斜齿轮、蜗杆蜗轮和锥齿轮外文文献翻译、中英文翻译、外文翻译

中北大学 2006 届本科毕业设计说明书  第  1 页   共  12 页  外文文献原文  Helical， Worm and Bevel Gears In the force analysis of spur gars, the forces are assumed to act in a single plain. In this lesson we shall study gears in which the forces have three dimensions. The reason for this, in the case of helical gears, is that the teeth are not parallel to the axis of rotation. And in the case of bevel gears, the rotational axes are not parallel to each other. There are other reasons, as we shall learn. Helical gears are used to transmit motion between parallel shafts. The helix angle is the same on each gear, but one gear must have a right hand helix and the other a left hand helix. The shape of the tooth is an involute helicoids. If a piece of paper cut in the shape of a parallclogram is wrapped around a cylinder, the angular  edge of the paper becomes a helix. If we unwind this paper, each point on the angular edge generates an involute curve. The surface obtained when every point on the edge generates an involute is called an involute helicoids. The initial contact of spur gear teeth is a line extending all the way across the face of the tooth. The initial contact of helical gear teeth is a point,which changes into a line as the teeth come into more engagement. In spur gears the line of contact is parallel to the axis of the rotation； in helical gears, the line is diagonal across the face of the tooth.It is this gradual engagement of the teeth and the smooth transfer of load from one tooth to another ,which give helical gears the ability to transmit heavy loads at high speeds. Helical gears subject the shaft bearings to both radial and thrust loads. When the thrust loads become high or are objectionable for other reasons, it may be desirable to use double helical gears. A double helical gear（ herringbone） is equivalent to two helical gears of opposite hand, mounted side by side on the same shaft. They develop opposite thrust reaction and thus cancel out the thrust load. When two or more single helical gears are mounted on the same shaft, the hand of the gears should be selected so as to produce the minimum thrust load. Crossed helical, or spiral, gears are those in which the shaft centerlines are neither 中北大学 2006 届本科毕业设计说明书  第  2 页   共  12 页  parallel nor intersecting. The teeth of crossed-helical gears have point contact with each other, which changes to line contact as the gears wear in. For this reason they will carry out very small loads and are mainly for instrumental applications, and are definitely not recommended for use in the transmission of power. There is no difference between a crossed helical gear and a helical gear until they are mounted in mesh with each other. They are manufactured in the same way. A pair of meshed crossed helical gears usually have the same hand； that is, a right-hand driver goes with a right hand driven. In the design of crossed-helical gears, the minimum sliding velocity is obtained when the helix angle are equal. However, when the helix angle are not equal, the gear with the larger helix angle should he used as the driver if both gears have the same hand. Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch cylinder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angular-velocity reduction between nonintersecting shafts which are usually at right angle. The worm gear is not a helical gear because its face is made concave to fit the curvature, nature of the worm in order to provide line contact instead of point contact. However, a disadvantage of worm gearing is the high sliding velocities across the teeth, the same as with crossed helical gears.  