外文翻译--液压管路和管接头

外文翻译--液压管路和管接头 设计巴巴工作室www.88doc88.com 附录 英语 原文 少年中国说原文俱舍论原文大医精诚原文注音大学原文和译文对照归藏易原文 Hydraulic Conductors and Fittings Eric Sandgren *, T.M. Cameron to account for uncertainty aMechanical Engineering, Virginia Commonwealth University, 601 West Main Street, P .O. Box843015, Richmond, VA 23284-3015, USA Received 19 October 2001;accepted 5 June 2002 1.1 INTRODUCTION In a hydraulic system, the fluid flows through a distribution system consisting of conductors and fittings, which carry the fluid from the reservoir through operating components and back to the reservoir. Since power is transmitted throughout the system by means of these conducting lines (conductors and fittings used to connect system components), it follows that they must be properly designed in order for the total system to function properly. Hydraulic systems use primarily four types of conductors: 1. Steel pipes 2. Steel tubing 3. Plastic tubing 4. Flexible hoses The choice of which type of conductor to use depends primarily on the sys-tem’s operating pressures and flow rates. In addition, the selection depends on en- vironmental conditions such as the type of fluid, operating temperatures, vibration, and whether or not there is relative motion between connected components. Conducting lines are available for handling work pressures up to 10,000 Pa or greater. In general, steel tubing provides greater plumbing flexibility and neater appearance and requires fewer fittings than piping. However, piping is less expensive than steel tubing. Plastic tubing is finding increased industrial usage because it is not costly and circuits can be very easily hooked up due to its 设计巴巴工作室www.88doc88.com flexibility. Flexible hoses are used primarily to connect components that experience relative motion. They are made from a large number of elastomeric (rubberlike) compounds and are capable of handling pressures exceeding 10,000 Pa. Stainless steel conductors and fittings are used if extremely corrosive envi-ronments are expected. However, they are very expensive and should be used only if necessary. Copper conductors should not be used in hydraulic systems because the copper promotes the oxidation of petroleum oils. Zinc, magnesium, and cadmium conductors should not be used either because they are rapidly corroded by water-glycol fluids. Galvanized conductors should also be avoided because the galvanized surface has a tendency to flake off into the hydraulic fluid. When using steel pipe or steel tubing, hydraulic fittings should be made of steel except for inlet, return, and drain lines, where malleable iron may be used. Conductors and fittings must be designed with human safety in mind. They must be strong enough not only to withstand the steady-state system pressures but also the instantaneous pressure spikes resulting from hydraulic shock. Whenever control valves are closed suddenly, this stops the fluid, which possesses large amounts of kinetic energy. This produces shock waves whose pressure levels can be two or four times the steady-state system design values. Pressure spikes can also be caused by sudden stopping or starting of heavy loads. These high-pressure pulses are taken into account by the application of an appropriate factor of safety. 1.2 CONDUCTOR SIZING FOR FLOW-RATE REQUIREMENTS A conductor must have a large enough cross-sectional area to handle the flow-rate requirements without producing excessive fluid velocity. Whenever we speak of fluid velocity in a conductor such as a pipe, we are referring to the average velocity. The concept of average velocity is important since we know that the velocity profile is not constant. As shown in Chapter 5 the velocity is zero at the pipe wall and reaches a maximum value at the centerline of the pipe. The average velocity is defined as the volume flow rate divided by the pipe cross-sectional area: In other words, the average velocity is that velocity which when multiplied by the pipe area equals the volume flow rate. It is also understood that the term diameter by itself always means inside diameter and that the pipe area is that area that corresponds to the pipe inside diameter. The maximum recommended veloc-ity for pump suction lines is 4 ft/s (1.2 m/s) in order to prevent excessively low suction pressures and resulting pump cavitation. The maximum recommended velocity for pressure lines is 20 ft/s (6.1 m/s) in order to prevent turbulent flow and the corresponding excessive head losses and elevated fluid temperatures. Note that these maximum recommended values are average velocities. 