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机械类毕业论文中英文对照文献翻译
机械类
毕业论文
中英文
对照
文献
翻译
螺纹
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【机械类毕业论文中英文对照文献翻译】螺纹,机械类毕业论文中英文对照文献翻译,机械类,毕业论文,中英文,对照,文献,翻译,螺纹
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1. ScrewsThreaded fasteners such as screws, nuts, and bolts are importantcomponents of mechanical structures and machines. Screws maybe used as removable fasteners or as devices for moving loads.1.1 Screw ThreadThe basic arrangement of a helical thread wound around a cylinder isillustrated in Fig. 1.1. The terminology of an external screw threads is (Fig.1.1):jPitch, denoted by p, is the distance, parallel to the screw axis,between corresponding points on adjacent thread forms havinguniform spacing.jMajor diameter, denoted by d, is the largest (outside) diameter of ascrew thread.jMinor diameter, denoted by dror d1, is the smallest diameter of ascrew thread.jPitch diameter, denoted by dmor d2, is the imaginary diameter forwhich the widths of the threads and the grooves are equal.Figure 1.1244Machine ComponentsMachine ComponentsThe standard geometry of a basic profile of an external thread is shown inFig. 1.2, and it is basically the same for both Unified (inch series) and ISO(International Standards Organization, metric) threads.The lead, denoted by l, is the distance the nut moves parallel to thescrew axis when the nut is given one turn. A screw with two or more threadscut beside each other is called a multiple-threaded screw. The lead is equalto twice the pitch for a double-threaded screw, and to three times the pitchfor a triple-threaded screw. The pitch p, lead l, and lead angle l arerepresented in Fig. 1.3. Figure 1.3a shows a single-threaded, right-handscrew, and Fig. 1.3b shows a double-threaded left-hand screw. All threadsare assumed to be right-hand, unless otherwise specified.A standard geometry of an ISO profile, M (metric) profile, with 60?symmetric threads is shown in Fig. 1.4. In Fig. 1.4 D(d) is the basic majordiameter of an internal (external) thread, D1?d1? is the basic minor diameterof an internal (external) thread, D2?d2? is the basic pitch diameter, andH ? 0:5?3?1=2p.Metric threads are specified by the letter M preceding the nominalmajor diameter in millimeters and the pitch in millimeters per thread. Forexample:M 14 ? 2M is the SI thread designation, 10mm is the outside (major) diameter, and thepitch is 2mm per thread.Figure 1.21.Screws245Machine ComponentsScrew size in the Unified system is designated by the size number formajor diameter, the number of threads per inch, and the thread series, likethis:5008? 18 UNF5008is the outside (major) diameter, where the double tick marks mean inches,and 18 threads per inch. Some Unified thread series areUNC, Unified National CoarseUNEF, Unified National Extra FineFigure 1.3246Machine ComponentsMachine ComponentsUNF, Unified National FineUNS, Unified National SpecialUNR, Unified National Round (round root)The UNR series threads have improved fatigue strengths.1.2 Power ScrewsFor application that require power transmission, the Acme (Fig. 1.5) andsquare