机械类英文翻译-Word版原创(英文+汉语)

STUDY ON SLIPPERS FOR RAW W ATER HYDRAULIC AXIAL PISTON

PUMPS AND MOTORS'

Yang Shudong, Yu Zuyao, He Xiaofeng, L, Zhuangyun

(School of Mechanical Science and Engineering

Huazhong University of Science and Technology

Wuhan, Hubei, P. R. China, 430074)

1. Abstract

As concerns for environmental compatibility, safetyand hygienic requirements, hydraulic systems using rawwater as pressure medium become more and moreattractive. A raw water hydraulic system has many advantages over conventional oil hydraulic systems,such as: environmentally compatibility, no pollution and no fire hazard, elimination of expensive oils with the associated problems of contamination, maintenance,storage, handling, elimination of the return hose, and elimination of health hazards, etc. But as a hydraulic medium, raw water has also drawbacks, such as very low viscosity, high vapor pressure, lack of lubrication and chemically active nature, etc., that all tend to promote problems of corrosion, wear, cavitation erosion, leakage, and so on, those problems must be overcome in the design and development of the raw water hydraulic components, especially the selection of materials and design of structure for the friction pairs in raw water hydraulic pumps and motors.

The slipper/swashplate pair is one of the very important friction pairs in axial piston pumps and motors. Under the lubrication of raw water. materials for slipper/swashplate combination should have superior mechanical strength, low friction, resistance to corrosion, abrasion, cavitation erosion and sliding wear, and the structure of the slipper should be suitable for the characteristics of raw water and materials used

Based on authois researches, a new slipper foraxial piston pumps and motors is introduced in this paper. From tests with the slipper/swashplate lest rig, it shows that the new type slipper combined with appropriate swashplate has good tribological characteristics. This slipper can operate with raw water, even sea water. The successful study on slippers will

provide good helps for design and development of raw water hydraulic axial piston pumps and motors with higher performance.

2. Introduction

The use of water as hydraulic fluid is not new. The first hydraulic machine as a means of transmitting not only energy but also control signals is raw water hydraulic press that manufactured by Joseph Bramah in 1795, which marks the beginning of the age of modern applied hydraulics. After that almost 100 years raw water was used as hydraulic medium, until the beginning of 20th century the mineral oil began to take the place of raw water. Because of the much better lubrication and anti-corrosi on properbes of mineral oil as compared with raw water and the development of oil resistant sealing materials, oil hydraulics boosted quickly and raw water hydraulics was left behind, gradually acquiring the image of an obsolete technology.

As concerns over safe or environmental issues a number of other hydraulic fluids have been developed over the past decades, such as synthetic base fluids, water base fluids, and vegetable oil base fluids, etc. These fluids have their own advantages and a certain range of applications. For a given application, engineers can make the hydraulic system have satisfactory performance by careful hydraulic fluid choice and system design. However, these hydraulic fluids also have its own shortcomings,so me shortcomings of these fluids are inherent and fatal. No one of these

hydraulic fluids can meet the requirements of fire resistance and environmentally protection at the same time, and most of these fluids are very expensive.

The re-emergence of using raw water as hydraulic fluid is mainly because of the following reasons.

(1) Environmental Protection Requirement

Without strict adherence to specific control techniques, it is nearly impossible to eliminate the threat of leakage in hydraulic systems. Industry observers believe that as much as 85% of all hydraulic fluids eventually leave their systems through slow leaks, catastrophic line breaks, or failures of fittings and seals. The leakage of hydraulic fluids with some toxic chemical additives not only make working conditions messy and unsafe, but also can not be biodegradable and have potential threat to the environment. Raw water has very good environmental compatibility and no pollution; water in the event of leakage eventually evaporates without leaving greasy or dirty residuals needs of applications for water hydraulics. The need of new applications is the intrinsic force of re-emergence and development of water hydraulics

(2) Requirement of Safety

Mineral oil are flammable, its leakage or spilling from systems may be result in a fire when in or near heat sources. Water is not flammable and does not present a fire hazard. In some areas, such as steel and glass production, iron making and foundry, injection molding, die casting, nuclear power, coal mining, etc. the requirement of safety is prime, so raw water hydraulics may be the best choice in the near future

(3) Hygienic Requirement

In some fields, such as gold mining, food and medicine processing, water supply industry, etc , where escaping of oil or chemical additives from hydraulic systems can smear the product and damage the quality of manufactured product. Under these conditions, raw water is an ideal pressure medium.

