טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentFeldman Yuri
SubjectAnalysis of Gas Lubrication with Textured Surfaces
DepartmentDepartment of Mechanical Engineering
Supervisors Dr. Yuri Kligerman
Professor Emeritus Izhak Etsion


Abstract

Surface texturing as a means for enhancing tribological properties of liquid lubricated mechanical components has been well known for many years. Macro or micro surface texturing of different types (for example waviness, grooves, protrusions or micro dimples) were investigated extensively in recent years. It was found that mutual sliding surface texturing of mechanical seals and hydrodynamic bearings is the most promising when it comes to providing a stable fluid film, sufficient load carrying capacity, and reducing wear during operation. However, of all the surface texturing options, laser textured sliding surfaces with regular micro dimple texture offer the most promising design. This is because the laser is extremely fast, environment friendly, and provides excellent control of the shape and size of the dimples, allowing the realization of optimal parameters.

The main goal of the present research is to study the potential use of partial Laser Surface Texturing - LST in shapes of spherical dimples, for improving tribological performance of hydrostatic gas seals. The partial LST consists of higher density dimples over a certain portion of the sealing dam width, adjacent to the high pressure side, leaving the remaining portion untextured. The textured portion provides an equivalent larger gap that results in converging clearance in the direction of pressure drop, and hence hydrostatic pressure build up, similar to that of the radial step seal.

New LST technology was developed by SurTech Ltd. The technology allows forming a regular micro surface texture of given parameters, which results in a significant reduction of friction force, wear ratio, and extending the life span of the seal. A detailed dimensionless analysis was performed to find the appropriate laser texturing parameters, which would provide maximum load carrying capacity and lubricant stiffness with minimum gas leakage through the seal boundaries.

A mathematical model was developed, based on the solution of the Reynolds equation for compressible Newtonian fluid in a narrow gap between two surfaces. The finite differences method was used for the numerical solution.

The pressure distribution and load carrying capacity for a single 3D dimple, representing the LST, were obtained via two different methods of analysis; a numerical solution of the exact full Navier-Stokes equations, and an approximate solution of the much simpler Reynolds equation.  Comparison between the two solution methods was performed, in order to investigate the validity limits of the Reynolds lubrication theory for realistic geometrical and physical parameters of the LST.