设计巴巴工作室www.88doc88.com EXAMPLE 1-1 A pipe handles a flow rate of 30 gprn. Find the minimum inside diameter that will provide an average fluid velocity not to exceed 20 ft/s. Solution Rewrite Eq. (3-26), solving for D: EXAMPLE 1-2 A pipe handles a flow rate of 0.002. Find the minimum inside diameter that will provide an average fluid velocity not to exceed 6.1 m/s. Solution Per Eq. 3-35) we solve for the minimum required pipe flow area: The minimum inside diameter can now be found, becauseSolving for D we have 1.3 PRESSURE RATING OF CONDUCTORS Tensile Stress A conductor must be strong enough to prevent bursting due to excessive tensile stress (called hoop stress) in the wall of the conductor under operating fluid pressure. The magnitude of this tensile stress, which must be sustained by the conductor material, can be determined by referring to Figure 4-1. In Fig. 4-1(a), we see the fluid pressure ( P ) acting normal to the inside surface of a circular pipe having a length (L). The pipe has outside diameter D, inside 0 diameter D, and wall thickness t. Because the fluid pressure acts normal to the i pipe’s inside surface, a pressure force is created that attempts to separate one half of the pipe from the other half. 设计巴巴工作室www.88doc88.com Figure 4-1(b) shows this pressure forcepushing downward on the bottom half of the pipe. To prevent the bottom half of the pipe from separating from the upper half, the upper half pulls upward with a total tensile force F. One-half of this force ( or F/2 ) acts on the cross-sectional area (tL) of each wall, as shown. Since the pressure force and the total tensile force must be equal in magnitude, we have where A is the projected area of the lower half-pipe curved-wall surface onto a horizontal plane. Thus, A equals the area of a rectangle of width Dand length L, i as shown in Figure 4-1(b). Hence, The tensile stress in the pipe material equals the tensile force divided by the wall cross-sectional area withstanding the tensile force. This stress is called a tensile stress because the force (F) is a tensile force (pulls on the area over which it acts). Substituting variables we have where = Greek symbol (sigma) = tensile stress. As can be seen from Eq. (4-2), the tensile stress increases as the fluid pres-sure increases and also as the pipe inside diameter increases. In addition, as ex-pected, the tensile stress increases as the wall thickness decreases, and the length of the pipe does not have any effect on the tensile stress. Burst Pressure and Working Pressure The burst pressure (BP) is the fluid pressure that will cause the pipe to burst. This happens when the tensile stress () equals the tensile strength ( S ) of the pipe material. The tensile strength of a material equals the tensile stress at which the material ruptures. Notice that an axial scribe line is shown on the pipe outer wall surface in Fig. 4-1(a). This scribe line shows where the pipe would start to crack and thus rupture if the tensile stress reached the tensile strength of the pipe 设计巴巴工作室www.88doc88.com material. This rupture will occur when the fluid pressure (P) reaches BR Thus, from Eq. (4-2) the burst pressure is The working pressure (WP) is the maximum safe operating fluid pressure and is defined as the burst pressure divided by an appropriate factor of safety (FS). A factor of safety ensures the integrity of the conductor by determining the maximum safe level of working pressure. Industry standards recommend the fol-lowing factors of safety based on corresponding operating pressures: FS = 8 for pressures from 0 to 1000 Pa FS = 6 for pressures from 1000 to 2500 Pa FS = 4 for pressures above 2500 Pa For systems where severe pressure shocks are expected, a factor of safety of 10 is recommended. Conductor Sizing Based on Flow Rate and Pressure Considerations The proper size conductor for a given application is determined as follows: 1. Calculate the minimum acceptable inside diameter (D) based on flow-rate i requirements. 2. Select a standard-size conductor with an inside diameter equal to or greater than the value calculated based on flow-rate requirements. 3. Determine the wall thickness (t) of the selected standard-size conductor using the following equation: 4. Based on the conductor material and system operating pressure (P), de-termine the tensile strength (S) and factor of safety (FS). 5. Calculate the burst pressure (BP) and working pressure (WP) using Eqs. (4-3) and (4-4). 