Environmentally adapted lubricants,Part II. Hydraulic fluids

Current technologies relating to hydraulic fluids are mostly either mineral based, synthetic based, or water‐based. Mineral oil based hydraulic fluids tend to be used for their excellent lubrication characteristics, economic viability, and so account for almost 90% of hydraulic fluids, while waterbased fluids tend to be employed in fire hazard applications. Synthetic hydraulic fluids possess superior properties to mineral oils, but their higher price limits their application to aerospace and special applications under severe conditions. In recent years, biodegradable hydraulic fluids, which are readily decomposed by micro‐organisms, have come into focus due to the rise in environmental consciousness in European countries, particularly Sweden and Germany, and with this, vegetable‐based fluids. In the present paper, the main categories of hydraulic fluids, including environmentally friendly fluids, are discussed in an overview of the state of technology in this area. Current governmental regulation, and the properties required of environmentally adapted fluids, and an appraisal of the current practices in various countries are also given. In an earlier paper*, the authors reviewed the key aspects of and requirements for environmentally adapted lubricants, namely, chemical composition, eco‐toxicity, biodegradability, bio‐accumulation, eco‐labelling schemes, and life‐cycle analysis. In the present paper, the main categories of hydraulic fluids, including environmentally friendly fluids, have been described. In Part I*, the authors reviewed the key aspects of and requirements for environmentally adapted lubricants.     

Laboratory parameters for high water based hydraulic fluid testing

A review of the composition and properties of current water-containing hydraulic fluids leads to the conclusion that current technology could be improved towards a high water containing fluid with good antiwear, low toxicity and high fire resistance characteristics. A modified pump test was used based on ASTM D2882, using a Vickers V105C apparatus. Wear rate data is presented for various candidate fluids including a full synthetic, showing differences between HFA, HFB, HFC and HWBF and looking at variations in break-in wear and subsequent wear behaviour. Data is also presented for candidate fluids tested in industrial-type hydraulic pumps, and illustrates the role of viscometric properties including shear stability.     

Temporary and Permanent Viscosity Loss Correlated to Hydraulic System Performance

ABSTRACT

Straight- and multigrade fluids were evaluated in a hydraulic dynamometer that incorporated a pressure-compensated axial piston pump and a fixed displacement axial piston motor. Pump, motor, pressure compensator, and directional control valve internal flow losses were determined under various conditions of pressure, speed, and temperature. Fluid samples were collected before and at various times during the dynamometer experiments, and viscosity measurements were performed to probe for correlations between viscosity, operating time, and system leakage flow losses. The low shear rate viscosities of the multigrade fluids decreased linearly throughout the duration of testing due to polymer degradation. However, system flow losses did not exhibit a statistically significant increase as the multigrade fluids sheared down. The fluids were also characterized by their permanent viscosity loss produced in sonic shear and tapered bearing tests and by their temporary shear thinning measured in an ultra-high-shear viscometer at several temperatures. The effects of these viscous properties were analyzed using an empirical model to identify which measures of viscosity were most correlated with flow loss. The results suggested that the relative contributions of temporary and permanent viscosity loss change as the fluid is used. Further, analysis of torque loss and input power revealed that input power and losses are more useful indicators of the effect of fluids on hydraulic system performance than pump efficiency.     

叶片泵在注塑机市场的配套趋势

面对新一代低能耗、高洁净注塑机面世给叶片泵配套带来冲击,该文介绍了轴向变量柱塞泵在低能耗塑机、内啮合齿轮泵在低噪声塑机的应用和无液压泵的全电动塑机,以及叶片泵在全液压塑机的应用现状。对高压叶片泵技术的未来与在注塑机市场的配套趋势作了预测。     

Ion Exchange/Vacuum Dehydration Treatment of Phosphate Esters in Industrial Applications

