機械零件設(shè)計外文翻譯

1、<p><b>　　附錄1 </b></p><p><b>　　機械零件設(shè)計</b></p><p>　　設(shè)計任何機械零件的理想情況為，工程師可以用大量的他所選用的這種材料的強度試驗數(shù)據(jù)。這些實驗應(yīng)該采用與所設(shè)計的零件有相同的熱處理，表面光潔度和尺寸大小的試件進行，而且試驗應(yīng)該在與零件使用過程中承受的載荷完全相同的情況下進行。這表明，

2、如果零件將要承受彎曲載荷，那么就應(yīng)該進行彎曲載荷實驗。如果零件將要承受彎曲和扭轉(zhuǎn)的復(fù)合載荷，那么就應(yīng)該進行彎曲和扭轉(zhuǎn)的復(fù)合實驗。這些種類的試驗可以提供非常游泳和精確的數(shù)據(jù)。它們可以告訴工程師應(yīng)該使用的安全系數(shù)和對于給頂?shù)氖褂脡勖目煽啃?。在設(shè)計工作中，只要能夠獲得這種數(shù)據(jù)，工程師就可以盡可能好的進行設(shè)計工作。</p><p>　　如果零件的失效可能會危害人的生命安全，或者零件有足夠大的產(chǎn)量，則在設(shè)計前收集這樣的數(shù)

3、據(jù)所花費的費用是值得的。例如，汽車和冰箱的零件產(chǎn)量非常大，可以在生產(chǎn)之前對它們進行大量的實驗，使其具有較高的可靠性能。如果把進行這些試驗的費用攤到所生產(chǎn)的零件上的話，則每一個零件的費用是非常低的。</p><p>　　你可以對下列四類的設(shè)計作出評價：</p><p>　　1.零件的失效可能危害人的生命安全，或者零件的產(chǎn)量非常大，為此在設(shè)計時安排一個完善的試驗程序是被認為合理的。</p

4、><p>　　2.零件的產(chǎn)量足夠大，可以進行適當(dāng)?shù)南盗性囼灐?lt;/p><p>　　3.零件的產(chǎn)量非常小，以至于進行試驗根本不合算；或者要求很快完成設(shè)計，以至于么有足夠的時間進行試驗。</p><p>　　4.零件已經(jīng)完成設(shè)計、制造和試驗，但結(jié)果不能令人滿意。這時候需要采用分析法來弄清楚不能令人滿意的原因和應(yīng)該如何進行改進。</p><p>　　我

5、們主要對后三種類型進行討論。這就是說，設(shè)計人員通常只能利用那些公開的屈服強度、極限強度和延伸率等數(shù)據(jù)資料。人們期望著工程師在利用這些不是很多的數(shù)據(jù)資料的基礎(chǔ)上，對靜載荷與動載荷、兩維應(yīng)力狀態(tài)與三維應(yīng)力狀太、高溫有低溫以及大零件與小零件進行設(shè)計。而設(shè)計中的，有充分的時間產(chǎn)生應(yīng)變。到目前為止，還必須利用這些數(shù)據(jù)來設(shè)計每分鐘承受幾千次復(fù)雜的動載荷的作用的零件，因此機械零件有時會失效是不足為奇的。</p><p>　　概

6、括來說，設(shè)計人員所遇到的基本問題是，不論對于哪一種應(yīng)力狀態(tài)或者載荷情況，都有利用通過簡單拉伸實驗所獲得的數(shù)據(jù)并將其與零件的強度聯(lián)系起來。</p><p>　　可能會有兩種完全相同的強度和硬度值的金屬，其中一種由于其本身的延展性而具有很好的承受載荷的能力。延展性是用材料斷裂時的延伸率來量度的。通常將5%的延伸率定義為延展性和脆性的分界線。斷裂時候延展率小于5%的材料成為脆性材料，大于5%的成為延性材料。</p

7、><p>　　材料的伸長量通常是在50mm的計算長度上測量的。因為這并不是對實際應(yīng)變量的測量，所以有時候也采用一種測量延展性的方法。這個方法是在試件斷裂后，測量其斷裂處的橫截面的面積。因此，延展性可以表示為橫截面的收縮率。</p><p>　　延展材料能夠承受較大的載荷這特性是設(shè)計中的一個附加的安全因素。延展材料的重要性在于他是材料冷變形性能的衡量尺度。諸如彎曲和拉延這類金屬加工過程中需要采用

8、延性材料。</p><p>　　在選用抗磨損、抗侵蝕或者抗塑性變形的材料時，硬度通常是最主要的性能。有幾種可供選用的硬度試驗方法，采用哪一種方法取決于最希望測量的材料的性能特性。最常用的四種硬度數(shù)值是布氏硬度、洛氏硬度、維氏硬度和努氏硬度。</p><p>　　大多數(shù)硬度實驗系統(tǒng)是將一個標準的載荷加在與被試驗材料相接觸的小球或者棱錐上。因此，硬度可以表示為所生產(chǎn)的壓痕尺寸的函數(shù)。這表明由于

