卡车螺旋锥齿轮的点蚀故障外文文献翻译、毕业中英文翻译、外文翻译

Pitting failure of truck spiral bevel gear Abstract Spiral bevel gears are some of the most important elements used in truck differential. In this study, the fracture of spiral bevel gear for truck differential produced from case hardening steel is investigated. In order to study the causes of the failure,specimens prepared from the damaged spiral bevel gears were subjected to experiments, such as visual inspection,hardness, chemical analysis and metallurgical tests. Pitting occurrence on gear surfaces was observed. The effect of microstructure on the fracture was considered. Low surface hardness values were found. The calculated contact stress was higher than the allowable contact stress which is emphasized in literature. 1. Introduction Differential drives are packaged units used for a wide range of power-transmission applications. The spiral bevel gears are beginning to supersede straight-bevel gears in differential drives. They have curved oblique teeth that contact each other gradually and smoothly from one end of the tooth to the other, meshing with a rolling contact similar to helical gears (Fig. 1). They have the advantage of ensuring evenly distributed tooth loads and carry more loads without surface fatigue. Thrust loading depends on the direction of rotation and whether the spiral angle of the teeth is positive or negative 1,2. The investigated spiral bevel gears are made of two different case hardening steel. The case hardening steel (20MnCr5, EN10084) has a low carbon chromium and the other steel (17NiCrMo6-4, EN10084) has a low nickel chromium molybdenum with medium hardenability, generally supplied in the as rolled condition with a maximum brinell hardness of 280 (30 HRC). It is characterized by good core strength and toughness in small to medium sections with case hardness up to 62 HRC when carburized, hardened and tempered. These steels can also be used (uncarburized) as high tensile steel, which when suitably hardened and tempered can be utilized for various applications requiring good tensile strength and reasonable toughness. Almost three gears are damaged every month in truck service. Therefore, the damaged spiral bevel gears of truck were evaluated, and the causes of fracture of a gear manufactured from case hardening steel were carried out. Some properties of truck differential are given in Table 1. Also, the main dimensions of the gears are shown in Fig. 2. A number of mechanical and microstructure analyses are carried out to determine the causes of fracture. 2. Techniques used in fracture analysis From one point of view, causes of gear failure may include a design error, an application error, or a manufacturing error. Design errors include such factors as improper gear geometry as well as the wrong materials, quality levels, lubrication systems, or other specifications. Application errors can be caused by a number of problems, including mounting and installation, vibration, cooling, lubrication, and maintenance. Manufacturing errors may show up in the field as errors in machining or heat treating 3. In this analysis, the four damaged spiral bevel gear specimens were subjected to various tests. The following experimental works and stress calculations were done: visual inspection and fractography； hardness tests； chemical analysis； metallographic analysis； contact stress calculation. 3. Analysis and results 3.1. Visual inspection and fractography The investigated gears are shown in Fig. 3. The failed gears showed similar failure and did bear indication of fatigue crack growth when the fracture surface was examined, indicating that the failure was of a brittle type of fracture. The pitting on gear teeth surfaces assisted the failure. Pitting is caused by excessive surface stress due to high normal loads, a high local temperature due to high rubbing speeds, or inadequate lubricant. The pitting occurrence and the fractured surfaces of gears are shown in Fig. 4. According to the fractured surfaces, it was said that the failure was due to pitting. 3.2. Hardness analysis Case-hardened gears are hardened only on the surface of the gear teeth, to a predetermined depth, to about 58 to 62 Rockwell C, or roughly as hard as a bearing race. The increased hardness improves the gear s durability rating by providing greater resistance to pitting and greater strength, or resistance to breakage 4 6. Hardness analysis of fractured gear materials was carried out using a Rockwell hardness test machine. The measurements were carried out on three different surface areas. The core and surface hardness values are given in Tables 2 and 3. Core hardness over 40 HRC is not recommended due to potential for distortion, residual stresses, and brittleness but the gear 1 core hardness value is higher than the recommended values. The surface hardness of gears was observed as 50 54 HRC which is lower than the values stated in the literature. 