threads (Fig. 1.6) are used.Power screws are used to convert rotary motion to linear motion of themeshing member along the screw axis. These screws are used to lift weightsFigure 1.4Figure 1.51.Screws247Machine Components(screw-type jacks) or exert large forces (presses, tensile testing machines).The power screws can also be used to obtain precise positioning of the axialmovement.A square-threaded power screw with a single thread having the pitchdiameter dm, the pitch p, and the helix angle l is considered in Fig. 1.7.Consider that a single thread of the screw is unrolled for exactly one turn.The edge of the thread is the hypotenuse of a right triangle and the height isthe lead. The hypotenuse is the circumference of the pitch diameter circle(Fig. 1.8). The angle l is the helix angle of the thread.The screw is loaded by an axial compressive force F (Figs. 1.7 and 1.8).The force diagram for lifting the load is shown in Fig. 1.8a (the force Practs to the right). The force diagram for lowering the load is shown in Fig.1.8b (the force Placts to the left). The friction force isFf? mN;Figure 1.6248Machine ComponentsMachine Componentswhere m is the coefficient of dry friction and N is the normal force. Thefriction force is acting opposite to the motion.The equilibrium of forces for raising the load givesPFx? Pr? N sinl ? mN cosl ? 0?1:1?PFy? F ? mN sinl ? N cosl ? 0:?1:2?Similarly, for lowering the load one may write the equationsPFx? ?Pl? N sinl ? mN cosl ? 0?1:3?PFy? F ? mN sinl ? N cosl ? 0:?1:4?Figure 1.7Figure 1.81.Screws249Machine ComponentsEliminating N and solving for PrgivesPr?F?sinl ? mcosl?cosl ? msinl;?1:5?and for lowering the load,Pl?F?mcosl ? sinl?cosl ? msinl:?1:6?Using the relationtanl ? l=pdmand dividing the equations by cosl, one may obtainPr?F?l=pdm? ? m?1 ? ?ml=tdm?1:7?Pl?F?m ? ?l=pdm?1 ? ?ml=pdm?:?1:8?The torque required to overcome the thread friction and to raise the load isTr? Prdm2?Fdm2l ? pmdmpdm? ml?:?1:9?The torque required to lower the load (and to overcome a part of the friction)isTl?Fdm2pmdm? lpdm? ml?:?1:10?When the lead l is large or the friction m is low, the load will lower itself. Inthis case the screw will spin without any external effort, and the torque TlinEq. (1.10) will be negative or zero. When the torque is positive, Tl 0, thescrew is said to be self-locking.The condition for self-locking ispmdm l:Dividing both sides of this inequality by pdmand using l=pdm? tanl yieldsm tanl:?1:11?The self-locking is obtained whenever the coefficient of friction is equal to orgreater than the tangent of the thread lead angle.The torque, T0, required only to raise the load when the friction is zero,m ? 