(4) Economy Requirement

Water is available everywhere, needing no purchase, transport, storage, maintenance and disposal costs, so using water instead of mineral oil and other hydraulic fluids may offer tremendous economy. In ambient water environment, the system using raw water as hydraulic fluid can be designed as an open circuit.That means the return lines and water reservoir can be eliminated, further more the heater and the cooler of system are no longer needed, so the volume and weight of hydraulic equipment will reduced and the efficiency of system increased. If used underwater, such as in marine engineering, ocean exploration engineering, subsea equipment, underwater operation tools and robots, etc., water hydraulics can automatically counterbalance the water hydrostatic head, this is very important for improving the efficiency and performance of the hydraulic systems.

(5) Need of New Applications

Along with the developments of modern science and technologies, many areas with special requirements provide many new opportunities of applications for water hydraulics. Such as fusion reactor equipment in nuclear power engineering, marine equipment and robots in ocean exploration engineering, etc，where the fire resistance, hygienic requirement, economy and environmental protection are all considered. Because of higher power density and smaller size of hydraulics than that of other power transmissions, there have urgent needs of applications for

water hydraulics.The need of new applications is the intrinsic force of re-emergence and development of water hydraulics.

3. Material Selection

The slipper/swashplate pair is one of the very important friction pairs in axial piston pumps and motors. Under the lubrication of raw water,ingenious material selection is necessary.

In a typical axial swashplate is stationary piston pump or motor, the swashplate is stationary ; the swashplate angle with the shaft centerline determines the length of the piston stroke (see Fig.

1)

When using raw water as lubricant,according to rawwater's chemically active nature, low viscositylubrication and high vapor pressure,more problem should be considered.

Firstly, raw water especially seawater is more aggressive , a large number of ions in seawater result in that seawater have much higher electric conductivity and may lead to electrochemistry erosion. The materials used for slipper and swashplate inevitably suffer aggressive corrosion from raw water , and the materials used for traditional oil hydraulic components will not be suitable here.

Secondly, the kinematic viscosity of water at 50℃is approximately 0.55cs ,which is less than 1/30 of the viscosity of a typical mineral oil fluid. The very low viscosity must increase the difficulty of developing hydrodynamic film between slipper and swashplate,and the very small change of water’s viscosity with pressure means that elastohydrodynamic lubrication with hard materials is unlikely to occur. Hydraulic fluids with additives that aid in the boundary lubrication of contacting surface permit metal-on-metal contact without large amounts of surface damage or wear. Raw water contains on such additives and its lubrication is very poor. The poor lubrication of water is clearly one of its major dtawbacks, and will lead to increase contact fraction and possibly wear of contacting conponents. Indeed it is well documented that wear was the greatest problem experienced by the early users of water based fluids in axial piston pumps. Researches indicate that the elastohydrodynamic film of water is about 0.1μm thick at 3m/s and 20-60℃, the elastohydtodynamic film of HWBF is about 0.15μm thick at 0.19~1.27m/s and 23.5℃. So there are risks as high dry friction and strong wear between slipper and swashplate under the lubrication

of raw water.

Thirdly, the vapor pressure of water is much higher than that of mineral oil, which means that water boils or vaporizes much easier. Due to water’s high vapor pressure and high velocity flow caused be water’s low viscosity, the slipper and swashplate will be exposed to strong and fast cavitation erosion.

So material selection for slipper/swashplate pair should depend on the operation conditions and the special properties of raw water. Materials for slipper/swashplate combination should have superior mechanical strength, low friction, resistance to aggressive corrosion, cavitation erosion,abrasion,and sliding wear, and should be easy available and cost low.

