外文翻译--液压系统与液压油地选择-精品

中文3960字

附件1：外文资料翻译译文

液压系统与液压油的选择

液压机直到工业革命时期才由英国机械师约瑟夫·布拉玛根据帕斯卡定律制造出来。1795年，他申请并获得了液压机的相关专利，从此布拉玛液压机声名鹊起。布拉玛通过计算发现如果在一个小面积面上施加一个不大的力，那么，它将在相对较大的面上产生一个较大的力，而唯一影响机器发挥这种力的因素是这个面上所施加力的大小。

1 什么是液压系统？

从集成钢的小型组装流程和造纸厂的应用可以发现，液压系统在今天已经有了非常广泛的应用。液压帮助操作员完成许多重要工作(抬沉重的负荷、转向轴、孔钻进精度等)，同时有效降低了机械联动的成本，这一切都归功于帕斯卡定律，帕斯卡定律表述如下：

“由于液体的流动性，封闭容器中的静止流体的某一部分发生的压强变化，将毫无损失地传递至流体的各个部分和容器壁（图1）。”

图1 帕斯卡定律

由布拉马对帕斯卡定律的应用可知，如果在一个10平方英寸的面上作用100磅的力，那么整个容器内的每平方英寸上将产生100磅的力。也就是说，这种力能在100平方英寸的面上产生1000磅的力。

液压系统是对帕斯卡定律的合理运用，它通过液压油在两点间传递能量。液压油几乎是不可压缩的，所以它能轻松地在瞬间传递力量。

2 液压系统的组成

液压系统的主要组成部分是液压缸，液压泵，阀和执行机构（马达，油缸等）。

2.1 液压油箱

液压油箱的作用是存储压油，传递出系统热量，回收排出的污染物质和促进系统中游离液体或气体的释放。

2.2 液压泵

液压泵通过作为传输媒介的液压油的运动，将机械能转化为液压能。液压泵有齿轮泵，叶片泵，柱塞泵几种类型。这些不同类型的泵都有特定的应用，如曲轴柱塞泵或变量叶片泵。所有泵的工作原理都是相同的，利用液体体积对抗负载或压力。

2.2 液压阀

液压阀主要是由锥阀芯或圆柱阀芯构成，它用于系统的启动，停止和引导流体流动。液压阀可以通过气动、液压、电气、人工或机械等方式驱动。

2.3 执行机构

液压执行机构是帕斯卡定律的终端，它的目的是将液压能转变回机械能。这可以通过液压缸转换为直线运动，或用液压马达将其转化为旋转运动。和液压泵一样，液压缸和液压马达也因特定的应用而设计成不同的类型。

3 液压系统润滑的重点组件

考虑到维修成本和任务的重要程度，液压系统的各组成元件中，泵和阀门是关键组成部分。从润滑的角度看，泵的几个部件必须单独进行维护，其中包括：

3.1 叶片泵

不同厂家生产的泵存在一定差异，但它们均以类似的设计原则工作既将转子连

接到驱动轴上后装入定子，同时使其与轴保持偏心。叶片则插入到转子上，并能沿定子内表面运动。

通常情况下叶片和定子内壁总是有接触的，因此会产生大量的磨损。这将导致叶片从槽中脱落。叶片泵花费巨大代价提供稳定的流动。在工作温度工作时，正常的粘度为14至160cSt。叶片泵一般不适用于液压油质量难以保证的高压系统，同时抗磨添加剂的优劣对泵有着巨大影响。

3.2 柱塞泵

和所有的液压泵相同，柱塞泵也被设计为定量泵和变量泵两种。柱塞式液压泵用途广泛且造型复杂，能应对各种类型系统的用途及要求。柱塞泵效率高，工作压力高达6000万磅，而它却只产生很小的噪音。同时柱塞式液压泵的抗磨损设计往往优于其余泵的设计。柱塞式液压泵正常工作的运动粘度值为10到160cSt。

