Investigating the Lubricity and Electrical Insulation Caused by Sanding in Dry Wheel–Rail Contacts

The adhesion (or available friction) in the wheel–rail contact is the most important parameter for the braking and traction operation of rail vehicles. Since the beginning of railway transportation, sanding from the locomotive has been a common practice to enhance the wheel–rail adhesion. In recent years, sanding from electrical multiple units (EMUs) and sand-based friction modifiers (FMs) have been adopted in some railway networks to overcome low adhesion incidents caused by leaf contamination in autumn. Although sanding has been proven to improve the adhesion under most of the typical contamination conditions, laboratory and field investigations have shown that sand may act as a solid lubricant in dry wheel–rail contacts. Nevertheless, the influence of the current sanding parameters on the solid lubrication effect has not been entirely investigated. Depending on the resulting adhesion coefficient, the traction and braking operations of rail vehicles could be affected. Furthermore, the influence of those parameters on the electrical insulation is also of special importance because it may affect the train detection. This article presents a laboratory investigation of the influence of three sanding parameters (i.e., feed rate, particle size, and slip) on the adhesion and electrical insulation in dry wheel–rail contacts. The tests have been carried out with a twin-disk roller rig in rolling-sliding motion under closely controlled conditions. Three different slips representative of the actual traction and braking operations have been considered. Sands of four different sizes and up to five feed rates have been used. The results show that using smaller particle sizes and higher feed rates promotes the lubrication and causes more electrical insulation in the wheel–rail contact. Furthermore, the increase in slip is found to reduce the lubrication, leading to a higher adhesion coefficient.     

Measurement of Pressure Distribution in EHL—Development of Method and Application to Dry Static Contacts

The development and application of a new technique to measure the pressure distribution in an elastohydrodynamic contact is described. The method uses optical interferometry to measure the local compression of a thin elastic layer sandwiched between the loaded surfaces. The elastic-layer thickness is mapped as a line profile across the contact and the measured compression is calibrated to give a pressure distribution. The data are acquired through a single triggered image rather than a scanning system so that transient pressures can be measured. The current study is limited to static contacts, and pressure profiles are presented for a number of contact conditions. These include smooth and textured surfaces and entrained debris. The results are compared to theoretical predictions for smooth surfaces.     

Experimental Study of the Spatial Resolution of a Spherical Quartz Crystal for X rays at a Wavelength of 8.42 Å

The results of an experimental study of the spatial resolution of a spherical quartz crystal for X rays at = 8.42 Å are presented. An experimental design for the two-dimensional X-ray imaging of test objects was used to determine the spatial resolution of such a crystal. The crystal resolution measured using an image scan was 2 m for the Gaussian point spread function.     

Environmental Effects on the Composition of Surface Films Produced by an Organo-Molybdenum Compound©

The influence, of environments on the properties of the surface films formed, with molybdenum dithiocarbamate (MoDTC) was examined under a reciprocating sliding condition. MoS₂ was formed on the rubbing surfaces in air and oxygen, and molybdenum compounds with an oxidation state lower than MoS₂ were produced in nitrogen and argon. The surface film composed of MoS₂ was effective in reducing the friction and wear, while the molybdenum compound formed in nitrogen or argon had no ability to prevent direct contact between the rubbing surfaces and to reduce the friction. It was a necessary condition for forming the surface film composed of MoS₂ that the environment to be rubbed contained oxygen at a concentration above a certain level.     

Analysis of Viscosity Interaction and Heat Transfer on the Dual Conical-Cylindrical Bearing©

Viscosity is an essential property in hydrodynamic lubrication. In general, the lubricant is not considered to have uniform viscosity within a given bearing. The viscosity of the lubricant is affected by both pressure and temperature. The viscosity of the lubricant increases with pressure and, for most lubricants, this effect is much larger than that of temperature or shear when the pressure is significantly above atmospheric pressure. This study analyzes the thermal effect of dual conical-cylindrical bearing performance parameters via the viscosity-pressure-temperature relationships of lubricants. The results reveal that pressure increases both the film viscosity and temperature.     

