Effect of Manufacturing Errors on Static Characteristics of Externally Pressurized Spherical Air Bearings

Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manufacturing errors are unavoidable, and the pursuit to enhance the manufacturing accuracy will increase the cost greatly. In order to provide some theoretical guideline for the tolerance choice in the design of the externally pressurized spherical air bearings with inherent compensation, the effects of several manufacturing errors on the static characteristics of the air bearing are studied. Due to the complex geometry of the computational domain, an unstructured meshing technology is used for mesh generation. A finite-volume method is adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations. A modified SIMPLE algorithm which is suitable for compressible flows is applied to solve the discretized governing equations. The effects of the dimension error and the roundness error of the ball head and the ball socket on the static characteristics are investigated. The investigation result shows that the positive dimension error and the oblate spheroid-type roundness error of the ball head as well as the negative dimension error and the prolate spheroid-type roundness error of the ball socket can improve the bearing capacity and static stiffness of the air bearings by reducing the mass flow. The calculation method proposed in this paper fits well for the general principle, which can be extended to the characteristics analysis of other air bearings.

Investigation on MoS_2 and Graphite Coatings and Their Effects on the Tribological Properties of the Radial Spherical Plain Bearings

With constant enlargement of the application areas of the spherical plain bearings,higher quality lubrication of the bearings is required.To solve the lubricating problems of spherical plain bearings under high temperature,high vacuum,high speed,heavy loads and strong oxidation conditions,it is urgent for us to develop more excellent self-lubricating technologies.In this paper,the bonded solid lubricant coatings,which use inorganic phosphate as the binder,the mixture of MoS2 and graphite with two different weight proportions as the solid lubricant,are prepared by spraying under three different spray gun pressures.The bonding strength tests on the coatings show that the best spraying pressure is 0.2 MPa and the better mixing proportion of MoS2 to Graphite is 3：1.Then for the radial spherical plain bearings with steel/steel friction pair,after the coatings are made on the inner ring outer surfaces,the friction coefficient,the wear loss and the friction temperature of the bearings under four oscillating frequencies are investigated by a self-made tribo-tester.The test results,SEM of the worn morphologies and EDS of worn areas show that tribological properties of the bearing are obviously improved by the bonded solid lubricant coatings.When sprayed under the spray gun pressure of 0.2 MPa,the bearings have better anti-friction and anti-wear properties than those sprayed under 0.1 MPa and 0.3 MPa.Further as proved from the XPS analysis,between the coating with 3：1 mixing ratio of MoS2 to Graphite and the coating with 1：1 ratio,the former has less oxidation occurred on the surface and therefore has better tribological characteristics than the latter.This paper provides a reference to developing a new product of the radial spherical plain bearings with high bonding strength,oxidation resistance and abrasion resistance.

Analysis of Thermoelastohydrodynamic Performance of Journal Misaligned Engine Main Bearings

To understand the engine main bearings＇ working condition is important in order to improve the performance of engine. However, thermal effects and thermal effect deformations of engine main bearings are rarely considered simultaneously in most studies. A typical finite element model is selected and the effect of thermoelastohydrodynamic（TEHD） reaction on engine main bearings is investigated. The calculated method of main bearing＇s thermal hydrodynamic reaction and journal misalignment effect is finite difference method, and its deformation reaction is calculated by using finite element method. The oil film pressure is solved numerically with Reynolds boundary conditions when various bearing characteristics are calculated. The whole model considers a temperature-pressure-viscosity relationship for the lubricant, surface roughness effect, and also an angular misalignment between the journal and the bearing. Numerical simulations of operation of a typical I6 diesel engine main bearing is conducted and importance of several contributing factors in mixed lubrication is discussed. The performance characteristics of journal misaligned main bearings under elastohydrodynamic（EHD） and TEHD loads of an I6 diesel engine are received, and then the journal center orbit movement, minimum oil film thickness and maximum oil film pressure of main bearings are estimated over a wide range of engine operation. The model is verified through the comparison with other present models. The TEHD performance of engine main bearings with various effects under the influences of journal misalignment is revealed, this is helpful to understand EHD and TEHD effect of misaligned engine main bearings.