3.3 齿轮泵

齿轮液压泵从结构上分有两种形式，内啮合式液压泵和外啮合式液压泵。两者都有各自的子类型，但它们都是通过两个啮合齿轮间流体的流动发展而来。总体上来说，齿轮泵的效率低于叶片泵和柱塞泵，齿轮泵的优点在于它有更强的抗污能力。

(1) 内啮合式齿轮液压泵所能产生的压力高达3000至3500帕斯卡。这一类的液压泵因为粘度的不同能应对很广的粘度范围，最大运动粘度值为2200cSt，而其此类液压泵的噪音极低。即便是内啮合式液压泵的液压油保持在很低的粘度，它的工作效率也很高。

(2) 外啮合式齿轮液压泵可处理的压力范围在3000至3500磅之间。这些泵一般应用于廉价，中压，中批量生产，定排量的系统中。在这一系列中泵的运动粘度值范围有限，一般不到300cSt。

4 液压油

现如今，液压油在液压系统中扮演了很多重要角色。它的主要功能是在系统间传递能量以保证系统动作顺利完成。同时，液压油还担负着润滑、散热、防污的重任。在选择液压油时因考虑粘度、密封相容性、存储和添加剂的封装。目前市面常售的液压油主要为石油基液压油、矿物液压油和合成液压油。

(1) 目前应用最为广泛的液压油是由石油或矿物质为基础制成。矿物液压油的

性能主要取决于添加剂的使用，原油的质量及其提炼的过程。添加剂对石油基液压油的主要性能特点起主导作用。常用的液压油添加剂主要包括防锈添加剂、抗氧化(R&O)添加剂、防腐蚀剂、反乳化剂、抗磨（AW）添加剂、极压(EP)添加剂、粘度指数增强剂和泡沫抑制剂。总体上来说，矿物液压油的性价比很高，是非常好的选择。

(2) 水基液压油由于其含水量高，故有较强的阻燃性。常见的类型有水包油乳化液、水型油乳液和水乙二醇混合物。水基液压油能起到合适的润滑作用，但是由于水基液压油的特点，需要随时监控以防出现问题。水基液压油往往用于要有耐火特性的情况下，此时液压系统会处在高温的环境中。温度升高将导致液压油内的水分加速蒸发，从而导致液压油粘度的增加。有时凝结的蒸馏水进入液压系统中，可能使液压油重新平衡。但当使用此类水基液压油时其中的几个组件的兼容性就必须检查，包括液压泵、过滤器、管道、管件及密封材料。水基液压油的价格比常规的石油基液压油高，而且它还有一些其它缺点（例如，较低的耐磨性），因此在使用时需权衡利弊。

(3) 合成液压油是人造润滑剂，此类液压油性能优秀，即使是在高温高压的液压系统中也能保持极好的润滑性。一般，合成液压油具有阻燃（磷酸酯）、低摩擦、自动清污（有机酯与增强酯合成的碳氢化合物）和热稳定性。同时合成液压油的缺点也很明显，它们比传统液压油更贵，需要特殊处理，甚至有些液压油可能略有毒性，而且它们常常不能与密封材料共存。

5 流体性质

在选择液压油时，需考虑以下几个特点：粘度、粘度指数、抗氧化性和耐磨性。这些特性对液压系统的正常运行有很大的影响。流体性质的测试工作可在美国试验与材料协会（ASTM）或其他任何公认的标准组织进行。

(1) 粘度（ASTM D445-97）是流体抵抗流动和剪切的措施。与低粘度的液压油相比，高粘度的液压油在流动时会受到更大的阻力。过高的粘度可能导致液压油温度的升高，无谓的消耗能源。粘度过高或过低都会损坏液压系统，所以液压油的选用是个关键因素。

(2) 粘度指数（ASTM D2270）是用来衡量流体粘度随温度变化程度的量。通常在相同条件下，液压油的粘度指数越高，它所能保持其粘度不变的温度范围越大。

故高粘度指数的液压油适用于极端温度的环境中。这对于在室外作业的液压系统来说尤为重要。

(3) 抗氧化性（ASTM D2272及其它）是指液压油抵抗由温度引起的氧化而使液压油降解的能力。氧化时液压油的寿命大大降低，而且会产生诸如污泥和清漆之类的副产品。清漆这种沉淀物极有可能卡死阀门，堵塞管道。

