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Research Papers: Lubricants

The Wall Effect in the Flow of Commercial Lubricating Greases

[+] Author and Article Information
Ryszard Czarny

Department of Mechanical Engineering,
Higher Vocational State School in Kalisz,
Nowy Swiat 4,
Kalisz 62-800, Poland

Maciej Paszkowski

Department of Fundamentals of Machine Design and Tribology,
Wroclaw University of Technology,
Ignacego Lukasiewicza 7/9,
Wroclaw 50-371, Poland
e-mail: maciej.paszkowski@pwr.edu.pl

Piotr Knop

Department of Fundamentals
of Machine Design and Tribology,
Wroclaw University of Technology,
Ignacego Lukasiewicza 7/9,
Wroclaw 50-371, Poland

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received January 6, 2015; final manuscript received March 10, 2016; published online May 17, 2016. Assoc. Editor: Mihai Arghir.

J. Tribol 138(3), 031803 (May 17, 2016) (6 pages) Paper No: TRIB-15-1007; doi: 10.1115/1.4033334 History: Received January 06, 2015; Revised March 10, 2016

The results of the studies on the formation of surface and boundary layers in commercial lithium (LT4-S3) and calcium (STP) greases near the walls of six different materials are presented. Two elastomeric materials (nitrile-butadiene rubber (NBR), silicone rubber (MVQ/VMQ)), two thermoplastic materials (polyoxymethylene (POM), polyethylene (PE)), and two metal (copper C11000 and steel 304) alloys were used in the tests. The tests were carried out using a rotational rheometer operating in the plate/plate configuration. Structural viscosity–shear rate curves were determined and dynamic oscillatory tests were carried out. The tests have shown that the metal alloys have the highest capacity to adsorb grease thickener particles on their surface. The elastomeric materials have the smallest effect on the change in structural viscosity in the vicinity of the wall, which indicates their low capacity to form a surface layer in the tested commercial greases.

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References

Figures

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Fig. 1

Distribution of yield stress τ* in boundary layer of grease as function of distance from wall

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Fig. 2

Distribution of shear stress and velocity in grease flowing through pipe

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Fig. 3

Schematic of rotational rheometer head 1, measuring spindle; 2, lubricating grease; 3, tested adsorbent; 4, Peltier element; 5, measuring plate; 6, counter cooling; and 7, insulating flange

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Fig. 4

Structural viscosity η versus shear rate γ˙ for lithium grease (a) and calcium grease (b) near tested adsorbents

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Fig. 5

Storage modulus G′ and loss modulus G″ versus shear stress τ for lithium grease in vicinity of tested adsorbents

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Fig. 6

Storage modulus G′ and loss modulus G″ versus shear stress for calcium grease in vicinity of tested adsorbents

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Fig. 7

Changes in storage modulus GLVR′ in critical point for greases in vicinity of tested adsorbents

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