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Research Papers: Other (Seals, Manufacturing)

A Subscale Experimental Test Method to Characterize Extrusion-Based Elastomer Seals

[+] Author and Article Information
Shiyan Jayanath

Department of Mechanical and
Aeronautical Engineering,
Clarkson University,
Potsdam, NY 13699
e-mail: wewalas@clarkson.edu

Ajit Achuthan

Department of Mechanical and
Aeronautical Engineering,
Clarkson University,
Potsdam, NY 13699
e-mail: aachutha@clarkson.edu

Aaron Mashue, Ming Huang

GE Oil & Gas,
Houston, TX 77205

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received September 16, 2015; final manuscript received November 22, 2015; published online April 27, 2016. Assoc. Editor: Sinan Muftu.

J. Tribol 138(3), 032201 (Apr 27, 2016) (7 pages) Paper No: TRIB-15-1339; doi: 10.1115/1.4032175 History: Received September 16, 2015; Revised November 22, 2015

Extrusion-based elastomer seals are used in many applications, such as the seal in a variable bore ram valve used in offshore oil and gas drilling. Performing full-scale closing pressure experiments of such valves to characterize the seal performance and material failure of elastomer, especially under various temperature conditions, are quite expensive and time consuming. Conversely, simple coupon tests to characterize the elastomer mechanical properties and failure do not capture the complex deformation associated with the extrusion and subsequent sealing type that these materials undergo in the valves. In view of this, a simple subscale experimental test method capable of simulating the extrusion and sealing type deformation is developed. The extrusion and sealing deformation are realized by bonding the rectangular elastomer sample to metal pieces on top and bottom surfaces, and then compressing the sample in the vertical direction, while the deformation of the three lateral surfaces is kept constrained. As a result, sample deforms and extrudes out of the front surface, eventually forming the seal against a flat rigid metal plate placed at an appropriate distance. Simple scaling rules to determine the appropriate sample size and initial sealing gap, equivalent to the full-scale valve in terms of similar strain conditions, are derived and then verified using finite element analysis (FEA). Finally, the experimental test method is demonstrated by characterizing the contact pressure of nitrile (NBR) samples under different operating temperatures, ranging from 21 °C to 160 °C using pressure-sensitive film sensor.

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Figures

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Fig. 1

(a) A top view of the basic design layout of an extrusion type seal (variable bore ram BOP) and (b) extrusion deformation of the unit cell—normal displacement (Un) is zero in callout surfaces

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Fig. 2

(a) Bonded elastomer samples that represent the representative unit cell (part 1), (b) extrusion fixture (part 2), and (c) and (d) complete fixture arrangement including rigidly held metal plate (part 3)

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Fig. 3

(a) Dimensions of the subscale test sample and (b) corresponding dimensions of the unit cell

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Fig. 4

(a) Undeformed sample and (b) deformed sample

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Fig. 5

Finite element model

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Fig. 6

Simple compression data of NBR at different temperatures, used for derive hyperelastic model and contact pressure calculation

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Fig. 7

Nominal strain in midsection of rubber samples for Poisson's ratio 0.47: (a) without sealing and (b) with sealing

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Fig. 8

Nominal strain in midsection of rubber samples for Poisson's ratio 0.49: (a) without sealing and (b) with sealing

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Fig. 9

FEA contact pressure results of different sample sizes for sample size scaling rule validation

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Fig. 10

Load versus displacement—experiment versus FEA

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Fig. 11

Comparison of the experimental and FEA contact pressure results at different temperatures: (a) sample at 21 °C, (b) sample at 70 °C, (c) sample at 90 °C, (d) sample at 126 °C, and (e) sample at 160 °C

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Fig. 12

Variation of contact pressure with temperature—experiment versus FEA

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