Richard F. Salant

Numerical Analysis of a Slider Bearing with a Heterogeneous Slip/No-Slip Surface

The behavior of a fluid-film bearing depends on the boundary conditions at the interfaces between the liquid and the solid bearing surfaces. For almost all solid surfaces, the no-slip boundary condition applies. However, a number of researchers have recently found that slip can occur with specially engineered surfaces. These include molecularly smooth surfaces and surfaces with micron-scale patterns. By constructing an engineered heterogeneous surface on which slip occurs in certain regions and is absent in others, the flow in the liquid film of a bearing can be altered, and such characteristics as load support and friction can be improved. In the present study, a numerical analysis of a slider bearing with such an engineered slip/no-slip surface is analyzed. Slip is assumed to occur when a critical shear stress is exceeded and follows the Navier relation. The results show that with a critical shear stress of zero, a significant increase in load support and decrease in friction can be achieved with an appropriate surface pattern. With nonzero values of critical shear stress, an instability occurs over a range of speeds. At speeds above this range, the bearing behaves similar to the case with zero critical shear stress, while below this range it behaves like a conventional bearing.

An Average Flow Model of Rough Surface Lubrication With Inter-Asperity Cavitation

An average Reynolds equation capable of predicting the effects of roughness induced inter-asperity cavitation is introduced. The average Reynolds equation is based on the JFO cavitation model and the Patir and Cheng flow factor method. The flow factors are calculated in numerical experiments as functions of the local surface separation, surface statistics, and cavitation number. The model is extended into a universal average Reynolds equation capable of predicting the combined effects of inter-asperity cavitation and macroscopic cavitation. Both the Patir and Cheng method and the present model are verified in numerical experiments.

A Mixed Soft Elastohydrodynamic Lubrication Model With Interasperity Cavitation and Surface Shear Deformation

A deterministic mixed lubrication model, governing the interface between a moving smooth rigid surface and a stationary rough elastic surface, has been developed. Both the normal and shear deformations of the elastic surface are considered, as well as interasperity cavitation. Utilizing an analogy between the hydrodynamic lubrication (with cavitation) problem and the asperity contact problem, a generalized computational formulation is derived and a unique solution scheme constructed to solve these seemingly different problems. The model has been applied to the rotary lip seal, and used to predict the performance characteristics over a range of shaft speeds.

Numerical Model of a Reciprocating Hydraulic Rod Seal

A numerical model of an elastomeric reciprocating hydraulic rod seal has been constructed. The model consists of coupled fluid mechanics, deformation mechanics and contact mechanics analyses, with an iterative computational procedure. The fluid mechanics analysis consists of the solution of the Reynolds equation, using flow factors to account for surface roughness. Deformation of the seal is computed through the use of influence coefficients, obtained from an off-line finite element analysis. The contact mechanics analysis uses the Greenwood and Williamson model. The seal model is used to predict leakage rate, friction force, fluid and contact pressure distributions, and film thickness distribution. Results for a typical seal show that the seal operates with mixed lubrication, and the seal roughness plays an important role in determining whether or not the seal leaks.Copyright

Mechanisms of Chemical-Mechanical Polishing of SiO2 Dielectric on Integrated Circuits

One of the fundamental mechanisms of chemical-Mechanical polishing (CMP) is the mechanical interaction between the wafer and polishing pad. This interaction was simulated in experiments. The vertical displacement of the wafer with respect to the polishing pad, the fictional drag of the wafer against the pad, and the pressure of the slurry trapped between the wafer and pad were measured. These experiments were performed over a range of commercially common CMP conditions. In addition, polishing rates were measured for CMP performed under induced hydrodynamic conditions where the wafer was separated from the pad by a film of slurry. It was found that no appreciable polishing occurred under hydrodynamic CMP conditions. Under commercial CMP conditions, it was found that the wafer contacts the polishing pad asperities as evidenced by near-zero wafer displacement and high friction coefficients (˜0.4). It was also found that pad conditioning (intentional roughening) causes a suction force to develop between the w...

Numerical Analysis of a Journal Bearing With a Heterogeneous Slip/No-Slip Surface

The no-slip boundary condition is part of the foundation of the traditional lubrication theory. It states that fluid adjacent to a solid boundary has zero velocity relative to the solid surface. For most practical applications, the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for certain engineered surfaces the no-slip boundary condition is not valid. Measured velocity profiles show that slip occurs at the interface. In the present study, the effect of an engineered slip/no-slip surface on journal bearing performance is examined. A heterogeneous pattern, in which slip occurs in certain regions and is absent in others, is applied to the bearing surface. Fluid slip is assumed to occur according to the Navier relation. Analysis is performed numerically using a mass conserving algorithm for the solution of the Reynolds equation. Load carrying capacity, side leakage rate, and friction force are evaluated. In addition, results are presented in the form of Raimondi and Boyd graphs. It is found that the judicious application of slip to a journal bearing’s surface can lead to improved bearing performance.

Numerical Study of a Rotary Lip Seal With a Quasi-Random Sealing Surface

In all previous numerical simulations of the rotary lip seal, the sealing surface was modeled by regular periodic structures. In the present study, a more realistic quasirandom surface is used. A mixed elastohydrodynamic analysis is used to generate predictions of such seal operating characteristics as friction coefficient, reverse pumping rate, film thickness distribution, hydrodynamic and contact pressure distributions, contact area, and cavitation area. The results are in qualitative agreement with previous experimental observations. In the course of the simulations, a new physical mechanism of reverse pumping has been identified.

Numerical Analysis of the Flow Field Within Lip Seals Containing Microundulations

The flow field within the lubricating film of a rotating shaft lip seal containing microundulations is analyzed numerically. The results demonstrate that the action of the microundulations can prevent leavage through the seal. The effects on leakage rate of shaft speed, undulation amplitude and wavelength, shear deformation of the undulations, flattening of the undulations, and axial lip profile are presented

Theory of lubrication of elastomeric rotary shaft seals

Abstract Current knowledge of the principles of rotary lip seal operation is assessed through a review of the experimental foundation and the key theoretical models. Studies of the existence of the lubricating film, the load support mechanism, the sealing mechanism, the thermal effects and the followability are described.

A Mixed Lubrication Model of Liquid/Gas Mechanical Face Seals

A mixed lubrication model for axisymmetric seals, intended as a practical design tool, has been developed. The model considers such physical mechanisms as surface roughness effects on the film lubrication, elastic-plastic face contact, face deformation caused by pressure and contact forces, thermal deformation due to viscous and frictional heating phase change, and temperature and viscosity variations in the film. A numerical scheme that utilizes the influence coefficient method to calculate the face deformations has been developed. This scheme considerably reduces computation time while still maintaining the accuracy of the results. Numerical results obtained through parametric studies show good agreement with available test data. Presented at the 52nd Annual Meeting in Kansas City, Missouri May 18–22, 1997