6. If the calculated working pressure is greater than the operating fluid pres-sure, the selected conductor is acceptable. If not, a different standard-size conduc-tor with a greater wall thickness must be selected and evaluated. An acceptable conductor is one that meets the flow-rate requirement and has a working pressure equal to or greater than the system operating fluid pressure. 设计巴巴工作室www.88doc88.com The nomenclature and units for the parameters of Eqs. (4-2), (4-3), (4-4), and (4-5) are as follows: BP = burst pressure (Pa, MPa) D= conductor inside diameter (in., m) i D = conductor outside diameter (in., m) 0 FS = factor of safety (dimensionless) P = system operating fluid pressure (Pa, MPa) S = tensile strength of conductor material (Pa, MPa) t = conductor wall thickness (in., m) WP = working pressure (Pa, MPa) = tensile stress (Pa, MPa) EXAMPLE 1-3 A steel tubing has a 1.250-in, outside diameter and a 1.060-in, inside diameter. It is made of SAE 1010 dead soft cold-drawn steel having a tensile strength of 55.000 Pa. What would he the safe working pressure for this tube assuming a factor of safety of 8? Solution First, calculate the wall thickness of the tubing: Next, find the burst pressure for the tubing: Finally, calculate the working pressure at which the tube can safely operate: Use of Thick-Walled Conductors Equations (4-2) and (4-3) apply only for thin-walled cylinders where the ratio D/ t is greater than 10. This is because in thick-walled cylinders (D / t i i 10), the tensile stress is not uniform across the wall thickness of the tube as assumed in the derivation of Eq. (4-2). For thick-walled cylinders Eq. (4-6) must be used to take into account the nonuniform tensile stress, 设计巴巴工作室www.88doc88.com Thus, if a conductor being considered is not a thin-walled cylinder, the calculations must be done using Eq. (4-6). As would be expected, the use of Eq. (4-6) results in a smaller value of burst pressure and hence a smaller value of working pressure than that obtained from Eq. (4-3). This can be seen by comparing the two equations and noting the addition of the 1.2t term in the denominator of Eq. (4-6). Note that the steel tubing of Example 4-3 is a thin-walled cylinder because = 1.060 in./0.095 in. =11.2 > 10. Thus, the steel tubing of Example 4-3 can operate safely with a working pressure of 1230 Pa as calculated using a factor of safety of 8. Using Eq. (4-6) for this same tubing and factor of safety yields As expected the working pressure of 1110 Pa calcu1ated using Eq. (4-6) is less than the 1230 Pa value calculated in Example 4-3 using Eq. (4-3). 1.4 STEEL PIPES Size Designation Pipes and pipe fittings are classified by nominal size and schedule number, as illustrated in Fig. 4-2. The schedules provided are 40, 80, and 160, which are the ones most commonly used for hydraulic systems. Note that for each nominal size the outside diameter does not change. To increase wall thickness the next larger schedule number is used. Also observe that the nominal size is neither the outside nor the inside diameter. Instead, the nominal pipe size indicates the thread size for the mating connections. The pipe sizes given in Fig. 4-2 are in units of inches. Figure 4-3 shows the relative size of the cross sections for schedules 40, 80, and 160 pipes. As shown for a given nominal pipe size, the wall thickness increases as the schedule number increases. Thread Design Pipes have tapered threads, as opposed to tube and hose fittings, which have straight threads. As shown in Fig. 4-4, the joints are sealed by an interference fit between the male and female threads as the pipes are tightened. This causes one of the major problems in using pipe. When a joint is taken apart, the pipe must be tightened farther to reseal. This frequently requires replacing some of the pipe with slightly longer sections, although this problem has been overcome somewhat by using Teflon tape to reseal the pipe joins. Hydraulic pipe threads are the dry-seal type. They differ from standard pipe threads because they engage the roots and crests before the flanks. In this way, spiral clearance is avoided. 设计巴巴工作室www.88doc88.com Pipes can have only male threads, and they cannot be bent around obstacles. There are, of course, various required types of fittings to make end connections and change direction, as shown in Fig. 4-5. The large number of pipe fittings required in a hydraulic circuit presents many opportunities for leakage, especially as pressure increases. Threaded-type fittings are used in sizes up to in. in diameter. Where larger pipes are required, flanges are welded to the pipe, as illustrated in Fig. 4-6. As shown, flat gaskets or 0-rings are used to seal the flanged fittings. 