Tribology,lubricants and lubrication engineering — a review

In this review paper more than 200 papers published between 1974 and 1976 are evaluated. These papers deal with the fundamentals of friction, wear and lubrication, including the state of friction, lubrication and materials. Another important subject is the analytical data and properties of mineral oil and synthetic lubricants, lubricating greases, additives and solid lubricants. Lubrication systems and lubricating devices as well as the lubrication of bearings, gears and internal combustion engines are also covered. Lubricants for machining processes and for metalworking are reviewed, as well as questions concerning the testing and evaluation of lubricants.     

The tribological performance of DLC-based coating under the solid–liquid lubrication system with sand-dust particles

Combination of solid and liquid lubricants to meet emission or environmental requirements of future tribological systems while providing the levels of desired friction and wear performance have received considerable research attention in the near term. The aim of the present work was to investigate the tribological behavior of oil-lubricated (PAO, PFPE, SO, IL and MAC) DLC coated surfaces under the conditions without and with sand-dust particles. The effects of applied load, frequency, and sand-dust particles on the tribological performance of DLC coating were systemically studied. The analysis results showed that solid–liquid lubricating coatings including SO and IL exhibited excellent anti-friction (～0.026) but relative poor wear-resistance performances under the conditions without and with sand-dust environments. But for PFPE and PAO, they demonstrated the worst tribological behaviors with high friction coefficient and wear rates. The added sand-dust particles lead to the wear rates to the one order of magnitude large than that without sand-dust conditions for all the selected liquid lubricants. The viscosity, contact angle and work of adhesion played an important part in affecting the tribological performances. The lubrication regimes in Stribeck curve for the five kinds of liquid lubricants were affected obviously by the sand-dust particles in different way. The formed transfer films on the coating surface and pin have much influence on the tribological behavior and the transition between lubrication regimes.     

Design of heavy-duty bearings with oil–air lubrication

Analytical formulas are obtained for the thermal state of a bearing with oil–air lubrication; the viscosity class of the lubricant is taken into account. Recommendations are made regarding the structure of the oil-supply channels and the sealing of the frictional module.     

Wheel/rail adhesion—Boundary lubrication by oily fluids

Oils on rails are present in minute quantities and are found to be complex mixtures containing an unusually high proportion of chemically active compounds. Laboratory experiments are described which study how such oils and related compounds affect friction when present in surface concentrations similar to those found on the track. The friction is sensitive to small changes in the quantities present, and this gives an explanation why adhesion varies on dry rails. All types of fluid give similar results. Simple mixtures can be dominated by an active, low-friction component but the friction of oils appears to be an “average” of their many components. High humidity during specimen preparation promotes lower friction. It is suggested this is due to its effect on the physical properties of the oxide formed on the steel surface.     

The joy of a ＂Greenfield＂

管理者为什么不是在每一个业务开始的时候就把精益包含进来,而是更愿意扩大规模直到意识到关键流程出了问题或者难以控制、开始影响继续增长或获利能力时,才想到精益呢？     

A study on the energy efficiency improvement of greenhouses — with a focus on the theoretical and experimental analyses

Most greenhouses in Korea are made according to European weather conditions, which leads to very low solar energy efficiency under the domestic weather conditions. Thus, greenhouses in Korea should be adapted to the regional weather conditions to improve their energy efficiency. This paper investigates the current greenhouses in Korea. It also analyzes the problems arising from the greenhouses and offers alternatives for improving their energy efficiency based on measurements and a theoretical analysis. The elements of greenhouses were also investigated. When using a partially non-transparent insulation with heat storage mass between the indoor and outdoor air, the temperature difference became greater than 20°C during the daytime and greater than 5°C during the night, which will reduce the cost of fossil fuels.     

