裝配圖大直徑樁基礎(chǔ)工程成孔鉆具(論文+DWG圖紙),裝配,直徑,樁基礎(chǔ),工程,成孔鉆具,論文,dwg,圖紙 GEAR Spur and helical gears. A gear having tooth elements that are straight and parallel to its axis is known as a spur gear. A spur pair can be used to connect parallel shafts only. Parallel shafts, however, can also be connected by gears of another type, and a spur gear can be mated with a gear of a different type. (Fig.1.1). To prevent jamming as a result of thermal expansion, to aid lubrication, and to compensate for avoidable inaccuracies in manufacture, all power-transmitting, gears must have backlash. This means that on the gear, and vice versa. On instrument gears, backlash can eliminated by using a gear split down its middle, one half being rotatable relative to the other. A spring forces the split gear teeth to occupy the full width of the pinion space. Helical gears have certain advantages; for example, when connecting parallel shafts they have a higher loadcarrying than spur gears with the same tooth numbers and cut with the same cutter. Because of the overlapping action of the teeth, they are smoother in action and can operate at higher pitch-line to the axis of rotation, helical gears create an axial thrust. If used singly, this thrust must be absorbed in the same blank. Depending on the method of manufacture, the gear may be of the continuous-tooth herringbone variety or a double-helical gear with a space between the two halves to permit the cutting tool to run out. Double-helical gears are well suited for the efficient transmission of power at highspeeds. Helical gears can also be used to connect nonparallel, non-intersecting shafts at any angle to one another. Ninety degrees is the commonest angle at which such gears are used. Worm and bevel gears. In order to achieve line contact and improve the loadcarrying capacity of the crossed-axis helical gears, the gear can be made to curve partially around the pinion, in somewhat the same way that a nut envelops a screw. The result would be a cylindrical worm and gear. Worm gears provide the simplest means of obtaining large rations in a single pair. They are usually less efficient than parallel-shaft gears, however, because of an additional sliding movement along the teeth. Because of their similarity, the efficiency of a worm and gear depends on the same factors as the efficiency of a screw. Single-thread worms of large diameter have small lead angles and low efficiencies. Multiple-thread worms have larger lead angles and higher efficiencies(Fig.1.2) For transmitting rotary motion and torque around corners, bevel gears are commonly used. The connected shafts, whose axes would intersect if extended, are usually but not necessarily at right angles to one another. When adapted for shafts that do