斜齒輪、蝸桿蝸輪和錐齒輪外文文獻翻譯、中英文翻譯、外文翻譯

中北大學 2006 屆本科畢業(yè)設計說明書  第  1 頁   共  12 頁  外文文獻原文  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 中北大學 2006 屆本科畢業(yè)設計說明書  第  2 頁   共  12 頁  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. 中北大學 2006 屆本科畢業(yè)設計說明書  第  3 頁   共  12 頁  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 中北大學 2006 屆本科畢業(yè)設計說明書  第  4 頁   共  12 頁  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. 中北大學 2006 屆本科畢業(yè)設計說明書  第  5 頁   共  12 頁  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 中北大學 2006 屆本科畢業(yè)設計說明書  第  6 頁   共  12 頁  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 中北大學 2006 屆本科畢業(yè)設計說明書  第  7 頁   共  12 頁  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. 中北大學 2006 屆本科畢業(yè)設計說明書  第  8 頁   共  12 頁  譯文  斜齒輪、蝸桿蝸輪和錐齒輪  在直齒圓柱齒輪的受力分析中，是假定各力作用在單一平面的。在這一課題中，我們將研究作用力具有三維坐標的齒輪。因此，在斜齒輪的情況下，其齒向是不平行于回轉(zhuǎn)軸線的。而在錐齒輪的情況中各回轉(zhuǎn)軸線互相不平行。像我們將要討論的那樣，尚有其他道理需要學習、掌握。  斜齒輪用于傳遞平行軸之間的運動。傾斜角度每個齒輪都一樣，但一個必須右旋斜齒，而另一個必須是左旋斜齒。齒的形狀是一漸開線螺旋面。如果一張被剪成平行四邊形 (矩形 )的紙張包圍在齒輪圓柱體上，紙上印出齒的角刃邊就變成斜線。如果我展開這張紙，在斜角刃邊上的每一個點就發(fā)生一漸開線曲線。  直齒圓柱齒輪輪齒的初始接觸處是跨過整個齒面而伸展開來的線。斜齒輪輪齒的初始接觸是一點，當齒進入更多的嚙臺時，它就變成線。在直齒圓 柱齒輪中，接觸線是平行于回轉(zhuǎn)軸線的。在斜齒輪中，該線是跨過齒面的對角線。它是輪齒逐漸進行嚙臺并平穩(wěn)地從一個齒到另一個齒傳遞運動，那樣就使斜齒輪具有高速重載下平穩(wěn)傳遞運動的能力。斜齒輪使軸的軸承承受徑向和軸向力。當軸向推力變得大了或由于別的原因而產(chǎn)生某些影響時，那就可以使用人字齒輪。雙斜齒輪 (人字齒輪 )是與反向的并排地裝在同一軸上的兩個斜齒輪等敬。他們產(chǎn)生相反的軸向推力作用，這樣就消除了軸向推力。當兩個或更多的單向齒斜齒輪被裝在同一軸上時，齒輪的齒向應作選擇，以便產(chǎn)生最小的軸向推力。  交錯軸斜齒輪或螺旋齒輪， 他們的軸中心線既不相交也不平行。交錯軸斜齒輪的齒彼此之間發(fā)生點接觸，它隨著齒輪的磨合而變成線接觸。因此他們只能傳遞小的載荷和主要用于儀器設備中，而且肯定不能推薦在動力傳動中使用。交錯軸斜齒輪與斜齒輪之間在被安裝后互相嚙合之前是沒有任何區(qū)別的。它們是以同樣的方法進行制造。一對相嚙合的交錯軸斜齒輪通常具有同樣的齒向，即左旋主動齒輪跟右旋從動齒輪相嚙舍。在交錯軸斜齒設計中，當該齒的斜角相等時所產(chǎn)生滑移速度最小。然而當該齒的斜角不相等時，如果兩個齒輪具有相同齒向的話，大斜角齒輪應該用作主動齒輪。  蝸輪與交錯軸斜齒輪 相似。小齒輪即蝸桿具有較小的齒數(shù)，通常是一到四齒由中北大學 2006 屆本科畢業(yè)設計說明書  第  9 頁   共  12 頁  于它們完全纏繞在節(jié)圓柱上，因此它們又被稱為螺紋齒。