(4) 耐磨性（ASTM D2266及其它）是润滑油减少边界接触摩擦磨损率的能力。这会使液压油在金属表面形成一层保护膜以防止元件表面的磨损、划伤和接触疲劳。

6 检查最佳粘度范围的十个步骤

在选择润滑油时，应确保润滑油能在液压泵和液压马达中有效运作。在系统动作的过程中，有明确的程序是十分重要的。假设有一个由一定量齿轮泵驱动液压缸的简单液压系统（图2）。

图2 简单液压系统

(1) 收集液压泵所有的相关数据。这其中包括泵在设计中的局限性和其出厂时所规定的最佳工作条件。通过咨询厂商，将可以知道泵工作时润滑油适宜的粘度范围。如，液压泵所需润滑油的粘度需在13cSt到54cSt之间，而最佳粘度为23cSt。

(2) 测试液压泵正常工作时的实际温度。这个步骤极其重要，因为液压泵工作时，使用任何润滑油，实际温度都是必不可少的参考条件。一般情况下，泵的正常工作温度在92oC左右。

(3) 研究液压泵正在使用的顺滑油的温度——粘度特性。这里推荐使用国际标准化组织粘度评级系统（适用于40o C 至 100oC）。如，在40 oC时的粘度值为32cSt，100 oC时的粘度值为5.1cSt。

(4) 一张ASTM D341的标准石油产品粘度-温度表是必不可少的。这种表较为普遍，一般在大多数工业润滑油的使用指南都附带此表，当然也可以从润滑油的生产厂商索取。

(5) 结合第三步研究润滑油粘度特性所得到的结论，首先在图表的温度轴（x 轴）上找出温度所对应的线如40 oC的线，再根据润滑油厂商提供的润滑油在40oC时的粘度在图上找出对应的粘度线，然后标记两条直线的交点（图3中红线）。

(6) 在润滑油温度为100 oC时，重复第五步，并标记点（图3中深绿色线）。

(7) 用直线连接这些标记点（图3中黄线）。这条线表示了在一系列温度时，润滑油的粘度。

(8) 在表中的粘度轴上找出厂商提供的相应润滑油最佳粘度值之对应点，然后在该点上画一条水平线与黄色线相交。接着从此交点引一条垂直线（图3中绿线）至表底部。上述黄线倍几条温度线分割，这条线所穿过的区域是泵中特定润滑剂的最佳工作温度（69oC）。

(9) 当粘度分别为泵所需粘度的最大值和最小值时，重复步骤8画出线（图3中棕色线）。介于最高温度和最低温度间的区域是为泵选择理想润滑油的根据既算选润滑油的温度范围必须在这个区域内。

(10) 在图表上找出步骤2所述测出温度所对应的值，如果这一值落在最高温度和最低温度所形成的区域之间，则表明该液压油适合这个系统。否则，就要更换液压油。因此，从表上可以看出，所举液压油的正常工作条件超出了合适范围，需要更换。

图3 粘度-温度表

此外，请遵守以下液压油的管理原则:

(1) 标记所有的输入液压油和液压油箱。这将最大限度地减少交叉污染，确保关键性能得到满足。

(2) 在液压油的存储设备中采用先入先出的方式。这种先入先出的系统将减少由于使用混乱和存储问题造成的液压油失效。

液压系统是以流体为基础的相对复杂的系统，它能轻松地将能量转变为有用的动作。但是只有根据系统要求选择了合适的液压油，液压系统才能正常工作。在选择液压油时，要合理考虑到液压油的粘度。当然需要考虑的重要参量还有很多，包括粘度指数、耐磨性和抗氧化性等。

附件2：外文原文

Hydraulic Systems and Fluid

Selection

I t wasn’t until the beginning of the industrial revolution when a British mechanic named Joseph Bramah applied the principle of Pascal’s law in the development of the first hydraulic press. In 1795, he patented his hydraulic press, known as the Bramah press. Bramah figured that if a small force on a small area would create a proportionally larger force on a larger area, the only limit to the force that a machine can exert is the area to which the pressure is applied.

