譯文：小齒輪和錐齒輪的失效分析

1、小齒輪和錐齒輪的失效分析畢業(yè)設(shè)計（論文）譯文題目名稱：工程失效分析13冊1285-1292頁 院系名稱： 機 電 學(xué) 院 班 級： 機 自 091 學(xué) 號： 200900814222 學(xué)生姓名： 徐東東 指導(dǎo)教師： 王瑋 2013年 03 月小齒輪和錐齒輪的失效分析摘要錐齒輪和小齒輪是汽車傳動裝置的重要組成部件。這些部件的失效對車輛運動有著強烈的影響。并將逐步導(dǎo)致修理時間的增加。除了他的功能受到影響外，這些部件也會增加危險性。用標(biāo)準(zhǔn)的材料力學(xué)去分析齒輪斷裂，以此來研究齒輪失效的原因。分析得出的結(jié)論表明制造材料的組成成分是失效的原因，在材料中可以明顯的發(fā)現(xiàn)含有大量錳而沒有鎳和鉬。這導(dǎo)致材料核心的

2、硬度很高，高硬度卻會使車輛傳遞系統(tǒng)中的重要部件產(chǎn)生早期的失效。關(guān)鍵字：滲碳；錐齒輪；齒輪齒的失效；金屬斷面的顯微鏡研究法來研究失效；奧氏體；1介紹機械系統(tǒng)的平均壽命總是依賴系統(tǒng)的最重要部分。 在動力傳動系統(tǒng)中通常是齒輪。齒輪設(shè)計通常按高速重載的的條件來設(shè)計最小的尺寸和重量。被用于重型車輛的一個典型錐齒輪和小齒輪。 他們是車輛的最重要的部分，因此要求抗磨損性好和抗接觸疲勞強度高。理想的錐齒輪和小齒輪應(yīng)該符合美國齒輪制造業(yè)協(xié)會（AGMA）的11項質(zhì)量標(biāo)準(zhǔn)，即均勻和適宜的金屬質(zhì)地，極好的抗扭矩變形，極大的抗沖擊力，耐磨性，最佳的傳動效率，比較小的噪聲，小的自由震動和齒輪幾何學(xué)。氣體深碳是達到這些標(biāo)準(zhǔn)

3、的一個工序。他使得齒輪耐磨損性和韌性增大。制造者應(yīng)該通過一些制造業(yè)標(biāo)準(zhǔn)選擇適當(dāng)?shù)牟牧虾驼_的熱處理參數(shù)來使重要的部件持久和高效。En353（15Ni Cr 1 Mo 12）和En207(20 Mn Cr 1)是用于制造這些重要部件比較多的細(xì)密紋理的鋼材。當(dāng)En207被廣泛的用于按規(guī)定尺寸制作齒輪和軸時，En353卻用于重型齒輪，軸，小齒輪，凸輪軸，連接銷，重型車輛的傳動部件的制造。2加工工序錐齒輪和小齒輪是在熱處理后從850-880等溫條件下獲得的均質(zhì)材料制造的。鍛造是計算機數(shù)字控制齒輪的外形幾何尺寸的精密制造。它在900 - 930下進行滲碳處理來得到均勻的表面薄膜。滲碳能達到1.524到1

4、.905毫米的深度。淬火是在780 - 820下進行的，為了避免扭曲變形，淬火后要在油中冷卻。對小齒輪來說，選擇淬火是盡力提高齒輪的抗磨損性。小齒輪的曲線被特別的處理，這是為了得到能抵抗更高的沖擊力和由固定產(chǎn)生的扭轉(zhuǎn)力矩。淬火后，錐齒輪和小齒輪還要降溫到150 - 200以此來消除內(nèi)應(yīng)力。最后，錐齒輪和小齒輪要做全面的檢測以防止早期的失效，同時保證無噪音的產(chǎn)生。齒輪隙被保證在0.2 0.3 毫米內(nèi)以使噪音和震動最小。3檢測嚙合的齒輪（也就是小齒輪）顯示齒輪表面的疲勞斷裂是由一個微小的裂紋引起的。大的碎片也遠(yuǎn)離了齒。表面的疲勞是由表面的比較硬的組織在壓應(yīng)力下造成的。然而，破裂形成的裂紋深度要比點

