On the shear-induced structural degradation of lubricating greases and associated activation energy: An experimental rheological study

Acar, Nazli; Franco, J.M.; Kuhn, Erik

doi:10.1016/j.triboint.2019.106105

Cited by 12 publications

(10 citation statements)

References 23 publications

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“…This critical deformation is influenced by the content of solid in a lubricating grease. The observation of [28] shows a decreasing value of the critical deformation with an increasing content of solid for the used greases. The physical bonds between the solid fibres are much weaker compared with the bond inside the base oil.…”

Section: Experimental Workmentioning

confidence: 85%

“…From the experimental work of [28], we can obtain some information of the grease behaviour during an increasing tribological stress. An amplitude sweep of an oscillating rheometer measurement delivers the possibility to obtain information about the transition from elastic range to plastic range.…”

Section: Experimental Workmentioning

confidence: 99%

“…Critical deformation γ critic vs. NLGI (National Lubricating Grease Institute)-grade as reported in[28].…”

mentioning

confidence: 99%

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Aspects of Self-Organization of Tribological Stressed Lubricating Greases

Kuhn

2020

Lubricants

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Lubricating greases are markedly visco-elastic materials. Stressed by a friction process, this special material shows a drop of a measured shear stress or viscosity. This typical behaviour is observed in a number of papers and, therefore, is well known. Some different explanations can be found but most of them describe a structural degradation caused by the friction process. This paper attempts to elucidate the conditions that promote that structural change and understand this behaviour as an intrinsic response of the system.

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Section: Experimental Workmentioning

confidence: 85%

Section: Experimental Workmentioning

confidence: 99%

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Aspects of Self-Organization of Tribological Stressed Lubricating Greases

Kuhn

2020

Lubricants

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“…So there are two regimes, with different degradation rates. Such uni-directional shear is also applied if grease is worked in a plate-plate rheometer such as done by Kuhn and co-workers (3,7). The disadvantage of using this type of rheometer is that the energy can only be small because grease may leak out from between the plates or form cracks (8).…”

Section: Introductionmentioning

confidence: 99%

The Grease Worker and Its Applicability to Study Mechanical Aging of Lubricating Greases for Rolling Bearings

Meijer

Lugt

2021

Tribology Transactions

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Mechanical degradation by shear is one of the mechanisms that limits the life-time of lubricating grease in a rolling bearing. It results in a change of the micro-structure of the thickener-oil system, leading to a change in bleed and consistency. The resistance to degradation can be quantified using a grease worker. In this paper a novel approach is described, where the grease worker is used to measure the rheological properties of a grease in-situ, while aging the grease. Mechanical energy and pressure losses are calculated using the measured force that is required to push the plate with holes through the grease in the cylinder of the grease worker. A pipe flow model in combination with a power law rheology model are used to analytically determine the power-law fluid consistency index and exponent while aging the grease. The model validity is verified using CFD simulations and measurements using a rheometer with plate-plate geometry.

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“…Moreover, bio-grease formulations, based on castor oil as the base oil and sorbitan and glyceryl monostearate or acylated chitosan as the thickener agents, generally yielded lower friction coefficient values than the reference lithium greases in several tribological tests [14]. The friction process leads to irreversible effects, namely wear, inside a tribological system; therefore, irreversible effects are the results of friction energy input into a tribological system [20]. This approach indicates that the friction and wear process is a cause-effect sequence [21].…”

Section: Introductionmentioning

confidence: 99%

Tribological Investigation on the Friction and Wear Behaviors of Biogenic Lubricating Greases in Steel–Steel Contact

et al. 2020

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The applications of biogenic lubricating greases to machine elements play important roles in the reduction of friction energy and minimizing wear in a tribological contact, as well as the prevention of environmental pollution. The aim of this work was to investigate completely biogenic lubricating greases from a tribological point of view. Model greases were examined using a ball on a disc tribometer at a constant normal force to investigate the friction and wear process according to Fleischer’s energetic wear model. Using the energy-based wear model, the friction and wear process could be interpreted as a cause–effect sequence. Moreover, the influence of the model grease composition on the friction and wear process was analyzed. In addition, rolling bearing tests were performed to investigate the tribological behaviors of some selected biogenic greases during real machine element contact. These tests allowed for the quantification of the friction torque behavior of the full bearing and the evaluation of the wear obtained through lubricant analysis procedures. This experimental work provides useful information regarding the influence that the composition of biogenic model greases has on friction and wear behaviors in a tribological contact.

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On the shear-induced structural degradation of lubricating greases and associated activation energy: An experimental rheological study

Cited by 12 publications

References 23 publications

Aspects of Self-Organization of Tribological Stressed Lubricating Greases

Aspects of Self-Organization of Tribological Stressed Lubricating Greases

The Grease Worker and Its Applicability to Study Mechanical Aging of Lubricating Greases for Rolling Bearings

Tribological Investigation on the Friction and Wear Behaviors of Biogenic Lubricating Greases in Steel–Steel Contact

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