4.Structure Design

The structure design of slipper is very important as well as the material selection.

The use of polymers as the material of slipper will derive a new problem-how to make the slipper wrap on the ball-shaped head of piston. Probably the solution is to use corrosion resistant metals combined with polymers. The slipper can be divided into two parts. One is slipper pad made of polymer, directly contact on the swashplate, its main function is making the slipper have good tribological properties. The other is shoe made of corrosion resistant alloy, its main function is making the slipper wrap on the ball-shaped head of piston. This structure can take the advantages of both metal’s ductility and polymer’s good tribological property(see Fig.2).

The main static forces exerted on slipper are show in Fig.3. The force F acted on slipper from piston head includes hydrostatic force Fp on the piston end, spring force Fs, inertia force Fa of piston and slipper, and friction force Ff between piston and cylinder bore as formula:

The reaction force N from swashplate can be divided into two components, component Nh of hydrostatic bearing force and component Nm of mechanical surface pressure,as following:

N=Nh+Nm

The relationship of N and F is:

F=N·cosα

5.Conclusions

Based on author’s researches, some conclusions about material selection and structure design of slipper under lubrication of raw water can be summarized as following:

(1)Slipper made of polymers combined with swashplate made of corrosion resistant alloys

has superior tribological properties.

(2)Cotton fiber-filled phenolics can be used to manufacture slipper for a certain

application range of operation pressure below 14MPa.

(3)The spring force exerted on slipper should be strong enough to keep about 0.1~0.2MPa

contacting pressuer on the surfaces of slipper and swashplate.

Farther tests are underway, and ceramics with good toughness will be introduced to manufacture slipper and swashplate. The experiences of study on slippers will provide good helps for design and development of raw water hydraulic axial piston pumps and motors.

References

[1] Joseph L. Foszcz, Hydraulic Fluid Choices, Plant Engineering, (8),1996,68.

[2]Li Zhuangyun, et al, Development of Hydraulic Pump to Operate with Raw water,

Proceedings of ASME Fluid Engineering Division Summer Meeting, Washington DC, USA, June 21-25,1998.

[4]吴仁荣，水润滑滑动轴承的设计计算，机电设备，（6），1997,30.

[5]许耀铭，油膜理论与液压泵和马达的摩擦副设计，北京；机械工业出版社，1987.

关于自然水液压轴向活塞泵和电动机的滑动部分的研究

1.摘要

基于环境和谐、安全和卫生需要的考虑，液压系统使用自然水作为压力介质这种现象变得越来越广泛。一个自然水液压系统相对于普通的油液压系统有很多优点，例如：环境和谐，没有污染，没有火的危害，与昂贵的油相关的危害、维护、贮存、管理问题的消除，返回塑料管的消除和健康危害的消除等等。但是作为液压系统的介质，自然水也有一些缺点，例如非常低的粘性，很高的水蒸气压力，缺少润滑和化学性自然等等，都加剧了腐蚀、磨损、气蚀侵蚀、泄露等问题，这些问题必须在设计和自然水液压元件的发展，尤其是材料和自然水液压泵和电动机的摩擦部分的结构设计中被克服。

滑动部分/旋转罗盘部分是轴向活塞泵和电动机中的重要摩擦部分。在自然水的润滑下，滑动部分和旋转罗盘结合部分的材料应该较好的机械强度、低摩擦力、腐蚀的抵抗性、磨损、气蚀侵蚀和滑动摩擦，并且滑动部分的结构应该对于自然水和使用材料的特性是适合的。

根据作者的研究，一种新型的用于轴向活塞泵和电动机上的滑块会在这篇文章中介绍。从滑块/旋转罗盘部分试验中表明这种新型的与合适旋转罗盘结合的滑块有着非常好的摩擦特性。这种滑块能够用自然水润滑，甚至是海水也可以。这个关于滑块的研究将会为自然水液压轴向活塞泵和电动机的更好发展提供好的帮助。