1.5 STEEL TUBING Size Designation Seamless steel tubing is the most widely used type of conductor for hydraulic systems as it provides significant advantages over pipes. The tubing can be bent into almost any shape, thereby reducing the number of required fittings. Tubing is easier to handle and can be reused without any sealing problems. For low-volume systems, tubing can handle the pressure and flow requirements with less bulk and weight. However, tubing and its fittings are more expensive. A tubing size designation always refers to the outside diameter. Available sizes include-in. increments from -in. outside diameter up to -in. outside diameter. For sizes from-in. to 1 in. the increments are -in. For sizes beyond 1 in., the increments are-in. Figure 4-7 shows some of the more common tube sizes (in units of inches) used in fluid power systems. SAE 1010 dead soft cold-drawn steel is the most widely used material for tubing. This material is easy to work with and has a tensile strength of 55,000 Pa. If greater strength is required, the tube can be made of AISI 4130 steel, which has a tensile strength of 75,000 Pa. 设计巴巴工作室www.88doc88.com Tube Fittings Tubing is not sealed by threads but by special kinds of fittings, as illustrated in Fig. 4-8. Some of these fittings are known as compression fittings. They seal by metal-to-metal contact and may be either the flared or flareless type. Other fittings may use 0-rings for sealing purposes. The 370 flare fitting is the most widely used fitting for tubing that can be flared. The fittings shown in Fig. 4-8(a) and (b) seal by squeezing the flared end of the tube against a seal as the compression nut is tightened. A sleeve inside the nut supports the tube to dampen vibrations. The standard 450 flare fitting is used for very high pressures. It is also made in an inverted design with male threads on the compression nut. When the hydraulic component has straight thread ports, straight thread 0-ring fittings can be used, as shown in Fig. 4-8(c). This type is ideal for high pressures since the seal gets tighter as pressure increases. Two assembly precautions when using flared fittings are: 1. The compression nut needs to be placed on the tubing before flaring the tube. 2. These fittings should not be over-tightened. Too great a torque damages the sealing surface and thus may cause leaks. For tubing that can’t be flared, or if flaring is to be avoided, ferrule, 0-ring, or sleeve compression fittings can be used [see Fig. 4-8(d), (e), (f)]. The O-ring fitting permits considerable variations in the length and squareness of the tube cut. Figure 4-9 shows a Swagelok tube fitting, which can contain any pressure up to the bursting strength of the tubing without leakage. This type of fitting can be repeatedly taken apart and reassembled and remain perfectly sealed against leak-age. Assembly and disassembly can be done easily and quickly using standard tools. In the illustration, note that the tubing is supported ahead of the ferrules by the fitting body. Two ferrules grasp tightly around the tube with no damage to the tube wall. There is virtually no constriction of the inner wall, ensuring minimum 设计巴巴工作室www.88doc88.com flow restriction. Exhaustive tests have proven that the tubing will yield before a Swagelok tube fitting will leak. The secret of the Swagelok fitting is that all the action in the fitting moves along the tube axially instead of with a rotary motion. Since no torque is transmitted from the fitting to the tubing, there is no initial strain that might weaken the tubing. The double ferrule interaction overcomes variation in tube materials, wall thickness, and hardness. In Fig. 4-10 we see the 450 flare fitting. The flared-type fitting was developed before the compression type and for some time was the only type that could successfully seal against high pressures. Four additional types of tube fittings are depicted in Fig. 4-11: (a) union el-bow, (b) union tee, (c) union, and (d) 45? male elbow. With fittings such as these, it is easy to install steel tubing as well as remove it for maintenance purposes. EXAMPLE 1-4 Select the proper size steel tube for a flow rate of 30 gpm and an operating pressure of 1000 Pa. The maximum recommended velocity is 20 ft/s, and the tube material is SAE 1010 dead soft cold-drawn steel having a tensile strength of 55,000 Pa, Solution The minimum inside diameter based on the fluid velocity limitation of 20 ft/s is the same as that found in Example 4-1 (0.782 in.). From Fig. 4-7, the two smallest acceptable tube sizes based on flow-rate re-quirements are 1-in. od , 0.049-in, wall thickness, 0.902-in. ID 1-in. od , 0.065-in, wall thickness, 0,870-in. ID Let’s check the 0.049-in, wall thickness tube first since it provides the smaller velocity: This working pressure is not adequate, so let’s next examine the 0.065-in, wall thickness tube: 设计巴巴工作室www.88doc88.com This result is acceptable, because the working pressure of 1030 Pa is greater than the system-operating pressure of 1000 Pa and10. 