Analysis of antiscoring and antifriction properties of greases

The paper describes an improved electric circuit of the method for estimating the scoring resistance of greases based on contact resistance measurement. Antiscoring and antifriction properties of greases under conditions of sliding and rolling friction are studied. The critical loads for the greases under testing are determined and the grease having the best antiscoring and antifriction properties is selected.     

Formation of antiscoring properties of materials during dynamic adaptation of surface layers to operational conditions

The relationship between the antiscoring properties of tribotechnical materials, estimated according to load-carrying capacity increase during running-in, and their inclination to dynamic adaptation under loading via self-organizing processes in their surface layers is studied.     

Biodegradable lubricants — Analysis of metalworking oils and hydraulic fluids by mass spectroscopy

Biodegradable metalworking oils and hydraulic fluids were screened for their base oil composition using a special mass spectrometric technique — direct exposure probe chemical ionisation mass spectrometry (CI(NH₃)-MS). All but one of the hydraulic fluid samples were rapeseed oil or trimethylolpropane trioleate based, the other sample being a neopentylglycol ester trimethylolpropane ester mixture. Ethylhexyl ester of rapeseed oil fatty acids (or similar) was present in some of the metalworking fluids in addition to rapeseed oil, whilst other samples were pure rapeseed oil. In several cases a trimethylolpropane/neopentylglycol ester base was found. Preliminary results for additive isolation/identification show the usefulness of preparative gel permeation chromatography.     

Boric acid and borax as antiscoring additives to glycerin-based lubricant

Boric acid and borax, which are used as antiscoring additives to an environmentally friendly glycerin-based lubricant, have been studied. It is shown that the adsorption of borax obeys the Langmuir isotherm. The equilibrium constants of the adsorption of the additives and the energy of the adsorption are estimated. It has been found that borax is a more effective antiscoring additive than boric acid. For borax used as the additive, the dependence of the coefficient of friction on the load applied to a friction unit is studied and interpreted.     

Development of a statistical method to formulate high‐VI hydraulic oils

Mobile hydraulic equipment is often subjected to a wide range of operating temperatures, and so must be lubricated with oils with a high viscosity index (VI) in order to maximise efficiency. Formulating high‐VI hydraulic oils is a complex task that requires testing numerous intermediate blends in order to achieve the desired viscosity at both low and high temperatures. With the introduction of the ASTM D 6080 hydraulic oil classification, which defines a separate grade at low and high temperature for high‐VI oils, and further includes VI and viscosity measurements after the sonic shear test, formulating high‐VI hydraulic oils has become even more complex. In order to determine the most effective VI improver to meet a given set of viscosity requirements, a large statistically designed experiment has been carried out. Empirical equations have been obtained that can be used to model the blending efficiency of VI improvers at different temperatures and to estimate their shear stability. This paper shows how the results obtained for 42 hydraulic oils have been used to develop a computer program aimed at facilitating the formulation of high‐VI hydraulic oils.     

The high‐temperature degradation of hydraulic oils and fluids©

The rapid darkening of hydraulic oils and fluids in use has occasionally been reported. This paper summarizes the past investigations into this phenomenon, which have largely focused on the compression of air bubbles in mineral hydraulic oil. The process leads to a form of high temperature degradation known as dieseling and the probable formation of sub‐micron carbonaceous particles. The importance of system design and particularly the choice of pumps, in this process, are discussed. The primary objective, however, is to examine the effects of dieseling on phosphate ester fire‐resistant fluids and to clarify if an analysis of the used fluid can indicate whether this process is taking place. An investigation of samples taken from systems displaying rapid degradation suggests that the presence of certain breakdown products may infer the approximate level of temperature to which, at least, small amounts of the fluid are being subjected. The presence of carbonaceous material in the dieseling process is also confirmed. Some suggestions made for the mechanism of its formation as well as the formation of other major degradation products. Lastly, recommendations are made for ways of minimizing this form of breakdown not only in terms of system design but also with respect to fluid properties, fluid maintenance and the use of in‐situ conditioning. Copyright © 2006 John Wiley & Sons, Ltd.     