Specific Film Thickness—A Closer Examination of the Effects of EHL Film Thickness and Surface Roughness on Bearing Fatigue

Analysis of literature bearing-fatigue life results shows that fatigue life is not a simple function of the widely accepted specific film thickness, λ, which is the ratio of the EHL film thickness h to composite surface roughness [sgrave]. Instead, the influence of film thickness on bearing life increases with increasing surface roughness; at about 0.20 micrometer (8 microinch) composite roughness life increases with the square root of h while at about 0.46 micrometer (18 microinches) life increases with h squared.

The negative effect of surface roughness on bearing life appears to be relatively independent of film thickness. This suggests that surface roughness affects fatigue life by some mechanism in addition to the degree of interaction of asperities through an intervening EHL film. Additional test results are needed to confirm this point.     

The Effect of Dwell Time on the Static Friction in Creeping Elastic–Plastic Polymer Spherical Contact

A theoretical model is developed to study the effect of dwell time on the junction growth and static friction of a creeping polymer sphere in contact with a rigid flat under full stick contact condition. A rapid normal loading into the elastic–plastic contact regime is followed by a rest period during which creep takes place causing contact area growth, and stress relaxation that can completely eliminate the plastic zone in the sphere. At the end of this rest time, an increasing tangential loading is applied to the flat till sliding inception occurs. During this loading step, further increase of the contact area and reappearing of a plastic zone in the sphere take place. An increase in static friction resulting from the dwell time during the creep stage is clearly demonstrated and explained.     

Comparison of the Dynamic Behavior and Lubrication Characteristics of a Reciprocating Compressor Crankshaft in Both Finite and Short Bearing Models©

The compression force of refrigerant gas, the viscous and inertial force of the piston, and the centrifugal force of balancer weight induce rotating whirl of the crankshaft in a small reciprocating compressor. It is necessary to develop an analytical model for the accurate prediction of dynamic behavior of the compressor mechanism having coupled characteristics between the piston and crankshaft. The reciprocating compression mechanism is dynamically modeled by considering the viscous frictional force of a piston and the variation in the contact length of the piston-cylinder system, and then numerical analysis is performed for the coupled dynamic behavior of the piston and crankshaft. For the accurate predictions of the dynamic behavior and characteristics of lubrication of the crankshaft-journal bearing system, a finite bearing model is adopted. In addition, the dynamic trajectory and characteristics of lubrication of the crankshaft such as power consumption and oil leakage are compared between the finite bearing model and the short bearing approximation. The influences of the variation in the radial clearance of the journal bearings, lubricant viscosity, and mass and mass moment of inertia of the piston and connecting rod on the dynamic behavior and characteristics of lubrication such as power consumption and oil leakage are investigated.     

An Experimental Setup for Studying the Solubility and Phase Transitions in a Hydrocarbon–Supercritical CO2 System in a Wide Range of Pressures and Temperatures

Instruments and Experimental Techniques - A system for saturating a porous medium with hydrocarbon and supercritical CO2 has been designed. A procedure for carrying out an experiment on the...     

Comparisons of TEHL Simulations of Newtonian Fluids in Line Contacts between the 3D FEM and the Reynolds Equation–Based Approaches*

Thermoelastohydrodynamic lubrication (TEHL) analysis of line or point contacts is usually done by simultaneously and numerically solving the Reynolds equation, the Boussinesq equation of an elastic semi-infinite body, the energy conservation equation, and the load balance equation. Although a number of publications are available in this field, there is still a lack of general-purpose and widely used TEHL software for engineering applications. On the other hand, commercial software for both the solid structure and fluid flow analyses have become easy design tools. To expand the application of the commercial software to TEHL simulation, coupling of structure and fluid analyses is required. This study gives some demonstrations of the 3D finite element method (FEM) simulations of line contact TEHL problems using ANSYS version 13.0. The equilibrium equations of momentum and continuity and the energy conservation equation of lubricating fluids are solved with CFX. The elastic deformation of solids is calculated with the ANSYS Structure module. Through the fluid–solid coupling interfaces, the fluid pressure, solid deformation, and thermal flow are transferred between the fluid and solid domains. The computational fluid domain is enlarged, enclosing the contact zone, in the 3D model. Further, the 3D model can treat the realistic constraint conditions of solid deformation, whereas conventional TEHL analysis uses the assumption of semi-infinite body. The simulation results for pressure, lubricant film thickness, and temperature distributions are compared with the traditional Reynolds approach, and reasonable agreement for pressure and film thickness distributions has been obtained.     