3.3. Chemical analysis Chemical analyses of 20MnCr5 and 17NiCrMo6-4 case hardening steels according to EN 10084 are shown in Table 4. The chemical composition of the piston materials was determined by spectroscopy chemical analysis. The chemical compositions of gear material are listed in Table 5. It was understood from the chemical composition that the material was case hardening steel. The gear 1 is 17NiCrMo6-4 and 2, 3 and 4 are 20MnCr5. The composition of gear materials contains low C and Cr, Ni and Mo content, which cause the structure to quench in a tough mode. The alloying additions improve the hardenability of the steel. Chromium improves corrosion resistance, while manganese contributes to deoxidation of the melt and also improves machinability. Nickel reduces distortion and cracking upon quenching. 3.4. Metallographic analysis The metallographic specimens were first ground, polished and etched using standard techniques in order to examine the inner structure. A light optical microscope was used in the investigations. It can be understood from the figures that the gears were carburized and then cooled in the oil ambient. The microstructures of the failed gear materials show that they are similar structures. From the observation, it is concluded that the case hardening process was not properly done. Also, because of the application of improper heat treatment, gears core structure have a wholly martensite which is depicted Fig. 5. The core structure should be tough in gears not martensite and brittle. 3.5. Stress calculation Since the pitting occurrence was observed at visual inspection, the contact stress on gear teeth was calculated.The stress experienced by the spiral bevel tooth during operation was estimated using the design torque of 250 Nm. The contact stress on the loaded tooth can be calculated using the equation 7。 The terms used in equation are explained in Table 6. Using Eq. (1) and Table 6, the contact stress was calculated to be 1994 MPa. According to literature 6,7, allowable contact stress is 1550 MPa. This value is lower than the calculated value. In this case, gears have about 0.77 safety factors and they have not contact strength. Thus, the pitting failure was observed on gear teeth surface. The occurring pits have contributed to the failure of gears. 4. Conclusion In this research, the influences of microstructure, chemical composition and hardness of the gears were investigated and contact stress was calculated. From the experimental observations and calculations, the following conclusions may be made: 1. In order to obtain same hardness and microstructure, the gear materials should be of same chemical composition. 2. The surface hardness of gears is low. In order to obtain maximum pitting resistance, the gears outer surface hardness should be increased to 58 60 HRC. 3. In order to obtain different microstructure between core and surface, carburising heat treatment should be made proper conditions, such as time, case depth. The case depth should be under control. 4. Due to the high tooth-contact pressures, oil film thickness may not be enough. The lubrication could be difficult. Therefore, the pitting occurrence increases. On the examination of fractured parts, it can be concluded that the gears expose to overloading. In order to decreasing contact pressure, the gears geometry can be optimized in design stage or the pinion design torque can be decreased. 卡车螺旋锥齿轮的点蚀故障 摘要： 螺旋锥齿轮是卡车差动齿轮中的重要组成部分。在这个研究当中，对因表面硬化钢齿轮而导 致卡车差动齿轮中锥齿轮的断裂进行了调查。为了研究引起失效的原因，专家们从损坏的锥齿轮样品中进行实验，如外观检查，硬度、化学分析和冶金测试。齿轮表面的点蚀是可以被观察到的。微观结构的效应在断裂中被考虑了进去。低表面硬度的价值被发现。被计算的接触应力高于可允许的接触应力是这篇文章介绍的重点。 1、 介绍 差分驱动器广泛应用于动力传输的单元。螺旋锥齿轮开始在差分驱动器中优于直锥齿轮。它们有弯曲的斜齿，并且逐渐接触从一端过渡到另一端，啮合的螺旋齿轮类似于滚动接触。它们的优点是确保负载均匀的分布在齿上，从而使其携带更多 的载荷且不发生表面疲劳。推力载荷取决于旋转的方向和螺旋角的正负，调查的螺旋锥齿轮是由俩种不同的表面硬化钢构成的，表面硬化钢（ 20MnCr5,EN10084)具有低的碳 -铬元素，其他钢（ 17NiCrMo6-4,EN10084)具有低的镍 -铬 -钼元素和中等的淬透性，在一般的轧制条件下，供给的最大布氏硬度为 280（ 30HRC）。它的特点是在经过渗碳、淬火和回火后，中型材表面硬度提升至 62HRC 时，可以承受较高的应力并且具有较小的韧性。这些钢（非渗碳）也可用于作为高强度钢，并且通过适当的淬火和回火后，产生较好的拉伸 强度和韧性，可满足多种应用。卡车运行的每个月中大约都有三个齿轮损坏。因此，对卡车中受损的螺旋锥齿轮进行了评估，并且分析了表面硬化钢制造的齿轮断裂的原因。 2、 断裂分析中应用的技术 从企业的角度来说，齿轮发生故障的原因可能有设计错误、程序错误或者制造错误。设计错误包括齿轮几何形状不当，材料不当，质量水平不够或是润滑系统不完善。程序错误包括安装、振动、冷却和维护多个因素构成。制造错误可能会发生在现场的热处理或是作业中的不当处理。 在这个分析中，四个损坏的螺旋锥齿轮样本进行各种实验。进行的实验以及测量结果如下 ： 1、外观和断口检验 2、硬度实验 3、化学分析 4、金相分析 5、接触应力的计算 3、 分析方法和结果 3.1 外观和断口检验 在图 3所示调查的齿轮中。失效的齿轮都表现出了类似的故 障，对疲劳裂纹扩展的断裂面进行了检查，表明故障时脆性的折断。 齿牙上的表面点蚀促进了齿轮的失效。点蚀是由于过多的表面承受高载荷，由于过高的摩擦速度导致局部温度过高，或是不充分润滑导致的。示于图 4的齿轮发生点蚀的断裂表面，通过其断面表面，可以说是由于点蚀导致的。 3.2 硬度分析 表面硬化的齿轮的硬化只发生在齿轮表面，达到预定深度，达到 58到 62洛氏温度。通过增加硬度来提高齿轮的耐用性可以通过增加抗点蚀能力和提高耐断裂强度来达到。使用洛氏