液壓系統(tǒng)和氣壓系統(tǒng)外文翻譯@中英文翻譯@外文文獻(xiàn)翻譯

Hydraulic system and Peumatic System Hui-xiong wan1 ,Jun Fan2 Abstract:Hydraulic system is widely used in industry, such as stamping, grinding of steel type work and general processing industries, agriculture, mining, space technology, deep sea exploration, transportation, marine technology, offshore gas and oil exploration industries, in short, Few people in their daily lives do not get certain benefits from the hydraulic technology. Successful and widely used in the hydraulic systems secret lies in its versatility and ease of maneuverability. Hydraulic power transmission mechanical systems as being not like the machine geometry constraints, In addition, the hydraulic system does not like the electrical system, as constrained by the physical properties of materials, it passed almost no amount of power constraints. Keywords: Hydraulic system, Pressure system, Fluid The history of hydraulic power is a long one, dating from mans prehistoric efforts to harness the energy in the world around him. The only source readily available were the water and the wind two free and moving streams. The watermill, the first hydraulic motor, was an early invention. One is pictured on a mosatic at the Great Palace in Byzantium, dating from the early fifth century. The mill had been built by the Romans. But the first record of a watermill goes back even further, to around 100BC, and the origins may indeed have been much earlier. The domestication of grain began some 5000 years before and some enterprising farmer is bound to have become tired of pounding or grinding the grain by hand. Perhaps, in fact, the inventor were some farmers wives. Since the often drew the heavy jobs. Fluid is a substance which may flow； that is, its constituent particles may continuously change their positions relative to one another. Moreover, it offers no lasting resistance to the displacement, however great, of one layer over another. This means that, if the fluid is at rest, no shear force (that is a force tangential to the surface on which it acts) can exist in it. Fluid may be classified as Newtonian or non-Newtonian. In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. In non Newtonian fluid there is a nonlinear relation between the magnitude of applied shear stress and the rate of angular deformation. The flow of fluids may be classified in many ways, such as steady or non steady, rotational or irrotational, compressible or incompressible, and viscous or no viscous. All hydraulic systems depend on Pascals law, such as steady or pipeexerts equal force on all of the surfaces of the container. In actual hydraulic systems, Pascals law defines the basis of results which are obtained from the system. Thus, a pump moves the liquid in the system. The intake of the pump is connected to a liquid source, usually called the tank or reservoir. Atmospheric pressure, pressing on the liquid in the reservoir, forces the liquid into the pump. When the pump operates, it forces liquid from the tank into the discharge pipe at a suitable pressure. The flow of the pressurized liquid discharged by the pump is controlled by valves. Three control functions are used in most hydraulic systems: (1) control of the liquid pressure, （ 2） control of the liquid flow rate, and (3) control of the direction of flow of the liquid. Hydraulic drives are used in preference to mechanical systems when(1) powers is to be transmitted between point too far apart for chains or belts； (2) high torque at low speed in required； (3) a very compact unit is needed； (4) a smooth transmission, free of vibration, is required；(5) easy control of speed and direction is necessary； and (6) output speed is varied steplessly. Fig. 1 gives a diagrammatic presentation of the components of a hydraulic installation. Electrically driven oil pressure pumps establish an oil flow for energy transmission, which is fed to hydraulic motors or hydraulic cylinders, converting it into mechanical energy. The control of the oil flow is by means of valves. The pressurized oil flow produces linear or rotary mechanical motion. The kinetic energy of the oil flow is