Worn gearing are either single or double enveloping. A single enveloping gearing is one in which the gear wraps around or partially encloses the worm, A gearing in which each element partially encloses the other is, of course, a double enveloping worm gearing. The important difference between the two is that area contact exists between the teeth of double enveloping gears while only line contact between those of single-enveloping gears. The worm and worm gear of a set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm is generally quite large, and that on the gear very small. Because of this, it is usual to specify the lead angle on the worm, which is the complement of the worm helix angle, and the helix angle on the gear； the two angles are equal for a 9O deg. 中北大学 2006 届本科毕业设计说明书  第  3 页   共  12 页  shaft angle. When gears are to be used to transmit motion between intersecting shafts, some form of bevel gear is required. Although bevel gears are usually made for a shaft angle of 9O deg., they may be produced for almost any shaft angle. The teeth may be east, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gear is often mounted outboard of the bearing. This means that shaft deflection can be more pronounced and have a greater effect on the contact of the teeth. Another difficulty, which occurs in predicting the stress in bevel gear teeth, is the fact that the teeth are tapered. Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and positively. As in the case of spur gears, however, they become noisy at higher values of the pitch-line velocity. In these eases it is often good design practice to go to he spiral bevel gear, which is the bevel counterpart of the helical gear, as in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered.    It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to bevel gears but with the shaft offset. Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution. The tooth action between such gears is a combination of rolling and sliding along a straight line and has much in common with that of worm gears SAND CASTING Most metal casting are made by pouring molten metal into a prepared cavity and allowing it to solidify. The process dates from antiquity. The largest bronze statue in existence to-day is the great Sun Buddha in Nara, Japan. Cast in the eighth century, it weighs 551 tons(500 metric tons) and is more than 71 ft (21m) high. Artisans of the Shang Dynasty in China ( 1766 - 1222B. C. ) created art works of bronze with delicate filigree as sophisticated as anything that is designed and produced today. There are many casting processes available today, mid selecting the best one to produced particular part depends on several basic factors, such as cost, size. production rate. finish, tolerance, section thickness, physical-mechanical properties, intricacy of 中北大学 2006 届本科毕业设计说明书  第  4 页   共  12 页  design mach inability, and weld ability. Sand casting. the oldest and still the most widely used casting process. will be presented in more detail than the other processes since many of the concepts carry over into those processes as well. Green Sand       Green sand generally consists of silica sand and additives coated by rubbing the sand