2.介绍

水用来作为液压流体已经不是新技术了。作为转换能源和控制信号的一种方式，第一台液压机器就是自然水液体压力，并且在1795年由杰瑟夫大量生产，同时也标志着现代液压时代的开始。在那之后几乎100年自然水被用作液压介质，直到20世纪的初期，油介质开始取代水介质。和自然水相比，油介质有更好的润滑和矿物油的抗腐蚀性，并且油抗性密封材料，油液压装置发展的很快，自然水液压装置就落后了，渐渐成为一种过时的技术了。

基于在安全和环境问题方面的考虑，许多其他液压流体已经在过去的几十年发展了，例如合成来源液体、水来源液体和蔬菜油来源液体等等。这些液体有着它们各自的优点和确定的用途。对于一种给定的用途，工程师能够通过合理的液压流体选择和系统设计来使液压系统满足这个条件。然而，这些液压流体也存在着自身的缺点，其中的某些缺点是内在的并且是重大的。这些液压流体中没有一种能同时满足防火性和环保性的要求，同时大部分液体是很昂贵的。

使用自然水作为液压流体主要由于以下几个原因：

（1）环境保护的需要

如果对于特殊控制技术没有严格的遵守，评估液压系统中的泄露威胁是不可能的。工业观察员相信所有液压流体中85%的流体最后都是通过缓慢泄露、严重的连接破损或者设备和密封的故障而离开液压系统的。液压流体和一些有毒的化学添加剂的泄露不仅使工作条件混乱和不安全，同时也不能生物降解和对环境存在潜在的危害。自然水拥有很好的环境适应性并且没有污染；水在泄露后也会消失而没有油腻和脏的残留物。

（2）安全的需要

矿物油是可燃的，当周围有热源的时候它的泄露可能会导致起火。水是不可燃的，所以不会存在起火隐患。在一些区域，例如钢铁和玻璃生产，钢铁制造和铸造，注射模具，拉模铸造，核动力，采煤等等，对于安全的要求是主要的，因此自然水液压可能会成为将来的最好选择。

（3）液压的需要

在一些领域，例如金矿开采，事物和药品生产，水提供工业等等，这些由于油或者化学添加剂从液压系统中泄露而弄脏产品或是损害大批产品的质量，在这些条件下，自然水是一种理想的压力介质。

（4）经济的需要

水在很多地方都是存在的，不需要购买、运输、贮存、保持和清理成本，因此使用水代替矿物油和其他液压流体可以提供极大的经济性。在包围的水环境中，系统使用自然水作为液压流体能够被设计成开式循环。那意味着返回线和水储藏可以消除，加热和冷却系统也不再需要了，因此液压设备的容积和重量也会减少而系统的效率会增加。如果水下作业，例如在海运的工程上，海洋探索工程，海底设备，水下操作工具和机器人等等，水液压能够自动的抵消水静力的前端，这对于提高效率和液压系统的性能是很重要的。

（5）新应用的需要

随着现代科学和技术的发展，许多有着特殊需求的领域为水液压提供了很多运用的机遇。例如在核电工程中的核聚变反应装置，在海洋探索工程中的海运设备和机器人等等，这些地方需要考虑抗燃性，清洁的设备，经济性和环保等方面。和其它的能源转换相比，由于液压系统有较高的力密度和较小的尺寸，所以对于水液压的应用是迫切需要的。新应用的需要是水液压的出现和发展的内在反应。