0, is obtained from Eq. (1.9):T0?Fl2p:?1:12?The screw efficiency e can be defined ase ?T0Tr?Fl2pTr:?1:13?250Machine ComponentsMachine ComponentsFor square threads the normal thread load, F, is parallel to the axis of thescrew (Figs 1.6 and 1.7). The preceding equations can be applied for squarethreads.For Acme threads (Figs 1.5) or other threads, the normal thread load isinclined to the axis because of the thread angle 2a and the lead angle l. Thelead angle can be neglected (is small), and only the effect of the thread angleis considered (Fig. 1.9). The angle a increases the frictional force by thewedging action of the threads. The torque required for raising the load isobtained from Eq. (1.9) where the frictional terms must be divided by cosa:Tr?Fdm2l ? pmdmsecapdm? ml seca?:?1:14?Equation (1.14) is an approximation because the effect of the lead angle hasbeen neglected. For power screws the square thread is more efficient thanthe Acme thread. The Acme thread adds an additional friction due to thewedging action. It is easier to machine an Acme thread than a square thread.In general, when the screw is loaded axially, a thrust bearing or thrustcollar may be used between the rotating and stationary links to carry the axialcomponent (Fig. 1.10). The load is concentrated at the mean collar diameterdc. The torque required isTc?Fmcdc2;?1:15?where mcis the coefficient of collar friction.Figure 1.91.Screws251Machine ComponentsEXAMPLEA double square-thread power screw has the major diameter d ? 64mm andthe pitch p ? 8mm. The coefficient of friction m is 0.08, and the coefficient ofcollar friction mcis 0.08. The mean collar diameter dcis 80mm. The externalload on the screw F is 10kN.Find:1.The lead, the pitch (mean) diameter and the minor diameter2.The torque required to raise the load3.The torque required to lower the load4.The efficiencySolution1.From Fig. 1.6a:The minor diameter isdr? d ? p ? 64 ? 8 ? 56 mm;the pitch (mean) diameter isdm? d ? p=2 ? 64 ? 4 ? 60 mm:The lead isl ? 2p ? 2?8? ? 16 mm:Figure 1.10252Machine ComponentsMachine Components南 京 理 工 大 学 紫 金 学 院毕业设计(论文)外文资料翻译系： 机械工程系 专 业： 机械工程及自动化 姓 名： 顾浩 学 号： 060104265 (用外文写)外文出处： Mechanical Engineers Handbook 附 件： 1.外文资料翻译译文；2.外文原文。指导教师评语：该生翻译了一篇有关螺纹及设计的论文，论文内容跟课题的研究领域相关，在将来的课题设计中可以借鉴。译文语句基本通顺，专业术语正确，标点符号运用无误。说明该生具备一定的英语水平和翻译能力。但文中仍有部分语句组织得不够完善，如：专业名称的准确性、公式的编排等，尚需要进一步修改。 签名： 2010 年 3 月 25 日 注：请将该封面与附件装订成册。附件1：外文资料翻译译文螺纹螺纹紧固件如螺纹，螺母，螺栓等，是重要的机械结构的组成部分和机器。螺纹可作为移动紧固件或移动装置负荷。1.1螺纹螺纹的形状如图所示 1.1。螺纹相关专业名称如图1.1螺距标记为P，平行于回旋轴，相邻牙在中径线上对应两点间的轴向距离且有相同的距离。大径（d），螺纹最大（外）的直径。小径（dr 或 d1），螺纹最小的直径。中径，标记为dm 或 d2，母线通过牙型上凸起和沟槽两者宽度相等的假想圆柱体直径。图1.1一个外螺纹的基本配置标准几何如图1.2，美国（英寸系列）和ISO（国际标准化组织，公制）基本上相似。螺纹导程（l），同一螺旋线上相邻牙在中径线上对应两点间的轴向距离。两个或多个螺纹线的螺纹叫做多线螺纹。螺纹导程等于一个双线螺纹螺距的两倍和一个三线螺纹螺距的三倍。螺距p、导程l、导程角的关系如图1.3所示。图1.3a表示单线、右旋螺纹，图1.3b表示双线、左旋螺纹。所有的螺纹都默认为右旋，除了有特别说明的。一个标准的ISO几何文件，M表示普通螺纹，图1.4显示了60的普通螺纹。在图1.4里，D（d）是螺纹的内外大径，D1（d1）是螺纹的内外小径，D2（d2）是中直径，H=0.5(3)P 公制螺纹以毫米为单位定义其工程直径和螺距。例如： M14*2M代表的是普通螺纹，10mm是其大径，每个螺纹的螺距是2mm。图1.2图1.3图1.4英制螺纹以英寸定义其大径尺寸、每英寸牙数量以及螺纹规格系列，例如： 5”818 UNF58是外径（大径），其中双刻度是以英寸为单位，每英寸有18个牙数。螺纹系列有：UNC 粗牙系列的统一螺纹UNEF 超细牙系列的统一螺纹UNF 细牙系列的统一螺纹UNS 特殊系列的统一螺纹UNR 圆弧牙底恒定螺距系列的统一螺纹 UNR 系列螺纹可以改善螺纹疲劳1.2 传动螺纹梯形螺纹和矩形螺纹通常应用于传递动力。传动螺杆是把旋转运动转换为沿着螺杆轴线的直线啮合运动。这些螺杆被用来提升重物（螺杆式千斤顶）或是施加压力（压力机、拉伸试验机）。传递也可 用于获取准确的轴向定位运动。图1.5矩形螺纹的中径为dm,螺距p，和螺旋角的矩形螺纹如图1.7所示。螺杆的一个线程被认为是一圈的展开。导程是一个直角三角形的斜边的高度的导程。斜边是螺距的中径（图1.8）。角是螺纹的螺旋角。当一个轴向力F加载在螺杆时如图1.7和1.8。举起重物的受力图如图1.8a（压力Pr向右）。降低重物的受力图如图1.8b（压力P1向左）。摩擦力是： Ff=N其中是干摩擦系数，N是其法向力。摩擦力方向与运动方向相反。举起重物的力平衡方程式为：Fx=Pr-Nsin-Ncos=0 (1.1) Fy=Pr+sin-Ncos=0 (
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