1.6 PLASTIC TUBING Plastic tubing has gained rapid acceptance in the fluid power industry because it is relatively inexpensive. Also, it can be readily bent to fit around obstacles, it is easy to handle, and it can be stored on reels. Another advantage is that it can be color-coded to represent different parts of the circuit because it is available in many colors. Since plastic tubing is flexible, it is less susceptible to vibration damage than steel tubing. Fittings for plastic tubing are almost identical to those designed for steel tub-ing. In fact many steel tube fittings can be used on plastic tubing, as is the case for the Swagelok fitting of Fig. 4-9. In another design, a sleeve is placed inside the tubing to give it resistance to crushing at the area of compression, as illustrated in Fig. 4-12. In this particular design (called the Poly-Flo Flareless Tube Fitting), the sleeve is fabricated onto the fitting so it cannot be accidentally left off. Plastic tubing is used universally in pneumatic systems because air pressures are low, normally less than 100 Pa. Of course, plastic tubing is compatible with most hydraulic fluids and hence is used in low-pressure hydraulic applications. Materials for plastic tubing include polyethylene, polyvinyl chloride, poly-propylene, and nylon. Each material has special properties that are desirable for specific applications. Manufacturers’ catalogs should be consulted to determine which material should be used for a particular application. 1.7 FLEXIBLE HOSES Design and Size Designation The fourth major type of hydraulic conductor is the flexible hose, which is used when hydraulic components such as actuators are subjected to movement. Examples of this are found in portable power units, mobile equipment, and hydraulically powered machine tools. Hose is fabricated in layers of elastomer (synthetic rubber) and braided fabric or braided wire, which permits operation at higher pressures. As illustrated in Fig. 4-13, the outer layer is normally synthetic rubber and serves to protect the braid layer. The hose can have as few as three layers (one be-ing braid) or can have multiple layers to handle elevated pressures. When multiple wire layers are used, they may alternate with synthetic rubber layers, or the wire layers may be placed directly over one another. 设计巴巴工作室www.88doc88.com Figure 4-14 gives some typical hose sizes and dimensions for single-wire braid and double-wire braid designs. Size specifications for a single-wire braid hose represent the outside diameter in sixteenths of an inch of standard tubing, and the hose will have about the same inside diameter as the tubing. For example, a size 8 single-wire braid hose will have an inside diameter very close to a-in. standard tubing. For double-braided hose, the size specification equals the actual inside diameter in sixteenths of an inch. For example, a size 8 double-wire braid hose will have a-in. inside diameter. The minimum bend radii values provide the smallest values for various hose sizes to prevent undue strain or flow interference. Figure 4-15 illustrates five different flexible hose designs whose constructions are described as follows: a. FC 194: Elastomer inner tube, single-wire braid reinforcement, and elastomer cover Working pressures vary from 375 to 2750 Pa depending on the size. b.FC195: Elastomer inner tube, double-wire braid reinforcement, and elastomer cover. Working pressures vary from 1125 to 5000 Pa depending on the size. c.FC 300: Elastomer inner tube, polyester inner braid, single-wire braid rein-forcement, and polyester braid cover. Working pressures vary from 350 to 3000 Pa depending on the size. d.1525: Elastomer inner tube, textile braid reinforcement, oil and mildew resis-tant, and textile braid cover. Working pressure is 250 Pa for all sizes. e.2791: Elastomer inner tube, partial textile braid, four heavy spiral wire rein-forcements, and elastomer cover. Working pressure is 2500 Pa for all sizes. Hose Fittings