EHL squeeze at pin-pulley interface in CVTs: Influence of lubricant rheology

In this paper we analyze the influence of fluid rheology on the strongly non-stationary squeeze process of an oil film sandwiched between the chain-pin and pulley in continuously variable transmission. As recently demonstrated [Carbone G, Scaraggi M, Soria L. The lubrication regime at pin-pulley interface in chain CVT transmissions. ASME Journal of Mechanical Design 2009;131(1)], the spatial pressure distribution is characterized by a non-central annular pressure peak, which first appears in the external region of the contact region and moves toward the center of the pin with rapidly decreasing speed. In this paper we show that the non-Newtonian viscoelastic rheology of the lubricant plays a crucial role in determining the actual value of pressure peaks and leads to a strong reduction of such pressure spikes in comparison to a perfect Newtonian lubricant. Even more, if the threshold value of shear stress τ_l, which characterizes the transition from Newtonian to non-Newtonian behavior of the lubricant, is sufficiently small the annular pressure peak may even disappear. In this case the squeeze process occurs faster, the film thickness distribution is reduced and the lubricant may not be able to avoid direct asperity contact between the two approaching surfaces.     

普通量仪测量凸轮的方法构思及测点坐标求解

论述了在通用光学测量仪器(“万工显”、“大工显”、投影仪)上,采用影像法模拟直动对心式(或偏置式)滚柱测头、刀口测头、平面测头测量发动机凸轮的方法.分析和实践表明,该方法测量简便、快速、准确度高,满足了没有专用凸轮测量仪的非专业生产厂家发动机凸轮精密测量的需要.     

A study of the effect of palm oil as MQL lubricant on high speed drilling of titanium alloys

The main objective was to study the potency of MQL palm oil (MQLPO) as a lubricant in the high speed drilling of Ti-6Al-4V. For the comparison, MQL synthetic ester (MQLSE), air blow and flood conditions were selected. Uniform flank wear, micro-chipping, thermal cracking and flaking were the dominant tool failure modes. It was found that MQLSE and MQLPO gave comparable performance with the flood conditions. In addition, MQLPO outperformed MQLSE on the cutting forces, temperature, power and specific cutting energy. This shows that palm oil can be used as a viable alternative to synthetic ester for MQL lubricant.     

高速回转件润滑状态测量方法的研究

本文提出一种测量高速回转件润滑状态的新方法，通地在摩擦副间施加一个大小可变的直流电压，利用润滑油（脂）膜瞬间被电压击穿的原理，进而对记录的信号波形进行分析，可分别获得摩擦副间的润滑膜厚度以及微观表面粗糙度等信息，用该方法对纺织机械中的高速回转件，诸如气流纺杯轴承和化纤锭子的润滑状态进行了测量，取得了较好的效果，从而为纺机高速回转零件在运转过程中润滑状态的测量提供了有效的测试手段。     

Numerical simulation of mold filling and deformation behavior in rheology forming process

Rheology forming is a novel semi-solid processing method, which is different from traditional mold forging and conventional casting processes. The rheological behavior of metallic alloys containing both solid and liquid phases investigated the low and high solid fraction ranges. Rheology forming has several obvious advantages including its excellent forming ability resulting in the easier production of complex work pieces, more flexibility in shaping pieces, and more compact inner quality because of its high pressure. This research paper presents the theory of the rheology forming process and the results of a finite element simulation of rheology forming for aluminum alloys. The algorithms for both a single- and two-phase flow model, developed for this study, gives the die filling patterns, velocities, temperatures and solid fractions of the rheology material during the rheology process. To calculate the velocity and temperature fields, the respective governing equations corresponding to the liquid and solid regions were used. Therefore, the respective numerical models that take the co-existing solid and liquid phases within the rheology material into consideration have been developed to predict the defects of parts manufactured by the rheology process. This study compares of the velocity, temperature, and solid fraction between the single- and two-phase flow models. And, to predict the liquid segregation in the parts, the deviation of velocity between the liquid and solid regions in the two-phase flow model was analyzed.     