grains together with clay uniformly wetted with water. More stable and refractory sands have been developed, such as fused silica, zircon, and mullets, which replace lower-cost silica and  have only 2% linear expansion at ferrous metal temperatures. Also, relatively un-stable water and clay bonds are being replaced with synthetic resins, which are much mores table at elevated temperatures. Green sand molding is used to produce a wide variety of castings in sizes of less than around to as large as several tons. This versatile process is applicable to both ferrous and nonferrous materials. Green sand can be used to produce intricate molds since it provides for rapid collapsibility: that is, the mold is much less resistant to the contraction of the casting as it solidifies than are other molding processes. This results in less stress and strain in the casting. The sand is rammed or compacted around the pattern high a variety of methods, including hand or pneumatic-tool ramming, jolting (abrupt mechanical shaking), squeezing (com-pressing the top and bottom mold surfaces), and driving the sand into the mold at high velocities (sad slinging). Sand slings are usually resented for use in making very large casting where great volumes of sand are handled. For smaller casting, a two-part metal box or flask referred to as a cope and drag issued. First the pattern is positioned on a mold board. and the drag or lower half of the flask is positioned over it. Parting powder is sprinkled on the paten and the box is filled with sand. A jolt squeeze machine quicky compacts the sand. The flask is then turned over and again parting powder is dusted on it. The cope is then positioned on the top half of the flask and is filled with sand, and the two-part mold with the patter board sandwiched in between is squeezed. Patterns Patterns for sand casting have traditionally been made of wood or metal. However, it has been found that wood patterns change as much as 3% due to heat and moisture. 中北大学 2006 届本科毕业设计说明书  第  5 页   共  12 页  This factor alone would put many casting out of acceptable tolerance for more exacting specifications. Now, patterns are often made from epoxies and from cold-setting rubber with stabilizing inserts. Patterns of simple design, with one or more flat surface, can be molded in one piece, provided that they can be withdrawn without disturbing the compacted sand. Other patterns may be split into two or more parts to facilitate their removal from the sand when using two-part flasks. The pattern must be tapered to permit easy removal from the sand. The taper is referred to as draft. When a part does not have some natural draft, it must be added. A more recent innovation in patterns for sand casting has been to make them out of foamed polystyrene that is vaporized by the molten metal. This type of casting, known as the full-mold process, does not require pattern draft. Spruces, Runners, and Gates. Access to the mold cavity for entry of the molten metal is provided by sprees, runners, and gates, as shown in Fig. 7 I. A pouring basin can be carved in the sand at the top of the spree, or a pour box, which provides a large opening, may be laid over the spree to facilitate pouring. After the metal is poured, it cools most rapidly in the sand mold. Thus the outer surface forms a shell that permits the still molten metal near the center to flow toward it. As a result, the last portion of the casting