The Role of Surface Films in the Frictional Behavior of Lubricated and “Dry” Contacts—A Unifying Influence in Tribological Theory

The paper identifies the essential physical ingredients of tribological systems. Using a simple model incorporating surface roughness and a surface film, the general behavior of both solid and lubricated films may be anticipated. Nonetheless, several important gaps in our physical knowledge of contacts are identified. Further work in these areas would greatly enhance the concepts presented in this paper.     

Tribological Characteristics of NiAl Matrix Composites with 1.5 wt% Graphene at Elevated Temperatures: An Experimental and Theoretical Study

In this study, the tribological properties of NiAl matrix composites with 1.5 wt% graphene nanoplatelets (NAG) at elevated temperatures were simulated and tested. NAG exhibits excellent characteristics at 100 and 200°C due to the formation of metal oxides and graphene nanoplatelets lubrication film. Furthermore, the removed layer thickness, the stress distributions, and the high stresses of the affected layer have been estimated theoretically. At 400°C, the friction coefficient increased due to the absence of the lubrication layer. In addition, the wear rate increased due to the excessive stresses, the increased layer thickness removal, and the propagation of subsurface cracks.     

Roll System and Stock’s Multi-parameter Coupling Dynamic Modeling Based on the Shape Control of Steel Strip

The existence of rolling deformation area in the rolling mill system is the main characteristic which distinguishes the other machinery. In order to analyze the dynamic property of roll system’s flexural deformation, it is necessary to consider the transverse periodic movement of stock in the rolling deformation area which is caused by the flexural deformation movement of roll system simultaneously. Therefore, the displacement field of roll system and flow of metal in the deformation area is described by kinematic analysis in the dynamic system. Through introducing the lateral displacement function of metal in the deformation area, the dynamic variation of per unit width rolling force can be determined at the same time. Then the coupling law caused by the co-effect of rigid movement and flexural deformation of the system structural elements is determined. Furthermore, a multi-parameter coupling dynamic model of the roll system and stock is established by the principle of virtual work. More explicitly, the coupled motion modal analysis was made for the roll system. Meanwhile, the analytical solutions for the flexural deformation movement’s mode shape functions of rolls are discussed. In addition, the dynamic characteristic of the lateral flow of metal in the rolling deformation area has been analyzed at the same time. The establishment of dynamic lateral displacement function of metal in the deformation area makes the foundation for analyzing the coupling law between roll system and rolling deformation area, and provides a theoretical basis for the realization of the dynamic shape control of steel strip.     

An ultrahigh-vacuum multifunctional apparatus for synthesis and in situ investigation of low-dimensional structures by spectral magnetoellipsometry in the temperature range of 85–900 K

This paper presents the results of modernizing an ultrahigh-vacuum multifunctional apparatus that allows one to obtain semiconductor or metallic nanostructures in a single technological cycle and to investigate their optical and magneto-optical properties in a temperature range of 85–900 K. The capabilities of the developed system were demonstrated based on the example of studying the temperature dependence of the bulk Si permittivity via spectral ellipsometric measurements.     

Friction and Wear Characteristics of TiN Coated Vane for the Rotary Compressor in a R410A Refrigerant©

HFC is a potential alternative refrigerant for CFC, which depletes the ozone layer. The rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. R410A, an HFC refrigerant, is used in a refrigerator compressor, but its frictional characteristic is not established. In this study, the influence of R410A refrigerant on the roller-vane surfaces was studied, and friction and wear characteristics of the TiN coated vane were investigated. The friction and wear data were obtained with a specially designed high-pressure wear tester. A testing environment charged with HFC refrigerant more closely simulates the operating conditions of a real rotary compressor. In pure oil without R410A, wear of the TiN coated vane was larger than that of the uncoated vane. But when the refrigerant was dissolved in oil, wear of the uncoated vane was larger than that of the TiN coated vane. This showed that a TiN coated vane is good relative to wear resistance in the refrigerant/lubricant mixed environment. As the rotating speed of the frictional motion increased, wear increased. But in the high-velocity region, wear decreased because the boundary lubrication is changed into the mixed lubrication in the lubrication region. As the pressure grew larger, wear volume and coefficient of friction became larger. This is because the amount of the refrigerants dissolved in oil increased and the viscosity of oil dropped as the pressure increased.