Hose assemblies of virtually any length and with various end fittings are available from manufacturers. See Fig. 4-16 for examples of hoses with the following permanently attached end fittings: (a) straight fitting, (b) 45? elbow fitting, and (c) 90? elbow fitting. The elbow-type fittings allow access to hard-to-get-at connections. They also permit better flexing and improve the appearance of the system. Figure 4-17 shows the three corresponding reusable-type end fittings. These types can be detached from a damaged hose and reused on a replacement hose. The renewable fittings idea had its beginning in 1941. With the advent of World War II, it was necessary to get aircraft with failed hydraulic lines back into opera- tion as quickly as possible. Hose Routing and Installation 设计巴巴工作室www.88doc88.com Care should be taken in changing fluid in hoses since the hose and fluid materials must be compatible. Flexible hose should be installed so there is no kinking during operation of the system. There should always be some slack to relieve any strain and allow for the absorption of pressure surges. It is poor practice to twist the hose and use long loops in the plumbing operation. It may be necessary to use clamps to prevent chafing or tangling of the hose with moving parts. If the hose is subject to rubbing, it should be encased in a protective sleeve. Figure 4-18 gives basic information on hose routing and installation procedures. 1.8 QUICK DISCONNECT COUPLINGS One additional type of fitting is the quick disconnect coupling used for both plastic tubing and flexible hose. It is used mainly where a conductor must be disconnected frequently from a component. This type of fitting permits assembly and disassembly in a matter of a second or two. The three basic designs are: 1. Straight through: This design offers minimum restriction to flow but does not prevent fluid loss from the system when the coupling is disconnected. 2.One-way shutoff: This design locates the shutoff at the fluid source con- nection but leaves the actuator component unblocked. Leakage from the system is not excessive in short runs, but system contamination due to the entrance of dirt in the open end of the fitting can be a problem, especially with mobile equipment located at the work site. 3.Two-way shutoff: This design provides positive shutoff of both ends of pres-surized lines when disconnected. See Fig. 4-19 for a cutaway of this type of quick disconnect coupling. Figure 4-20 shows an external view of the same coupling. Such a coupling puts an end to the loss of fluids. As soon as you release the locking sleeve, valves in both the socket and plug close, shutting off flow. When connecting, the plug contacts an 0-ring in the socket, creating a positive seal. There is no chance of premature flow or waste due to a partial connection. The plug must be fully seated in the socket before the valves will open. 设计巴巴工作室www.88doc88.com 1.9 METRIC STEEL TUBING In this section we examine common metric tube sizes and show how to select the proper size tube based on flow-rate requirements and strength considerations. Figure 4-21 shows the common tube sizes used in fluid power systems. Note that the smallest od size is 4 mm (0.158 in.), whereas the largest od size is 42 mm (1.663 in.). These values compare to 0.125 in. and 1.500 in., respectively, from Fig. 4-7 for common English units tube sizes. It should be noted that since 1 m = 39.6 in. then 1 mm = 0.0396 in. Factors of safety based on corresponding operating pressures become FS = 8 for pressures from 0 to 1000 Pa (0 to 7 MPa or 0 to 70 bars) FS = 6 for pressures from 1000 to 2500 Pa (7 to 17.5 MPa or 70 to 175 bars) FS = 4 for pressures above 2500 Pa (17.5 MPa or 175 bars) The corresponding tensile strengths for SAE 1010 dead soft cold-drawn steel and AISI 4130 steel are: SAE 1010 55,000 Pa or 379 MPa AISI 4130 75,000 Pa or 517 MPa EXAMPLE 1-5 3Select the proper metric size steel tube for a flow rate of 0.00190m/s and an operating pressure of 70 bars. The maximum recommended velocity is 6.1 m/s and the tube material is SAE 1010 dead soft cold-drawn steel having a tensile strength of 379 MPa. Solution The minimum inside diameter based on the fluid velocity limitation of 6.1 rn/s is found using Eq. (3-18): Solving for A we have: Since we have the final resulting equation: (4-7) 设计巴巴工作室www.88doc88.com Substituting values we have: From Fig. 4-21, the smallest acceptable od tube size is: 22-mm od, 1.0-mm wall thickness, 20-mm ID From Eq. (4-3) we obtain the burst pressure. Then we calculate the working pressure using Eq. (4-4). This pressure is not adequate (less than operating pressure of 70 bars), so let’s examine the next larger size od tube having the necessary ID. 28-mm od, 2.0-mm wall thickness, 24-mm ID This result is acceptable. 