與其相配的齒輪叫做蝸輪，蝸輪不是真正的斜齒輪。蝸桿和蝸輪通常是用于向垂直相交軸之間的傳動提供大的角速度減速比。蝸輪不是斜齒輪，因為其齒頂面做成中凹形狀以適配蝸桿曲率，目的是要形成線接觸而不是點接觸。然而蝸桿蝸輪傳動機構(gòu)中存在齒問有較大滑移速度的缺點，正像變錯軸斜齒輪那樣。     蝸桿蝸輪機構(gòu)有單包圍和雙包圍機構(gòu)。單包圍機構(gòu)就是蝸輪包裹著蝸桿或部分地包圍著蝸桿的一種機構(gòu)。當然，如果每個構(gòu)件各自局部地包圍著對方 的蝸輪機構(gòu)就是雙包圍蝸輪蝸桿機構(gòu)。這兩者之間的重要區(qū)別是，在雙包圍蝸輪組的輪齒間有面接觸，而在單包圍蝸輪組的輪齒間只有線接觸。一個裝置中的蝸桿和蝸輪正像交錯軸斜齒輪那樣具有相同的齒向，但是其斜齒齒角的角度是極不相同的。蝸桿上的齒斜角度通常很大，而蝸輪上的則極小。因此慣常規(guī)定蝸桿的導角，那就是蝸桿齒斜角的余角；也規(guī)定了蝸輪上的齒斜角，該兩角之和就等于 90。的軸線交角。     當齒輪要用來傳遞相交軸之網(wǎng)的運動時，就需要某種形式的錐齒輪。雖然錐齒輪通常制造成能構(gòu)成 90 度軸交角，但它們也可產(chǎn)生任何角度的軸交角。輪齒 可以鑄出、銑制或滾切加工。僅就滾齒而言就可達一級精度。在典型的錐齒輪安裝中，其中一個錐齒輪常常裝于支承的外側(cè)。這意味著軸的撓曲情況更加明顯而使在輪齒接觸上具有更大的影響。  另外一個難題，發(fā)生在難于預示錐齒輪輪齒上的應力實際上是由于輪齒被加工成錐狀造成的。  直齒錐齒輪易于設計且制造簡單，如果他們安裝的精密而確定，在運轉(zhuǎn)中會產(chǎn)生良好效果。然而在直齒圓柱齒輪情況下，在節(jié)線速度較高時，他們將發(fā)出噪音。在這些情況下，通常設計使用螺旋錐齒輪，實踐證明是切實可行的，那是和配對斜齒輪很相似的配對錐齒輪。當在斜齒輪情況下， 螺旋錐齒輪比直齒輪能產(chǎn)生平  穩(wěn)得多的嚙合作用，因此碰到高速運轉(zhuǎn)的場合那是很有用的。當在汽車的各種不同用途中，有一個帶偏心軸的類似錐齒輪的機構(gòu)，那是常常所希望的。這樣的齒輪機構(gòu)叫做準雙曲面齒輪機構(gòu)，因為他們的節(jié)面是雙曲回轉(zhuǎn)面。這種齒輪之間的輪齒作用是沿著一根直線上產(chǎn)生滾動與滑動相結(jié)合的運動并和蝸輪蝸桿的輪齒作用有著更多的共同之處。  砂型鑄造  大多數(shù)金屬鑄件。是通過將熔化的金屬注入預先做好的型腔凝固而成的，這  中北大學 2006 屆本科畢業(yè)設計說明書  第  10 頁   共  12 頁  種方法可溯及古代 ,  現(xiàn)存最大的青銅鑄件是日本奈良市的太陽大佛它鑄于八世紀，重 551(美國 )叫 (500噸 )高度超過 71英尺 (21米 )  小國商朝 (公元前 1766 1222 年 )的工匠們制造的精美的青銅制品其復雜程度可與當代設計制造的工藝品媲美  目前，有許多鑄造方法，對特定鑄件所選擇的最好的鑄造方法，取決于幾個基本因素。比如成本、尺寸、生產(chǎn)率、光潔度 (我國標準名詞術語現(xiàn)稱作表面粗糙度 譯者 )、公差、截面厚度、物理化學降性、設計難度、可加工件和可焊件等  砂則鑄造是最古老且仍廣泛應用的鑄造方法。本文將詳細地介紹這種方法，因為它的許多概念也適用于其他方法  型砂  型砂通常含有石英砂和添加劑、通過砂粒與用水均勻 濺濕的粘土的攪拌、使砂粒及添加劑表面包復 ,層粘結(jié)薄膜   更穩(wěn)定耐熔的砂子，如熔融石英砂、鈷土砂、富鋁石砂已開始使用、用來替代低成本石英砂。它們在澆注溫度下僅有 2%的線件擴張 ,問時用在高溫下更穩(wěn)定的合成樹脂來取代相對不穩(wěn)定的水和粘土粘結(jié)劑。  型砂鑄型可用來制造重量從小于 1 磅到幾噸的許多鑄件可適用于黑色金屬和有色金屬材料、     型砂可用來制造復雜鑄型因為它具有很好的退讓性，即鑄型對鑄件凝固時的收縮抗力比其他鑄型要小，這樣鑄件中的應力、應變就小 .    可用許多力法將模型周圍的砂子搗實和壓緊、包括手工壓緊、 氣錘壓緊、振動緊實 (劇烈地機械振動 )、擠