机械【经典外文翻译】-液压机hydraulic-machine-毕业论文.doc

Hydraulic Machine
From: The Columbia Encyclopedia, Sixth Edition    Date: 2008
Hydraulic machine that derives its power from the motion or pressure of water or some other liquid. Hydraulic equipment and technology is something that we are all at least passingly familiar with. If we think about it, we know that the principles of hydraulics are applied to make many common machines work. For example hydraulics are used in agricultural equipment, giant earth moving and mining machines, they are used to steer and stabilize giant ocean liners, help airplanes climb and turn, and make the brakes in our cars work. So hydraulics can provide great force, are obviously very adaptable and used in all kinds of applications, but how do they actually work?
What is this hydraulics stuff?
Hydraulics is based on a very simple fact of nature - you cannot compress a liquid. You can compress a gas (think about putting more and more air into a tire, the more you put in, the higher the pressure). If you're really strong you can compress a solid mass as well. But no matter how much pressure you apply onto a liquid, it isn't possible to compress it. Now if you put that liquid into a sealed system and push on it at one end, that pressure is transmitted through the liquid to the other end of the system. The pressure is not diminished.
. Hydraulics is Old Stuff
The basic concept of hydraulics is not new. The Greeks understood about using water to provide lift and force, and the name hydraulics come form the Latin word for water - "HYDRA". In the middle Ages, Leonardo da Vinci formulated the basic principle of hydraulics called continuity and Galileo experimented with hydraulics. Hydraulics were even used during the construction of the Eiffel Tower in Paris in the late 1880's. Hydraulic jacks were used to level the tower and align the metal girders to an accuracy of 1 millimeter。Today most hydraulic systems utilize oil rather than water but the principle is the same. You can compress a liquid, and a force that is applied at one point is transmitted to another point by that incompressible fluid. Because of its liquid nature, hydraulic systems can transmit force through pipes of any shape and length, so the force can be applied at one central point and transmitted efficiently to another point or to multiple points far away. Think about the master cylinder in you car's brakes and how, by stepping on the brake pedal, you apply stopping pressure on the brakes on all four wheels.
Physics
Basic physics tells us that we can trade off force for distance in all mechanical systems. In a hydraulic system, we do this by changing the relative size of the pistons at each end of the system. For example, a small piston moving a relatively large distance (say a foot) will exert pressure on a larger piston at the other end. The force will be enough to move a heavy weight a small distance (much less than a foot). Engineers and physicists can calculate exactly how much distance needs to be traveled and the relative sizes of the pistons required to move a particular weight.

Hydraulic Engines

Water falling from one level to a lower one is used to drive machines like the water wheel and the turbine . The difference in height between the highest and the lowest level is called the head。 The amount of work produced per pound of falling water is proportional to the head. Water power can be produced in this way from many natural sources, such as waterfalls and dammed rivers.。Where no natural sources are available, an artificial reservoir can be made. When energy is plentiful, it is used to pump water into the reservoir; the water is then available as a power source to drive turbines when energy becomes scarce.

In driving certain industrial hydraulic machines an apparatus called an accumulator is employed to supply high power for short periods of time. One type consists essentially of a cylinder enclosing a piston loaded with weights. When water is slowly pumped into the cylinder, the piston and weights are forced up to a position where they are held. When they are released, they force the water out of the cylinder rapidly, providing the machine with hydraulic power.

Hydrostatic Devices

Water or oil under pressure is commonly used as a source of power for many types of presses, riveting machines, capstans, winches, and other machines. The hydraulic press, or hydrostatic press, was invented by Joseph Bramah and is therefore sometimes called the Bramah press. It consists essentially of two cylinders each filled with liquid and each fitted with a piston; the cylinders are connected by a pipe also filled with the liquid. One cylinder is of small diameter, the other of large diameter. According to Pascal's law , pressure exerted on the smaller piston is transmitted undiminished through the liquid to the surface of the larger piston, which is forced upward. Although the pressure force per unit of area) is the same for both pistons, the total upward force on the larger piston is as many times greater than the force on the smaller piston as the area of the larger piston is greater than the area of the smaller piston. If , for example, the smaller piston has an area of 2 sq in. and a force of 100 lb is exerted on it, then the force on the larger piston having an area of 50 sq in. would be 2,500 lb (100× 50/2 =2,500).However, when the pistons move, the distance the smaller piston travels is proportionately greater than the distance the larger piston travels, satisfying the law of conservation of energy. If the smaller piston moves 25 in., the larger one will only move 1 in. The hydraulic press is used, for example, to form three-dimensional objects from sheet metal and plastics and to compress large objects. The hydraulic jack, also an application of Pascal's law, is used to exert large forces or to lift heavy loads. Like the hydraulic press it consists essentially of two different-sized pistons contained in cylinders that are connected by a pipe. When the smaller piston is moved back and forth by a handle connected to it, it pumps a liquid into the cylinder of the larger piston, forcing the larger piston to move. In this way a weak force applied to the smaller piston can raise a heavy load on the larger one. The hydraulic elevator is also an application of Pascal's law.
Totally understanding hydraulics is very complicated, but a basic understanding of the principle of how it works is actually very straightforward.