comparatively low, and therefore the term hydrostatic driver is sometimes used. There is little constructional difference between hydraulic motors and pumps. Any pump may be used as a motor. The quantity of oil flowing at any given time may be varied by means of regulating valves( as shown in Fig.7.1) or the use of variable-delivery pumps. The application of hydraulic power to the operation of machine tools is by no means new, though its adoption on such a wide scale as exists at present is comparatively recent. It was in fact in development of the modern self-contained pump unit that stimulated the growth of this form of machine tool operation. Hydraulic machine tool drive offers a great many advantages. One of them is that it can give infinitely-variable speed control over wide ranges. In addition, they can change the direction of drive as easily as they can vary the speed. As in many other types of machine, many complex mechanical linkages can be simplified or even wholly eliminated by the use of hydraulics. The flexibility and resilience of hydraulic power is another great virtue of this form of drive. Apart from the smoothness of operation thus obtained, a great improvement is usually found in the surface finish on the work and the tool can make heavier cuts without detriment and will last considerably longer without regrinding. Hydraulic and pneumatic system There are only three basic methods of transmitting power:electrical,mechanical,and fluid power.Most applications actually use a combination of the three methods to obtain the most efficient overall system. To properly determine which principle method to use,it is important to know the salient features of each type. For example, fluid systems can transmit power more economically over greater distances than can mechanical types. However, fluid systems are restricted to shorter distances than are electrical systems. Hydraulic power transmission system are concerned with the generation, modelation, and control of pressure and flow， and in general such systems include: 1. Pumps which convert available power from the prime mover to hydraulic power at the actuator. 2. Valves which control the direction of pump-flow, the level of power produced, and the amount of fluid-flow to the actuators. The power level is determined by controlling both the flow and pressure level. 3. Actcators which convert hydtaulic power to usable mechanical power output at the point required. 4. The medium, which is a liquid, provides rigid transmission and control as well as lubrication of componts, sealing in valves, and cooling of the system. 5. Conncetots which link the various system components, provide power conductors for the fluid under pressure, and fluid flow return to tank(reservoir). 6. Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well as cooling of the fluid. Hydraulic systems are used in industrial applications such as stamping presses, steel mills, and general manufacturing, agricultural machines, mining industry, aviation, space technology, deep-sea exploration, transportion, marine technology, and offshore gas and petroleum exploration. In short, very few people get through a day of their lives without somehow benefiting from the technology of hydraulicks. The secret of hydraulic systems success and widespread use is its versatility and manageability. Fluid power is not hindered by the geometry of the machine as is the case in mechanical systems. Also, power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of materials as are the electrical systems. For example, the performance of an electromangnet is limited by the saturation limit of steel. On the other hand, the power limit of fluid systems is limited only by the strength capacity of the material. Industry is going to depend more and more on automation in order to increase productivity. This includes remote and direct control of production operations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories. 1. Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power system can readily start, stop, speed up or slow down, and position forces which provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch. 2. Multiplication of force. A fluid power system(without using cumbersome gears, pulleys, and levers) can multiply forces simply and efficiently from a fraction of an ounce to several hundred tons of output. 3. Constant force or torque. Only fluid power systems are capable of providing contant force or torque regardless of speed changes. This is accomplished whether the work output moves a few inches per hour, several hundred inches per minute, a few revolutions per hour, or thousands of revolutions per minute. 4. Simplicity, safely, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, companctness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on many off-highway vehicles. The steering unit consists of a manually operated directional control valve and meter in a single body. Because the steering unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, etc, are eliminated. This provides a simple, compact system. In addition, very little input torque is required to produce the control needed for the toughest applications. This is important where limitations of control space require a small steering wheel and it becomes necessary to reduce operatotr fatique. Additonal benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of fluid power, it is not a panacea for all power transmission problems. Hydraulic systems also have some drawbacks. Hydraulic oils are messy, and leakage is impossible to completely eliminate. Also, most hydraulic oils can cause fires if an oils occurs in an area of hot equipment. Peumatic System Pneumatic systems use pressurized gases to tansmit and control power. A s the name implies, pneumatic systems typically use air(rather than some other gas) as the fluid medium because air is a safe, low-cost, and readily available fluid. It is particularly safe in environments where an electrical spark could ignite leaks from system components. In pneumatic systems ,compressors are used to compress and supply the necessary quantities of air. Compressors are typically of the piston, vane or screw type. Basically a compressor increases the pressure of a gas by reducing its volume as described by the perfect gas laws.Pneumatic systems normally use a large centralized air compressor which is considered to be an infinite air source similar to an electrical system where you merely plug into an electrical outlut for electricity. In this way, pressurized air can be piped from one source to various locations throughout an entire industrial plant. The air then flows through a pressue regulator which redeces the pressure to the desired level for the particular circuit application. Because air is not a good lubircant（ contains about 20% oxygen） , pneumatics systems required a lubricator to inject a very fine mist of oil into the air discharging from the pressure regulator. This prevents wear of the closely fitting moving parts of pneumatic components. Free air from the atmosphere contains varying amounts of moisure. This moisure can be harmful in that it can wash away lubricants and thus cause excessive wear and corrosion. Hence ,in some applications ,air driers are needed to remove this undesirable moisture. Since pneumatics systems exhaust directly into the atmosphere, they are capable of generating excessive noise. Therefore, mufflers are mounted on exhaust ports of air valves and actuators to reduce noise and prevent operating personnel from injury resulting not only from exposure to noise but also from high-speed airborne particles. There are several reasons for considering the use of pneumatic systems instead of hydraulic systems. Liquids exhibit greater inertia than do gases. Therefore, in hydraulic systems the weight of oil is a potential problem when accelerating and decelerating actuators and when suddenly opening and closing valves. Due to Newtons law of motion(force equals mass multiplied by acceleration), the force required to accelerate oil is many times greater than that required to accelerate an equal volume of air. Liquids also exhibit greater viscosity than do gases. This results in larger frictional pressure and power losses. Also ,since hydraulic systems