Effect of transverse surface roughness and additives in TEHD contacts

Surface roughness effects in mixed rheological thermal EHL of rolling/sliding line contacts are investigated numerically. The surface roughness is assumed to be transverse and its profile is generated by a sinusoidal function defined in terms of its amplitude and wavelength. A homogeneous mixture of Newtonian base oil and power law fluid additive with varying volume fraction, viscosity ratio and power law index is used to represent polymer-modified oils. The velocity profile for the mixed rheological fluid model is obtained using perturbation method to derive Reynolds and mean temperature equations. It is found that the surface roughness effects on EHL characteristics are significantly modified due to the presence of polymeric fluid additives.     

指数率流体热弹流润滑分析

应用多重网格技术,求得了指数率非牛顿流体线接触热弹流润滑的数值解,分析了油膜压力、厚度和温度等随流变指数、速度参数、滑滚比及载荷参数的变化关系,并与相同工况下的等温解进行了比较。结果表明,随着流变指数的增加,油膜厚度和温度、入口处的当量粘度、最小膜厚、中心膜厚和最大温升均增大,而油膜压力和摩擦因数的变化较小。指数率流体弹流润滑问题的热效应不可忽略;与压缩功项相比,油膜能量方程中的热耗散项对温度的影响最大。同时,无量纲速度参数、滑滚比和载荷参数等均影响热弹流润滑特性。     

Polyolefin and poly(alkyl methacrylate) mixed additives as mineral lubricating oil rheology modifiers

Some rheological properties of mineral lubricating oils containing polyolefin (OCP) (ethylene/propylene copolymer) and poly(alkyl methacrylate) (PAMA) mixed additives over a wide composition range have been examined. Increasing the OCP content significantly increases the viscosity and shear stability of solutions, whereas the viscosity index is directly proportional to the PAMA content. The pour point values of the additive solutions investigated are lower than −30°C even for the smallest concentration of PAMA in the polymer mixture of 15 wt.% (at a total polymer mixture concentration in oil of 2 wt.%). The viscosities of dilute mixed additive solutions obey the typical Krigbaum‐Wall equation and, due to the negative viscometric interaction parameter values (Δb₁₂ < 0), the OCP/PAMA mixture is found to be immiscible. The immiscibility becomes more pronounced on increasing the overall polymer concentrations. The viscosities of concentrated mixed additive solutions decrease significantly with an increase of OCP content, showing a minimum of half the initial value at a polymer ratio of about 50/50. On decreasing the polymer concentration to practical levels as well as increasing the temperature, the viscosity values approach the ideal additivity law. Based on the ratio of specific viscosities at 40 and 100°C (Q), the OCP additive solution shows a better thickening effect at lower temperatures (Q < 1). On the other hand, the PAMA additive solution shows a better effect at higher temperatures (Q > 1) with more coherent thickening with temperature change. The mixed polymer additive, containing ∼10 wt.% OCP and ∼90 wt.% PAMA, is a nearly optimal viscosity‐index improver showing the same thickening effect at different temperatures. The results obtained are promising as regards the design of lubricant formulations with mixed polymeric additives.     

合成基润滑油聚α-烯烃低温摩擦润滑性能研究

在低温条件下,润滑油黏度变大,流动性变差,添加剂活性降低,对润滑性能产生显著影响。为研究PAO润滑油的低温摩擦润滑性能,以不同黏度级别PAO基础油为研究对象,采用流变仪MCR302、SRV摩擦磨损试验机,研究PAO润滑油样及添加极压抗磨添加剂的油样在低温条件下的流变性能和磨损润滑性能。试验结果表明：在低温环境下,随着温度降低,PAO油样的黏度急剧增大,黏度越大的油样其受低温条件影响越明显;PAO油样在低温环境下,表现出明显的剪切稀化现象;低温环境使得极压抗磨剂添加剂的活性变低,添加剂并未表现出减摩抗磨作用。因此,低温试验条件对PAO基础油和添加剂的摩擦学性能产生显著影响,阻碍了基础油和润滑油添加剂减摩抗磨作用的发挥。     

Base fluid parameters for elastohydrodynamic lubrication and friction calculations and their influence on lubrication capability