Elastohydrodynamic properties of water-based fire-resistant hydraulic fluids

The elastohydrodynamic (ehd) lubricating properties of commercial fire-resistant hydraulic fluids in rolling point contacts are described. Earlier work is reviewed and new work presented on water-in-oil and oil-in-water emulsions. It is shown that in general, elastohydrodynamic film thicknesses of water-in-oil emulsions are close to those of their base oils. For very fine particle size emulsions, however, thicker films are observed. Commercial oil-in-water emulsions in fully flooded conditions have not been found to give measurable elastohydrodynamic films. However, when the emulsions are destabilized, a localized pool of oil collects in the contact zone which enables ehd films to form, though these films do not survive very high rolling speeds. Polyglycol solutions give low ehd film thicknesses, approximately one third those of mineral oils of corresponding viscosity. This can be attributed to the low pressure—viscosity coefficient of these solutions.     

Lubricating properties of rapeseed‐based oils

Three commercially available hydraulic/transmission lubricants based on rapeseed oil have been investigated for their lubricating properties. The coefficient of friction, scuffing‐load capacity, and pitting resistance were evaluated, and the results compared with a corresponding commercial mineral‐based oil. The results showed in general a substantially lower coefficient of friction and better pitting resistance for rapeseed‐based oils than for the mineral oil. Scuffing load capacity was, with one exception, the same for all oils. As a result of lower shear stresses during contact, and a higher viscosity index, the temperatures in the gearbox were lower for the rapeseed oils tested than for the mineral oil. Insufficient antiwear behaviour at high loads was found to be a major drawback of these vegetable oils.     

Thermophysical properties of compressor oils for refrigerating plant

In the present study, an accurate experimental information for the widely used commercial refrigerating compressor oils ONF 46, ACD 100 FY, Azmol, FR 32, XC 15, XC 40 and WF 15A is presented. Experimental data on the capillary constant, surface tension, density, refractive index and kinematic viscosity at the temperature range from 293 to 353 K for seven commercial compressor oils are reported. In addition, the experimental data on the isobaric heat capacity at temperature range from 288 to 393 K, the vapor pressure at liquid‐saturated curve and average molecular weight for four commercial compressor oils are firstly presented in the paper. The data obtained are fitted by few‐constant correlations. Based on results obtained, the values of pseudocritical temperature for the compressor oils have been determined. Copyright © 2008 John Wiley & Sons, Ltd.     

Lubricating properties of rapeseed oils compared to mineral oils under a high load oscillating movement

The use of rapeseed‐based lubricating oils has become more widespread in recent years. When these oils have been tested for their tribological properties, some imperfections have been found, especially in conditions of highfrequency and low‐amplitude oscillating movements. In the present work, we compare the tribological properties of commercially available rapeseed‐ and mineral‐based oils, rapeseed and mineral base oils, and these base oils mixed with two additives for improving lubricity. The results are compared for a wide range of contact pressures.     

Improvement of antioxidation and antiwear properties of polyalphaolefin oils

Polyalphaolefin-based lubricating oils were tested on a four-ball tester, and in a stability test, with antiwear and antioxidant additives of different types, along with other (petroleum and alkylbenzene) base oils and additives. Antioxidant additives for PAOs essentially influence their thermo-oxidation stability. It was found that binary inhibitors increased thermo-oxidation stability effectively. In the antiwear tests, the addition of additives to PAOs sharply decreased wear scar diameters. A significant difference was observed in the action of small concentrations of antiwear additives as between PAO, alkylbenzene and mineral oils. Explanations of this behaviour are put forward.     

Influence of aldehydes in make-up oils on antioxidation properties

The addition of more antioxidant to aged oils is not always effective in preventing autoxidation. To investigate this phenomenon, a solution of antioxidant and model oxide in hexadecane was examined by means of the induction period method. Aldehydes were found to be the most active species for reducing the antioxidation properties of zinc dialkyldithiophosphate (ZDTP), 2,6-di(tert. butyl)-4-methylphenol (DBPC), and N-phenyl-1-naphtylamine (PNA). Carboxylic acids, ethers, alcohols, and ketones to some extent reduced the induction period with these antioxidants. Esters showed almost no influence on reducing their antioxidant properties. Reaction of ZDTP with aldehyde was studied by means of ³¹P-NMR analysis. It was found that (a) aldehydes accelerate conversion of ZDTP, and thereby reduce its antioxidant performance. (b) Conversion of ZDTP in the presence of aldehydes under oxygen at 130° in hexadecane and no reaction was observed under nitrogen at the same temperature. Active intermediates derived by the autoxidation of aldehyde were suspected. (c) Reaction of peroxycarboxylic acid with ZDTP took place smoothly at 0°C under nitrogen to give bis(dialkylthiorophosphoro)disulphide and the corresponding carboxylic acid. Reaction of hydroperoxide with ZDTP took place at room temperature to give oxo-hexa(dialkylphosphorothiorothionato)-tetrazinc. Two mechanisms for decomposition of ZDTP promoted by aldehydes, namely hydroperoxide and peroxycarboxylic acid mechanisms, are proposed. Reaction of peroxycarboxylic acid with DBPC or PNA barely took place at room temperature: for these antioxidants, the peroxycarboxylic acid mechanism would be excluded. Radical species derived by the autoxidation of aldehydes were considered as active intermediates. It is considered that classification of the types of oxides that exist in used oils in the key to optimising the effect of re-added antioxidants.     