英文翻译
液压机
来源：哥伦比亚百科全书,第六版 日期: 2008.
液压机的能量来源于水或其它液体的压力或动力。液压装置与技术是我们平时非常熟悉的事物，如果我们仔细的思考一下，就会发现很多机械的工作都是依靠液压原理来完成的。例如液压被用于农业机械和矿山机械，它们被用于推动和保持巨轮的稳定，帮助飞机的飞行与转动，在汽车中，它可以很快的制刹，由于液压可以提供很大的推力，所以非常实用，被用于各种事物中，但它们是如何工作的呢？
液压的本质是什么？
液压以自然界中的简单现象为基础——你不必压缩液体，你可以压缩气体（想一下，当你向轮胎中注入气体的时候，越多那么压力越大）如果你足够强壮的话，你可以尽最大力量作用于固体上，但是不论你加多大的力量，它都不会被压缩。现在如果你将液体注入容器中，然后在一边施加压力，通过液体压力被传到了另一边，且压力无损失。
悠久的液压原理
. 液压的基本原理有悠久的历史，古稀腊人已懂得利用水来提供提升力与压力，液压的名字来源拉丁语中的水。在中世纪的时候，大卫建立了水压基本原理，称为连续，嘎里以水压做试验。后来1880年法国巴黎艾非尔铁塔的建设中，水压原理曾被使用。液压千斤顶被用来校平铁塔与校准铁制横梁，此时它的精确度可以达到1毫米。今天液压系统使用油而不是水，但工作原理还是一样的。你可以压缩液体，施加于一点上的压力通过那些没有被压缩的液体而传到另一点，由于液体的自然属性，液压系统可以通过任何形状与长度的管道来传送压力，所以施加于中心点的压力可以很容易的传到另一点或更远的地方。想一下你车刹中的主液压缸，是怎样通过刹车来完成四轮停转的。
物理学定律
. 物理学基本定律告诉我们：在任意机械系统中可以控制压力与距离的关系。在液压系统中，通过改变相连活塞的尺寸来控制。例如，小活塞运动一个较大的距离（译为步）将会在另一端的大活塞上产生一个力，这个力将会足够推动大活塞移动一个较小的距离（原小于一步）工程师与物理学家可以精确的计算出要移动多大的距离和相对应的活塞尺寸根据需要移动的重量。

液压引擎
水从高处流到低处所释放的能量被用来驱动水轮机和涡轮机这样的机器。最高端与最低端之间的高度差被称为势能. 每一磅水所做的功与势能成比例，通过这种办法，水能的形成可以来源于许多自然资源，诸如 瀑布和大坝。没有一个自然资源是可靠的，所以必须建造人工水库来解决这个弊端，当自然资源所产生的能量过于充足时，我们通过水泵将多余的水抽到水库中储存，当水资源产生的能量不够使用的时候，这时候库中的水就可以被利用作为能量来驱动涡轮机。在使用特定的工业液压机的时候，设备要求能量源能够在短时间内提供高压。任意类型的液压机都包含液压缸和被液压缸包围的液压活塞这些装置。当水慢慢地被灌入液压机圆筒（液压缸）的时候，活塞和其负载被向上推，直到某个位置（液压缸的低部）停下来。当它们被释放的时候，设备通过为机器提供液压力，强迫水从液压缸中快速流出。

流体静力学设备
在压力下的水或油通常被许多类型的压力机，铆钉机， 起锚机，绞车，以及其他的机器作为动力源。液压或流体液压的发现者是英国的发明家约瑟夫布拉马，因此也叫布拉马压力。这个装置包括两个液压缸，每个里面都有充满的液体和一个合适的活塞，两个缸之间通过充满液体的管道连接。一个液压缸的直径比较小，另一个相对大一些。根据帕斯卡原理，施加到较小活塞上的压力传播不受减损的，通过液体传到表面较大的活塞上，这是被动向上。即使压力（每单位面积的压力）对于活塞来说作用是等同的，作用于大活塞上的压力要比小活塞上的压力大许多倍，倍数等于大活塞的面积与小活塞面积的商。举例来说，如果规模较小的活塞的面积为2平方英寸，并在其上施加一百磅的力，那么，施加到一个面积为50平方英寸面积的活塞上的力将是2500磅。然而，当活塞移动时，距离较小的活塞行程与距离较大的活塞的行程成比例，满足能量守恒原则。如果规模较小的活塞动作25英寸，规模较大的仅仅只会移动1英寸。举例来说，液压被用于形成三维立体从钣金，塑胶到压缩大型物体。液压千斤顶一般被用于施加大压力或顶起重物的场合，它也遵循帕斯卡定律。和普通液压机一样，它由两个液压缸组成，两个液压缸的活塞有不同尺寸，中间通过管连接。当规模较小的活塞移回或移出来推动液体进入大活塞液压缸，强迫大活塞运动。通过这种方法一个较小的作用于小活塞上的力可以顶起一个较大物体的大载荷。液压升降机也遵循帕斯卡法则。
总之，掌握液压是非常困难的，但是理解一些基本的工作原理还是非常简单的。

附录二 产品实例数据库

公称压力(KN)
缓冲缸有无
液压缸快降速度
液压缸压制速度
工作台长度
工作台宽度
样本 1
2000
1
90
7
640
400
样本 2
2000
0
88
9
800
640
样本 3
3150
1
85
10
800
600
样本 4
3150
0
95
8
800
600
样本 5
3150
1
100
8
1000
800
样本 6
4000
1
95
9
800
600
样本 7
4000
0
87
7
800
600
样本 8
5000
0
100
8
1200
900
样本 9
6300
0
84
7
800
640
样本10
6300
1
96
11
1200
800
样本11
8000
1
100
12
1600
1400
样本12
8000
1
125
14
1600
1200