5、蝕所形成的深，并且它的內(nèi)力的作用與交替變化的應(yīng)力有關(guān)系。這經(jīng)常被當(dāng)成至關(guān)重要的，但因為它導(dǎo)致了表面低碳部分的疲勞斷裂，先前的命名將被經(jīng)常使用。 嚙合的齒輪（也就是小齒輪）顯示齒輪表面的疲勞斷裂是由一個微小的裂紋引起的。大的碎片也遠(yuǎn)離了齒。表面的疲勞是由表面的比較硬的組織在壓應(yīng)力下造成的。然而，破裂形成的裂紋深度要比點蝕所形成的深，并且它的內(nèi)力的作用與交替變化的應(yīng)力有關(guān)系。這經(jīng)常被當(dāng)成至關(guān)重要的，但因為它導(dǎo)致了表面低碳部分的疲勞斷裂，先前的命名將被經(jīng)常使用。4點蝕通常，齒輪失效是由幾個機械裝置失效引起，但是大多數(shù)是由齒輪的齒面點蝕導(dǎo)致。實際上，齒面點蝕是機械裝置失效的主要原因。這些失效都是由滾動

6、接觸磨損和部件表面壽命在應(yīng)用的負(fù)荷下的磨損造成。因此，我們用一個立體顯微鏡來對失效的部件進行大量的研究以次來探索齒面磨損齒輪的齒面磨損的特點是由齒輪接觸面上的凹坑的出現(xiàn)。表面磨損的過程可以看作是表面破損或裂縫，他們都是在長期的接觸負(fù)載下產(chǎn)生。當(dāng)裂縫變的足夠大時不穩(wěn)定的生長就發(fā)生，而這則會導(dǎo)致一部分表層材料的崩落。導(dǎo)致這些發(fā)生的就是凹坑。在兩個部件中凹坑有效性很少。相對來說，在小齒輪上的凹坑數(shù)目要比差動齒輪的多，并且齒輪變形量也要比差動齒輪的高。這說明事實上失效是因為齒輪的工藝不夠而不是點蝕。5化學(xué)分析因為沒有關(guān)于齒輪的化學(xué)組成和熱處理條件可用信息，下面的任務(wù)就是對材料進行鑒定。一件小的樣品是用

7、磨削輪在差動輪進行切割，并用發(fā)光攝譜儀和顯微照片來進行研究與分析?；瘜W(xué)分析在兩個不同的部分進行，一個是在部件表面，另一個在部件的核心部分?；瘜W(xué)分析有助于確定那些選來準(zhǔn)備加工成部件的原材料的基本成分，在炭化處理過程中的含碳量以及基本組成在由制造者加工過程中的中和 。6硬度分析作為滲碳材料的一種情況，硬度的傾向是從外至里，外部比內(nèi)部的硬度大。大體上, 為計算有效表面深度 (ECD) 所采取的表面壓力值是 540 HV， 并且它的深度期望在 1.524 和 1.905 毫米之間。 在最初含炭量（硬度關(guān)于深度保持不變）所達到的深度叫做完全表面深度。因此，完全表面深度超過有效表面深度。在同一硬度中，完全

8、表面深度和有效表面深度分別是 737 HV ， 1.4 和 1.22 毫米。對于失效的部分，核心硬度在齒根的中心測量，其數(shù)值是458 HV。 通常，期望的核心硬度在 317 和 401HV 之間，最大值可達 430 HV,超過這個值零件可能會被破壞。這對重型機械的要求是非常高的，高硬度材料是因為含錳比較多。高的核心硬度造成附屬表面疲累和抗擠壓力的下降。這也是導(dǎo)致早期失效的原因。在這一項研究， ECD 只有 1.22 毫米,他不能充分確定表面深度。不夠的表面深度造成了小齒輪牙齒破碎狀而且依次減少頂輪的耐久性。這是由于在滲碳期間溫度過低或者由于碳供給不充足。7微觀結(jié)構(gòu)雖然殘留奧氏體對增加接觸疲累強

