bearings was studied by Gershuni et al 19 and Van Zoelen et al 20,21 More recently, Scaraggi 22 showed that inducing a local flow reconditioning by surface textures results in a friction reduction in pad thrust bearings.…”

Section: Introductionmentioning

confidence: 99%

Effects of out-of-contact lubricant channeling on friction and film thickness in starved elastohydrodynamic lubrication point contacts

Ali

Křupka

Hartl

2016

Proceedings of the Institution of Mechanical Engineers, Part J:

View full text Add to dashboard Cite

This study presents experimental results on the effect of out-of-contact lubricant channeling on the tribological performance of nonconformal contacts under starved lubrication. Channeling of lubricant was carried out by adding a slider with a limited slot for scraping the displaced lubricant on one of mating surfaces (ball). Thus, the scraped lubricant is forced to flow back into the depleted track through the limited slot resulting in robust replenishment. The measurements have been conducted using optical tribometer (ball-on-disc) equipped with a digital camera and torque sensor. The effect of lubricant channeling was compared to the original contact condition by means of measuring friction and film thickness. The results show that the out-of-contact lubricant channeling leads to a significant enhancement of film thickness and friction reduction under starved conditions. Indeed, the starved elastohydrodynamic lubrication contacts transformed to the fully flooded regime after introducing the flow reconditioning. Moreover, the film thickness decay over time, which is common with starved elastohydrodynamic lubrication contacts, has not been observed in the case of lubricant channeling. However, the beneficial effect of lubricant channeling diminishes as the original contact condition tends to the fully flooded regime. The results of this study can be easily implemented in practical applications such as radial and thrust rolling-element bearings.

show abstract

Shear-degradation of grease and base oil availability in starved EHL lubrication

Cited by 36 publications

References 7 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

An Experimental Study on Film Thickness in a Rolling Bearing for Fresh and Mechanically Aged Lubricating Greases

Effects of out-of-contact lubricant channeling on friction and film thickness in starved elastohydrodynamic lubrication point contacts

Contact Info

Product

Resources

About