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Thrust 3: Effectiveness

Title

3D.1: Leakage Reduction in Fluid Power Systems

Project Leader

Dr. Richard Salant (Georgia Tech)

Statement of Project Goals

The general goal of this project is the development of realistic numerical models of the seals and seal systems used in fluid power systems, which would be capable of predicting the key seal performance characteristics, especially seal leakage and friction, and serve as design tools. A further aim is to develop a fundamental understanding of the physics of sealing through the model development.

Project Role in Support of Strategic Plan

The project attacks the effectiveness barrier by providing tools and physical understanding that will allow the development of seals that will eliminate or substantially reduce leakage from fluid power components such as actuators, valves and pumps. It constitutes fundamental research, which will have long term benefits.

Description and Explanation of Research Approach

The fluid power industry has recognized that the reduction or elimination of leakage of hydraulic fluid from fluid power systems is a fundamental prerequisite for the expanded use of fluid power. At virtually every major fluid power manufacturer, leakage reduction is at or near the top of the list of urgent technological needs. Leaking rod seals are the most significant sources of environmental pollution in fluid power systems. At the present time, these seals are developed through empirical means, using trial and error techniques, since the fundamental physics of seal operation has been poorly understood.

Rod seals are reciprocating seals. Past research on such seals is described in a recent review paper [1]. Serious studies date back to at least 1964. Since that time many studies have been performed, but these have not had a significant impact on the practical aspects of seal design due to the complexity of modeling the operation of rod seals and the need to make many simplifying assumptions. In particular, both the roughness of the seal surface and mixed lubrication in the seal-rod interface, were generally ignored.

Taking advantage of improved computational techniques and increased computational power, the present author and his students had made a start in developing a more realistic model of rod seal operation [2]-[4], under a project funded by the National Fluid Power Association, Cooperative Network for Research. The present project, in the CCEFP, builds on that work. At the same time, several other researchers have been making advances in this area [5]-[9].  

The models developed in this project simulate the dominant physical processes governing the behavior of rod seals and take account of mixed lubrication and seal roughness. They include analyses of the fluid mechanics, contact mechanics, thermal processes (in some cases) and deformation mechanics, and an iterative computational procedure. Inputs to the models include the operating conditions, material properties, macro-geometry, and micro-geometry of the sealing surfaces.

Model development involves analyzing the fundamental physics of the various processes, setting up numerical analyses and computational strategies, constructing appropriate algorithms and writing code. Model validation makes use of experimental results obtained from industrial collaborators. As required, simulations of seals suitable for the test bed are performed and, based on the results of the simulations, design recommendations are made for the test bed seals. As the project progresses and more is learned about the physics of seal behavior, that information is transmitted to the test bed projects.