A coupled thermal–mechanical analysis of a mold-billet system during continuous casting

The three-dimensional (3-D) thermal–mechanical behavior of a mold–billet system under actual casting conditions is investigated with an finite element approach, taking into account the main influencing factors, such as solidification heat, latent heat released during phase transformation, heat transfer, as well as the interaction between the moving billet and the mold. It is based on the coupled thermal–mechanical analysis for the whole mold–billet system, instead of analyzing the thermal–mechanical behavior of the mold and the billet individually, as is often used in practice. Comparison shows that the former approach can provide satisfactory results without making use of the empirical estimation of the heat flux through the inboard surface of the mold based on the difference between the temperature of inlet and outlet cooling water at steady-state and the temperature distribution near the surface of the inboard plate measured experimentally, which are usually necessarily required for the latter approach to be applied in practice.     

A lubrication equation including slip velocity for hydrodynamic porous bearings in the lower turbulent regime — a perturbation approach

A first attempt is made to analyse pressure development in the form of a new lubrication equation including slip velocity for finite self-acting hydrodynamic porous metal bearings operating in the turbulent regime (fully developed) with a single phase Newtonian incompressible lubricant. The derivation is based on the analogy of boundary layer theory wherein lubricant motion is treated as a generalized turbulent channel flow in which the impermeable wall is in motion and the porous wall is stationary. The type of flow varies from pure couette flow to shear flow coupled with codirectional and transverse pressure flow. A linearization (or perturbation) technique is used to decouple the two orthogonal flows by assuming that the shear stress in a finite bearing is a small perturbation of the shear stress valid for couette flow. Using Boussinesq's eddy viscosity formulation and the wellestablished power law as a universal law of wall, the governing pressure distribution equation is obtained from considerations of the conservation of momentum and continuity. The surfaces are considered to be hydrodynamically smooth. The whole treatment is approached from the viewpoint of fluid film design rather than from a fundamental fluid mechanics approach. No slip model has been used. The lubrication equation is fully analytical and can be applied to a number of particular bearing problems by using the simplifying restrictive conditions. The lubrication equation derived can be used to predict the bearing performance characteristics even in situations where the permeability of the bearings is anisotropic and the Poiseuille flow in the porous matrix does not obey Darcy's law.     

Vibroacoustic: The challenges of a mission impossible?

Why it is difficult to solve a vibroacoustic problem; what are the hidden pitfalls that one is called to overcome; are there methods or techniques suggested in other fields of physics that can help to formulate an efficient vibroacoustic prediction model? The authors provide personal answers to these questions and suggest also a classification of the numerous prediction methods proposed in the literature.     

Assessment of a turbulence model for numerical predictions of sheet-cavitating flows in centrifugal pumps?

Various approaches have been developed for numerical predictions of unsteady cavitating turbulent flows. To verify the influence of a turbulence model on the simulation of unsteady attached sheet-cavitating flows in centrifugal pumps, two modified RNG k-? models (DCM and FBM) are implemented in ANSYS-CFX 13.0 by second development technology, so as to compare three widespread turbulence models in the same platform. The simulation has been executed and compared to experimental results for three different flow coefficients. For four operating conditions, qualitative comparisons are carried out between experimental and numerical cavitation patterns, which are visualized by a high-speed camera and depicted as isosurfaces of vapor volume fraction α _v = 0.1, respectively. The comparison results indicate that, for the development of the sheet attached cavities on the suction side of the impeller blades, the numerical results with different turbulence models are very close to each other and overestimate the experiment ones slightly. However, compared to the cavitation performance experimental curves, the numerical results have obvious difference: the prediction precision with the FBM is higher than the other two turbulence models. In addition, the loading distributions around the blade section at midspan are analyzed in detail. The research results suggest that, for numerical prediction of cavitating flows in centrifugal pumps, the turbulence model has little influence on the development of cavitation bubbles, but the advanced turbulence model can significantly improve the prediction precision of head coefficients and critical cavitation numbers.     