What is a Hydraulic System?

Hydraulic systems can be found today in a wide variety of applications, from small assembly processes to integrated steel and paper mill applications. Hydraulics enable the operator to accomplish significant work (lifting heavy loads, turning a shaft, drilling precision holes, etc.) with a minimum investment in mechanical linkage through the application of Pascal’s law, which states:

“Pressure applied to a confined fluid at any point is transmitted undiminished throughout the fluid in all directions and acts upon every part of the confining vessel at right angles to its interior surfaces and equally upon equal areas (Figure 1).”

Figure 1

By applying Pascal’s law and Brahma’s application of it, it is evident that an input force of 100 pounds on 10 square inches will develop a pressure of 10 pounds per square inch throughout the confined vessel. This pressure will support a 1000-pound weight if the area of the weight is 100 square inches.

The principle of Pascal’s law is realized in a hydraulic system by the hydraulic fluid that is used to transmit the energy from one point to another. Because hydraulic fluid is nearly incompressible, it is able to transmit power instantaneously.

Hydraulic System Components

The major components that make up a hydraulic system are the reservoir, pump, valve(s) and actuator(s) (motor, cylinder, etc.).

Reservoir

The purpose of the hydraulic reservoir is to hold a volume of fluid, transfer heat from the system, allow solid contaminants to settle and facilitate the release of air and moisture from the fluid.

Pump

The hydraulic pump transmits mechanical energy into hydraulic energy. This is done by the movement of fluid which is the transmission medium. There are several types of hydraulic pumps including gear, vane and piston. All of these pumps have different subtypes intended for specific applications such as a bent-axis piston pump or a variable displacement vane

pump. All hydraulic pumps work on the same principle, which is to displace fluid volume against a resistant load or pressure.

Valves

Hydraulic valves are used in a system to start stop and direct fluid flow. Hydraulic valves are made up of poppet’s or spools and can be actuated by means of pneumatic, hydraulic, electrical, manual or mechanical means.

Actuators

Hydraulic actuators are the end result of Pascal’s law. This is where the hydraulic energy is converted back to mechanical energy. This can be done through use of a hydraulic cylinder which converts hydraulic energy into linear motion and work, or a hydraulic motor which converts hydraulic energy into rotary motion and work. As with hydraulic pumps, hydraulic cylinders and hydraulic motors have several different subtypes, each intended for specific design applications.

Key Lubricated Hydraulic Components

There are several components in a hydraulic system, that due to cost of repair or criticality of mission, are considered vital components. Pumps and valves are considered key components. Several different configurations for pumps must be treated individually from a lubrication perspective, including:

Vane Pumps

There are many variations of vane pumps available between manufacturers. They all work on similar design principles. A slotted rotor is coupled to the drive shaft and turns inside of a cam ring that is offset or eccentric to the drive shaft. Vanes are inserted into the rotor slots and follow the inner surface of the cam ring as the rotor turns.

The vanes and the inner surface of the cam rings are always in contact and are subject to high amounts of wear. As the two surfaces wear, the vanes come further out of their slot. Vane pumps deliver a steady flow at a high cost. Vane pumps operate at a normal viscosity range between 14 and 160 cSt at operating temperature. Vane pumps may not be suitable in critical high-pressure hydraulic systems where contamination and fluid quality are difficult to control. The performance of the fluid’s antiwar additive is generally very important with vane pumps.

Piston Pumps

As with all hydraulic pumps, piston pumps are available in fixed and variable displacement designs. Piston pumps are generally the most versatile and rugged pump type and offer a range of options for any type of system. Piston pumps can operate at pressures beyond 6000 psi, are highly efficient and produce comparatively little noise. Many designs of piston pumps also tend to resist wear better than other pump types. Piston pumps operate at a normal fluid viscosity range of 10 to 160 cSt.

