Chapter 4 Grease lubrication

This paper has examined the influence of bearing design and operation in controlling lubricant supply to the contact zone. Grease lubricated contacts are liable to starvation and as a result the film thickness is reduced, this can result in surface damage or premature bearing failure. It is of obvious importance to know when starvation occurs and the effect of grease type, bearing design and operation on lubrication replenishment. The aim therefore is to develop a starvation parameter capable of predicting the operating limits for a particular bearing/grease system. A number of bearing design parameters are examined in the paper, these include cage design, ball spin and bearing size. Ball spin and cage effects can be efficient mechanisms for maintaining the lubricant supply to the track. Increased bearing size, line contact geometries and high load result in reduced lubricant replenishment of the contact. Using this analysis it will be possible to establish operating limits for families of bearings.

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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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Optical Analysis of Ball Bearing Starvation

Journal of Lubrication Technology ◽

10.1115/1.3451591 ◽

1971 ◽

Vol 93 (3) ◽

pp. 349-361 ◽

Cited By ~ 172

Author(s):

L. D. Wedeven ◽

D. Evans ◽

A. Cameron

Keyword(s):

Film Thickness ◽

Ball Bearing ◽

Point Contact ◽

Experimental Measurements ◽

Line Contact ◽

Optical Analysis ◽

Grease Lubrication ◽

Theoretical Predictions ◽

Pressure Stress ◽

Starvation Conditions

Elastohydrodynamic oil film measurements for rolling point contact under starvation conditions are obtained using optical interferometry. The experimental measurements present a reasonably clear picture of the starvation phenomenon and are shown to agree with theoretical predictions. Starvation inhibits the generation of pressure and, therefore, reduces film thickness. It also causes the overall pressure, stress, and elastic deformation to become more Hertzian. Additional experiments using interferometry illustrate: the cavitation pattern, lubricant entrapment, grease lubrication, ball spin, and edge effects in line contact.

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