译文：小齿轮和锥齿轮的失效分析

1、小齿轮和锥齿轮的失效分析毕业设计（论文）译文题目名称：工程失效分析13册1285-1292页 院系名称： 机 电 学 院 班 级： 机 自 091 学 号： 200900814222 学生姓名： 徐东东 指导教师： 王玮 2013年 03 月小齿轮和锥齿轮的失效分析摘要锥齿轮和小齿轮是汽车传动装置的重要组成部件。这些部件的失效对车辆运动有着强烈的影响。并将逐步导致修理时间的增加。除了他的功能受到影响外，这些部件也会增加危险性。用标准的材料力学去分析齿轮断裂，以此来研究齿轮失效的原因。分析得出的结论表明制造材料的组成成分是失效的原因，在材料中可以明显的发现含有大量锰而没有镍和钼。这导致材料核心的

2、硬度很高，高硬度却会使车辆传递系统中的重要部件产生早期的失效。关键字：渗碳；锥齿轮；齿轮齿的失效；金属断面的显微镜研究法来研究失效；奥氏体；1介绍机械系统的平均寿命总是依赖系统的最重要部分。 在动力传动系统中通常是齿轮。齿轮设计通常按高速重载的的条件来设计最小的尺寸和重量。被用于重型车辆的一个典型锥齿轮和小齿轮。 他们是车辆的最重要的部分，因此要求抗磨损性好和抗接触疲劳强度高。理想的锥齿轮和小齿轮应该符合美国齿轮制造业协会（AGMA）的11项质量标准，即均匀和适宜的金属质地，极好的抗扭矩变形，极大的抗冲击力，耐磨性，最佳的传动效率，比较小的噪声，小的自由震动和齿轮几何学。气体深碳是达到这些标准

3、的一个工序。他使得齿轮耐磨损性和韧性增大。制造者应该通过一些制造业标准选择适当的材料和正确的热处理参数来使重要的部件持久和高效。En353（15Ni Cr 1 Mo 12）和En207(20 Mn Cr 1)是用于制造这些重要部件比较多的细密纹理的钢材。当En207被广泛的用于按规定尺寸制作齿轮和轴时，En353却用于重型齿轮，轴，小齿轮，凸轮轴，连接销，重型车辆的传动部件的制造。2加工工序锥齿轮和小齿轮是在热处理后从850-880等温条件下获得的均质材料制造的。锻造是计算机数字控制齿轮的外形几何尺寸的精密制造。它在900 - 930下进行渗碳处理来得到均匀的表面薄膜。渗碳能达到1.524到1

4、.905毫米的深度。淬火是在780 - 820下进行的，为了避免扭曲变形，淬火后要在油中冷却。对小齿轮来说，选择淬火是尽力提高齿轮的抗磨损性。小齿轮的曲线被特别的处理，这是为了得到能抵抗更高的冲击力和由固定产生的扭转力矩。淬火后，锥齿轮和小齿轮还要降温到150 - 200以此来消除内应力。最后，锥齿轮和小齿轮要做全面的检测以防止早期的失效，同时保证无噪音的产生。齿轮隙被保证在0.2 0.3 毫米内以使噪音和震动最小。3检测啮合的齿轮（也就是小齿轮）显示齿轮表面的疲劳断裂是由一个微小的裂纹引起的。大的碎片也远离了齿。表面的疲劳是由表面的比较硬的组织在压应力下造成的。然而，破裂形成的裂纹深度要比点

5、蚀所形成的深，并且它的内力的作用与交替变化的应力有关系。这经常被当成至关重要的，但因为它导致了表面低碳部分的疲劳断裂，先前的命名将被经常使用。 啮合的齿轮（也就是小齿轮）显示齿轮表面的疲劳断裂是由一个微小的裂纹引起的。大的碎片也远离了齿。表面的疲劳是由表面的比较硬的组织在压应力下造成的。然而，破裂形成的裂纹深度要比点蚀所形成的深，并且它的内力的作用与交替变化的应力有关系。这经常被当成至关重要的，但因为它导致了表面低碳部分的疲劳断裂，先前的命名将被经常使用。4点蚀通常，齿轮失效是由几个机械装置失效引起，但是大多数是由齿轮的齿面点蚀导致。实际上，齿面点蚀是机械装置失效的主要原因。这些失效都是由滚动

6、接触磨损和部件表面寿命在应用的负荷下的磨损造成。因此，我们用一个立体显微镜来对失效的部件进行大量的研究以次来探索齿面磨损齿轮的齿面磨损的特点是由齿轮接触面上的凹坑的出现。表面磨损的过程可以看作是表面破损或裂缝，他们都是在长期的接触负载下产生。当裂缝变的足够大时不稳定的生长就发生，而这则会导致一部分表层材料的崩落。导致这些发生的就是凹坑。在两个部件中凹坑有效性很少。相对来说，在小齿轮上的凹坑数目要比差动齿轮的多，并且齿轮变形量也要比差动齿轮的高。这说明事实上失效是因为齿轮的工艺不够而不是点蚀。5化学分析因为没有关于齿轮的化学组成和热处理条件可用信息，下面的任务就是对材料进行鉴定。一件小的样品是用