to freeze will be deficient in metal and, in the absence oaf supplemental metal-feed source, will result in some form of shrinkage.2 This shrinkage may take the form of gross shrinkage (large cavities) or the more subtle micro shrinkage ( finely dispersed porosity). These porous spots can be avoided by the use of risers, as shown in Fig.7-1, which provide molten metal to make up for shrinkage losses. Cores Cores are placed in molds wherever it is necessary to preserve the space it occupies in the mold as a void in the resulting castings. As sown in Fig.7-1, the core will be put in place after the pastern is removed. To ensure its proper location, the pattern has extensions known as core prints that leave cavities in the mold into which the core is seated. Sometimes the core may be molded integrally with the green sand and is then referred to as a green-sand core. Generally, the core is made of sand bonded with core oil, some organic bonding materials, and water. These materials are thoroughly blended and placed in a mold or core box. After forming, they are removed and baked at 350to 450F ( 177to 232C). Cores that consist of two or more parts are pasted together after 中北大学 2006 届本科毕业设计说明书  第  6 页   共  12 页  baking. CO2 Cores CO2 cores are made by ramming up moist sand in a core box. Sodium silicate is used as a binder, which is quickly hardened by blowing CO2 gas over it. The C02 system has the advantage of making the cores immediately available. Pouring the Metal Several types of containers are used to move the molten metal from the furnace to the pouring area. Large castings of the floor-and-pit type are poured with a ladle that has a plug in the button, or, as it is called, a bottom-pouring ladle. It is also employed in mechanized operations where the molds are moved along a line and each is poured as it is momentarily stopped beneath the large bottom-pour ladle. ladles used for pouring ferrous metals are lined with a high alumina-content refractory. After long use and oxidation, it can be broken out and replaced. Ladles used in handling ferrous metals most be preheated with gas flames to approximately 2600 to 2700F ( 1427 to 1482C) before filling. Once the ladle is filled, it is used constantly until it has been emptied. For nonferrous metals, simple clay-graphite crucibles are used. While they are quite susceptible to breakage, they are very resistant to the metal and will hold up a long time under normal condition. They usually do not require preheating, although care must he taken to avoid moisture pickup. For this reason they are sometimes baked out to assure dryness. The pouring process must he carefully controlled, since the temperature of the melt greatly affects the degree of liquid contraction before solidification, the rate of solidification, which in turn affects the around of columnar growth present at the mold wall, the extent and nature of the dendrite growth, the degree of alloy burnout, and the feeding characteristics of the rise ring system. Finishing Operations After the castings have solidified and cooled somewhat. they are placed on a shakeout table or grating on which the sand mold is broken up, leaving the casting free to be picked out. The casting is then taken to the finishing room where the gates and risers are removed. Small gates and risers may he broken off with a hammer if the material is bride. Larger ones requiem sawing, cutting with a roach, or