Gear Pumps

There are two common types of gear pumps, internal and external. Each type has a variety of subtypes, but all of them develop flow by carrying fluid between the teeth of a meshing gear set. While generally less efficient than vane and piston pumps, gear pumps are often more tolerant of fluid contamination.

1. Internal gear pumps produce pressures up to 3000 to 3500 psi. These types of pumps offer

a wide viscosity range up to 2200 cSt, depending on flow rate and are generally quiet. Internal gear pumps also have a high efficiency even at low fluid viscosity.

2. External gear pumps are common and can handle pressures up to 3000 to 3500 psi. These gear pumps offer an inexpensive, mid-pressure, mid-volume, fixed displacement delivery to a system. Viscosity ranges for these types of pumps are limited to less than 300 cSt.

Hydraulic Fluids

Today’s hydraulic fluids serve multiple purposes. The major function of a hydraulic fluid is to provide energy transmission through the system which enables work and motion to be accomplished. Hydraulic fluids are also responsible for lubrication, heat transfer and contamination control. When selecting a lubricant, consider the viscosity, seal compatibility, base stock and the additive package. Three common varieties of hydraulic fluids found on the market today are petroleum-based, water-based and synthetics.

1. Petroleum-based or mineral-based fluids are the most widely used fluids today. The properties of a mineral-based fluid depend on the additives used, the quality of the original crude oil and the refining process. Additives in a mineral-based fluid offer a range of specific performance characteristics. Common hydraulic fluid additives include rust and oxidation inhibitors (R&O), anticorrosion agents, demulsifies, antiwar (AW) and extreme pressure (EP) agents, VI improvers and defoamants. Mineral-based fluids offer a low-cost, high quality, readily available selection.

2. Water-based fluids are used for fire-resistance due to their high-water content. They are available as oil-in-water emulsions, water-in-oil (invert) emulsions and water glycol blends. Water-based fluids can provide suitable lubrication characteristics but need to be monitored closely to avoid problems. Because water-based fluids are used in applications when fire resistance is needed, these systems and the atmosphere around the systems can be hot. Elevated temperatures cause the water in the fluids to evaporate, which causes the viscosity to rise. Occasionally, distilled water will have to be added to the system to correct the balance of the fluid. Whenever these fluids are used, several system components must be checked for compatibility, including pumps, filters, plumbing, fittings and seal materials. Water-based fluids can be more expensive than conventional petroleum-based fluids and have other disadvantages (for example, lower wear resistance) that must be weighed against the advantage of fire-resistance.

3. Synthetic fluids are man-made lubricants and many offer excellent lubrication characteristics in high-pressure and high- temperature systems. Some of the advantages of

synthetic fluids may include fire-resistance (phosphate esters), lower friction, natural detergency (organic esters and ester-enhanced synthesized hydrocarbon fluids) and thermal stability. The disadvantage to these types of fluids is that they are usually more expensive than conventional fluids, they may be slightly toxic and require special disposal, and they are often not compatible with standard seal materials.

Fluid Properties

When choosing a hydraulic fluid, consider the following characteristics: viscosity, viscosity index, oxidation stability and wear resistance. These characteristics will determine how your fluid operates within your system. Fluid property testing is done in accordance with either American Society of Testing and Materials (ASTM) or other recognized standards organizations.

1. Viscosity (ASTM D445-97) is the measure of a fluid’s resistance to flow and shear. A fluid of higher viscosity will flow with higher resistance compared to a fluid with a low viscosity. Excessively high viscosity can contribute to high fluid temperature and greater energy consumption. Viscosity that is too high or too low can damage a system, and consequently, is the key factor when considering a hydraulic fluid.

2. Viscosity Index (ASTM D2270) is how the viscosity of a fluid changes with a change in temperature. A high VI fluid will maintain its viscosity over a broader temperature range than a low VI fluid of the same weight. High VI fluids are used where temperature extremes are expected. This is particularly important for hydraulic systems that operate outdoors.