转轴扭振测量方法研究

设计了扭振测量的多种方法。在两轴断面上装置编码器,测量一个编码器脉冲间隔时间、两个编码器相同编号的脉冲间滞后时间,用多种算法处理脉冲间隔时间和脉冲滞后时间,实时获取振动数据,分析测量精度。比较了各种方法,介绍采用高性能DSP(DigitalSignalProcessor)数字信号处理器实现转轴扭振测量中的关键技术。     

A method for measuring the inertia properties of rigid bodies

A method for the measurement of the inertia properties of rigid bodies is presented. Given a rigid body and its mass, the method allows to measure (identify) the centre of gravity location and the inertia tensor during a single test. The proposed technique is based on the analysis of the free motion of a multi-cable pendulum to which the body under consideration is connected. The motion of the pendulum and the forces acting on the system are recorded and the inertia properties are identified by means of a proper mathematical procedure based on a least square estimation. After the body is positioned on the test rig, the full identification procedure takes less than 10 min. The natural frequencies of the pendulum and the accelerations involved are quite low, making this method suitable for many practical applications. In this paper, the proposed method is described and two test rigs are presented: the first is developed for bodies up to 3500 kg and the second for bodies up to 400 kg. A validation of the measurement method is performed with satisfactory results. The test rig holds a third part quality certificate according to an ISO 9001 standard and could be scaled up to measure the inertia properties of huge bodies, such as trucks, airplanes or even ships.     

Effect of lubricant viscosity grade on mechanical vibration of roller bearings

This work aims to characterize vibration behavior of roller bearings as a function of lubricant viscosity. Experimental tests were performed in NU205 roller bearings, lubricated with mineral oil of three different viscosity grades (ISO 10, 32 and 68). The mechanical vibration was determined through the processing and analysis of bearing radial vibration data, obtained from each of the lubrication conditions, during 2 h of test run for temperature stabilization and under several bearing shaft speeds. The applied radial load was 10% of the bearing nominal load. Through root mean square (RMS) analysis of the vibration signals, it was possible to identify specific frequency bands modulated by the change in lubricant viscosity, which was related to change in oil film thickness.     

一种观察溶液浓度轮廓的新方法

提出了一种能够对溶液的浓度轮廓进行观察与测量的新的显微成像测量方法--暗场纹影法.这种方法是在纹影法(Schlieren Method)的基础上加以改进后形成的,能够用来对溶液的浓度轮廓进行观察.还给出了该方法原理性实验的观察结果,并与微分干涉显微镜的观察结果进行了对比.     

On the friction and wear performance of boric acid lubricant combinations in extended duration operations

Lubrication is critical for minimizing wear in mechanical systems that operate for extended time periods. Developing lubricants that can be used in engineering systems without replenishment – particularly those that are environmentally friendly – is very important for increasing the functional lifetime of mechanical components. In the present investigation, extended duration pin-on-disk experiments were carried out to determine the relative performance of a wide range of lubricant combinations in a commercial brake valve assembly. In the experiments, the lubricants were initially applied to the disk surface but were not replenished over a sliding distance of more than 6000 m. The experimental results revealed that the environmentally friendly lubricant boric acid was highly ineffective for reducing the wear in the surfaces tested. When combined with a commercial transmission fluid, however, the boric acid mixture proved to be highly effective in terms of both friction and wear performance. Based on the success of the combined lubricant experiments, the boric acid was then mixed with canola oil to form a completely natural lubricant combination. Based on further pin-on-disk experiments, this lubricant combination yielded the best wear performance of all the lubricants tested. The importance of these results, as related to the use of the natural lubricant combination in other engineering systems such as sheet metal stamping, was subsequently ascertained and discussed.     

