A Friction–Wear Correlation for Four-Ball Extreme Pressure Lubrication

Chung-Hung Chan; Wen Huei Lim; Shoot Kian Yeong; Kien Woh Kow; Yong Kuen Ho

doi:10.1115/1.4044879

A Friction–Wear Correlation for Four-Ball Extreme Pressure Lubrication

Journal of Tribology ◽

10.1115/1.4044879 ◽

2019 ◽

Vol 142 (2) ◽

Author(s):

Chung-Hung Chan ◽

Wen Huei Lim ◽

Shoot Kian Yeong ◽

Kien Woh Kow ◽

Yong Kuen Ho

Keyword(s):

Thermodynamic Analysis ◽

Entropy Generation ◽

Test Method ◽

Extreme Pressure ◽

Specific Load ◽

Wear Model ◽

Model Parameter ◽

Dissipative Coefficient ◽

Calculated Probability ◽

Wear Index

Abstract A first-ever friction–wear model for four-ball extreme pressure (EP) lubrication is developed in this work based on 12 oil samples comprising minerals, esters, and other formulated lubricants. The model considers the rate of entropy generation and dissipation within the lubricated tribosystem to describe the interaction between the friction and the wear behaviors at extreme pressure conditions. The model can be used to calculate the probability to pass or fail at a specific load to estimate the weld point of a lubricant. The calculated probability exhibited a similar trend as a load-wear index from the ASTM D2783 EP test method. Besides, the model is able to estimate the EP performance of an unknown lubricant based on the model parameter, namely the dissipative coefficient. This parameter describes the proportionality between the friction and the wear phenomena from the perspective of thermodynamic analysis. This work provides useful tools to better understand the fundamentals of EP lubrication and to characterize the lubricants without overly relying on tribotest machines.

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On the Fictitious Grease Lubrication Performance in a Four-Ball Tester

Lubricants ◽

10.3390/lubricants9030033 ◽

2021 ◽

Vol 9 (3) ◽

pp. 33

Author(s):

Sravan K. Joysula ◽

Anshuman Dube ◽

Debdutt Patro ◽

Deepak Halenahally Veeregowda

Keyword(s):

Critical Factor ◽

Maximum Load ◽

Test Method ◽

Extreme Pressure ◽

Motor Speed ◽

Low Friction ◽

Grease Lubrication ◽

Additive Package ◽

Variable Frequency Drive ◽

Lubrication Performance

The extreme pressure (EP) behavior of grease is related to its additives that can prevent seizure. However, in this study following ASTM D2596 four-ball test method, the EP behavior of greases was modified without any changes to its additive package. A four-ball tester with position encoders and variable frequency drive system was used to control the speed ramp up time or delay in motor speed to demonstrate higher grease weld load and lower grease friction that were fictitious. A tenth of a second delay in speed ramp up time had showed an increase in the weld load from 7848 N to 9810 N for grease X and 6082 N to 9810 N for grease Y. Further increase in the speed ramp up time to 0.95 s showed that the greases passed the maximum load of 9810 N that was possible in the four-ball tester without seizure. The mechanism can be related to the delay in rise of local temperature to reach the melting point of steel required for full seizure or welding, that was theoretically attributed to an increase in heat loss as the speed ramp-up time was increased. Furthermore, the speed ramp up time increased the corrected load for grease X and Y. This resulted in lower friction for grease X and Y. This fictitious low friction can be attributed to decrease in surface roughness at higher extreme pressure or higher corrected load. This study suggests that speed ramp up time is a critical factor that should be further investigated by ASTM and grease manufacturers, to prevent the use of grease with fictitious EP behavior.

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