Film Thickness and Friction Relationship in Grease Lubricated Rough Contacts

Gonçalves, David; Vieira, António; Carneiro, Antônio Adilton Oliveira; Campos, A.; Seabra, Jorge

doi:10.3390/lubricants5030034

Cited by 32 publications

(19 citation statements)

References 28 publications

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“…Recent work by several authors like Cousseau et al [2,3], Goncalves et al [4,5], De Laurentis et al [6,7], and Cen et al [8,9] compare the film formation under fully flooded lubrication between grease and oil lubricated contacts. The film thickness measurements were performed on a ball-on-disc tribometer under variation of rolling speed.…”

Section: Introductionmentioning

confidence: 99%

Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts

et al. 2018

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The service life of rolling bearings is significantly affected by the film formation in elastohydrodynamic (EHD) contacts, which depends on the operating conditions, like rotational speed or temperature. In grease lubricated EHD contacts, the film formation is determined by the grease consistency and composition, i.e., thickener and base oil type as well as properties of the bleed oil, which is released from the grease during operation. Thus, the film formation of grease lubricated contacts as compared to base oil lubricated contacts can be different. With increasing rolling speed, the film thickness of oil lubricated contacts usually grows. However, in case of grease lubricated contacts, which are not fully flooded, the film thickness remains constant or even decreases with further increasing rotational speed. This effect is referred to as starvation. Since the onset of starvation depends on the grease composition, the film formation of two different grease compositions is investigated in this study. The film thickness measurements are performed on a ball-on-disc tribometer for each grease, as well as the corresponding bleed and pure base oils. Thereby, the characteristic rotational speed leading to the onset of starvation has been identified in dependence of the grease composition and the differences in the lubricating film formation of base oil, bleed oil, and grease lubricated EHD contacts have been discussed. The investigations should help to establish an advanced understanding of the physical mechanisms leading to the onset of starvation to encourage future work with focus on a method to predict the film formation in grease lubricated EHD contacts.

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Section: Introductionmentioning

confidence: 99%

Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts

et al. 2018

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“…Morales-Espejel et al [15], Cen et al [16], and Gonçalves at al. [7,12] observed the same increase in the film thickness for lithium grease at very low speeds. They also showed that the increase in film thickness strongly depends on the temperature; with increasing temperature, the film thickness of grease deviates from the base oil at higher speeds.…”

Section: Introductionmentioning

confidence: 57%

“…The dominant thickener behavior at low speeds was observed in the numerous previous studies [7][8][9][10][11]. The thickener type, operating conditions, temperature, and base oil viscosity appear to be the most significant factors in the film formation process [12,13]. De Laurentis et al [3,14] showed that the calcium sulphonate complex grease reaches almost the constant film thickness development with decreasing entrainment speed, while in the case of lithium and polyurea greases, the film thickness significantly increases.…”

Section: Introductionmentioning

confidence: 84%

On the Relation between Friction Increase and Grease Thickener Entraining on a Border of Mixed EHL Lubrication

Zapletal¹,

Šperka²,

Křupka³

et al. 2020

Lubricants

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This paper deals with an experimental study of film thickness and friction of commercial-grade grease and its base oil in a highly loaded contact. In-situ measurements were conducted for two surface textures on a ball-on-disc optical tribometer at the border of mixed lubrication. At high speeds, the film thickness and the friction of grease correspond with the base oil, while, the thickener enters the contact area and locally affects the film thickness and friction at low speeds. It was found out that the thickener starts to enter the contact area approximately at the same speed when the base oil friction increases on Stribeck curve but without direct solid to solid contact. It indicates that both effects can have the same origin. Change of lubricant flow in contact inlet area was discussed as a possible explanation.

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“…When there are high numbers of vibrational and rotational states, it takes higher energy input to raise the averaged kinetic energy, e.g., the temperature. The thermal conductivity of BO was correlated to the molecular diffusivity in the fluid (Gedde, 1995). The easier the molecules of a lubricant pass through each other, the higher the lubricant thermal conductivity.…”

Section: Thermal Propertiesmentioning

confidence: 99%

Performance Characteristics of Lubricants in Electric and Hybrid Vehicles: A Review of Current and Future Needs

et al. 2020

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Electric and hybrid vehicles are gaining increasing attention in recent years. The distinguished difference between electric/hybrid vehicles from conventional ones is the intermittent on-and-off control of the internal combustion engine, whereas the electric vehicles operate on electrical motors. This difference creates new requirements in lubricants with performance characteristics that are otherwise uncritical: electrical properties (such as electrical conductivity and breakdown voltage) and thermal properties (thermal conductivity, specific heat, among others), in addition to fluidic performance that we have studied for decades. In this review, we discuss about lubricants for electric and hybrid vehicles in the following aspects. Starting with a brief historic review, we gathered information about current needs and challenges in electric and hybrid vehicles. We then compared the properties of lubricants, followed by the performance difference of those vehicles in terms of frictional performance, thermal management, and dielectric breakdown. Performance parameters are critically dependent on the properties of lubricants that are crucial for energy efficiency and reliability. This review can be used as a guidance for the future design of advanced lubricants for electric and hybrid vehicles.

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Film Thickness and Friction Relationship in Grease Lubricated Rough Contacts

Cited by 32 publications

References 28 publications

Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts

Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts

On the Relation between Friction Increase and Grease Thickener Entraining on a Border of Mixed EHL Lubrication

Performance Characteristics of Lubricants in Electric and Hybrid Vehicles: A Review of Current and Future Needs

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