9、度有益,當(dāng)奧氏體以行列的形式排列時，對空間結(jié)構(gòu)和表面的硬度有益。在操作期間，亞穩(wěn)定奧氏體將會在壓應(yīng)力和拉應(yīng)力下轉(zhuǎn)變成馬氏體,這將使體積變大。體積的增大可能產(chǎn)生扭曲變形，從而產(chǎn)生壓力，這可經(jīng)過欠穩(wěn)定和噪音造成壽命減短。過多的殘留奧氏體也將會降低材料硬度和早期的抗疲勞強度?；旧?，除了避免不必要的馬氏體轉(zhuǎn)換產(chǎn)物，如調(diào)質(zhì)珠光體，鋼必須要有充足合適的合金元素的加入來使金屬的表面光滑和核心硬度提高。含碳量控制核心硬度，其他的合金元素幫助控制核心硬度和馬氏體變化物的含量。馬氏體的轉(zhuǎn)化物如珠光體和貝氏體比馬氏體的質(zhì)地軟，而且會使鋼的抗疲勞強度降低。因此，這種情況應(yīng)該被避免。添加的元素如碳，錳，鎳，鉬和鉻會降

10、低馬氏體開始的溫度，并且會增加奧氏體的含量。8齒接觸研究用失效的零件來進行接觸研究是為了知道其中的細(xì)節(jié)和失效的順序。用小齒輪的前齒面在錐齒輪的后錐面上進行旋轉(zhuǎn)試驗來研究齒的接觸。錐齒輪齒的失效指數(shù)是17,18,19,27,29,30,31,32和38，然而小齒輪的失效指數(shù)是3。當(dāng)傳動比是6.5時，每一次試驗的小齒輪的失效齒數(shù)并沒有增加，而是和下次的試驗一樣。錐齒輪失效的齒依次是17,31,38,18,32,29,30和27。小齒輪的失效齒并沒有影響與他配對的錐齒輪的齒。從中也可證實失效并沒有在錐齒輪的一次旋轉(zhuǎn)中發(fā)生。在首次失效后再旋轉(zhuǎn)七倍的時間，全部的齒就會失效。失效會逐漸的發(fā)生，最后就會發(fā)生

11、冷焊現(xiàn)象。這一點表明冷焊現(xiàn)象發(fā)生在錐齒輪和全部的零件上，當(dāng)工作時間超過失效時間的6倍時。失效的試驗品部分也發(fā)生齒根斷裂。 齒根全部有裂紋的錐齒輪齒接觸研究是在有標(biāo)記(黃色油漆)的小齒輪幫助下完成的。然后它在錐齒輪上進行旋轉(zhuǎn)。這證明小齒輪與錐齒輪只是部分的接觸，可能是由于校正的不好。這會在接觸的齒上產(chǎn)生高的接觸應(yīng)力，導(dǎo)致更大的負(fù)載作用在非常小的面積上。這種情況導(dǎo)致齒的破裂發(fā)生在齒的邊上。9結(jié)論這個不正確的選擇導(dǎo)致材料內(nèi)部硬度高 ，致使早期失效產(chǎn)生。硬度分析得出的結(jié)論是有效的表面深度沒有達到要求的水平是因為在滲碳時溫度不夠或者是碳元素不夠。不正確的熱處理會使奧氏體在表面殘留過多（大概25%），這對

12、工作的零件有害。失效首先發(fā)生在小齒輪上，不管失效的齒與錐齒輪是在哪接觸的，這都引起錐齒輪的早期失效 。局部的倒根是錐齒輪失效的典型事件。因此，重要零件必須進行熱處理，使其有最少的網(wǎng)狀碳素體，少的含碳量，少的奧氏體，來避免在工作時發(fā)生破裂，減少齒的快速磨損，和防止工作時扭曲變形。奧氏體的存在能用常規(guī)的熱處理替代低溫處理的方法來減少。淬火后馬上低溫處理，接著進行回火處理可以增強零件的耐磨損性和剛度。在將來可以生產(chǎn)更耐用的零件。本文摘譯自： 安娜大學(xué)機械工程學(xué)院和印度大學(xué)的教授Tamil NaduA. Benselya, S. Stephen Jayakumara, D. Mohan Lala, G