Phosphate esters are widely used in a variety of hydraulic systems in industrial applications. These fluids typically exhibit good lubricity and oxidative stability. The fire‐retarding characteristics of phosphate esters make them attractive for use in applications where petroleum‐based fluids would constitute a fire hazard. However, in the presence of water, these fluids hydrolyse and form acidic partial phosphates. Because this process accelerates in an acidic environment, the reaction is referred to as autocatalytic. Moreover, fluid degradation becomes extremely difficult to reverse once acidity reaches an acid number of I mg KOH/g. From that point on, it is increasingly hard to stabilise the fluid with conventional treatment methods such as fuller's earth or activated alumina. In contrast, fluid treatment based on a combined application of ion exchange and vacuum dehydration (IX/VD) was found to be highly effective in arresting fluid degradation and restoring fluid properties to within limits acceptable for continued operation. This paper presents data collected over a period of several years at a number of power plants throughout the USA and Europe. The data confirm that fluids that initially exceeded manufacturer specifications even by a wide margin were successfully stabilised through a combined treatment of IX/VD under normal operating conditions.     

Fault diagnosis of axial piston pumps with multi-sensor data and convolutional neural network

Axial piston pumps have wide applications in hydraulic systems for power transmission. Their condition monitoring and fault diagnosis are essential in ensuring the safety and reliability of the entire hydraulic system. Vibration and discharge pressure signals are two common signals used for the fault diagnosis of axial piston pumps because of their sensitivity to pump health conditions. However, most of the previous fault diagnosis methods only used vibration or pressure signal, and literatures related to multi-sensor data fusion for the pump fault diagnosis are limited. This paper presents an end-to-end multi-sensor data fusion method for the fault diagnosis of axial piston pumps. The vibration and pressure signals under different pump health conditions are fused into RGB images and then recognized by a convolutional neural network. Experiments were performed on an axial piston pump to confirm the effectiveness of the proposed method. Results show that the proposed multi-sensor data fusion method greatly improves the fault diagnosis of axial piston pumps in terms of accuracy and robustness and has better diagnostic performance than other existing diagnosis methods.     

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.     

Wear and fatigue problems in connection with water-based hydraulic fluids

Water-containing fluids are widely used in hydraulic applications where there is a significant risk of fire, as in underground mining and metal working applications. Although primarily intended as power transmitting media, hydraulic fluids need to possess a modicum of lubricating ability to limit wear, seizure and contact fatigue of pumps and other rubbing parts. Unfortunately water-based hydraulic fluids generally show significantly poorer wear and rolling-contact fatigue performance than mineral or synthetic oil-based fluids of similar viscosity and this means that pumping equipment usually has to be derated when used with water-based fluids. This paper examines the poor wear and fatigue performance of water-based fluids and discusses, in some detail, the origins of this poor performance and the ways it can be mitigated.     

An Investigation of Hydraulic Motor Efficiency and Tribological Surface Properties

Hydraulic motor efficiency does not depend upon viscosity alone. Under low-speed, high-torque conditions, hydraulic motors operate in the boundary regime and, therefore, surface interactions of lubricant additives can affect friction and efficiency. This article presents an investigation of boundary film formation, friction, and surface topography in benchtop tribometers and hydraulic motors. Fluids investigated included those with varied antiwear packages (zinc dialkyldithiophosphate [ZDDP], ashless) and friction modifiers (with and without) and base oil (Group I, Group III). The mechanical efficiencies of geroler, axial piston, bent-axis, and radial piston motors were measured under low-speed, high-torque conditions. The addition of a friction modifier to an ashless hydraulic fluid increased the efficiency of the motors at low speed. Energy-dispersive X-ray spectroscopy (EDX) analysis of motor surfaces after testing revealed the presence of tribochemical films from the hydraulic fluid additives. In benchtop tribometer testing, the friction modifier reduced friction significantly but also increased wear. This could be related to surface competition of the friction modifier and antiwear chemistries, as evidenced by the reduced concentration of phosphorus on the surface. These findings are significant because they provide insights toward the development of fluids that can enhance motor efficiency but also demonstrates the need for a well-balanced additive package so that improved motor efficiency can be achieved without affecting other important properties of the fluid.     