3．材料选择

滑动部分/旋转罗盘部分是轴向活塞泵和电动机中的重要摩擦部分。在自然水的润滑下，巧妙地选择材料是有必要的。

在一个典型的轴向活塞泵或电动机中，旋转罗盘固定不动的，旋转罗盘与轴线的角度决定了活塞盘的长度。

当使用自然水作为润滑剂时，由于自然水的化学活性自然，低粘性，润滑性差和较高的蒸汽压力，所以需要考虑很多问题。

首先，自然水，尤其海水是活性的，海水中的大量离子导致海水有很强的导电性并且会导致电化学腐蚀。用在滑块和旋转罗盘上的材料会不可避免地遭到自然水的活性腐蚀，并

且用于传统油液压器件也不适合用在这里。

第二点，水的运动粘性在50℃时接近0.55cs，少于典型矿物油液体粘性的1/30。过低的粘性一定会增加发展滑块和旋转罗盘之间水力薄层的困难程度，并且水的粘性伴随着压力的很小变化意味着硬质材料的流体动力润滑是不容易发生的。带有添加剂的液压流体使得金属与金属表面之间没有大量表面破坏或是磨损。自然水不包含如此多的添加剂并且它的润滑性是很差的。水的润滑性差很明显是它的一个主要缺点，并且会导致接触、破碎、和接触器件之间摩擦的加剧。事实上摩擦是早期用水作为轴向活塞泵的流体的使用者遇到的最大问题。研究表明水的流体弹性动力薄层在3m/s和20~60℃时大约是0.1μm厚，HWBF的流体弹性动力薄层在0.19~1.27m/s和23.5℃时大约是0.15μm厚。因此在自然水润滑下，滑块和旋转罗盘之间有干摩擦和强烈摩擦时会存在危险。

第三点，水的蒸汽压力要比矿物油的高很多，这意味着水沸腾或是蒸发会更加容易。由于水的高蒸汽压力和高速流动性由水的粘性地决定的，所以滑块和旋转罗盘会受到强烈和快速的气穴气蚀损害。

因此，对于滑块和旋转罗盘部分材料的选择应该依据工作条件和自然水的特殊性质。滑块和旋转罗盘之间的连接部分应该有很好的机械强度、低摩擦、抗腐蚀性、和气穴气蚀、磨损和滑动摩擦，并且应该有很好的实用性和低成本。

4.结构设计

滑块的结构设计和材料的选择是同样重要的。

用在滑块上的高分子材料会产生一个新的问题，就是怎样使滑块包围住活塞前端的球形部分。其中一个解决办法就是使用抗腐蚀材料与高分子材料连接。滑块可以分成两部分。一部分就是由高分子材料制成的滑块垫，直接与旋转罗盘相连，他的主要的功能就是使滑块有很好的摩擦性能。另一部分是由抗腐蚀的合金材料制成的鞋，它的主要功能是使滑块在活塞的球形头上摩擦。这个结构能够很好的利用金属的展延性和高分子材料的摩擦性。（见图2）

在滑块上的主要的静力在图3中有表示。滑块上的力F来自活塞头，包括活塞尾端的液体压力Fp，反弹力Fs, 活塞和滑块的惯性力Fa,还有活塞与圆孔之间的摩擦力Ff。

来自旋转罗盘的反作用力N能够被分成两部分液压轴承力Nh和机械表面压力Nm，如下所示：N=Nh+Nm

N和F的关系是：F=N·cosα

5.结论

根据作者的研究，一些关于滑块在自然水润滑下的材料选择和结构设计结论可以总结为如下几条：

（1）用高分子材料制作成的滑块与用抗腐蚀性合金制成的旋转罗盘结合有很好的摩擦性。

（2）在滑块的大量制造中棉布纤维填充的酚醛塑料被使用，目的是使工作压力低于14MPa。

（3）在滑块上的反弹力应该足够强以确保滑块和旋转罗盘表面上的连接压力在

0.1~0.2MPa。

除此之外还有一些实验需要进行，并且拥有良好韧性的陶瓷材料也会被引进用来大

量制造滑块和旋转罗盘。在滑块研究上的经验将会为自然水液压轴向活塞泵和电动机的设计和发展提供很大的帮助。

参考文献：

[1] Joseph L. Foszcz, Hydraulic Fluid Choices, Plant Engineering, (8),1996,68.

[2]Li Zhuangyun, et al, Development of Hydraulic Pump to Operate with Raw water,

Proceedings of ASME Fluid Engineering Division Summer Meeting, Washington DC, USA, June 21-25,1998.

[4]吴仁荣，水润滑滑动轴承的设计计算，机电设备，（6），1997,30.

[5]许耀铭，油膜理论与液压泵和马达的摩擦副设计，北京；机械工业出版社，1987.