Research Papers: Friction and Wear

Tribological Behavior of Polymer Seal Materials in Water-Based Hydraulic Fluids

[+] Author and Article Information
S. Bernat

NTNU, Tribology Lab,
Department of Mechanical and Industrial
Richard Birkelandsvei 2b,
Trondheim 7491, Norway

A. Brink, M. Lucas

SINTEF, Tribology Lab,
Institute of Materials and Chemistry,
Richard Birkelandsvei 2b,
Trondheim 7465, Norway

N. Espallargas

NTNU, Tribology Lab,
Department of Mechanical and Industrial
Richard Birkelandsvei 2b,
Trondheim 7491, Norway

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received November 15, 2017; final manuscript received April 18, 2018; published online May 21, 2018. Editor: Michael Khonsari.

J. Tribol 140(6), 061605 (May 21, 2018) (7 pages) Paper No: TRIB-17-1438; doi: 10.1115/1.4040078 History: Received November 15, 2017; Revised April 18, 2018

In this work, two polymer materials have been tested in a lubricated reciprocating pin-on-plate contact geometry using water-based hydraulic fluids to simulate sliding conditions of seal materials used in offshore equipment. The effect of load, speed, water content of the lubricant, and soaking of the ultra-high molecular weight polyethylene (UHMWPE) and a polyketone (PK) sliding against a super-duplex stainless steel (SDSS) was studied. The results showed that for UHMWPE, an increase in normal force leads to a decrease in coefficient of friction for all velocities. While under the same sliding conditions, no relevant influence of load on friction coefficient was found for PK. On the other hand, an increase in sliding speed decreased the coefficient of friction for both materials. The effect of the water content of the hydraulic fluid on the tribological performance was also studied. In UHMWPE-SDSS system, increasing water content in the hydraulic fluid resulted in steady growth of the transfer film. One reason for this might be the decreasing lubricant viscosity, which moves the system toward the boundary lubrication regime. In addition, it was found that the incubation of both UHMWPE and PK in water-based lubricants showed a beneficial effect on friction and wear, which was explained by the change in polymer visco-elastic behavior.

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Fig. 1

Kinematic viscosity of the lubricant with various water content

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Fig. 2

Percentage weight change over days of PK and UHMWPE in 45% water-based lubricant

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Fig. 3

Results for 24 h test at 600 N with 100 m/s: (a) weight loss of polymer pins and (b) coefficient of friction averaged over the last 7 h of the experiment

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Fig. 4

SEM micrographs of worn steel surfaces with traces of PK and UHMWPE transferred film for both soaked and nonsoaked polymers tested at 600 N and 100 mm/s sliding conditions during 24 h

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Fig. 5

Effect of sliding speed and normal load on the coefficient of friction of UHMWPE and PK under lubricated conditions

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Fig. 6

Stribeck curves for UHMWPE and PK materials tested in reciprocating pin on plate tribometer. The dashed lines indicate roughly the transition between (I) boundary, (II) mixed, and (III) hydrodynamic regimes.

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Fig. 7

SEM image of the transfer UHMWPE film on SDSS after testing in water-based lubricant. EDS spots 1 and 2 were performed inside and outside the transfer film, respectively.

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Fig. 8

SEM micrographs of the SDSS surfaces sliding against UHMWPE in water-based lubricant

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Fig. 9

SEM micrographs of the SDSS surfaces sliding against PK in water-based lubricant

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Fig. 10

Kinematic viscosity of four different dilutions of lubricant and their effect on friction of UHMWPE-SDSS and PK-SDSS tribopairs (applied load of 600 N, sliding velocity of 100 mm/s)

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Fig. 11

SEM micrographs of steel surfaces after sliding at 600 N and 100 mm/s against (a) UHMWPE specimens and (b) PK specimens




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