The Use of Entropy in Modeling the Mechanical Degradation of Grease

The aim of the paper was to discuss different effects, such as, among others, agglomeration of selected nanoparticles, particularly those from zirconia, on the tribological behavior of lubricants. The explanation of the difference between the concepts of ‘aggregation’ and ‘agglomeration’ for ZrO2 nanoparticles is included. The factors that influence such an agglomeration are considered. Classification and thickeners of grease, the role of additives therein, and characteristics of the lithium grease with and without ZrO2 additive are discussed in the paper. The role of nanoparticles, including those from ZrO2 utilized as additives to lubricants, particularly to the lithium grease, is also discussed. The methods of preparation of ZrO2 nanoparticles are described in the paper. The agglomeration of ZrO2 nanoparticles and methods to prevent it and the lubrication mechanism of the lithium nanogrease and its tribological evaluation are also discussed. Sample preparation and a ball-on disc tester for investigating of spinning friction are described. The effect of ZrO2 nanoparticles agglomeration on the frictional properties of the lithium grease is shown. The addition of 1 wt.% ZrO2 nanoparticles to pure lithium grease can decrease the friction coefficient to 50%. On the other hand, the agglomeration of ZrO2 nanoparticles in the lithium grease can increase twice the friction coefficient relative to that for the pure grease.

Section: Degradation Systems Of Greasesmentioning

confidence: 99%

“…According to Reference [11], if the operating temperature is significantly lower than the oxidation one and there is no contamination or evaporation of the grease, the life of grease is determined by mechanical degradation.…”

Section: Degradation Systems Of Greasesmentioning

confidence: 99%

The Effect of Addition of Nanoparticles, Especially ZrO2-Based, on Tribological Behavior of Lubricants

Rylski

Siczek

2020

“…In recent years, the general investigations of friction and wear were transferred to the special material and lubricant-lubricating grease. This means that, in addition to the friction investigations, irreversible structural changes, as an intrinsic reaction, are also of interest [6,11,[18][19][20][21].…”

Section: The General Grease Behaviourmentioning

confidence: 99%

Aspects of Self-Organization of Tribological Stressed Lubricating Greases

Kuhn

2020

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.

“…Over time, overall grease consistency can permanently change due to the shear irreversibly breaking the structure, due to oil bleed, leakage, and evaporation, due to contamination, and due to chemical reactions [15]. This change in consistency has been used to track the degree of degradation a grease has undergone [5,16,17]. A sampling of in-service grease in conjunction with a degradation model can be used to estimate the remaining useful life.…”

Section: Introductionmentioning

confidence: 99%

Testing Grease Consistency

Gurt

Khonsari

2021

Because of the influential role of consistency in selecting a grease for a given application, accurate and meaningful methodologies for its measurements are vitally important. A new method, recently introduced, uses a rheometer to compress a grease sample to evaluate a relative consistency between a fresh and degraded grease; however, the results of this approach compared to a standard penetrometer and other methods of assessing consistency have not been studied. This paper takes a closer look at the relevant parameters involved in the rheometer penetration test and establishes a recommended procedure for its use. The consistency of various greases is then tested using this method and compared to results obtained from yield stress, crossover stress, and cone penetration tests. The results indicate that rheometer penetration may be used to assess the change in consistency for a given grease but should not be used to compare different greases. For this purpose, the crossover stress method is recommended, which is shown to correlate very well with cone penetration while using a simple procedure and allowing the use of a substantially smaller sample. A strong power law correlation between crossover stress and cone penetration was found for all greases tested and is presented in Figure 12.