In this study, base fluid parameters for elastohydrodynamic lubrication (EHL) and friction analyses have been determined experimentally. The viscosity at atmospheric pressure, η₀, the pressure‐viscosity index, α, and the EHL friction coefficient, γ, are important parameters in EHL theory and they are crucial in the selection of efficient lubricants for different applications. This investigation focuses on three important lubrication mechanisms: the capability of forming a separating lubricant film, the friction generated in a lubricated contact, and the height of pressure peaks, such as the outlet pressure spike and pressure ripple caused by surface roughness. The influence of different lubricant parameters on these three mechanisms is discussed. The value of α is measured in a Couette high‐pressure viscometer, and the value of γ is obtained from a jumping‐ball device. Other parameters discussed are temperature‐viscosity coefficient, β, bulk modulus, B₀, thermal conductivity at atmospheric pressure, λ₀, and heat capacity unit volume, ρc_p0. A comparison between traditional mineral base oils and environmentally adapted oil based on rapeseed oil and synthetic esters contributes to the further understanding of the performance of these new materials in lubrication applications. It is shown that rapeseed oil and synthetic esters have good lubricating properties and are, in most cases, better than mineral oils.     

Influence of viscosity modifiers on the rheological properties of synthetic oils

The study of the effect that the molecular weight and concentration of the polymer gelling additive PMMA (polymethylmethacrylate) introduced into the synthetic base oil PAO6 has on viscosity. The empirical dependence of the viscosity of the thickened oil on the content of additives has been established and the coefficients of the thickening efficiency of additive have been determined. An experimental study of the viscosity of synthetic oils on the shear rate has been carried out at different contents of viscosity modifier PMMA with different molecular weights in a base of PAO6. The ranges of velocities have been determined at which the oil exhibits properties of non-Newtonian fluid. It has been shown that, with an increase in the molecular weight of PMMA of additive at the same concentration in its base, the non-Newtonian behavior of oil begins to emerge at lower shear rates. It has been found that the use of an acoustic arsenal of the operational control of the viscosity of lubricating oils based both on the piezoelectric and the magnetoelastic interaction is promising for the operational control of the viscosity of lubricating oils.     

The Non-Newtonian Characteristics of Lubricating Oils

Interest is growing concerning the influence of polymeric additives upon the viscosity of mineral oils at extremes of temperature, pressure, and shear. In this paper the author discusses the viscometry of mineral oils and mineral oil-polymer blends at moderate temperatures and high shear and at low temperatures and low shear.

The non-Newtonian influences of two common polymeric additives, polyalkylmethacrylate and polyisobutylene, are shown to vary considerably at low temperatures in their effects on a common base oil. Shear dependence of polymer-containing oils at high shear rates is experimentally indicated to reduce the viscosity of the blend to approximately that of the base oil.

Conclusions of practical interest are drawn from the experimental results.     

Film-forming tendencies of some base fluids and viscosity modifiers

The film-forming tendencies of selected mineral base oils and synthetic base fluids were investigated with and without conventional GL-5 additive packages. A pressurised falling-body viscometer and a concentrated contact simulator were used to measure low-shear viscosities, central film thicknesses, and traction coefficients. Analysis of the mineral—based oils showed that a paraffinic base oil and a naphthenic base oil had similar film thicknesses, even though the naphthenic base oil has higher pressure-viscosity coefficients. A very high viscosity index oil gave thinner film thicknesses and lower pressure—viscosity coefficients than the paraffinic or naphthenic base oils. Analysis of the synthetic base fluids showed that a PAO-4 base fluid gave thicker film thicknesses than an ester base fluid. The analysis of fully-formulated oils showed that the PAO-4 oil containing a proprietary polyolefin provided a similar filnz thickness to the PAO-4 oil containing a more expensive PAO-100.     

汽油机油配方对节能发动机试验的影响

介绍了汽油机油节能发动机试验的发展状况,讨论了油品配方对节能性能的影响。发动机试验表明,基础油、粘度指数改进剂及添加剂都是影响汽油机油节能性能的因素,在不同的发动机试验中基础油、粘度指数改进剂、抗氧抗腐剂、摩擦改性剂、清净剂、分散剂的影响存在不同的表现形式,在配方设计中要根据具体的发动机试验来确定。     

Lubricant components from vegetable oils of indian origin

A number of transesterified and alkarylated derivatives have been synthesised from available vegetable oils of Indian origin. The viscosity, viscosity index, freezing points, load-carrying characteristics, friction coefficient, and thermo-oxidative stability of these derivatives as compared to highly refined hydrorefined hydrocarbon oils have been studied. It has been found that several esters of fatty acids of these vegetable oils have a high natural viscosity index, low pour points, and high thermooxidative stability, and can meet the requirements as base fluid components for energy-efficient, eco-friendly, long-drain interval, multigrade oils. These oils have markedly lower viscosities at 40°C, higher load-carrying characteristics, and lower friction coefficients than the base fluids of currently marketed multigrade oils. A 50% blend with hydrorefined hydrocarbon oils could prove highly viable. The above results clearly establish the potential for utilising these esters, either alone, or in combination with mineral oils, for formulating cost-effective high-performance, energy-efficient, and environmentally friendly lubricants. Performance characteristics of these oils as engine oils, automotive gear oils, and 2 stroke oil with conventional additives and with alternative additives are under investigation in comparison to the most advanced hydrocarbon based multigrade oil formulations of long-drain interval.     