Rheology of Perfluoropolyalkylether Fluids in Elastohydrodynamic Lubrication

The rheological characteristics of two branched and two linear, commercial perfluoropolyalkylether (PFPAE) fluids were studied under high pressures and temperatures. The effects of branching and carbon-to-oxygen (C:O) ratio on the pressure-viscosity-temperature behavior and on the non-Newtonian behavior of these fluids were studied experimentally under high pressures and temperatures. The branching and the higher C:O ratio seemed to increase the pressure-viscosity coefficients of these fluids. The effects of the viscosity and the pressure-viscosity coefficient on the capabilities of these fluids to generate elastohydrodynamic lubrication (EHL) film thickness were studied and compared with experimental measurements. All of the fluids studied seemed to follow the Roelands viscosity model and classical EHL theory (1). The C:O ratio also influenced the temperature dependence of the limiting-shear-strength proportionality constant. The results show that for similar-viscosity fluids, the linear PFPAE with higher C:O ratio is most desirable for wide temperature use.     

Measuring the tribological performance of all the tappets in a production engine using magnetometer sensors and the effect of lubricant rheology

Tappet rotation is one of the key tribological parameters that play an important role in component wear. Lack of available techniques has discouraged researchers from performing such studies on real production engines. In this research work, a novel experimental technique has been developed that allows the measurement of tappet rotation speed on any engine having direct acting tappets. This unique method does not require any changes or modifications to the components or engine itself. Using this innovative technique, for the first time, all the tappets of a single camshaft have been instrumented, and tappet speed was measured at different operating conditions verifying that not all the tappets behave in the same way. Experimental results clearly showed that all tappets do not respond to the change in lubricant viscosity and the direction of tappet rotation may be one of the factors influencing the performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Non-Newtonian Effects of Powder-Lubricant Slurries in Hydrostatic and Squeeze-Film Bearings

This paper presents the result of pressure measurements made in hydrostatic and squeeze-film bearings lubricated with a powder-lubricant slurry. The powder lubricant was powdered graphite and the carrier fluid was ethylene glycol. Pressure measurements compared favorably with analytical predictions based on a power law rheological model.

The behavior of ethylene glycol acting alone as a lubricant was also analyzed to provide a baseline for comparing the effects of the graphite powder additive on pressure and flow rate.

The hydrostatic bearing test showed that the addition of graphite powder into ethylene glycol can raise the load-carrying capacity of a lubrication system however pumping requirements are also raised. Squeeze-film bearing tests showed that the damping factor is increased with the addition of powdered graphite into the carrier fluid.     

Hydrodynamical modelling of lubricant friction between rough surfaces

The steady Couette flow of a Newtonian fluid between two plates, one of them a plane, the other one provided with riblets aligned perpendicular to the flow direction, is taken as a model for lubricant friction with wall roughness. In cases where the amplitude of the riblets is small compared to the riblet spacing, Reynolds lubrication approximation leads to an explicit solution. In contrast to this, a treatment of the full hydrodynamic equations is required for higher amplitudes. Under creeping flow conditions, an analytical treatment of the Stokes equations based on complex function theory allows for a reduction of the problem to the solving of ordinary differential and integral equations for functions of one variable. After this problem reduction, the resulting equations are solved by Fourier analysis and computer algebra.The resulting streamline patterns of the flow reveal the formation of vortices under certain conditions. Since these vortices act like a kind of fluid roller bearings, their influence on the drag force and material transport of the lubricant is studied.     

Compatibility between tribological surfaces and lubricant additives—How friction and wear reduction can be controlled by surface/lube synergies

This paper reviews the recent trends in materials technology and lubricant additive technology in engines. The paper will review key developments in surface engineering, application of nanocomposite materials and other advanced materials (including light alloys). It will also assess the trends towards “greener” lubricant additives, driven by environmental legislation and will discuss the implications for lubrication in the next decade. The key part of the paper will be to review the extent to which materials and lubricants are being used in partnership in engineering systems to capitalize on the synergies, which can exist between surfaces and lubricants in boundary lubrication. In a similar manner there are some important antagonisms that need to be identified—an appreciation of such compatibility issues can assist engineers in selecting a lubrication system.The paper will review existing literature from outside the work conducted by the authors and will substantiate some of the important aspects of boundary lubrication surface/lubricant compatibility through reference to some recent work conducted by the authors.     