not intersect, spiral bevel gears are called hypoid gears. The pitch surfaces of these gears are not rolling cones, and the ratio of their mean diameters is not equal to the speed Consequently, the pinion may have few teeth and be made as large as necessary to carry the load. The profiles of the teeth on bevel gears are not involutes; they are of such a shape that the tools for the teeth are easier to make and maintain than involute cutting tools. Since bevel gears come in, as long as they are conjugate to one another they need not be conjugate to other gears with different both numbers. 1 Early History of Gearing The earliest written descriptions of gears are said to have been made by Aristotle in the fourth century B.C. It has been pointed out that the passage attributed to Aristotle by some was actually from the writings of his school, in “Mechanical Problems of Aristotle”(Ca.280 B.C). In the passage in question, there was no mention of gear teeth on the parallel wheels, and they may just as well have been smooth wheels in frictional contact. Therefore, the attribution of gearing to Aristotle is, most likely, incorrect. The real beginning of gearing was probably with Archimedes who about 250 B.C. invented the endless screw turning a toothed wheel, which was used in engines of war. Archimedes also used gears to simu-early forms of wagon mileage indicators (odometer) and surveying instruments. These devices were probably “thought” experiments of Heron of Alexandria (ca. A.D.60), who wrote on the subjects of theoretical mechanics and the basic elements of mechanism. The oldest surviving relic containing gears is the Antikythera mechanism, so named because of the Greek island of that name near which the mechanism was discovered in a sunken ship in 1900. Professor Price of Yale University has written an authoritative account of this mechanism. The mechanism is not only the earliest relic of gearing, but it also is an extremely complex arrangement of epicyclic differential gearing. The mechanism is identified as a calendrical computing mechanism for the sun and moon, and has been dated to about 87 B.C. The art of gearing was carried through the European dark ages after the fall of Rome, appearing in Islamic instruments such as the geared astrolabes which were used to calculate the positions of the celestial bodies. Perhaps the art was relearned by the clock-and instrument-making artisans of fourteenth-century Europe, or perhaps some crystallizing ideas and mechanisms were imported from the East after the crusades of the eleventh through the thirteenth centuries. It appears that the English abbot of St.Alban’s monastery, born Richard of Wallingford, in A.D. 1330, reinvented the epicyclic gearing concept. He applied it