1.10 KEY EQUATIONS Fluid velocity: (41) Pipe tensile stress: (4-2) Pipe burst pressure: (4-3) Pipe working pressure: (4-4) 设计巴巴工作室www.88doc88.com 设计巴巴工作室www.88doc88.com 中文译文 液压管路和管接头 Eric Sandgren *, T.M. Cameron 弗吉尼亚联邦大学机械工程系, Richmond西部大街601号, 邮编843015, VA23284-3015收稿2001 年10月19 日; 修回2002 年6月5 日。 1.1 介绍 在液压系统中, 液压油经过的系统包括管路和管接头, 这些液压油从油箱经过各机构的组成部分又回到油箱。因为在这过程中能量是通过这些管路传送到液压系统的各个部分(用来连接系统组分的管路和管接头), 所以为了总系统能够很好的发挥效率，必须进行恰当地设计。 液压系统主要使用四种管路: 1. 钢管 2. 无缝钢管 3. 塑料管 4. 软管 选用管路类型主要取决于系统的工作压力和流量。另外, 它的选择还取决于环境条件譬如油液的类型, 操作温度, 振动, 而且和连接部分之间是否有相对行动也有关系。 管路可以通过的工作压力可以达到1000 Pa或者更大。一般情况下, 钢管材与管道相比，配管的灵活性更好、更加洁净而且管接头也比较少，更加的方便。但是, 用管道输送比钢管材较便宜。塑料管材因为它资源利用率高并且由于它的灵活性连接比较方便，增加了它的工业用途。软管主要用来连接相对行动组分的部分。它们由大量的弹性化合物组成，能处理超出10,000 Pa的压力 。 在腐蚀性比较强的条件下一般使用不锈钢管路和管接头。但是, 它们比较昂贵, 只有在需要的情况下才可使用。铜管路不应该用在液压机构中，因为铜具有促进石油氧化作用。锌, 镁, 和钙管路也不应该被使用，因为由于水甘醇它们会迅速地被腐蚀掉。应该避免使用镀锌的管路，因为它的表面很容易剥落并且会融设计巴巴工作室www.88doc88.com 入液压液体。当使用钢管或钢管材, 液压管接头应该由钢制成除了一些回路等地方，这些地方可以使用铸铁。 在设计管路和管接头时必须慎重地考虑它的安全性。它们必须具有足够的强度，不仅能够承受稳定系统压力而且还要承受由于液压震动而产生的瞬间压力。当控制阀突然被关闭时, 停止液压,这需要很多的动能。稳定系统设计时，应该考虑到这一过程可能需要二倍或四倍的冲击力。并且考虑由于突然停止或重载初可能造成的压力冲击。在设计时应该考虑到这些高压冲击的安全因素。 1.2管路尺寸 管路必须有一个足够大的面积，用来处理变速的要求。在一个管路中当我们谈到可变的速度譬如管子, 我们提到平均速度。因为速率是变化的所以平均速度的概念非常重要。依照章节5 里速度是在管壁和在管子的中心线上达到一个最大值。由管子断面划分平均速度被定义为容量流速: 换句话说, 平均速度是以管子合计容量流速的速度。一般被理解为流经管子最大内径的那个区积的速度。泵吸油管路的最大被允许速度为4ft/s (1.2 m/s)，是为了防止压力太低同时引起泵的运转。规定可通过的最大流速是20 ft/s (6.1 m/s)，这样是为了防止冲击、损失和油液的升温过大。规定这些最大值就是平均速度。 例子1-1 管子通过的流速是30gprn 。最小内径允许液压通过的平均速度不超出20 ft/ s 。 解答 由式(3-26),求D: 例子1-2 通过管子的流量为0.002。求出可以通过平均速度低于6.1 m/ s的最小内径。 解答 我们求得最小需要的管子截面积为: 设计巴巴工作室www.88doc88.com 现在可以求出最小内径, 因为，可以求D为: 1.3 管路压力规定值 拉伸力 由于在液压运动下管路壁上会产生的强大压力(叫做强压)，所以管路必须具有足够强度用来防止爆裂。这巨大的压力, 必须由管路 材料 关于××同志的政审材料调查表环保先进个人材料国家普通话测试材料农民专业合作社注销四查四问剖析材料 承受, 由图4-1可确定。在图 4-1(a), 我们变化的压力(p) 相对一个圆管子的长度(l)。管子外径D0, 内径D,并且壁厚为t。由于液压的压力一般在管子的内表面上,它试图把有i 压力的一半从管子的另外一半分离出来。 图4-1(b) 显示这压力作用在管子的底下一半。为了防止管子的底下一半从上半方分离, 上半方总的向上的拉伸量为F。二分之一力(或F/2 )作用在各壁的断面(tL), 如显示。 重要的是压力大小和总拉力必须是相等,可以有: A是管子曲壁表面区积平分线以下的一半。因而,均等宽度D和长度L长方i形的区积, 如上图4-1(b)。因此, 作用在管子上的压力由壁断面划分承受的总力。这压力称压强，因为力(f) 是拉伸力(作用在它)的区积。 设计巴巴工作室www.88doc88.com 替代变换我们可以求得: 这里= 希腊标志(斯格码)= 压强 由式 (4-2)我们可以求得,当液压的压力增加，压强随着增加，当管子内径并且增加。 另外, 当管厚减小压强增加，并且管子的长度对压强没有任何影响。 爆裂压力和工作压力 爆裂压力(BP)是可以导致管子裂裂的液压的压力。当压强 ()大于抗拉强度(s)是 管子发生爆裂。材料爆裂的压强取决于材料的抗拉强度。注意,一个轴向划线被显示在管子外壁表面如图4-1(a)。这个划线行显示何处管子会发生崩裂和如果压强达到了管子的抗拉强度时材料因而爆裂。当液压压力(p)达到BR 时，这爆裂将发生。因而,由式(4-2) 爆裂压力是 工作压力(WP) 是安全工作的最大液压压力并且被定义为划分了由爆裂压力安全(FS) 一个适当的因素。 安全因素是保证管路的坚固用来确定工作压力的最高安全水平。根据对应的工作压力 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 推荐下面的安全因素: FS=8 为压力从0 到1000 Pa FS=6 为压力从1000 年到2500 Pa FS=4 为压力在2500 Pa之上 为了达到期望压力的系统, 规定10种安全因素。 管路尺寸根据流速和压力考虑 通过给定条件确定管路尺寸如下: 1.根据流速要求计算最小内径(D)。 i 2.根据流速要求选择管路的标准内径大于或等于计算出来的值。 3.由选出的标准使用以下等式确定壁厚(t): 设计巴巴工作室www.88doc88.com 4.根据管路材料和系统工作压力(p), 确定抗拉强度(s)和安全因素(FS)。 5. 由式(4-3)和(4-4)计算爆裂压力(BP) 和工作压力(WP) 。 6. 如果计算的工作压力大于液压的工作压力, 选择的管路是可接受的。如果不是,必须重新选择管路的标准尺寸以及壁厚。一个可用的管路必须是一个符合流速要求和等于或大于系统的工作压力。 命名原则和参量单位 式s(4-2), (4-3), (4-4),和(4-5)如下: BP=裂裂了压力(Pa, MPa) D=管路内径(in., m) i D=管路外部直径(in., m) 0 FS=安全因素(dimensionless) P=系统工作的可变压力(Pa, MPa) S=管路材料抗拉强度(Pa, MPa) t=管路壁厚(in., m) WP=工作压力(Pa, MPa) =压强(Pa, MPa) 例子1-3 钢管材有外部直径a 1.250m,和内径a 1.060m。它由SAE 1010 冷制钢制成，抗拉强度有55.000 Pa。这支管会它安全工作压力为承担安全因素8? 首先解答,计算管材的壁厚: 其次,管材爆裂压力为: 最后,计算管安全工作压力: 设计巴巴工作室www.88doc88.com 厚壁管管路的用途 等式(4-2)和(4-3)只能允许厚壁圆筒比率D/t大于10。这是因为在厚壁圆i 筒里(D /t10), 依照式(4-2)假设拉力管的壁厚和管径不是一致的。式(4-6)i 为厚壁圆筒，使用时必须考虑到不均匀的拉力, 因而,如果考虑管路不是一个薄壁圆筒, 计算时必须使用式(4-6)。如被期望的那样，由式(4-6)计算比由式(4-3)计算，可以获得更小的爆裂压力和工作压力。这能比较二个等式并且注意发现在式(4-6)分母上加1.2t。 注意钢管材例子4-3 是一个薄壁圆筒，因为=1.060/0.095=11.2>10。因而, 依照计算，钢管材例子4-3可以1230 Pa安全地工作，使用工作压力安全因素8。用式(4-6) 为这个同样管材和安全因素 例子用式(4-6)计算出来的工作压力为1110 Pa要比用式(4-3)计算出的1230 Pa更小。 1.4 钢管 指定尺寸 管子和管子管接头划分不同的大小和数字,在图4-2上说明。表提供有40,80,和160, 这些在液压机构中是最常用的几种。注意各个不同的大小它的外径是不改变的。为了增加壁厚，用下个更大的表中的数字。并且观察,外部和内径都是尺寸不想同的。同时,不同管子大小表明联接的螺纹尺寸。管子大小显示在图4-2 ，单位是英寸。 图4-3 显示横剖面的相对大小为安排40, 80, 和160个管子。依照显示指定的管子大小,当表数字增加时壁厚度增加。 螺纹设计 管子逐渐变细螺纹,与管和管接头相对,有平直的螺纹。依照图4-4显示,当管子被拉紧，在两螺纹之间的接点由干涉被密封。这造成的最大问题是其中一个在使用管子。 当联接分开, 管子必须被拉紧重新密封。在细长的部分要求频繁地替换一些管子, 虽然这个问题由使用加入聚四氟乙烯磁带重新密封管子克服设计巴巴工作室www.88doc88.com 了一部分。液压管子螺纹是干燥密封类型。 它们从标准管子分出，因为在这之前它们参与了处理。这样,螺旋清除被避免了。 管子可能有唯一主螺纹, 并且它们不能在障碍附近弯曲。当然也有各种各样的必需的管接头类型做终端连接和用来改变方向, 依照图4-5显示大量的管子管接头需要液压油路提供机会用来泄漏,特别是当压力增量时。穿线类型管接头被使用在尺寸达到直径的。耳轮缘焊接到管子上，这里是大管子必需的,在图4-6说明。根据显示 平的垫圈或0 圆环被使用密封被安装边缘的管接头。 1.5 钢管材 指定尺寸 无缝的钢管材是广泛被应用的管路类型因为它为液压机构在管子上提供了非常大的好处。