极限剪切状态下的线接触Reynolds方程

本文导出了考虑极限剪切状态的线接触流变热弹流Reynolds方程,该方程以Evans—Johnson流变模型为基础,可用于求解线接触流变热弹流润滑问题的油膜厚度、压力分布、剪应力分布和牵曳系数曲线。计算实例表明,润滑油的流变特性对弹流润滑的油膜形状和压力分布影响不大,但对Hertz接触区的剪应力分布有显著影响。     

Novel viscosity determination method: Validation and application to fuel flow

The kinematic viscosity is a major physical property to be used in numerical, experimental and analytical work in all the related fields of fluid flow research. Its determination can be based on experiments with viscometer and on calculations for single or multi-species components, possibly through the use of mixture law and other intermediate parameters. Its experimental estimation for multi-species and/or supercritical hydrocarbon mixtures under high temperature and pressure remains quite absent. The novel approach proposed in this paper is based on fluid permeation through characterized porous media. The Darcian law or the Darcy–Forchheimer equation are used depending on the flow regime. First tests have been realized with pure gaseous nitrogen at ambient then high temperature (1200 K) for several varying pressures (up to 60 bar). The accuracy of the methods can be as low as 5% by comparison to National Institute of Standards and Technology data. The main source of uncertainty is found to be linked to the characteristics of sensors. The method has been applied to liquid dodecane (from 300 to 700 K and up to 60 bar) with the same order of accuracy before testing it on supercritical n-dodecane (658–700 K up to 60 bar) for which no validation data have been found. By comparisons with computations for multi-species mixture, even multi-phase, a reasonable agreement is found. The novel viscosity determination technique opens a new field of fluid characterization in extreme operating conditions.     

Performance of slot-entry hybrid journal bearings considering combined influences of thermal effects and non-Newtonian behavior of lubricant

This paper presents theoretical investigations of the thermal and rheological effects of lubricant on the performance of symmetric and asymmetric slot-entry hybrid journal bearing system. FEM has been used to solve the Reynolds equation governing flow of lubricant in bearing clearance space along with restrictor flow equation, energy equation and conduction equation using suitable iterative technique. The thermohydrostatic (THS) rheological performance of slot-entry hybrid journal bearings are studied for small temperature variation of the lubricant. The computed results reveal that variation of viscosity due to temperature rise and non-Newtonian behavior of lubricant affects the bearing performance quite significantly.     

An elasto-plasto-hydrodynamic model of strip rolling with oil/water emulsion lubricant

We review the problem of metalworking lubrication and include the hitherto much neglected elastic deformation in our analysis. This analysis is carried out for both pure oil lubricant and for lubrication with oil-in-water emulsion. For the latter, we make use of the extended Reynolds equations of Al-Sharif et al. (Ph.D. dissertation, University of Pittsburgh, 1992), which were derived for lubrication with binary mixtures of Newtonian fluids. The results of this paper demonstrate several experimentally observed phenomena of metalworking lubrication, the most significant being that an increase in the value of the elastic modulus enhances oil pooling ahead of the roll bite and results in a thicker film in the working zone.     

精确测量微量液体折射率的新方法

介绍了一种用玻璃毛细管精确测量微量液体折射率的新方法.该方法基于共轴球面光学系统的成像原理,通过读数显微镜对吸入待测液体后毛细管的焦点位置进行单一参数的测量,进而计算出待测液体的折射率.用此方法测量了纯水、乙醇、乙二醇、丙三醇的折射率,各种待测样品的需要量＜0.002 ml;测量结果表明,纯水和乙醇样品的折射率测量精度优于0.000 3;乙二醇和丙三醇样品的折射率测量精度优于0.000 7.选用适当的毛细管参数,可以进一步提高这种测量方法的测量精度,扩展折射率的测量范围.分析和讨论了实验测量误差以及进一步提高测量精度的方法.该方法具有待测液体用量极少、使用设备简单、操作方便和折射率测量精度高的特点.