卡車螺旋錐齒輪的點(diǎn)蝕故障外文文獻(xiàn)翻譯、畢業(yè)中英文翻譯、外文翻譯

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. 卡車螺旋錐齒輪的點(diǎn)蝕故障 摘要： 螺旋錐齒輪是卡車差動齒輪中的重要組成部分。在這個研究當(dāng)中，對因表面硬化鋼齒輪而導(dǎo) 致卡車差動齒輪中錐齒輪的斷裂進(jìn)行了調(diào)查。為了研究引起失效的原因，專家們從損壞的錐齒輪樣品中進(jìn)行實(shí)驗(yàn)，如外觀檢查，硬度、化學(xué)分析和冶金測試。齒輪表面的點(diǎn)蝕是可以被觀察到的。微觀結(jié)構(gòu)的效應(yīng)在斷裂中被考慮了進(jìn)去。低表面硬度的價值被發(fā)現(xiàn)。被計(jì)算的接觸應(yīng)力高于可允許的接觸應(yīng)力是這篇文章介紹的重點(diǎn)。 1、 介紹 差分驅(qū)動器廣泛應(yīng)用于動力傳輸?shù)膯卧?。螺旋錐齒輪開始在差分驅(qū)動器中優(yōu)于直錐齒輪。它們有彎曲的斜齒，并且逐漸接觸從一端過渡到另一端，嚙合的螺旋齒輪類似于滾動接觸。它們的優(yōu)點(diǎn)是確保負(fù)載均勻的分布在齒上，從而使其攜帶更多 的載荷且不發(fā)生表面疲勞。推力載荷取決于旋轉(zhuǎn)的方向和螺旋角的正負(fù)，調(diào)查的螺旋錐齒輪是由倆種不同的表面硬化鋼構(gòu)成的，表面硬化鋼（ 20MnCr5,EN10084)具有低的碳 -鉻元素，其他鋼（ 17NiCrMo6-4,EN10084)具有低的鎳 -鉻 -鉬元素和中等的淬透性，在一般的軋制條件下，供給的最大布氏硬度為 280（ 30HRC）。它的特點(diǎn)是在經(jīng)過滲碳、淬火和回火后，中型材表面硬度提升至 62HRC 時，可以承受較高的應(yīng)力并且具有較小的韌性。這些鋼（非滲碳）也可用于作為高強(qiáng)度鋼，并且通過適當(dāng)?shù)拇慊鸷突鼗鸷?，產(chǎn)生較好的拉伸 強(qiáng)度和韌性，可滿足多種應(yīng)用。卡車運(yùn)行的每個月中大約都有三個齒輪損壞。因此，對卡車中受損的螺旋錐齒輪進(jìn)行了評估，并且分析了表面硬化鋼制造的齒輪斷裂的原因。 2、 斷裂分析中應(yīng)用的技術(shù) 從企業(yè)的角度來說，齒輪發(fā)生故障的原因可能有設(shè)計(jì)錯誤、程序錯誤或者制造錯誤。設(shè)計(jì)錯誤包括齒輪幾何形狀不當(dāng)，材料不當(dāng)，質(zhì)量水平不夠或是潤滑系統(tǒng)不完善。程序錯誤包括安裝、振動、冷卻和維護(hù)多個因素構(gòu)成。制造錯誤可能會發(fā)生在現(xiàn)場的熱處理或是作業(yè)中的不當(dāng)處理。 在這個分析中，四個損壞的螺旋錐齒輪樣本進(jìn)行各種實(shí)驗(yàn)。進(jìn)行的實(shí)驗(yàn)以及測量結(jié)果如下 ： 1、外觀和斷口檢驗(yàn) 2、硬度實(shí)驗(yàn) 3、化學(xué)分析 4、金相分析 5、接觸應(yīng)力的計(jì)算 3、 分析方法和結(jié)果 3.1 外觀和斷口檢驗(yàn) 在圖 3所示調(diào)查的齒輪中。失效的齒輪都表現(xiàn)出了類似的故 障，對疲勞裂紋擴(kuò)展的斷裂面進(jìn)行了檢查，表明故障時脆性的折斷。 齒牙上的表面點(diǎn)蝕促進(jìn)了齒輪的失效。點(diǎn)蝕是由于過多的表面承受高載荷，由于過高的摩擦速度導(dǎo)致局部溫度過高，或是不充分潤滑導(dǎo)致的。示于圖 4的齒輪發(fā)生點(diǎn)蝕的斷裂表面，通過其斷面表面，可以說是由于點(diǎn)蝕導(dǎo)致的。 3.2 硬度分析 表面硬化的齒輪的硬化只發(fā)生在齒輪表面，達(dá)到預(yù)定深度，達(dá)到 58到 62洛氏溫度。通過增加硬度來提高齒輪的耐用性可以通過增加抗點(diǎn)蝕能力和提高耐斷裂強(qiáng)度來達(dá)到。使用洛氏