13、. Nagarajana 和 A. Rajaduraib的工程失效分析，這篇論文在2005年9月14日發(fā)表，2005年10月31日被收錄，并于2006年二月9日可在線使用。參考書目1 S. Farfan, C. Rubio-González, T. Cervantes-Hernández and G. Mesmacque, High cycle fatigue, low cycle fatigue and failure modes of a carburized steel, Int J Fatigue 26 (2004), pp. 673678. 2 H.S. Avne

14、r, Introduction to physical metallurgy, Tata McGraw-Hill Publishing Company Limited (2002). 3 S.N. Bagchi and P. Kuldip, Industrial steel reference book, Wiley Eastern Limited (1986). 4 COMET 4X4. Ashok leyland service manual, 1969. 5 K.J. Abhay and V. Diwakar, Metallurgical analysis of failed gear,

15、 Eng Fail Anal 9 (2002), pp. 359365. 6 K.H. Prabhudev, Handbook of heat treatment of steels, Tata McGraw-Hill Publishing Company Limited (2000). 7 Fatigue and failures. ASM handbook, vol. 19, 2002. p. 698700. 8 Failure analysis and prevention. ASM handbook, vol. 11, 2002. p. 70027. 9 R.F. Barron, Ef

16、fect of cryogenic treatment on lathe tool wear, Prog Refrigeration Sci Technol 1 (1973), pp. 529533. 16Failure investigation of crown wheel and pinion Abstract The crown wheel and pinion are the critical components in the transmission system of an automobile. Failure of these components has drastic

17、effect on the vehicular movement. This in turn leads to increased downtime for repairs. The cost of these components adds to the criticality in addition to its function. A fractured gear was subjected to detailed analysis using standard metallurgical techniques to identify the cause for failure. The

18、 study concludes that the failure is due to the compromise made in raw material composition by the manufacturer, which is evident by the presence of high manganese content and non-existence of nickel and molybdenum. This resulted in high core hardness (458 HV) leading to premature failure of th

19、e vital component of transmission system in a vehicle. Keywords: Carburization; Crown wheel; Gear-tooth failures; Failure investigation fractography; Retained austenite 1. Introduction Life expectancy of mechanical systems is always dependent on the most critical component of the system . In power t

20、ransmission system this is usually the gear. Gear design is commonly bounded by the requirements that gear should carry high loads at high speeds with minimal size and weight. A typical crown wheel and pinion used in heavy vehicles . They are the most stress prone parts of a vehicle and demands high

21、 wear resistance, high contact fatigue strength. An ideal crown wheel and pinion should have uniform and optimum metallurgical quality, excellent heat distortion control, maximum impact strength, stiff wear resistance, optimal transmission efficiency, less noise, vibration-free operation and gear ge

22、ometry in accordance with American Gear Manufacturers Association (AGMA) 11 qualities. Gas carburizing is a process employed to achieve some of these properties. It produces a very high wear resistant case and a soft tough core . The manufacturer should make the critical components durable and effic

23、ient through accurate and consistent manufacturing standards by selecting appropriate material and correct heat treatment parameters. En 353 (15 Ni Cr 1 Mo 12) and En 207 (20 Mn Cr 1) are the two widely used fine-grained steel billet materials used in manufacturing of these critical components. Typi

24、cal applications of En 353 being heavy-duty gears, shaft, pinions, camshafts, gudgeon pins, heavy vehicles transmission components while En 207 being used widely for medium sized gear wheels and shafts . 2. Manufacturing process Crown wheel and pinion are manufactured from forged blanks that are iso

25、thermally annealed at 850880 °C to obtain uniform properties after heat treatment. The forgings are precision machined by computer numerical control gear generators to high dimensional accuracy. It is followed by gas carburizing at 900930 °C to have uniform case, which can vary f