Computer modeling of rheological properties of base oil compositions with selected additives

An analysis of the rheological properties of various oils and their formulations with selected rheological additives (Visconyl-200 and ECA-6911) was performed. Base oils (OS and OU) obtained on a large laboratory scale were the primary subject of the investigation. They were produced according to classical and modified base oil technologies. The modification introduced an additional process of mild oxidation of atmospheric residue before vacuum distillation. Other oils, such as aromatic and saturated hydrocarbons separated from the OS and OU oils, as well as oil fractions (1S–5S and 1U-5U) obtained from the base oils by vacuum distillation, have also been investigated. Using the rheological properties determined for the distillate oil fractions formulated with the Visconyl and ECA additives, the empirical formulae describing the dependence of kinematic viscosity v_{50, c} and v_{100, c} and of the pour point of the compositions, on the basic physico-chemical properties of the base oils, and on the type and concentration of additive, have been found. The theoretical viscosity index values of the oil compositions were also characterised indirectly by using the empirical formulae describing kinematic viscosities of the compositions at 50 and 100°C. The formulae obtained were successfully tested with several selected base oils.     

Tribological behaviour of antiwear additives used in hydraulic applications: Synergistic or antagonistic with other surface-active additives?

This paper examines the friction and antiwear (AW) properties using SRV (Schwing–Reib–Verschleiss) tribometer and film-forming properties using atomic force microscope (AFM) of one simple model formulation containing solely AW additive and seven oils containing mixture of additives including three zinc-based packages (ZP), ZP with additional AW additives, ZP with extreme pressure (EP) additives, ZP with viscosity index improvers (VII) and one zinc-free ashless package in steel/steel contacts. VII-containing oil show lower boundary and mixed friction coefficients than the other oils. Although all AW additive-containing oils formed tribofilms, AW properties of ZPs appear to be affected antagonistically by EP additives while synergistically by VII. Zn-free additives investigated in this study show higher wear than ZPs.     

EHL Properties of Polyalkylene Glycols and Their Aqueous Solutions

Polyalkylene glycols (PAGs) are a type of synthetic lubricants widely used as compressor lubricants, gear oils, hydraulic fluids, and metal working fluids. The PAGs with typical molecular structure can dissolve in water, which makes it a candidate for the base stock of water-based lubricants. Till now, most of the investigations on the water-based lubrication have focussed on the additives. In this work, the potential of PAGs aqueous solutions to replace water as base stocks has been investigated. Four types of PAGs with different molecular weight and their aqueous solutions with different concentrations were studied to reveal their elastohydrodynamic lubrication (EHL) behavior. It has been found that the PAGs solutions can form EHL film like traditional oils. The film-forming capability depends on the viscosity, the pressure–viscosity coefficient, and the molecular weight of PAGs. The results indicate that the PAGs aqueous solution can be employed as base stocks of water-based lubricant.     

Tribological Properties of Vegetable Oils Modified by Reaction with Butanethiol

Corn, canola, and castor-lauric estolide oils were chemically modified by photochemical direct reaction of butanethiol with the double bonds on the hydrocarbon chains. The effect of chemical modifications on viscosity, viscosity index (VI), pour point (PP), cloud point (CP), oxidation stability (RPVOT), 4-ball anti-wear (AW), and extreme pressure (EP) were investigated. The sulfide modified (SM) corn and canola oils showed increased viscosity, increased RPVOT time (more than one order of magnitude), reduced PP (9?C18 °C), and reduced VI. The SM estolide displayed similar trends in VI and RPVOT but showed no change in viscosity or cold flow. The SM oils, along with commercial mono- and polysulfide additives were also investigated as additives, at 0.6% (w/w) S concentration, in corn and polyalphaolefin (PAO) base fluids. In both fluids, the additives resulted in minor changes of PP, CP, coefficient of friction, wear scar diameter (WSD), and weld point (WP). Only the commercial polysulfide EP additive displayed large WP increases in the fluids. The additives resulted in no change of oxidation stability of corn oil, but displayed big improvement in the oxidation stability of PAO (8 to 16-fold increase in RPVOT time). The difference in the effect of the additives on the oxidation stability of PAO versus corn oil was attributed to the difference in the reactive hydrogen contents in the two base fluids relative to those in the additives. An empirical equation, for correlating change in RPVOT time with change in bond dissociation energy of reactive protons before and after chemical modification, is proposed.     