INVESTIGATION ON THE APPLICATION OF THE BOUNDARY ELEMENT METHOD TO THE SPILL GROOVED THRUST BEARING

An application of the boundary element method (BEM) is presented to calculate the behaviors of a spiral grooved thrust bearing (SGTB). The basic reason is that the SGTB has very complex boundary conditions that can hinder the effective or sufficient applications of the finite difference method (FDM) and the finite element method (FEM), despite some existing work based on the FDM and the FEM. In other to apply the BEM, the pressure control equation, i. e., Reynolds' equation, is first transformed into Laplace's and Poisson's form of the equations. Discretization of the SGTB with a set of boundary elements is thus explained in detail, which also includes the handling of boundary conditions. The Archimedean SGTB is chosen as an example of the application Of BEM, and the relationship between the behaviors and structure parameters of the bearing are found and discussed through this calculation. The obtained results lay a solid foundation for a further work of the design of the SGTB.

A Pipeline Fracture Model of Hydrogen-induced Cracking

The relationship between hydrogen concentration and crack tip stress, strain field, hydrogen diffusion and internal pressure respectively in the crack tip process zone was investigated, and the length of the crack tip process zone of hydrogen-induced cracking （HIC） was determined. Based on the mechanism of fracture of micro-crack nucleation, a dislocation model was presented for the fracture criteria of HIC. The influence factors of pipeline tube fracture ductile KISCC in the presence of hydrogen was analyzed, and the critical pressure bearing capability of a pipeline with hydrogeninduced cracking and the critical J-integrity （JISCC） were calculated, which is very important for pipeline safety.

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relation- ship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.

The Relationship between Natural Resources and Population Development in Liaocheng City

According to the relevant data about the land resources and population in Liaocheng City from 1999 to 2008, by using the research method of bearing capacity of natural resources, the thesis analyzes the relationship between natural resources and dynamic change of population in Liaocheng City. The results show that the farmland tends to diminish on the whole, and forests, garden land, urban-rural settlements and land for enterprises and mining increase slowly. Based on the analysis of the dynamic relationship between land resources and population, we conclude that the land resources still can bear the current population in Liaocheng City, but the population development inflict critical pressure on the forest resources and water resources.

Design and Key Technology of Oil-Free Centrifugal Air Compressor for Hydrogen Fuel Cell

For a 120 kW hydrogen fuel cell system,a centrifugal air compressor with fixed power of 22 kW fuel cell is designed.Firstly,the theoretical calculation is carried out for the aerodynamic characteristics of a ultra-high-speed permanent magnet synchronous motor,an air compressor,and an aerodynamic foil bearing.Then,a prototype is trial-produced and a related test bench is built for test verification.Finally,both the simulation and test results indicate that the designed centrifugal air compressor meets the overall requirements of the hydrogen fuel cell system,and the relevant conclusions provide both theoretical and experimental references for the subsequent series development and design of the centrifugal air compressor.

Adjustable superlubricity system using polyalkylene glycol with various acid aqueous solutions

Polyalkylene glycol(PAG)aqueous solutions have recently been demonstrated to exhibit an ultralow friction coefficient(COF,μ<0.01).However,the prolonged running-in period and low bearing capacity have limited its widespread application.In this study,we determined that the running-in period can be decreased by more than 75%when the pH value of the lubricant is controlled at 3 by introducing various acid solutions.Additionally,less time was required to realize stable superlubricity with inorganic acid at lower pH values.This was mainly attributed to the acceleration effect of hydrogen ions around the contact region.In case of PAG aqueous solution with organic acid,the wear loss between sliding solid surfaces was reduced,and thus the bearing pressure during the superlubricity period was significantly improved from approximately 30 to 160 MPa.Furthermore,the organic acid molecules were considered to form strong hydrogen bonds with PAG macromolecules and solid surfaces.This in turn strengthened the structure of the adsorption layers.The unique effect of different acids in aqueous polymer lubrication can potentially significantly aid in advancing the study of polymer tribology and broadening industrial applications.