to an astronomical clock, which he began to build at that time and which was completed after his death. A mechanical clock of a slightly later period was conceived by Giovanni de Dondi(1348-1364). Diagrams of this clock, which did not use differential gearing, appear in the sketchbooks of Leonardo da Vinci, who designed geared mechanisms himself. In 1967 two of da Vinci’s manuscripts, lost in the National Library in Madrid since 1830, were rediscovered. One of the manuscripts, written between 1493 and 1497 and known as “Codex Madrid I” , contains 382 pages with some 1600 sketches. Included among this display of Lenardo’s artistic skill and engineering ability are his studies of gearing. Among these are tooth profile designs and gearing arrangements that were centuries ahead of their “invention”. 2 Beginning of Modern Gear Technology In the period 1450 to 1750, the mathematics of gear-tooth profiles and theories of geared mechanisms became established. Albrecht Durer is credited with discovering the epicycloidal shape(ca. 1525). Philip de la Hire is said to have worked out the analysis of epicycloids and recommended the involute curve for gear teeth (ca. 1694). Leonard Euler worked out the law of conjugate action(ca.1754). Gears deigned according to this law have a steady speed ratio. Since the industrial revolution in mid-nineteenth century, the art of gearing blossomed, and gear designs steadily became based on more scientific principles. In 1893 Wilfred Lewis published a formula for computing stress in gear teeth. This formula is in wide use today in gear design. In 1899 George B.Grant, the founder of five gear manufacturing companies, published “A Treatise on Gear Wheels” . New inventions led to new applications for gearing. For example, in the early part of this century (1910), parallel shaft gears were introduced to reduce the speed of the newly developed reaction steam turbine enough to turn the driving screws of ocean-going vessels. This application achieved an overall increase in efficiency of 25 percent in sea travel. The need for more accurate and quiet-running gears became obvious with the advent of the automobile. Although the hypoid gear was within our manufacturing capabilities by 1916, it was not used practically until 1926, when it was used in the Packard automobile. The hypoid gear made it possible to lower the drive shaft and gain more usable floor space. By 1937 almost all cars used hypoid-geared rear axles. Special lubricant antiwear additives were formulated in the 1920s which made it practical to use hypoid gearing. In 1931 Earle Buchingham, chairman of an American Society of Mechanical Engineers (ASME) research committee on gearing, published a milestone report on gear-tooth dynamic loading. This