7、磨削轮在差动轮进行切割，并用发光摄谱仪和显微照片来进行研究与分析。化学分析在两个不同的部分进行，一个是在部件表面，另一个在部件的核心部分。化学分析有助于确定那些选来准备加工成部件的原材料的基本成分，在炭化处理过程中的含碳量以及基本组成在由制造者加工过程中的中和 。6硬度分析作为渗碳材料的一种情况，硬度的倾向是从外至里，外部比内部的硬度大。大体上, 为计算有效表面深度 (ECD) 所采取的表面压力值是 540 HV， 并且它的深度期望在 1.524 和 1.905 毫米之间。 在最初含炭量（硬度关于深度保持不变）所达到的深度叫做完全表面深度。因此，完全表面深度超过有效表面深度。在同一硬度中，完全

8、表面深度和有效表面深度分别是 737 HV ， 1.4 和 1.22 毫米。对于失效的部分，核心硬度在齿根的中心测量，其数值是458 HV。 通常，期望的核心硬度在 317 和 401HV 之间，最大值可达 430 HV,超过这个值零件可能会被破坏。这对重型机械的要求是非常高的，高硬度材料是因为含锰比较多。高的核心硬度造成附属表面疲累和抗挤压力的下降。这也是导致早期失效的原因。在这一项研究， ECD 只有 1.22 毫米,他不能充分确定表面深度。不够的表面深度造成了小齿轮牙齿破碎状而且依次减少顶轮的耐久性。这是由于在渗碳期间温度过低或者由于碳供给不充足。7微观结构虽然残留奥氏体对增加接触疲累强

9、度有益,当奥氏体以行列的形式排列时，对空间结构和表面的硬度有益。在操作期间，亚稳定奥氏体将会在压应力和拉应力下转变成马氏体,这将使体积变大。体积的增大可能产生扭曲变形，从而产生压力，这可经过欠稳定和噪音造成寿命减短。过多的残留奥氏体也将会降低材料硬度和早期的抗疲劳强度。基本上，除了避免不必要的马氏体转换产物，如调质珠光体，钢必须要有充足合适的合金元素的加入来使金属的表面光滑和核心硬度提高。含碳量控制核心硬度，其他的合金元素帮助控制核心硬度和马氏体变化物的含量。马氏体的转化物如珠光体和贝氏体比马氏体的质地软，而且会使钢的抗疲劳强度降低。因此，这种情况应该被避免。添加的元素如碳，锰，镍，钼和铬会降

10、低马氏体开始的温度，并且会增加奥氏体的含量。8齿接触研究用失效的零件来进行接触研究是为了知道其中的细节和失效的顺序。用小齿轮的前齿面在锥齿轮的后锥面上进行旋转试验来研究齿的接触。锥齿轮齿的失效指数是17,18,19,27,29,30,31,32和38，然而小齿轮的失效指数是3。当传动比是6.5时，每一次试验的小齿轮的失效齿数并没有增加，而是和下次的试验一样。锥齿轮失效的齿依次是17,31,38,18,32,29,30和27。小齿轮的失效齿并没有影响与他配对的锥齿轮的齿。从中也可证实失效并没有在锥齿轮的一次旋转中发生。在首次失效后再旋转七倍的时间，全部的齿就会失效。失效会逐渐的发生，最后就会发生

11、冷焊现象。这一点表明冷焊现象发生在锥齿轮和全部的零件上，当工作时间超过失效时间的6倍时。失效的试验品部分也发生齿根断裂。 齿根全部有裂纹的锥齿轮齿接触研究是在有标记(黄色油漆)的小齿轮帮助下完成的。然后它在锥齿轮上进行旋转。这证明小齿轮与锥齿轮只是部分的接触，可能是由于校正的不好。这会在接触的齿上产生高的接触应力，导致更大的负载作用在非常小的面积上。这种情况导致齿的破裂发生在齿的边上。9结论这个不正确的选择导致材料内部硬度高 ，致使早期失效产生。硬度分析得出的结论是有效的表面深度没有达到要求的水平是因为在渗碳时温度不够或者是碳元素不够。不正确的热处理会使奥氏体在表面残留过多（大概25%），这对

12、工作的零件有害。失效首先发生在小齿轮上，不管失效的齿与锥齿轮是在哪接触的，这都引起锥齿轮的早期失效 。局部的倒根是锥齿轮失效的典型事件。因此，重要零件必须进行热处理，使其有最少的网状碳素体，少的含碳量，少的奥氏体，来避免在工作时发生破裂，减少齿的快速磨损，和防止工作时扭曲变形。奥氏体的存在能用常规的热处理替代低温处理的方法来减少。淬火后马上低温处理，接着进行回火处理可以增强零件的耐磨损性和刚度。在将来可以生产更耐用的零件。本文摘译自： 安娜大学机械工程学院和印度大学的教授Tamil NaduA. Benselya, S. Stephen Jayakumara, D. Mohan Lala, G

13、. Nagarajana 和 A. Rajaduraib的工程失效分析，这篇论文在2005年9月14日发表，2005年10月31日被收录，并于2006年二月9日可在线使用。参考书目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