shearing. Unwanted metal protrusions such as fins, bosses, and small portions of gates and risers 中北大学 2006 届本科毕业设计说明书  第  7 页   共  12 页  need to be smoothed off to blend with the surface. Most of this work is done with a heavy-duty grinder and the process is known as snagging or snag grinding. On large castings it is easier to move the grinder than the work, so swing-type grinders are used. Smaller castings are brought to stand or bench-type grinders. Hans and pneumatic chisels are also used to trim castings. A more recent method of removing  excess metal from famous castings is with a carbon air torch. This consists of a carbon rod and high-amperage current with a stream of compressed air blowing at the base of it. This oxidizes and removes the metal as soon as it is molten, In many foundries this method has replaced nearly all chipping and grinding operation. 中北大学 2006 届本科毕业设计说明书  第  8 页   共  12 页  译文  斜齿轮、蜗杆蜗轮和锥齿轮  在直齿圆柱齿轮的受力分析中，是假定各力作用在单一平面的。在这一课题中，我们将研究作用力具有三维坐标的齿轮。因此，在斜齿轮的情况下，其齿向是不平行于回转轴线的。而在锥齿轮的情况中各回转轴线互相不平行。像我们将要讨论的那样，尚有其他道理需要学习、掌握。  斜齿轮用于传递平行轴之间的运动。倾斜角度每个齿轮都一样，但一个必须右旋斜齿，而另一个必须是左旋斜齿。齿的形状是一渐开线螺旋面。如果一张被剪成平行四边形 (矩形 )的纸张包围在齿轮圆柱体上，纸上印出齿的角刃边就变成斜线。如果我展开这张纸，在斜角刃边上的每一个点就发生一渐开线曲线。  直齿圆柱齿轮轮齿的初始接触处是跨过整个齿面而伸展开来的线。斜齿轮轮齿的初始接触是一点，当齿进入更多的啮台时，它就变成线。在直齿圆 柱齿轮中，接触线是平行于回转轴线的。在斜齿轮中，该线是跨过齿面的对角线。它是轮齿逐渐进行啮台并平稳地从一个齿到另一个齿传递运动，那样就使斜齿轮具有高速重载下平稳传递运动的能力。斜齿轮使轴的轴承承受径向和轴向力。当轴向推力变得大了或由于别的原因而产生某些影响时，那就可以使用人字齿轮。双斜齿轮 (人字齿轮 )是与反向的并排地装在同一轴上的两个斜齿轮等敬。他们产生相反的轴向推力作用，这样就消除了轴向推力。当两个或更多的单向齿斜齿轮被装在同一轴上时，齿轮的齿向应作选择，以便产生最小的轴向推力。  交错轴斜齿轮或螺旋齿轮， 他们的轴中心线既不相交也不平行。交错轴斜齿轮的齿彼此之间发生点接触，它随着齿轮的磨合而变成线接触。因此他们只能传递小的载荷和主要用于仪器设备中，而且肯定不能推荐在动力传动中使用。交错轴斜齿轮与斜齿轮之间在被安装后互相啮合之前是没有任何区别的。它们是以同样的方法进行制造。一对相啮合的交错轴斜齿轮通常具有同样的齿向，即左旋主动齿轮跟右旋从动齿轮相啮舍。在交错轴斜齿设计中，当该齿的斜角相等时所产生滑移速度最小。然而当该齿的斜角不相等时，如果两个齿轮具有相同齿向的话，大斜角齿轮应该用作主动齿轮。  蜗轮与交错轴斜齿轮 相似。小齿轮即蜗杆具有较小的齿数，通常是一到四齿由中北大学 2006 届本科毕业设计说明书  第  9 页   共  12 页  于它们完全缠绕在节圆柱上，因此它们又被称为螺纹齿。与其相配的齿轮叫做蜗轮，蜗轮不是真正的斜齿轮。蜗杆和蜗轮通常是用于向垂直相交轴之间的传动提供大的角速度减速比。蜗轮不是斜齿轮，因为其齿顶面做成中凹形状以适配蜗杆曲率，目的是要形成线接触而不是点接触。然而蜗杆蜗轮传动机构中存在齿问有较大滑移速度的缺点，正像变错轴斜齿轮那样。     蜗杆蜗轮机构有单包围和双包围机构。单包围机构就是蜗轮包裹着蜗杆或部分地包围着蜗杆的一种机构。当然，如果每个构件各自局部地包围着对方 的蜗轮机构就是双包围蜗轮蜗杆机构。这两者之间的重要区别是，在双包围蜗轮组的轮齿间有面接触，而在单包围蜗轮组的轮齿间只有线接触。一个装置中的蜗杆和蜗轮正像交错轴斜齿轮那样具有相同的齿向，但是其斜齿齿角的角度是极不相同的。蜗杆上的齿斜角度通常很大，而蜗轮上的则极小。因此惯常规定蜗杆的导角，那就是蜗杆齿斜角的余角；也规定了蜗轮上的齿斜角，该两角之和就等于 90。的轴线交角。     当齿轮要用来传递相交轴之网的运动时，就需要某种形式的锥齿轮。虽然锥齿轮通常制造成能构成 90 度轴交角，但它们也可产生任何角度的轴交角。轮齿 可以铸出、铣制或滚切加工。仅就滚齿而言就可达一级精度。在典型的锥齿轮安装中，其中一个锥齿轮常常装于支承的外侧。这意味着轴的挠曲情况更加明显而使在轮齿接触上具有更大的影响。  另外一个难题，发生在难于预示锥齿轮轮齿上的应力实际上是由于轮齿被加工成锥状造成的。  直齿锥齿轮易于设计且制造简单，如果他们安装的精密而确定，在运转中会产生良好效果。然而在直齿圆柱齿轮情况下，在节线速度较高时，他们将发出噪音。在这些情况下，通常设计使用螺旋锥齿轮，实践证明是切实可行的，那是和配对斜齿轮很相似的配对锥齿轮。当在斜齿轮情况下， 螺旋锥齿轮比直齿轮能产生平  稳得多的啮合作用，因此碰到高速运转的场合那是很有用的。当在汽车的各种不同用途中，有一个带偏心轴的类似锥齿轮的机构，那是常常所希望的。这样的齿轮机构叫做准双曲面齿轮机构，因为他们的节面是双曲回转面。这种齿轮之间的轮齿作用是沿着一根直线上产生滚动与滑动相结合的运动并和蜗轮蜗杆的轮齿作用有着更多的共同之处。  砂型铸造  大多数金属铸件。是通过将熔化的金属注入预先做好的型腔凝固而成的，这  中北大学 2006 届本科毕业设计说明书  第  10 页   共  12 页  种方法可溯及古代 ,  现存最大的青铜铸件是日本奈良市的太阳大佛它铸于八世纪，重 551(美国 )叫 (500吨 )高度超过 71英尺 (21米 )  小国商朝 (公元前 1766 1222 年 )的工匠们制造的精美的青铜制品其复杂程度可与当代设计制造的工艺品媲美  目前，有许多铸造方法，对特定铸件所选择的最好的铸造方法，取决于几个基本因素。比如成本、尺寸、生产率、光洁度 (我国标准名词术语现称作表面粗糙度 译者 )、公差、截面厚度、物理化学降性、设计难度、可加工件和可焊件等  砂则铸造是最古老且仍广泛应用的铸造方法。本文将详细地介绍这种方法，因为它的许多概念也适用于其他方法  型砂  型砂通常含有石英砂和添加剂、通过砂粒与用水均匀 溅湿的粘土的搅拌、使砂粒及添加剂表面包复 ,层粘结薄膜   更稳定耐熔的砂子，如熔融石英砂、钴土砂、富铝石砂已开始使用、用来替代低成本石英砂。它们在浇注温度下仅有 2%的线件扩张 ,问时用在高温下更稳定的合成树脂来取代相对不稳定的水和粘土粘结剂。  型砂铸型可用来制造重量从小于 1 磅到几吨的许多铸件可适用于黑色金属和有色金属材料、     型砂可用来制造复杂铸型因为它具有很好的退让性，即铸型对铸件凝固时的收缩抗力比其他铸型要小，这样铸件中的应力、应变就小 .    可用许多力法将模型周围的砂子捣实和压紧、包括手工压紧、 气锤压紧、振动紧实 (剧烈地机械振动 )、挤