离心式固液两相流泵叶片形状对流体动力特性影响的研究

给出了考虑离心力作用时的叶片近壁表面固液两相流体粘性流动的分析方法,以实泵为例从理论上分析和阐述了叶片形状对流体的动力特性的影响,并通过对比试验对其进行了验证。明确了这种影响主要体现在三个方面,即泵的水力效率及其动力性能和理论扬程。同时给出了叶片型线的优劣评价依据和如何实现或获得一条合理叶片型线的方法。所得结论对离心式固液两相流泵叶片型线的选型和设计具有指导意义。     

轴向柱塞泵配流副润滑特性的研究进展

介绍了国内外有关轴向柱塞泵配流副润滑特性方面的研究成果，并进行了综合分析和比较。指出需借鉴国外现有的关于轴向柱塞泵配流副压力分布规律的理论，确定最佳剩余压紧系数，现有的配流副结构设计方法和理论依据需进一步完善。建立了轴向柱塞泵配流副润滑特性试验平台，可在不同压力、温度、转速、结构下测试配流副间隙并得出配流副润滑膜的形成及变化规律。通过润滑特性测试平台还可以确定最佳水液压柱塞泵配流副润滑结构和材料配对，为研制出性能良好的轴向柱塞式水液压泵奠定实验基础。     

电动静液作动器用高速轴向柱塞泵能耗分布特性试验测试研究

随着飞机功率电传技术的发展,电静液作动器(EHA)对液压轴向柱塞泵提出了高功率密度的要求,轴向柱塞泵不可避免地向着高压高转速方向发展。在更高参数要求下,了解能耗分布特性有助于针对性地改进泵的性能。对高转速的轴向柱塞泵进行性能测试,将功率损失分成容积损失、搅拌损失和摩擦损失三个部分,在不同转速和压力等级下,分析其分布特性,并对测试物理量的不确定度进行分析。测试结果表明,摩擦损失是造成功率损失的主要原因,在泵的设计过程中应考虑使摩擦副在工况范围内得到充分润滑,以期提高效率。另外,测试中某些工况下存在着较大的不确定度,为了避免这类情况在选择传感器量程时应该更接近测试数值大小。     

Relation between pressure variations and noise in axial type oil piston pumps

Pressure variation is one of the major sources on noise emission in the axial type oil piston pumps. Therefore, it is necessary that the pressure variation characteristics of the oil hydraulic piston pumps be clarified to reduce the pump noise. Pressure variations in a cylinder at the discharge region and the pump noise were simultaneously measured with discharge pressures and rotational speeds during the pump working. To investigate the effects of the pre-compres-sion and the V-notch in the valve plate, we used the three types of valve plates. In this research, it is clear that the pressure variation characteristics of axial type oil piston pumps is deeply related to the pre-compression and to the V-notch design in valve plate. Therefore, we could reduce the pump noise by using the appropriate pre-compression angle and the notch design that are between the suction port and the discharge port in valve plate.     

A practical investigation of wear in piston pumps operated with HFA fluids with different additives

This paper examines the use of water-based hydraulic fluids in hydraulic pumps, Four different types of HFA fluid are reviewed in terms of properties and usage. In a research programme, two principal fluids, a HFA micro emulsion and a HFA solution, were evaluated in relation to their wear protection capability in a short-term test procedure, and their operational behaviour and confirmation of the short-term test procedure in a long-term test. The differences between the fluids are mainly in terms of wear of the test pumps. It is concluded that a performance standard similar to oil-based fluids has not yet been reached.     

A comparative life cycle assessment of the manufacture of base fluids for lubricants

A comparative life cycle assessment (LCA) study of three types of base oils used in the manufacture of hydraulic fluids has been carried out, and is reported here. The fluid types investigated are a mineral oil, a synthetic ester, and a rape seed triglyceride oil. The applications chosen for the finished lubricants are in mobile hydraulic systems in forestry operations, some of which are almost 100% total loss applications. The scope and limitations of the LCA model are discussed, and conclusions drawn concerning the application of LCA models as evaluation tools for the development of environmentally adapted lubricants. The methodology used is compatible with the ISO 14000‐type industrial standard.     

