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Research Papers: Other (Seals, Manufacturing)

Impact Phenomena in a Noncontacting Mechanical Face Seal

[+] Author and Article Information
Philip Varney

Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318
e-mail: pvarney3@gatech.edu

Itzhak Green

Professor
Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318
e-mail: itzhak.green@me.gatech.edu

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received November 20, 2015; final manuscript received March 31, 2016; published online August 11, 2016. Assoc. Editor: Sinan Muftu.

J. Tribol 139(2), 022201 (Aug 11, 2016) (8 pages) Paper No: TRIB-15-1419; doi: 10.1115/1.4033366 History: Received November 20, 2015; Revised March 31, 2016

Noncontacting mechanical face seals are often described as unpredictable machine elements, gaining this moniker from numerous instances of premature and unexpected failure. Machine faults such as misalignment or imbalance exacerbate seal vibration, leading to undesirable and unforeseen contact between the seal faces. A hypothesis explaining the high probability of failure in noncontacting mechanical face seals is this undesired seal face contact. However, research supporting this hypothesis is heuristic and experiential and lacks the rigor provided by robust simulation incorporating contact into the seal dynamics. Here, recent developments in modeling rotor–stator rub using rough surface contact are employed to simulate impact phenomena in a flexibly mounted stator (FMS) mechanical face seal designed to operate in a noncontacting regime. Specifically, the elastoplastic Jackson–Green rough surface contact model is used to quantify the contact forces using real and measurable surface and material parameters. This method also ensures that the seal face clearance remains positive, thus allowing one to calculate fluid-film forces. The seal equations of motion are simulated to indicate several modes of contacting operation, where contact is identified using waveforms, frequency spectra, and contact force calculations. Interestingly, and for the first time, certain parameters generating contact are shown to induce aperiodic mechanical face seal vibration, which is a useful machine vibration monitoring symptom. Also for the first time, this work analytically shows a mechanism where severe contact precipitates seal failure, which was previously known only through intuition and/or experience. The utility of seal face contact diagnostics is discussed along with directions for future work.

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Figures

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Fig. 1

Schematic of an FMS mechanical face seal

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Fig. 2

Reference frames used to model the FMS mechanical face seal

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Fig. 3

Contact between two rough surfaces is reduced to that of contact between a rigid flat and a composite rough surface

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Fig. 4

Validation versus the results provided by Green and Etsion [10]

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Fig. 5

Comparison of coned-face FMS minimum film thickness with and without contact (parameter set 1: γr=2 mrad, γsi=5 mrad, and n = 1000 rad/s). The “no-contact” case considers a surface height standard deviation σ=1×10−7m, which does not generate contact with these operating conditions. (a) Minimum film thickness, min(h(r, θ, t)) and (b) frequency content of steady-state FMS tilt γξ (similar frequency content is seen in γη).

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Fig. 6

Example contact pressure and fluid pressure profiles for parameters provided in the Appendix (n = 1000 rad/s): (a) contact pressure (Pa) Pc(r,θ,t) and (b) fluid-film pressure (MPa), Pf(r,θ,t)

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Fig. 7

FMS response to heavy contact (parameter set 2: γr=1 mrad, γsi=5 mrad, and n = 2000 rad/s): (a) minimum film thickness, min(h(r, θ, t)), (b) frequency content of steady-state FMS tilt γξ (similar frequency content is seen in γη), and (c) angular orbit and Poincaré section

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Fig. 8

Severe contact condition in a flat-faced seal. Parameters used are found in set 1 except for the coning, which is set as β = 0 (γr = 2 mrad, γsi = 5 mrad, and n = 1000 rad/s). (a) Minimum film thickness h(r,θ,t)/C0, (b) frequency spectrum of γξ, and (c) axial contact force, Fzc.

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