9、硬度是非破壞性試驗，而且不需要專門的試件，因而硬度是一個容易測量的性能。通?？梢灾苯釉趯嶋H的機械零件上進行硬度試驗。</p><p>　　對于球軸承和磙子軸承，一個機械設(shè)計人員應(yīng)該考慮下面五個方面：a.壽命與載荷的關(guān)系；b.剛度，也就是在載荷作用下的變形；c.摩擦；d.磨損；e.噪音。對于中等載荷和轉(zhuǎn)速，根據(jù)額定負荷選定一個標準軸承，通常都可以保證其具有令人滿意的工作性能。當(dāng)載荷較大時，軸承零件的變形，盡管它通常

10、小于軸和其他與軸承一起工作的零部件的變形，將會變得重要起來。在轉(zhuǎn)速高的場合需要有專門的冷卻裝置，而這可能會增大摩擦阻力。磨損主要是由于污染進入引起的，必須采用密封裝置防止周圍環(huán)境的不良影響。</p><p>　　因為大批量生產(chǎn)這種方式?jīng)Q定了球軸承和磙子軸承不但質(zhì)量高，而且價格低，因而機器設(shè)計人員的任務(wù)是選擇而不是設(shè)計軸承。滾動軸承通常是用硬度為900HV、整體淬火鋼制成。但在許多機構(gòu)上不使用專門的套圈，而是將相互

11、作用的表面淬硬到600HV。滾動軸承由于在工作時會產(chǎn)生高的應(yīng)力，其主要失效形式是金屬疲勞，這一點并不奇怪，目前正在進行大量的工作以求改進這種軸承的可靠性。抽成設(shè)計可以基于能夠被人們所接受的壽命值來進行。在軸承行業(yè)中，通常將軸承的承載能力定義為這樣的值，即承擔(dān)的載荷小于這個值時，一批軸承中的會有90%的軸承具有超過100萬轉(zhuǎn)的壽命。</p><p>　　盡管球軸承和磙子軸承的基本設(shè)計責(zé)任不在軸承的制造廠家，機器設(shè)計

12、人員必須對軸承所要完成的任務(wù)做出正確的評價，不僅要考慮軸承的選擇，而且還要考慮軸承的正確安裝條件。</p><p>　　軸承套圈與軸或軸承坐的配合非常重要，因為他們之間的配合不僅僅應(yīng)該保證所需要的過盈量，而且也應(yīng)該保證軸承的內(nèi)部間隙。不正確的過盈會產(chǎn)生微震腐蝕從而導(dǎo)致嚴重的故障。內(nèi)圈通常是通過靠近在軸肩上進行軸向定位的。軸肩處的圓弧半徑主要是為了避免應(yīng)力集中。在軸承內(nèi)圈上加工出一個圓弧或者倒角，用來提供容納軸肩處

13、圓弧半徑的空間。</p><p>　　在使用壽命不是設(shè)計中的決定因素的場合，通常根據(jù)軸承受載荷時產(chǎn)生的變形量來確定其最大載荷。因此“靜態(tài)承載能力”這個概念可以理解為對處于靜止狀態(tài)或者進行緩慢轉(zhuǎn)動的軸承所能施加的載荷。這個載荷對軸承在隨后進行旋轉(zhuǎn)運動時的質(zhì)量沒有不利影響。按照實踐經(jīng)驗確定，靜態(tài)承載能力是這樣一個載荷，當(dāng)他作用在軸承上時，滾動體與套圈在任何一個接觸點處的總變形量不超過滾動體直徑的0.01%。這相當(dāng)于為

14、25mm的球產(chǎn)生0.0025mm的永久變形。</p><p>　　只有將軸承與周圍環(huán)境適當(dāng)?shù)馗綦x開，許多軸承才能夠成功的實現(xiàn)他們的作用。在某些情況下，必須保護環(huán)境，使其不受潤滑劑和軸承表面磨損生成污染物的污染。軸承設(shè)計的一個重要組成部分是使密封裝置起到應(yīng)有作用。此外，對摩擦學(xué)研究人員來說，，為了任目的而應(yīng)用于運動零部件上的密封裝置都是他們感興趣的。因為密封裝置是軸承的一部分，只有根據(jù)適當(dāng)?shù)妮S承理論才能設(shè)計出令人滿

15、意的密封系統(tǒng)。雖然它們很重要，與軸承其他方面的研究工作相比，在密封裝置的研究方面所做的工作還是比較少的。</p><p><b>　　附錄2 </b></p><p>　　Machine element designing</p><p>　　Ideally in designing any machine element, the engin

16、eer should have at his diposal the results of a great many strengh tests of the particular material chosen. These tests should have been made on specimens having the same heat treatment, surface finish, and size as the e

17、lement he propose to design; and the tests should be made under exactly the same loading conditions as the part will experience in service. This means that, if the part is to experience a bending load, it should be teste

18、d with a </p><p>　　The cost of gathering such extensive date prior to design is justified if failure of the part may endanger human life, or if the part is manufactured in sufficiently large quantities. Auto

19、mobiles and refrigerators, for example, have very good reliabilities because the parts are made in such large quantities that they can be thoroughly tested in advance of manufacture. The cost of making these tests is ver