Comparison of vickers V‐104C and 20VQ5 vane pump wear rates for various water‐glycol hydraulic fluids

Work is currently under way within the ASTM D.02 N.07 ‘Hydraulic Fluid Testing’ Committee to evaluate the potential of replacing the Vickers V‐104C vane pump with a newer, more current model 20VQ5 vane pump for use in an updated ASTM D 2882 standard and other national standards. All the round robin work conducted within the Committee thus far has involved the use of non‐aqueous hydraulic oils. Although there are some significant inter‐laboratory reproducibility problems, it appears that the overall ranking of these hydraulic oils by most laboratories appears to be consistent. To further evaluate the potential utility of replacing the Vickers V‐104C pump with the 20VQ5 pump, a series of different water‐glycol hydraulic fluid formulations with significantly different wear rates were evaluated using a ‘modified’ ASTM D 2882 testing procedure. The results showed that expected catastrophic pump failures, which occurred with the V‐104C pump, not only did not occur with the 20VQ5 pump, but the relative orders of wear rates for some of the fluids were also different.     

Wear testing and specification of hydraulic fluid in industrial applications

The aim of this paper was to investigate the possibilities to use a model test to simulate the wear between cylinder bore and piston in a radial piston hydraulic motor. The tests were performed in a reciprocating test rig where the contact geometry is of the cylinder–plate type. The influence of different types of commercially available hydraulic fluids on wear protection and friction was studied. From the study, it was concluded that the use of water glycols can cause increased wear in hydraulic motors operating in low speed applications. It was also seen that the FZG test alone appears not to be enough as a hydraulic fluid wear test, at least not in the tribological conditions present in the performed wear test.     

煤油介质轴向柱塞泵设计的关键技术

轴向柱塞泵结构组成复杂,是技术含量较高的液压元件,其工作涉及到固体场、流场和热场等多场耦合问题,以煤油为工作介质的轴向柱塞泵更是增加了设计难度。根据煤油介质黏度低、易泄漏的特点,从柱塞泵的结构形式、运动分析、轴尾密封和摩擦副材料四个方面入手,研究了煤油介质轴向柱塞泵设计的关键技术,为煤油泵的研发奠定了基础,同时可为其他低黏度介质柱塞泵的设计提供参考。     

The kinematic analysis of axial-piston pumps

This investigation describes the kinematics of axial hydraulic pumps with spherical ended pistons. The results, however, apply to the basic kinematics of all axial piston pumps. The current hypothesis is that sliding at the piston/swash plate interface contributes to the wear of these parts. The analysis concludes that sinusoidal sliding is inherent at the piston/swash plate contact point, and that its magnitude is a function of the pump design variables. Therefore, manipulation of the basic design variables of the pump is the key to controlling the amount of sliding and related wear at the contact point.     

Evaluation of water glycol hydraulic fluids: a tribological approach

Water glycol fluids are commonly used as fire‐resistant hydraulic fluids, particularly in areas where fires cannot be tolerated, such as foundries, steel mills and mines. However, they have the disadvantage that their wear resistance is unsatisfactory. Hence, there is a need for an additive package which overcomes this poor wear resistance. In order to design an effective water glycol hydraulic fluid for this purpose, four additive packages were considered. The performance of the lubricant composition developed with these packages is studied in detail. The physico‐chemical and tribological properties of the formulations were determined using standard methods. The load‐carrying properties were studied by four‐ball and Timken load methods. The antiwear performance and coefficient of friction were studied by using four‐ball and Schwingung Reibung Verschleiss test methods. The topography and surface analysis were carried out using scanning electron microscopy and X‐ray photoelectron spectroscopy techniques. Copyright © 2006 John Wiley & Sons, Ltd.