Friction and wear performance of MoDTC‐containing and ester‐containing lubricants over steel surfaces under reciprocating conditions

Lubricant oil can be regarded as a complex mixture of base oils and additives, each one with its specific functions and behaviour. In this paper, the interaction of a molybdenum dialkyldithiocarbamate (MoDTC)‐based additive and combinations of a polyalphaolefin and a synthetic ester is investigated. A reciprocating ball‐on‐disc configuration was used for tribological tests. The effect of MoDTC is seen as a sharp drop in the coefficient of friction. This friction reduction is affected by the base fluid: the effect is more intense and lasts longer when the ester content is decreased. The applied normal force also affects the MoDTC effect, which is not sustainable at higher loads. Copyright © 2014 John Wiley & Sons, Ltd.     

Seal Material and Base Fluid Compatibility: An Overview

This study compares the seal material compatibility of environmentally adapted base fluids with that of mineral and synthetic base fluids. The seal materials studied were nitrite rubber (NBR), hydrogenated nitrile rubber ( HNBR), and fluorine rubber (FKM) elastomers, which are common in lubricated applications. The base fluids studied were synthetic esters (monoester, polyol ester, complex ester, and diester), a natural ester (i.e., vegetable oil), different types of mineral base oils, polyalphaolefin, and a fluid of very high viscosity index. The base fluids have been studied without additives. The elastomeric properties measured include volume, hardness, tensile strength, and elongation. A small elastomer volume increase was observed for mineral base oils whereas a significant increase was noted for all synthetic esters when tested on NBR and HNBR. The mechanical properties of the elastomers deteriorated in all cases. The amount of deterioration (i.e., in the tensile strength and the elongation) was in general less than 30%.     

The influence of chemical composition on the pour-point depressant properties of methacrylate copolymers used as additives for lubricating oils

Methacrylate polymers are much used as additives in lubricating oils, as pour-point depressants and viscosity index improvers. Although the mechanism of such pour-point depression is still controversial, it is thought to be related to the length of the alkyl side chains of the polymethacrylates, and to the nature of the base oil. In this paper, work is reported on: (a) the depressant activity of polymethacrylate copolymers in relation to the content of short alkyl methacrylates and styrene, and the average side-chain length of the basic methacrylate constituents; (b) the pour point of the base stock; and (c) the additive concentration.     

An In-Line Method for Measuring Oxidation in Gear Oils and Hydraulic Fluids

A study was conducted to examine degradation of a gear oil and a hydraulic fluid using an in-line polymeric bead matrix (PBM) system that correlates oil oxidation with a relative change in the solvent properties of a fluid. The solvent property is an inherent aspect of an oil and allows oxidation to be measured independent of the base type, additive package, and viscosity. Samples of gear oil were heated to simulate a typical oxidized condition. Hydraulic fluids from a turbine were run for a limited time to provide discrete oxidized samples and test the sensitivity of the method. Results for the gear oils with the PBM are shown to compare favorably with infrared (IR) spectroscopy at room temperature. Elevated temperatures available with the PBM were needed to resolve oxidation levels for the hydraulic fluids.     

Study of Influence of Lubricating Oil and Tooth Height on Friction Characteristics of Helical Gears

It is of utmost importance to know the friction loss of helical gears because they are produced quite widely used. However, basic research, e. g., load carrying characteristics of helical gears and friction loss, is extremely scarce.

In this paper the authors focused on the influence of the kind of lubricating oil on the friction loss of helical gears. Further they dealt with the influence of height of teeth on friction loss of helical gears. The authors carried out experiments to study the influence of lubricating oil viscosity, additive, and base oil type as well as rotational speed on friction loss of helical gears. Not only mineral oils but also synthetic oils were used as base oils, e. g., paraffin, poly-α-olefin, and polyglycol type oils. As additives the authors used EP additive and ZnDTP. Further they investigated the influence of tooth height on friction loss.

The experimental results gained make it possible to drastically reduce friction loss of helical gears.