26、rom 1.5241.905 mm in its depth. Hardening is done at 780820 °C in controlled atmospheric temperature and press quenched in oil to avoid distortion. In the case of pinion, selective case hardening is done to impart maximum strength to the pinion to maximize wear resistance. The pinion

27、thread is specially treated to soft conditions to withstand higher shock loading and yielding arising out of torque tightening. After hardening, the crown wheel and pinion are tempered at 150200 °C to remove thermal stresses. Finally, the crown wheel and pinion are checked thoroughly for h

28、ard spots to prevent premature failure and also to ensure noise-free operation. The backlash is kept within 0.20.3 mm band to keep noise and vibration to a bare minimum . 3. Visual examination The companion gear (i.e. pinion) shows sub case fatigue fracture initiated by fine cracks. Large fragm

29、ents have spalled away from the tooth. Sub case fatigue is fracture of case hardened components by the formation of crack below the contact surface within the hertzian stress field. However, the depth at which the crack forms is much greater than the macro pitting fatigue and it is a function of mat

30、erial strength in conjunction with the alternating hertzian shear stress. It is also sometimes referred as case crushing but since it results from fatigue crack that initiates below the effective case depth or in the lower carbon portion of the case, the former nomenclature will be used frequently.

31、Thin case depth relative to radius of curvature is the factor that controls the occurrence of sub case fatigue. he companion gear (i.e. pinion) shows sub case fatigue fracture initiated by fine cracks. Large fragments have spalled away from the tooth. Sub case fatigue is fracture of case hardened co

32、mponents by the formation of crack below the contact surface within the hertzian stress field. However, the depth at which the crack forms is much greater than the macro pitting fatigue and it is a function of material strength in conjunction with the alternating hertzian shear stress. It is also so

33、metimes referred as case crushing but since it results from fatigue crack that initiates below the effective case depth or in the lower carbon portion of the case, the former nomenclature will be used frequently. Thin case depth relative to radius of curvature is the factor that controls the occurre

34、nce of sub case fatigue. 4. Pitting Generally, gears fail due to several mechanisms but most often due to surface pitting of gear teeth. Surface pitting is in fact the principal mode of failure of mechanical elements that are subjected to rolling contacts and governs the surface life of a component

35、under applied load . Hence, the failed components were subjected to macro examination using a stereomicroscope for pitting failure. The pitting of gear teeth is characterized by the occurrence of small pits on the contact surfaces.The process of surface pitting can be visualized as formation of surf

36、ace-breaking or sub surface initial cracks, which grow under repeated contact loading. Eventually the crack becomes large enough for unstable growth to occur, which results in a part of the surface material layer breaking away. The resulting void is a pit. The availability of pits in both the compon

37、ents was very less. Relatively, the number of pits in pinion is larger as the number of revolutions of pinion is higher than crown wheel. This confirms to the fact that the failure is premature and not due to pitting. 5. Chemical analysis As no information with respect to the chemical composition an

38、d the heat treatment condition of the pinion material was available, the next task in the failure analysis was the material identification.Specimen was cut using abrasive cut off wheel from location A of the crown wheel and subjected for optical emission spectrometer studies and metallographic exami

39、nation. Chemical analysis was carried out at two different locations, one at the surface (case) and another at the central portion (core) of the component. The chemical analysis helps to identify the basic composition of the raw material selected for the component, carbon potential used for carburiz

40、ing process and any compromise on the basic composition with respect to the component that made by the manufacturer. 6. Microhardness survey Being a case carburized material a gradient of decreasing hardness exists from the case to the core. In general, the cut off value taken for calculating the ef

41、fective case depth (ECD) is 540 HV and it is expected to be between 1.524 and 1.905 mm. The depth at which the original carbon content (hardness remains the same with respect to the depth) of the material is reached is called the total case depth. Hence, the total case depth is more than t