References

1.    Nikas, G. K., "Research on the Tribology of Hydraulic Reciprocating Seals," Tribology Research Trends, Hasegawa, T. editor, Nova Science Publishers Inc., Hauppauge, NY, 11-56, 2008.
2.    Salant, R. F., Maser, N. and Yang, B., "Numerical Model of a Reciprocating Hydraulic Rod Seal, Including Seal Roughness and Mixed Lubrication," Plenary Lecture, 14th International Sealing Conference, Stuttgart, Germany, 2006.
3.    Salant, R. F., Maser, N. and Yang, B., "Elastohydrodynamic Model of a Reciprocating Hydraulic Rod Seal," AITC-AIT 5th International     Conference on Tribology, Parma, Italy, 2006.
4.    Salant, R. F., Maser, N. and Yang, B., "Numerical Model of a Reciprocating Hydraulic Rod Seal," Journal of Tribology, Vol. 129, pp. 91-97, 2007.
5.    Nikas, G. K., "Elastohydrodynamics and Mechanics of Rectangular Elastomeric Seals for Reciprocating Piston Rods," J. of Tribology, 125, pp. 60-69, 2003.
6.    Nikas, G. K, "Transient Elastohydrodynamic Lubrication of Rectangular Elastomeric Seals for Linear Hydraulic Actuators," J. of Engineering Tribology, 217, pp. 461-473, 2003.
7.    Öngün, Y., André, M., Bartel, D. and Deters, I., "An Axisymmetric Hydrodynamic Interface Element for Finite-Element computations of Mixed Lubrication in Rubber Seals," ImechE Journal of Engineering Tribology, Vol. 222, pp. 471-481, 2008.
8.    Schmidt, T., Andre, M. and Poll, G., "A Transient 2D-Finite-Element Approach for the Simulation of Mixed Lubrication Effects and Wear Progress of Reciprocating Hydraulic Rod Seals," Leeds-Lyon Symposium on Tribology, Lyon, France, 2009.
9.    Stupkiewicz, S. and Marciniszyn, A., "Elastohydrodynamic Lubrication and Finite Configuration Changes in Reciprocating Elastomeric Seals, Tribology International, Vol. 42, pp. 615-627, 2009.
10.    Thatte, A. M. and Salant, R. F., "Piezo-Array Embedded Polymeric Seals for Effective Micro-Control of Sealing," Georgia Tech Patent Disclosure, GRRC ID 5480, Nov. 17, 2010.
11.    Yang, B. and Salant, R. F., "Numerical Model of a Reciprocating Rod Seal with a Secondary Lip," Tribology Transactions," Vol. 51, pp. 119-127, 2008.
12.    Yang, B. and Salant, R. F., "Numerical Model of a Tandem Reciprocating Hydraulic Rod Seal," Journal of Tribology," Vol. 130, 032201-1 - 032201-7, 2008, and STLE/ASME Tribology Conference, pp. IJTC2007-44066, San Diego, 2007.
13.    Yang, B. and Salant, R. F., "Soft EHL Simulations of U-cup and Step Hydraulic Rod Seals," Journal of Tribology, Vol. 131, pp. 021501 -1 - 021501-7, 2009.
14.    Thatte, A. and Salant, R. F., "Transient EHL Analysis of an Elastomeric Hydraulic Seal," Tribology International, Vol. 42, pp.  1424-1432, 2009.
15.    Thatte, A. and Salant, R. F., "Elastohydrodynamic Analysis of an Elastomeric Hydraulic Seal during Fully Transient Operation," Journal of Tribology, Vol. 131, pp. 031501-1 - 031501-11, 2009.
16.    Salant, R. F., Yang, B. and Thatte, A., "Simulation of Hydraulic Seals," Journal of Engineering Tribology, Vol. 224, pp. 865-876, 2010.
17.    Thatte, A. and Salant, R. F. "Visco-Elastohydrodynamic Model of a Hydraulic Rod Seal During Transient Operation," Journal of Tribology, Vol. 132, pp. 041501-1 - 041501-13, 2010.
18.    Yang, B. and Salant, R. F., "EHL Simulation of O-ring and U-cup Hydraulic Seals," Journal of Engineering Tribology, submitted 8-13-10, under review.
19.    Salant, R. F. and Yang, B., "Elastohydrodynamic Model of Reciprocating Hydraulic Seals," Plenary Lecture, Rotrib '07, 10th International Conference on Tribology, Bucharest, Romania, 2007.
20.    Salant, R. F., "Recent Research and Future Challenges in Simulating Hydraulic Seals," Keynote Address, 4th World Tribology Congress, Kyoto, Japan, 2009.
21.    Salant, R. F., Yang, Bo and Thatte, A., "Simulation of Hydraulic Seals," Invited Paper, 36th Leeds-Lyon Symposium on Tribology, Lyon, France, 2009.
22.    Thatte, A. and Salant, R. F., "Soft EHL Analysis of an Elastomeric Hydraulic Seal During Transient Operation," Invited Paper, 4th World Tribology Congress, Kyoto, Japan, 2009.
23.    Salant, R. F. and Yang, B., "Numerical Modeling of Reciprocating Hydraulic Rod Seals," XI International Conference on Seals and Sealing Technology, Kudowa Zdroj, Poland, 2007.
24.    Yang, B. and Salant, R. F., "Elastohydrodynamic Model of a Reciprocating Hydraulic Rod Seal with a Double Lip,"  Proc. 19th     International Conference on Fluid Sealing, BHRG, pp. 5-18, 2007.
25.    Yang, B. and Salant, R. F., "Effects of Speed and Pressure on Hydraulic Rod Seal Behavior," 63rd Annual Meeting, STLE, Cleveland, 2008.
26.    Thatte, A. and Salant, R. F., "Transient EHL Analysis of an Elastomeric Hydraulic Seal," Nordtrib 2008, 13th Nordic Symposium on Tribology, Tampere, Finland, 2008.
27.    Salant, R. F. and Thatte, A., "Transient Model of a Hydraulic Rod Seal," 15th International Sealing Conference, Stuttgart, Germany, 2008.
28.    Salant, R. F. and Yang, B., "Numerical Modeling of Reciprocating Fluid Power Seals," 7th JFPS International Symposium on Fluid Power, Toyama, Japan, 2008.
29.    Yang, B. and R. F. Salant, "Soft EHL Analysis of a Reciprocating Hydraulic Step Seal," STLE/ASME Tribology Conference, IJTC2008-71043, Miami, 2008.
30.    Thatte, A. and Salant, R. F., "Hybrid Finite Element-Finite Volume Algorithm for solving Transient Multi-Scale Non-Linear Fluid-Structure Interaction during Operation of a Hydraulic Seal, COMSOL 2008, Boston, 2008.
31.    Salant, R. F., "Numerical Modeling of Hydraulic Seals for Zero Leakage," IFPE, Las Vegas, March 12, 2008.
32.    Flitney, R. K. and Salant, R. F., "A Review of the Development of Reciprocating Seals," Focus on Reciprocating Seals Conference, IMechE, London, June 25, 2008.
33.    Salant, R. F. and Yang, B., "Hydraulic Rod Seal with a Mico-Patterned Sealing Surface - Simulation Results," Ecotrib 09, 2nd European Conference on Tribology, Pisa, Italy, 2009.
34.    Yang, B. and Salant, R. F., Numerical Analysis of a Reciprocating Hydraulic Rod Seal with a Micro-Scale Surface Pattern," Proc. 20th International Conference on Fluid Sealing, BHRG, pp. 109-118, 2009.
35.    Yang, B. and Salant, R. F., "Simulation of a Hydraulic Rod Seal with a Micro-Patterned Sealing Surface," 64th STLE Annual Meeting, Orlando, 2009.
36.    Salant, R. F., Yang, B. and Thatte, A., "Recent Research and Future Challenges in Simulating Hydraulic Seals," STLE/ASME International Joint Tribology Conference, Memphis, 2009.
37.    Thatte, A. and Salant, R. F., "Transient Elastohydrodynamic Simulation of a Viscoelastic Hydraulic Rod Seal," 65th STLE Annual Meeting, Las Vegas, 2010.
38.    Yang, B. and Salant, R. F., "EHL Simulation of O-ring and U-cup Hydraulic Seals," Nordtrib 2010, 14th Nordic Symposium on Tribology, Lulea, Sweden, 2010.
39.    Thatte, A. and Salant, R. F., "Role of Multi-Scale Viscoelasticity on Transient Elastohydrodynamics during High Frequency Reciprocating Sealing Applications," STLE/ASME International Joint Tribology Conference, San Francisco, 2010.