led to a better understanding of why faster-running gears sometimes could not carry as much load as slower-running gears. High-strength alloy steels for gearing were developed during the 1920s and 1930s . Nitriding and case-hardening was introduced in 1950. Extremely clean steels produced by vacuum melting processes introduced in1960 have proved effective in prolonging gear life. Since the early 1960s there has been increased use of industrial gas turbines for electric power generation. In the range of 1000 to 14000 hp, epicyclic gear systems have been used successfully. Pitch-line velocities are form 50 to 100m/s(10000 to 20000 ft/min). These gear sets must work reliably for 10000 to 30000 hp between overhaule. In 1976 bevel gears produced to drive a compressor test stand ran stand ran successfully for 235h at 2984kw and 200m/s. form all indications these gears could be used in an industrial application if needed. A reasonable maximum pitch-line velocity for commercial spiral-bevel gears with curved teeth is 60m/s. Gear system development methods have been advanced in which lightweight, highly loaded gears are used in aircraft applications. The problems of strength and dynamic loads, as well as resonant frequencies for such gearing, are now treatable with techniques such as finite-element analysis, siren and impulse testing for mode shapes, and application of damping treatments where required. 齒 輪 直齒輪和斜齒輪 輪齒是直的、而方向又與其軸平行的齒輪稱作直齒輪。一對直齒輪只能用來連接平行軸。然而，平行軸也可以用其他形式的齒輪來連接，一個直齒輪可以同一個不同形式的齒輪互相嚙合，如圖1-1。 為了避免由于熱膨脹而出現(xiàn)的卡住現(xiàn)象；為了便于潤滑和補(bǔ)償制造中不可避免的誤差，所有傳遞動力的齒輪必須具有側(cè)向間隙。這就是說在互相嚙合齒輪的節(jié)圓上，小齒輪的間隙寬度必須稍大于大齒輪的齒厚，反之亦然。在儀表齒輪上，可以利用從中間分開的拼合齒輪來消除側(cè)向間隙，它的一半可相對于另一半轉(zhuǎn)動。彈簧迫使拼和齒輪的齒占滿小齒輪間隙的整個寬度。 斜齒輪具有某些優(yōu)點(diǎn)。例如：連接兩平行軸時，斜齒輪比齒數(shù)相同、用相同刀具切削的直齒輪有較高的承載能力。由于輪齒的重迭作用，斜齒輪工作比較平穩(wěn)、允許比直齒輪有更高的節(jié)線速度。節(jié)線速度是節(jié)圓的速度。由于輪齒與旋轉(zhuǎn)軸傾斜，所以斜齒輪會產(chǎn)生軸向推力。如果單個使用，這一推力必須由軸承來承受。推力問題可以通過在同一坯見切削兩組斜齒來克服。根據(jù)制造方法的不同，齒輪可以是連續(xù)人字形的，或者在兩列斜齒之間留一間隙的雙斜齒形的，以便切削刀具通過。雙斜齒齒輪非常使用于高速高效的傳遞動力。 斜齒輪也能用來連接既不平行也不相交的相互成任何角度的軸。最常用的角度為。 蝸輪蝸桿和傘齒輪 為了使交叉軸斜齒輪獲得線接觸和提高承載能力，可以把大齒輪做成部分繞小齒輪彎曲，就象螺母套在螺桿上一樣，結(jié)果就形成一個柱形蝸桿和蝸輪。蝸輪蝸桿提供了獲得一對大速比齒輪的最簡單的方法。然而，由于沿齒的附加滑動使蝸輪蝸桿的效率通常低于平行軸齒輪。同樣，其效率還取決于影響螺紋效率的那些因素。大直徑的單頭蝸桿的導(dǎo)角很小，效率很低，而多頭蝸桿的導(dǎo)角較大，效率也比較高，見圖1-2。 為了使傳遞的轉(zhuǎn)動和扭矩能轉(zhuǎn)一個角度，常常是用傘齒輪。所連的兩跟軸，如果延長其軸線就會相交，它們通常互成。 兩軸不相交的螺旋傘齒輪稱作偏軸傘齒輪。這種齒輪的節(jié)面不是滾錐，它們的平均直徑比不等于速比。因此，小齒輪的齒數(shù)較小，其大小能適應(yīng)承載的需要。 傘齒輪的齒廓不是漸開線形的。它們的形狀使切齒刀具比漸開線刀具更易于制造和維修。由于傘齒輪是成對使用的，因此，只要它們能互相共軛，就不需要與齒數(shù)不同的其他齒輪共軛。 圖1直齒輪 圖2螺蝸輪蝸桿船 齒輪的早期發(fā)展史 有關(guān)齒輪的最早的論著認(rèn)為，齒輪是在公元前四世紀(jì)由Aristotle發(fā)明的。書中指出：齒輪是由Aristotle發(fā)明的這段文字實(shí)際上出自其母校的論著：“關(guān)于Aristotle的機(jī)械問題”（約公元前280年）。問題是在有關(guān)章節(jié)中，并沒有體積在平行的輪子上有齒輪，而只是光華的輪子，靠摩擦接觸。因此，認(rèn)為齒輪是由發(fā)明的說法不見得是正確的。 