液压活套自激振动分析

从精轧机活套液压缸销轴与轴套的间隙、活套液压缸的内泄两个方面,对液压活套系统的自激振动进行了分析。提出了临时消除或减小“销轴与轴套的间隙”对活套系统的影响的方法,并利用活套曲线来监测设备状态。     

闸门双吊点液压启闭机液压同步系统分析

双吊点液压启闭机在大中型闸门的启闭上应用广泛,针对其液压同步系统进行分析。分析了双吊点液压启闭机双缸同步误差形成的原因;介绍了双缸同步闭环控制方案;结合闸门双吊点液压启闭机液压同步控制的工程实际,分析了目前典型同步回路的工作原理及特点;最后归纳了双吊点液压启闭机同步回路的发展趋势。     

液压油对液压系统副作用分析

依据液压油变劣的特征,分析了外界环境对液压油性能影响的原因,阐述了液压油对液压系统的副作用,并提出改善措施。     

Study of the hydraulic properties of the cylindrical crested weirs

Since the cylindrical and circular crested weirs are economical and easily made compared to some other weirs, they can be used to measure the flow velocity, the water discharge and flow surface control structures in the canals and reservoirs. In this paper, the hydraulic properties of the cylindrical and circular crested weirs, such as the discharge coefficient, the depth on the crest of the weir and the energy loss in 18 laboratory models categorized in 5 categories have been investigated. The results of the experiments indicated that in both the cylindrical and circular crested weirs by increasing the total partial head, the discharge coefficient increases and any changes in the upstream wall slope has no effect on the discharge coefficient. Also, the partial energy loss more occurs in the cylindrical weirs than the half shaped cylindrical weirs and by increasing the downstream inclination angle, the partial energy loss increases subsequently. The partial flow depth on the crest of both the cylindrical and half shaped cylindrical weirs is equal to 0.7 and by increasing of the upstream inclination angle, the partial flow depth on the crest in the values greater than 0.6, increases slightly and the downstream inclination angle changes of the partial flow depth has no effect on the crest.     

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.     

Experimental analysis of tribological properties of lubricating oils with nanoparticle additives

This study examined the tribological properties of two lubricating oils, an API-SF engine oil and a Base oil, with CuO, TiO₂, and Nano-Diamond nanoparticles used as additives. The friction and wear experiments were performed using a reciprocating sliding tribotester. The experimental results show that nanoparticles, especially CuO, added to standard oils exhibit good friction-reduction and anti-wear properties. The addition of CuO nanoparticles in the API-SF engine oil and the Base oil decreased the friction coefficient by 18.4 and 5.8%, respectively, and reduced the worn scar depth by 16.7 and 78.8%, respectively, as compared to the standard oils without CuO nanoparticles. In addition, investigations were performed using TEM, OM, SEM, and EDX to interpret the possible mechanisms of anti-friction and anti-wear with nanoparticles.     

液压泵效率与排量特性试验研究

为实现工程机械液压系统的高效节能,对液压泵的效率和控制特性进行试验研究.基于液压试验台,测试了液压泵在不同压力、转速和排量下的效率,并进行了建模分析.之后对液压泵排量的动态与静态电比例控制特性进行了对比试验.研究结果表明液压泵的高效区分布于等值线图的右上角,即中高转速和排量范围内.液压泵排量控制特性基本不受转速影响,受负载压力影响较大,新旧液压泵的排量控制特性基本相同.研究为工程机械动力匹配奠定了基础.     

液压油的污染分析及其控制方法

随着国民经济的迅猛发展和科学技术的进步，起重设备对液压系统工作的灵敏性、稳定性和寿命提出了越来越高的要求，而油液污染不仅会影响系统的正常工作和使用寿命，甚至会引起设备事故。据不完全统计，由于油液污染引起的液压系统故障占总故障的70％-80％，可见要保证液压系统工作灵敏、稳定、可靠和延长液压元件使用寿命，就必须加强对液压油污染的控制，以保持液压系统良好的运行状态。