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.     

Wear mechanisms in materials with granitic textures—Applicability of a lateral crack system model

In petreous materials, the mechanisms causing wear are several depending on which system we need to focus in. This work describes how it is possible to employ the lateral crack system, initially outlined to explain the wear of ceramic materials, to understand the wear of materials with granitic textures (granite, granodiorite, gabbro, quartzite,…) while being processed by diamond tools. For assessing the wear parameters of ten types of stones a new experimental procedure was developed and optimised to provide accurate measurements of specific energies and resultant forces as, at the same time, considers the impact that each stone has in the wear of a standard tool. The experimental results show the applicability of the lateral crack system in stones. Following a lateral crack system model, it was possible to attain a relation between the volume loss caused by a diamond tool and the macro-mechanical properties of the stone (hardness, Young's modulus and fracture toughness) while knowing the normal force applied during the erosive wear.     

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.     

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.     

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.     

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.     

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 mechanism of fretting — A review

The article attempts to bring up-to-date the known facts concerning the mechanism of fretting wear in metals with special reference to the common engineering materials iron and steel under normal conditions. The process can be divided into three stages, those of initial adhesion and metal transfer, the production of debris in a normally oxidised state and, finally, the steady-state wear condition. Once metallic contact is established, the ease of which is represented by the oxide-metal hardness ratio, the resultant adhesion coefficient reflects the subsurface deformation involved. Oxidation occurs as a direct result of mechanical deformation promoting free surface and internal defects favouring adsorption of gaseous oxygen followed, subsequently, by its dissociation. Abrasion as a cause of fretting damage is favoured only as a minor factor, the majority of damage being initiated in the initial stages and being reflected in the steady-state dispersal of debris.     

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.     

The natural frequencies of portal frames—I

The oscillations of a single-storey, single-bay portal frame have been investigated. The particular case of a frame having identical columns which differ from the cross-beam has been studied in detail for the limiting cases of (a) encastré footing, (b) pinned footing. The effect of weight ratio, stiffness ratio and length ratio between columns and cross-beam on the lowest asymmetrical mode and on the lowest symmetrical mode has been determined, and the results have been prepared as tables in terms of dimensionless parameters. These tables allow the natural frequencies of a particular frame to be determined accurately by linear interpolation for wide ranges of frame proportions.     

The natural frequencies of portal frames—II

The oscillations of plane single-storey multi-bay portal frames in which the columns are identical and the cross-beams form a continuous uniform beam have been investigated. The frequency equations, allowing for the effects of footing restraints, and for the effects of mass ratio, stiffness ratio, and length ratio between columns and cross-beams, have been developed. The computed solutions of the frequency equations have been compared with the experimental results for a number of frames and good agreement has been found.     

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.     

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.     

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.