實(shí)際上，齒輪機(jī)構(gòu)可能是在公元前約250年由Archimedes發(fā)明的，他發(fā)明了螺桿用以驅(qū)動一個帶齒的輪子，這種輪子用于軍用發(fā)動機(jī)。Archimedes也用齒輪來仿造天體比例儀。Archimedian螺旋機(jī)構(gòu)一直用語測程計(jì)及高度和角度測量裝置，這是早期使用的四輪馬車?yán)锍逃?jì)（里程表）和測量儀。這些裝置被認(rèn)為是埃及及亞力大實(shí)驗(yàn)裝置，他寫了關(guān)于理論力學(xué)及基本機(jī)械零件的論著。所查到的最早的齒輪的遺物是Antikythera機(jī)構(gòu)，這是根據(jù)希臘島嶼的名字而命名的，因?yàn)檫@中機(jī)構(gòu)是1900年在靠近Antikythera島發(fā)現(xiàn)的沉船中出現(xiàn)的。yale大學(xué)的Price教授寫了論述這一機(jī)構(gòu)的權(quán)威專著。這一機(jī)構(gòu)不僅是齒輪傳動機(jī)構(gòu)的最早遺物，也是極為復(fù)雜的行星齒輪傳動機(jī)構(gòu)，它也被認(rèn)為是用于表示太陽和月亮運(yùn)行的日歷計(jì)算機(jī)構(gòu)，并可追溯到公元前87年。在羅馬衰敗之后的蕭條時期，齒輪傳動技術(shù)傳遍了整個歐洲并在穆斯林儀表中得到應(yīng)用，如計(jì)算天體位置的齒輪觀測儀。也許是這一技術(shù)又被14世紀(jì)歐洲的鐘表儀器制造專家再次采用，也許是一些奇特的構(gòu)思，在十一世紀(jì)至十三世紀(jì)的改舉運(yùn)行之后，這些機(jī)構(gòu)又從東方引入。 似乎是英國St.Alba的住持于1930年又發(fā)明了行星齒輪的構(gòu)思，他將其用于天文鐘表，并實(shí)施建造，但當(dāng)他死后才竣工。 稍后機(jī)械鐘表是由Giovanni de Dondi設(shè)計(jì)的。根據(jù)Lenonardo da Vinci手稿，鐘表設(shè)計(jì)圖中并沒有差動齒輪傳動系統(tǒng)，而他自行設(shè)計(jì)了齒輪機(jī)構(gòu)。1967年又發(fā)現(xiàn)了1830年在國立圖書館失竊的davinci的兩本手稿，其中一本為“CodexMadridl”,是1493年至1497年間寫的，共382頁約1600幅圖，展示Leonardo的藝術(shù)及工程才華的便是他對齒輪機(jī)構(gòu)的研究，其中一些便是齒廓設(shè)計(jì)及齒輪傳動機(jī)構(gòu)設(shè)計(jì)，但這些機(jī)構(gòu)早在幾百年前就有了。 現(xiàn)代齒輪技術(shù)的開端 1450～1750年間，建立了輪齒廓形的數(shù)學(xué)表達(dá)式及齒輪傳動機(jī)構(gòu)的理論。 Albrecht Du rer設(shè)計(jì)了外擺線齒形，Philip dela Hire對擺線齒輪作了分析，并推薦輪齒采用漸開線形狀，Leonard Euler研究了相配合齒輪定律根據(jù)這一定律可以獲得穩(wěn)定的速比。 由于19世紀(jì)中葉的工業(yè)革命，齒輪傳動機(jī)構(gòu)被廣泛采用，齒輪設(shè)計(jì)也符合科學(xué)原理。1893年Wilfred Lewis發(fā)表了計(jì)算輪齒應(yīng)力的公式，這一公式至今仍在齒輪設(shè)計(jì)中廣泛應(yīng)用。1899年George B.Grant這位五家齒輪公司的創(chuàng)始人發(fā)表了關(guān)于齒輪的專題論文。新的發(fā)明使得齒輪傳動機(jī)構(gòu)有了新的應(yīng)用。例如在本世紀(jì)早期，將平行軸齒輪傳動機(jī)構(gòu)用于當(dāng)時研制的反應(yīng)式汽輪機(jī)降速，它足以帶動遠(yuǎn)洋船的傳動螺桿。這一應(yīng)用使航海行程效率提高了25％。 隨著汽車的發(fā)明，則需要更精確且運(yùn)行平穩(wěn)的齒輪。雖然早在1916年就有能力制造直角交錯軸雙曲面齒輪，但直到1926年才開始用Packard汽車，它的應(yīng)用能簡短驅(qū)動軸并減少了所占空間。到1937年幾乎所有的汽車都用直角交錯軸雙曲面齒輪為后橋。1930年左右研制了含抗磨損添加劑的特殊潤滑劑并用于直角交錯軸雙曲面齒輪。1931年，美國機(jī)械工程師學(xué)會齒輪機(jī)構(gòu)研究委員會主席Earle Buckingham發(fā)有一篇關(guān)于輪齒動態(tài)承載方面的具有里程碑意義的技術(shù)報(bào)告。這使人們更好地了解為什么轉(zhuǎn)動較快地齒輪有時承載能力不如轉(zhuǎn)動較慢地齒輪。 二十世紀(jì)20至30年代期間研制了制造齒輪的高強(qiáng)度合金剛；30年代又將滲氮及表面硬化技術(shù)用以增加齒輪傳動機(jī)構(gòu)的表面強(qiáng)度；1950年應(yīng)用感應(yīng)淬火技術(shù)；1960年應(yīng)用了由真空熔化工藝所煉的高度清潔鋼材，這對于延長齒輪的使用壽命是很有效的。 自本世紀(jì)六十年代初期以來，發(fā)電用的工業(yè)燃?xì)廨啓C(jī)被廣泛應(yīng)用。由于成功地采用了行星齒輪機(jī)構(gòu)，其功率達(dá)1000－14，000馬力，節(jié)線速度為50－100m/s。在兩次檢修期間，齒輪組必須可靠工作10，000至30，000小時。 1976年生產(chǎn)的用于驅(qū)動壓縮機(jī)試驗(yàn)臺的傘齒輪在功率為2984KW（4000馬力），速度為200m/s(40,000ft/min)的工作環(huán)境下成功地運(yùn)行了235小時。所有指標(biāo)表明，如果需要，這些齒輪均可作為工業(yè)應(yīng)用。作為商用的弧齒螺旋傘齒輪合理的最大節(jié)線速度為60m/s(12000ft/min)。 已經(jīng)提出了齒輪機(jī)構(gòu)設(shè)計(jì)的新方法，所設(shè)計(jì)的質(zhì)量輕，速度高，承載能力強(qiáng)的齒輪已用于航空工業(yè)。齒輪傳動機(jī)構(gòu)的強(qiáng)度，動載，以及諧振頻率等問題現(xiàn)在可用有限元分析，對模型進(jìn)行回聲試驗(yàn)，阻壓試驗(yàn)等技術(shù)來解決