42、he effective case depth. The case hardness, total case depth and effective case depth were found to be 737 HV, 1.4 and 1.22 mm, respectively. For the failed component the core hardness was measured at the center of tooth base. It was found to be 458 HV. Normally, the desired core hard

43、ness is between 317 and 401 HV and is tolerable up to 430 HV, beyond that the component is highly prone to failure. This is very high for heavy-duty application and is due to high manganese content in the raw material. The high core hardness results in sub case fatigue and poor resistance

44、to impact. It is also the reason for the premature failure. In this study, the ECD was only 1.22 mm, which confirms inadequate case depth. Insufficient case depth resulted in spalling of a pinion tooth and in turn reduces durability of the crown wheel. This is due to low temperature employed du

45、ring carburization or may be due to inadequate gas feed. 7. Microstructure Although retained austenite has been claimed to benefit contact fatigue life, there are situations when austenite can be determinantal to dimensional stability and surface hardness. During operation metastable retained austen

46、ite will transform under stress and strain to untempered martensite, which result in a volume expansion. This volume expansion can create distortion, induce stress and may result in a decreased life through misalignment and noise. Excess retained austenite will also lower material hardness and resis

47、tance to fatigue initiation. Basically, steel must have sufficient quantities of correct alloying elements to produce component with proper surface and core hardness in addition to avoiding unwanted non-martensitic transformation products (NMTP), such as quenched-in pearlite . Carbon content control

48、s surface hardness and other alloying elements aid in controlling the core hardness and the amount of NMTP. The NMTP microconstituents like ferrite, pearlite and bainite are softer than the martensite and reduce the contact fatigue resistance of steel. Hence, it should be avoided. Alloying element,

49、such as carbon, manganese, nickel, molybdenum and chromium lower the martensite start temperature of iron and thus produce greater levels of retained austenite. A small specimen cut from the failed component is further subjected to microstructural study using optical microscope. 8. Tooth contact stu

50、dies The failed component is subjected to contact studies in order to know the contact details and sequence of failure. Tooth contact analysis was carried out by revolving the failed pinion on crown wheel by referring the index number given in the back cone face of the crown wheel and the shank of t

51、he pinion. The index number of failed teeth of crown wheel is identified as 17, 18, 19, 27, 29, 30, 31, 32 and 38, whereas for the pinion it is 3. As the gear ratio is 6.5, for every revolution the failed teeth of pinion does not come and mate at the same teeth in the next revolution. The sequence i

52、n which the fracture in crown wheel has occurred is 17, 31, 38, 18, 32, 29, 19, 30 and 27. it is observed that the failed pinion teeth does not affect all the teeth of crown it mate. It also confirms that failure has not taken place in one revolution of crown wheel. For the failure to occur in all t

53、he identified teeth, definitely the crown wheel has revolved seven times after the initial failure. The sequence indicates fairly a gradual progression of the damage and ends with the cold weld at the end. This confirms that cold welding has occurred in seventh revolution of crown and all other frac

54、ture in the preceding 6 revolutions. The mode of failure of crown wheel is by partial uprooting. The teeth chipping have occurred all around the edges of crown wheel tooth contact analysis was carried out with the help of marking medium (a yellow paint) on one of the pinion tooth. Then it is rotated

55、 over the crown wheel. It reveals a partial mating between the pinion and crown wheel and this could have been due to improper alignment. It develops high stress between the teeth in contact leading to larger load acting on a very small area during sliding. This resulted in teeth chipping all around

56、 the edges of the crown wheel. 9. Conclusions The investigation on crown wheel and pinion helps to identify the reason for the failure, importance in selecting a correct material and also to know the intricacies of heat treatment. The present study shows that the failure is due to improper selection

57、 of material for heavy-duty application, the compromise made for nickel by cheaper substitute manganese so as to reduce the overall cost of the component. This improper selection resulted in high core hardness finally leading to premature failure of the components. The microhardness study concludes

58、that the effective case depth was not up to the desired level and is due to low temperature employed during carburizing or may be due to inadequate gas feed. The improper heat treatment is also evident by the high levels of retained austenite (25%) in the case, which is detrimental to the component under service. Failure has