管材可以弯曲成任一形状,因此减少了一些必需的管接头的数量。管材更加容易处理并且可以被重复利用而且没有任何质量问题。为低流量系统, 管材可能要求以少量轻质来处理压力和流量。但是,管材和它的管接头是相对昂贵的。管材尺寸设计总提到外部直径。可利用的大小包括从1/8增加1/16。外部直径增加到3/8。外部直径从3/8增加到1寸。增加是1/8大小在1in.之外,增加是1/4。 图4-7显示一些相同尺寸(在英寸单位) 被使用在液压能力系统。 SAE 1010 冷制钢是为钢管广泛使用的材料。 这种材料容易加工并且有55,000Pa抗拉强度。 如果需要足够拉力,管可能由AISI 4130 钢制成, 这些有75,000 Pa抗拉强度。 管接头 设计巴巴工作室www.88doc88.com 管材不是由螺纹密封而是由特别种类管接头密封, 依照被说明在图4-8。 这些管接头当压缩管接头被了解一些。它们密封是由金属和金属联结,有固定或移动的类型。其它管接头也许使用0 圆环来密封。370 火光管接头是广泛被应用在可移动管材的管接头。管接头显示在图4-8(a)和(b)，密封是由紧压管末端的滑动反作为密封压缩的。标准450 火光管接头被使用在高压。并且它被做在一个被倒置的设计里与螺纹压缩。当液压组分有平直的螺纹, 平直的螺纹0 圆环管接头可能被使用, 依照被显示在图4-8(c)。这是理想的类型，因为当压强增加时高压密封会更紧。 当使用移动的管接头时两种防备措施是: 1. 压缩需要被安置在管材在移动之前。 2. 这些管接头不应该被过分拧紧。太大的扭矩也许会损坏密封接面并且可能因而导致泄漏。 为无法移动的管材,或如果移动将被禁止,线代,0 圆环,或压缩管接头可能被使用[参见图4-8(d),(e),(f)]。在管的长度和方形上O环管接头的许可有很大的变化。 图4-9 显示Swagelok 管管接头, 这些可能包含任一压力由管材的爆裂力决定没有漏出。 这类型管接头可能分开一再被采取和被重新召集和保留完全密封防止泄漏。能容易地和迅速完成拆卸可使用标准工具。在例证,注意管材支持在线代之前由贴合身体。 二线代紧紧掌握在管附近没有对管墙壁的损伤。有实际上内在墙壁的没有收缩, 保证极小的 流程 快递问题件怎么处理流程河南自建厂房流程下载关于规范招聘需求审批流程制作流程表下载邮件下载流程设计 制约。详尽的测试证明,管材将产生在Swagelok 管管接头将漏之前。Swagelok 管接头的关键是,所有在管接头沿管轴向地行动代替了以转台式行动。 因为从管接头给管材不传递扭矩,也许没有减弱管材的最初的张力。双重线作用克服在管的变化上 设计巴巴工作室www.88doc88.com 在图4-10我们看450 火光管接头。移动类型管接头在压缩类型之前被开发好久，并且能成功地密封防止高压的唯一的类型。 在图4-11四种其它类型的管管接头，(a)轴型,(b)联合区积,(c)联合,和(d) 45.肘。譬如这些以管接头, 钢管材容易安装并且为维护目的拆开它。 例子1-4 选择适当的大小钢管流速为30 gpm 和工作压力1000 Pa。最大被规定的速度是20 ft/s, 管材料是SAE 1010 冷制钢抗拉强度有55,000 Pa。 解答 最小内径根据限制20ft/s 的液压速度被发现在例子4-1(0.782寸)是相同的. 从图4-7, 根据流速需要两个最小的可允许的管大小是 1-in. 外径 , 0.049-in, 壁厚, 0.902-in. ID 1-in. 外径 , 0.065-in, 壁厚, 0,870-in. ID 我们检查0.049, 管壁厚首先因为它提供更小的速度 这工作压力是不够的, 如此让我们再次审查0.065, 管壁厚度: 这个结果是可接受的,因为1030Pa工作压力大于系统操作的压力1000 Pa 和10 。 1.6 塑料管材 塑料管材在液压产业中获得了迅速支持，因为它是相当便宜的。并且,它容易弯曲适合在障碍附近,它容易处理, 和它可存放在卷轴中。其它优点是,它可以不同颜色的不同的零件代表不同的电路，因为它在许多颜色中是可用的。因为塑料管材塑性好,它和钢管材相比不易受振动损伤。 设计巴巴工作室www.88doc88.com 塑料管材管接头的设计几乎与设计为钢管是相同的。实际上许多钢管管接头可被使用在塑料管材,象盒为图Swagelok 管接头4-9 。在其它设计,是被放在压缩区积里面，管给它击碎的抵抗,依照说明在图4-12 。在这个特殊设计(称多管管接头), 管子被制造管接头因此它无法停止。 塑料管材普遍地使用在气动系统，因为气压是小的,通常少于100 Pa。当然,塑料管材是与多数液压机液体兼容，因此被应用在低压液压。 管材材料为塑料包括聚乙烯,聚氯乙烯, 丙稀和尼龙。各材料有的是为了具体应用的特别制造。制造商的编目应该被咨询确定哪材料应该被使用为一种特殊应用。 1.7 软管 设计确定大小 第四种主要液压管路类型是软管,这些用液压组分用做相对运动譬如作动器。这种例子被运用在便携式的电源装置, 流动设备, 和液压机械工具。被制造在弹性体(合成橡胶) 层数和编织物或结辨的导线, 这些允许以更高的压力操作。 依照图4-13说明,外面层数通常是合成橡胶和用于保护层数。有的只有三层数(一个是编织物) 或可能有多层数处理上升压力。当多导线层数被使用,它们也许与合成橡胶层数交替,或导线层数直接地互相安置。 图4-14 给一些典型的大小并且维度为唯一导线编并且双重导线编织物设计。估量唯一导线编织物的规格外部直径在一英寸的标准管材,并且将有同样的内径作为管材。例如,尺寸为8的导线编织物内径非常紧挨的标准管材。为双重结辨的,大小规格合计实际内径在一英寸。例如,大小8 双重导线编织物将有a 内径。最小的弯曲半径值提供最小的值因为各种大小防止过度的张力或流程干涉。 图4-15 说明建筑被描述的五个不同灵活的设计如下: a .FC 194: 弹性体内胎, 增强唯一导线编织物, 和弹性体盖子。工作压力根据大小变化从375 到2750 Pa。 b.FC195: 弹性体内胎, 增强双重导线编织物, 和弹性体盖子。工作压力变化根据大小从1125 到5000 Pa。 c. FC300: 弹性体内胎, 聚酯内在编织物,增强唯一导线编织物,和聚酯编织物盖子。 工作压力根据大小变化从350 到3000 Pa。 设计巴巴工作室www.88doc88.com d. FC1525 : 弹性体内胎,纺织品编织物, 增强油和霉,和纺织品编织物盖子。工作压力为250 Pa。 e.2791: 弹性体内胎, 部份纺织品编织物,增强四重的螺旋导线, 并且弹性体盖子。 工作压力为2500 Pa。 管接头 实际上任一长度管道装置和以各种各样的终端部件是可以买到的。参见图 4-16 以下为附属固定终端部件: (a) 平直的管接头, (b) 45度弯管接头,和(c) 90度弯管接头。 弯类型管接头允许对坚硬对得到在连接的通入。它们允许更好屈曲和并且改进系统的出现。 图4-17 显示三对应的可再用类型终端部件。 这些型可能是分隔的从一个损坏的和重复利用了在替换。1941 年可更新的管接头想法有它的起点。 以第二次世界大战出现, 它是必要尽快上航空器以未通过的液压线回到工作中。 发送和设施 因为液压材料必须是兼容的，所以应该保证在变化的液压里。软管应该被安装在系统没有纠缠的操作过程。那里应该总是解除任一张力和考虑到压力的吸收。在配管操作它是粗劣的实践扭转和使用长的圈。它也许是必要使用钳位防止擦伤或缠结以运动机件。如果是依于摩擦, 它应该被装箱在一个防护套子。图4-18在发送和安装程序给出基本的信息。 1.8 快速断开联结 一种其它的管接头类型是快速断开联结，被使用为塑料管材和灵活的。它主要被使用在管路必须频繁地从一个整体分开的地方。这类型管接头在一两秒内可以集中也可以分开。三个基本的设计是: 1. 直接通过: 这个设计提供最小的制约流动，但当联结是分离的不能防止系统损失当联结是分离的。 设计巴巴工作室www.88doc88.com 2. 单程关掉: 这个设计找出关掉流动性来源结合但作动器组分疏导的部分。在短程中从系统漏出不是过多的，但由于入口在管接头的系统污染可能是个问题, 特别是与流动设备位于工作地点。 3. 双向关掉: 这个设计提供两个结尾正面关掉当压力线分开。参见图4-19为切掉这类型快速断开联结。图4-20显示同样联结的一个其它看法。这样联结结束对液压损失。当您发布锁的阀门在插口和插座关闭,关闭流程。当在插口连接, 插座与一个0 圆环联系,创造正面密封。由于部份连接，没有过早的流出或浪费的机会。插座在阀门将打开之前必须充分地坐在插口。 1.9钢管材 在这个部分我们检查相同的管的尺寸，根据流速要求和压力考虑如何选择适当的管的大小。 图4-21表示不同大小的管使用在液压系统。显示最小的外径 大小是4毫米(0.158寸),但是最大的外径 大小是42 毫米(1.663 寸)。这些价值比较到0.125寸和1.500寸,各自地,从图。4-7为共同的英国单位管大小。值得注意的是, 1 m = 39.6 寸，并且1 毫米=0.0396 寸。 和安全因素对应的工作压力为: FS =8 为压力从0到1000 Pa (0 到7 MPa 或0 个到70 Pa) FS =6 为压力从1000到2500 Pa (7 到17.5 MPa 或70 个到175 Pa) FS =4 为压力在2500 Pa (17.5 MPa 或175 Pa之上) 对应的抗拉强度为SAE 1010 ，冷制 钢和AISI 4130 钢是: SAE 1010 55,000 Pa或379 MPa AISI 4130 75,000 Pa或517 MPa 设计巴巴工作室www.88doc88.com 例子1-5 选择适当的大小钢管，流速为0.00190m3/s，工作压力为70 Pa。最大允许流速是6.1m/s，管材料是SAE 1010，冷制钢抗拉强度为379 MPa 。 解答极小值内径根据可变的速度局限6.1 rn/s 被发现使用式 。 (3-18): 求A ，可得: 因为，可以得出: (4-7) 代入有: 从图4-21, 可接受的外径 管最小值是: 22毫米外径, 1.0毫米壁厚度, 20毫米内径 从式(4-3) 获得爆裂压力: 然后我们计算工作压力使用式(4-4)。 这压力不是充分的(较少比70 Pa工作压力), 如此让我们检查下支更大的大小外径 管有必要的内径。 28毫米外径, 2.0毫米壁厚度, 24毫米内径 设计巴巴工作室www.88doc88.com 这个结果是可接受的。 1.10 公式 小学单位换算公式大全免费下载公式下载行测公式大全下载excel公式下载逻辑回归公式下载 可变的速度: (4-1) 管子拉伸强度: (4-2) 管子爆裂压力: (4-3) 管子工作压力:: (4-3) 设计巴巴工作室www.88doc88.com