3. Oxidation Stability (ASTM D2272 and others) is the fluid’s resistance to heat-induced degradation caused by a chemical reaction with oxygen. Oxidation greatly reduces the life of a fluid, leaving by-products such as sludge and varnish. Varnish interferes with valve functioning and can restrict flow passageways.

4. Wear Resistance (ASTM D2266 and others) is the lubricant’s ability to reduce the wear rate in frictional boundary contacts. This is achieved when the fluid forms a protective film on metal surfaces to prevent abrasion, scuffing and contact fatigue on component surfaces.

Ten Steps to Check Optimum Viscosity Range

When selecting lubricants ensure that the lubricant performs efficiently at the operating parameters of the system pump or motor. It is useful to have a defined procedure to follow through the process. Consider a simple system with a fixed-displacement gear pump that drives a cylinder (Figure 2).

Figure 2

1. Collect all relevant data for the pump. This includes collecting all the design limitations and optimum operating characteristics from the manufacturer. What you are looking for is the optimum operating viscosity range for the pump in question. Minimum viscosity is 13 cSt, maximum viscosity is 54 cSt, and optimum viscosity is 23 cSt.

2. Check the actual operating temperature conditions of the pump during normal operation. This step is extremely important because it gives a reference point for comparing different fluids during operation. Pump normally operates at 92o C.

3. Collect the temperature-viscosity characteristics of the lubricant in use. The ISO viscosity rating system (cSt at 40o C and 100oC) is recommended. Viscosity is 32 cSt at 40oC and 5.1 cSt at 100o C.

4. Obtain an ASTM D341 standard viscosity-temperature chart for liquid petroleum products. This chart is quite common and can be found in most industrial lubricant product guides or from lubricant suppliers.

5. Using the viscosity characteristics of the lubricant found in Step 3, start at the temperature axis (x-axis) of the chart and scroll along until you find the 40 o C line. At the 40o C line, track upward until you find the line corresponding to the viscosity of your lubricant at 40o C as published by your lubricant manufacturer. When you find the corresponding line, make a small mark at the intersection of the two lines (red lines, Figure 3).

6. Repeat Step 5 for the lubricant properties at 100o C and mark the intersection point (dark blue line, Figure 3).

7. Connect the marks by drawing a line through them with a straight edge (yellow line, Figure 3). This line represents the lubricant’s viscosity at a range of temperatures.

8. Using the manufacturer’s data for the pump’s optimum operating viscosity, find the value on the vertical viscosity axis of the chart. Draw a horizontal line across the page until it hits the yellow viscosity vs. temperature line of the lubricant. Now draw a vertical line (green line, Figure 3) to the bottom of the chart from the yellow viscosity vs. temperature line where it is intersected by the horizontal optimum viscosity line. Where this line crosses, the temperature axis is the optimum operating temperature of the pump for this specific lubricant (69oC).

9. Repeat Step 8 for maximum continuous and minimum continuous viscosities of the pump (brown lines, Figure 3). The area between the minimum and maximum temperatures is the minimum and maximum allowable operating temperature of the pump for the selected lubricant product.

10. Find the normal operating temperature of the pump on the chart using the heat gun scan done in Step 2. If the value is within the minimum and maximum temperatures as outlined on the chart, the fluid is suitable for use in the system. If it is not, you must change the fluid to a higher or lower viscosity grade accordingly. As shown in the chart, the normal operating conditions of the pump are out of the suitable range (brown area, Figure 3) for our particular lubricant and will have to be changed.

Figure 3

Also, observe the following hydraulic fluid management practices.

?Implement a procedure for labeling all incoming lubricants and tagging all reservoirs. This will minimize cross-contamination and assure that critical

performance requirements are met.

?Use a First-In-First-Out (FIFO) method in your lubricant storage facility. A properly executed FIFO system reduces confusion and storage-induced lubricant

failure.

Hydraulic systems are complicated fluid-based systems for transferring energy and converting that energy into useful work. Successful hydraulic operations require the careful selection of hydraulic fluids that meet the system demands. Viscosity selection is central to a correct fluid selection. There are other important parameters to consider as well, including viscosity index, wear resistance and oxidation resistance.