use a fluid foreign to the atmosphere, they require special reservoirs and noleak system designs. Pneumatic system use air which is exhausted directly back into the surrounding environment. Generally speaking, pneumatic systems are less expensive than hydraulic systems. However, because of the compressibility of air, it is impossible to obtain precise controlled actuator velocities with pneumatic systems. Also, precise positioning control is not obtainable. While pneumatics pressures are quite low due to compressor design limitations(less than 250 psi), hydraulic pressures can be as high as 10000 psi. Thus, hydraulics can be high-power systems, whereas pneumatics are confined to low-power applications. Industrial applications of pneumatics systems are growing at a rapid pace. Typical examples include stamping, drilling, hoist, punching, clamping, assembling, riveting, materials handling, and logic controlling operations. 液壓系統(tǒng)和氣壓系統(tǒng) 萬輝雄 1 ，范軍 2 摘要：液壓系統(tǒng)在工業(yè)中應(yīng)用廣泛，例如沖壓、鋼類工件的磨削及一般加工業(yè)、農(nóng)業(yè)、礦業(yè)、航天技術(shù)、深?？碧?、運(yùn)輸、海洋技術(shù)，近海天然氣和石油勘探等行業(yè)，簡(jiǎn)而言之，在日常生活中很少有人不從液壓技術(shù)得到某些益處。液壓系統(tǒng)成功而又廣泛使用的秘密在于它的通用性和易操作性。液壓動(dòng)力傳遞不會(huì)像機(jī)械系統(tǒng)那樣受到機(jī)器幾何形體的制約，另外，液壓系統(tǒng)不會(huì)像電氣系統(tǒng)那樣受到材料物理性能的制約，它對(duì)傳遞功率幾乎沒有量的限制。 關(guān)鍵詞：液壓系統(tǒng)，氣壓系統(tǒng)，流體 流體和液壓系統(tǒng) 水力的歷史由來已久，始于人類為利用它周圍的能源而做出的 努力。容易利用的能源就是水和風(fēng) 兩種自由的流動(dòng)流體。 第一臺(tái)液力裝置水車是最早的發(fā)明。從 15 世紀(jì)早期，水車圖畫就出現(xiàn)在大宮殿的馬賽克上。磨粉機(jī)由羅馬人發(fā)明，而水磨機(jī)的歷史更早，可以追溯到大約公元前 100 年。當(dāng)一些上進(jìn)的農(nóng)場(chǎng)主厭惡由手工沖擊、研磨谷物時(shí)，谷物的家庭養(yǎng)殖已開始 5000 多年。也許，真正的發(fā)明家是那些農(nóng)場(chǎng)主的妻子，因?yàn)樗齻兘?jīng)常要干重的農(nóng)活。 流體是可以流動(dòng)的物體，與就是說，構(gòu)成物質(zhì)的粒子可以連續(xù)地改變它們之間的相對(duì)位置，而且，它提供流體層間流動(dòng)非連續(xù)的阻力。這意味著流體在靜止時(shí)，在其內(nèi)部沒有剪切力 （作用表面切向方向的受力）存在。 流體可以分為牛頓流體或非牛頓流體。在牛頓流體中，流體層間作用的剪切力和角度變形總量的大小成線性關(guān)系。在非牛頓流體中，流體層間作用的剪切力和角度變形總量的大小成非線性關(guān)系。 流體的流動(dòng)可按多種方式分類，如定常或非定常流、有旋流或無旋流、可壓縮或不可壓縮流以及黏性流或無黏性流。 所有的液壓系統(tǒng)遵守與帕斯卡定律，命名是由帕斯卡而來的，是他發(fā)明了此定律。這條定律指出在密封容積內(nèi)壓縮的液體 例如圓柱筒或管子 在容積的各個(gè)不同面上作用著相等的力。 在實(shí)際液壓系統(tǒng)中，帕斯卡定律是解釋 從系統(tǒng)中獲得的各種結(jié)果的基礎(chǔ)。因此，泵使液體在系統(tǒng)中流動(dòng)，泵的進(jìn)口連接液流源，經(jīng)常叫油槽或油箱。作用在油箱液面上的氣壓使流體進(jìn)入油泵。當(dāng)油泵工作是，在適當(dāng)?shù)膲毫ψ饔孟?，油泵迫使流體從油箱流動(dòng)到出口。 由油泵泵出的壓縮液體通過各種閥門來控制。在大多數(shù)液壓系統(tǒng)中采用 3種控制功能：（ 1）液體壓力的控制（ 2）液體流速的控制（ 3）液體流動(dòng)方向的控制 當(dāng)處于下列幾種情況時(shí)，液壓驅(qū)動(dòng)被優(yōu)先使用，（ 1）對(duì)于鏈傳動(dòng)和皮帶傳動(dòng)來說，功率的傳遞位置太遠(yuǎn)：（ 2）低速高轉(zhuǎn)矩的場(chǎng)合（ 3）很緊湊的結(jié)構(gòu)（ 4）要求傳動(dòng)平穩(wěn)、避免振動(dòng)的場(chǎng)合（ 5）速度和方向容易調(diào)節(jié)的場(chǎng)合（ 6）輸出速度無級(jí)可調(diào)的情況。 由電氣驅(qū)動(dòng)的油泵供有傳遞能量的油量，并可傳遞給液壓電動(dòng)機(jī)或油缸，從而將液壓能轉(zhuǎn)換成機(jī)械能。通過閥門控制油的流動(dòng)，壓力油流產(chǎn)生線性的或旋轉(zhuǎn)的機(jī)械運(yùn)動(dòng)。油流的動(dòng)能相對(duì)比較低，因此有時(shí)采用靜壓傳動(dòng)。液壓電動(dòng)機(jī)和液壓油缸之間幾乎不存在構(gòu)造上的不同。任一油泵可以被用作液壓電動(dòng)機(jī)。在任一時(shí)間里的油流量可以通過調(diào)節(jié)閥門或采用變量泵來改變。 液壓傳動(dòng)運(yùn)用到機(jī)床的運(yùn)行中絕不是新的，雖說現(xiàn)在的大規(guī)模采用出現(xiàn)不久?，F(xiàn)代油泵的發(fā)展促進(jìn)了這類機(jī)床的增多。 機(jī)床的液壓驅(qū)動(dòng)具有 許多優(yōu)點(diǎn)。其中一個(gè)是液壓驅(qū)動(dòng)在廣泛的范圍內(nèi)提供無限變化的速度。另外，它們能像改變速度一樣容易來改變驅(qū)動(dòng)的方向。像許多其他類型的機(jī)床一樣，許多復(fù)雜的機(jī)械裝置能夠被簡(jiǎn)單化或者由于液壓驅(qū)動(dòng)的使用完全取消。 液壓驅(qū)動(dòng)的另一個(gè)優(yōu)點(diǎn)是它的柔性和緩沖性。除了運(yùn)行平穩(wěn)外，還發(fā)現(xiàn)了許多改進(jìn)，如工件表面光潔度的改善，在不損壞刀具的前提下能加大刀具的負(fù)荷，并能在刃磨刀具的情況下工作更長時(shí)間。 液壓與氣壓系統(tǒng) 僅有以下三種基本方法傳遞動(dòng)力：電氣、機(jī)械和物流。大多數(shù)應(yīng)用系統(tǒng)實(shí)際上是將三種方法組合起來而得到最有效的最全面的系統(tǒng)。為了合 理地確定采取哪些方法，重要的是了解各種方法的顯著特征。例如液壓系統(tǒng)在長距離上比機(jī)械系統(tǒng)更能經(jīng)濟(jì)地傳遞動(dòng)力。然而液壓系統(tǒng)與電氣相比，傳遞動(dòng)力的距離較短。 液壓動(dòng)力傳遞系統(tǒng)涉及電動(dòng)機(jī)、調(diào)節(jié)裝置和壓力和流量控制，總的來說，該系統(tǒng)包括：泵：將原動(dòng)機(jī)的能力轉(zhuǎn)換成作用在執(zhí)行部件上的液壓能。閥：控制泵產(chǎn)生流體的運(yùn)動(dòng)方向、產(chǎn)生的功率的大小，以及到達(dá)執(zhí)行部件液體的流量。功率大小取決于對(duì)流量和壓力大小的控制。 執(zhí)行部件：將液壓能轉(zhuǎn)換成可用的機(jī)械能。 介質(zhì)即油液：可進(jìn)行無壓縮傳遞和控制，同時(shí)可以潤滑部件，使閥體密封和系統(tǒng)冷卻。 聯(lián)接件：聯(lián)接各個(gè)系統(tǒng)部件，為壓力流體提供功率傳輸通路，將液體返回油箱。油液儲(chǔ)存和調(diào)節(jié)裝置：用來確保提供足夠質(zhì)量和數(shù)量并冷卻的液體。 液壓系統(tǒng)在工業(yè)中應(yīng)用廣泛，例如沖壓、鋼類工件的磨削及一般加工業(yè)、農(nóng)業(yè)、礦業(yè)、航天技術(shù)、深?？碧?、運(yùn)輸、海洋技術(shù)，近海天然氣和石油勘探等行業(yè)，簡(jiǎn)而言之，在日常生活中很少有人不從液壓技術(shù)得到某些益處。 液壓系統(tǒng)成功而又