20、y low when it is divided by the total number of parts manufactured.</p><p>　　You can now appreciate the following four design categories:</p><p>　　(1) Failure of the part would endanger human li

21、fe, or the part is made in extremely large quantities; consequently, an elaborae testing program is justified during design.</p><p>　　(2) The part is made in large enough quantities so that a moderate series

22、 of tests is feasible.</p><p>　　(3) The part is made in such small quantities that testing is not justified at all; or the design must be completed so rapidly that there is not enough time of testing.</p&

23、gt;<p>　　(4) The part has already been designed, manuactured, and tested and found to be unsatisfactiry. Analysis is required to understand why the part is unsatisfactory and what to do to improve it.</p>&

24、lt;p>　　It is with the last three categories that we shall be mostly concerned. This means that the designer will usually have only published values of yield strenth, ultimate strenth, and percentage elongation. With t

25、his meger information the engineer is expected to design against static and dynamic loads, biaxial and triaxial stress states, high and low temperratures, and large and small pars! The date usually available for design h

26、ave been obtained from the simple tension test, where the load was app</p><p>　　To sum up, the fundamental problem of the designer is to use the simple tension-test date and relate thenm to the strength of t

27、he part, regardless of the stress state of the loading situation.</p><p>　　It is possible for two metals to have exactly the same strength and hardness, yet one of these metals may have a superior ability to

28、 absorb overloads, because of the property called ductility. Ductility is measured by the percentage elongation which occurs in the material at fracture. The usual dividing line between ductility and brittleness is 5 per

29、cent elongation. A material having less than 5 percent elongation at fracture is said to be brittle, while one having more is said to be ductile.</p><p>　　The elongation of a material is usually measured ove

30、r 50mm gauge length. Since this is not a measure of the actual strain, another method of determining ductility is sometimes used. After the specimen has been fractured, measurements are made of the area of the cross sect

31、ion at the fracture. Ductility can then be expressed as the percentage reduction in cross-sectional area.</p><p>　　The characteristic of a ductile material which permits it to absorb large overloads is an ad

32、dition safety factor in design. Ductility is also important because it is a measure of that property of a material which metal-processing operations which require ductile materials.</p><p>　　When a material

33、is to be selected to resist wear, erosion, or plastic deformation, hardness is generally the most important priperty. Several methods of hardness testing are available, depending upon which particular property is most de

34、sired. The four hardness numbers in greatest use are the Brinell, Rockwell, Vickers, and Knoop.</p><p>　　Most hardness-testing systerm employ a standard load which is applied to a ball or pytamid in contact

35、with the material to be tested. The hardness is then expressed as a function of the size of the resulting indentation. This means that hardness is an easy property to measure, because the test is nondestructive and test

36、specimens are not required. Usually the test can be conducted directly on an actual machine element.</p><p>　　The concern of a machine designer with ball and roller bearings is fivefold as follows: (a) life

37、in relation to load; (b) stiffness, i.e. deflections under load; (c) friction; (d) wear; (e) noise. For moderate loads and speeds the correct seletion of a standard bearing on the basis of load rating will usually secure

38、 satisfactory performance. The deflection of the bearing elements will become important where loads are high, although this is usually of less magnitude than that of the shafts or oth</p><p>　　Because the hi

39、gh quality and low price of ball and roller bearings depends on quantity production, the task of the designer becomes one of selection rather than design. Rolling-contact bearings are generally made with steel which is t

40、hough-hardened to above 900 HV, although in many mechanisms special races are not provided and the interacting surfaces are hardened to above 600 HV. It is not surprising that, owing to the high stresses involved, a pred

41、ominant form of failure should be metal fatigu</p><p>　　Notwithstanding the fact that responsibility for the basic design of ball and roller bearings rests with the bearing manufacturer, the machine designer

42、 must form a correct appreciation of the duty to be performed by the bearing and be concerned not only with bearing selection but with conditions for correct instalation.</p><p>　　The fit of the bearing race

43、s onto the shaft or onto the housings is of critical importance because of their combined effect on the internal clearance of the bearing as well as preserving the desired degree of interference fit. Inadequate interfere

44、nce can induce serious trouble from fretting corrosion . The inner race is frequently located axially by abutting against a shoulder. A radius at this point is essential for the avoidance of stress concentration and ball

45、 races are provided with a radius</p><p>　　Where life is not the determining factor in design, it is usual to determine maximum loading by the amount to which a bearing will deflect under load. Thus the conc

46、ept of "static load-carrying capacity" is understood to mean the load that can be applied to a bearing, which is its running qualities for subsequent rotational motion. This has been determined by practical exp

47、erience as the load which when applied to a bearing results in a total deformation of the rolling element and raceway at any p</p><p>　　The successful functioning of many bearings depends upon providing them

48、 with adequate protection against their environment, and in some cicumstances the environment must be protected from lubricants or products of deterioration of the bearing surfaces. Achievement of the corrct functioning

49、of seals is an essential part of bearing design. Moreover, seals which are applied to moving parts for any purpose are of interest to tribologists because they are bearing systems and can only be designed sati</p>