Use of a higher order Heydemann–Welch model to characterize a controlled clearance piston gauge

We present a new method for characterizing a controlled-clearance piston gauge as a primary pressure standard. This method requires operating the piston gauge to jacket pressures of over 80% of the system pressure. We present measurements on a hydraulic piston gauge with a 290 MPa maximum pressure and a nominal piston diameter of 3.27 mm. Measurements showed that the cylinder becomes stiffer as the jacket pressure increases, and that non-linear models of the Heydemann–Welch parameters improve the determination of the effective area. The relative standard uncertainty in the effective area of the piston gauge ranges from 16.0 × 10⁻⁶ to 17.6 × 10⁻⁶, and the agreement to the present NIST pressure scale is within the standard uncertainty.     

Capacity sharing in a network of enterprises using the Gale–Shapley model

In this paper, we analyze a model of capacity sharing for a set of independent firms, geographically distributed, that often have to implement an opportune tool to integrate their resources and demand forecasts in order to gather a specific production objective. We formulate the problem as a cooperative game and identify a capacity sharing solution using the Gale–Shapley model. The allocation rule takes into account the utility functions of the involved firms, and we show how the capacity allocation rule can be designed to induce all firms to report truthfully their information. Moreover, we show that, under this allocation rule, truth telling is a dominant strategy, with each firm reporting truthfully its private information, regardless of the reporting decisions of other firms. Moreover, the proposed research develops a distributed approach able to facilitate the capacity sharing process by using a multi-agent architecture; then a discrete simulation environment has been developed to compare the proposed approach with a centralized one. Several simulation scenarios were conducted to analyze the performances' trends in various environment conditions.     

The Analysis of the Lubrication Condition and Friction Losses of a Single Acting Cross Head Guide Shoe of a Low Speed Cross Head Diesel Engine: Part I—An Alogrithm For The Prediction of Oil Film Thickness

The lubrication condition pertaining to the cross head guide shoe of a low speed cross head diesel engine is evaluated in this paper under the principles of hydrodynamic lubrication. The Reynolds differential equation which describes the pressure and oil film thickness distribution of the cross head guide shoe system operating under unsteady load will be solved using a finite difference method. The influence of the width to length ratio of the rectangular cross head guide shoe plate will be considered in terms of variation of the pressure distribution within the bearing and its load carrying capacity.     

Ester Oxidation—The Effect of an Iron Surface

Carboxy ester oxidation on a low-carbon steel (iron) surface was studied at temperatures of 448 to 523 K to determine the extent of surface reaction between iron and oxidation products. The reaction was followed by semiquantitative analysis of dissolved iron using atomic absorption spectroscopy and by measuring the amount and molecular weight of the polymeric oxidation products using gel permeation chromatography. In contrast to reaction at an aluminum surface, reaction at the iron surface appeared to affect the molecular weight distribution of oxidation polymer and produced soluble iron products that homogeneously catalyzed ester degradation. The formation of soluble iron products was found to be extremely temperature-dependent, related to the degree of oxidation, and almost totally suppressed by a known metal coater—tricresyl phosphate (TCP). Evidence of a similar chemical reaction between carboxy ester oxidation products and an iron surface in the contact zone of an ester-lubricated, four-ball wear test is discussed.     

Cryoprocessing of cutting tool materials—a review

Cryoprocessing, a supplementary process to conventional heat treatment process, is the process of deep-freezing materials at cryogenic temperatures to enhance the mechanical and physical properties of materials being treated. The execution of cryoprocessing on cutting tool materials increases wear resistance, hardness, and dimensional stability and reduces tool consumption and down time for the machine tool set up, thus leading to cost reductions. The effects of cryoprocessing on tool steels and carbides, metallurgical aspects including reduced amount of retained austenite, precipitation of η-carbides, phase change in carbides, improvement in wear resistance, and applications are reviewed for manufacturing industry. Although it has been confirmed that cryogenic processing can improve the service life of tools, the degree of improvement experienced and the underlying mechanism remains ambiguous. The steps involved in cryoprocessing are critical enough to account for the significant incongruity in post-treated performance.