Failure investigation of the bucket wheel excavator crawler chain link

The high mobility of open pit machines in heavy duty conditions provides fertile ground for the occurrence of various failures of the traveling mechanisms’ vital parts such as chain links. The goal of the study presented in this paper was to diagnose the cause of the damage of the bucket wheel excavator crawler chain links. In order to identify the reasons behind chain link failures, stress state calculations were performed as well as experimental investigations which, given the nature of the failure, included visual and metallographic examinations, chemical composition analysis and tests of mechanical properties. Based on the results of the numerical–experimental analyses, it was concluded that the chain link breakdowns are caused by ‘manufacturing-in’ defects. The results of the presented analyses also emphasize the importance of a comprehensive quality control of chain links.     

Failure analysis and redesign of the bucket wheel excavator two-wheel bogie

This paper discusses the cause of the failure in the vital part of the crawler travel gear of the bucket wheel excavator (BWE) – two-wheel bogie (TWB). The results of the finite element analysis (FEA) point out that the main reason of the TWB failure is its insufficient strength under lateral forces acting during curve travel. The weak points in the TWB structure are removed by suitable redesign while keeping in mind all restrictions ensuing from installation conditions and functionality of the existing crawler travel gear. In addition to the numerical analysis (FEA), a parallel experimental analysis of the original as well as the redesigned TWB is conducted on a test board especially designed for this purpose. The experimental results have confirmed the considerably improved response on lateral loads of the redesigned TWB. The exploitation of the redesigned TWB with no failures has confirmed the validity of the reconstruction design.     

Examination of the causes of a bucket wheel fracture in a bucket wheel excavator

A bucket wheel excavator failure occurred in a brown-coal mine. The failure was caused by a fractured shaft of the bucket wheel. An attempt to determine the causes of the bucket wheel shaft fracture has been made. To that end, the character of changing loads and their maximum amplitudes has been determined by performing measurements on the excavator. A discreet model of the shaft was built and a numerical simulation of the shaft operation using the FEM method was achieved. An analysis of the materials in the fracture area was also implemented. Macroscopic and microscopic images of the fracture area are provided. The shaft fracture was mainly caused by a non-metallic inclusion located below the surface of the shaft as a result of its being rolled. Moreover, it was discovered that the shaft had not been heat-treated.     

‘Designing-in’ failures and redesign of bucket wheel excavator undercarriage

The traveling mechanism of the C-700S bucket wheel excavator is of the two-crawler type. Rigid connections between the undercarriage and the crawler beams offer a very high factor of safety against tipping but at the same time create unfavorable conditions for ground surface adaptation. Connections between the crawler beams and the undercarriage cylindrical girder were realized by means of connection girders with open cross sections (I sections). In order to eliminate the occurrence of cracks, the original undercarriage structure (variant I) has been redesigned (variant II). The key idea was to strengthen the already mentioned connection girders by building in vertical plates. In this way the cross-sections were closed and their torsional rigidity became considerably greater, which led to the adaptation of the traveling mechanism to the ground surface becoming practically impossible. Because of that alone, and within a very short period after the reconstruction, new cracks occurred on elements of the original structure and even on added structural elements. Based on the FEA results, it was concluded that cracks occurrence for variants I and II of the undercarriage structure is caused by highly pronounced stress concentration. Subtle load and stress analyses in various working regimes, presented in the paper, led to the achievement of a re-redesigned undercarriage structure (variant III) with more uniform stress distribution. Stress level in the critical zone for variant III of the undercarriage structure is considerably lower than stress levels for both variant I (≈2.1 times) and variant II (≈2.5 times). It is very important to note that the weight of the new built-in elements for variant II is six times greater than that for variant III. During ensuing exploitation in extremely heavy duty conditions, no damages for variant III of the considered structure were observed.     

Cracks,repair and reconstruction of bucket wheel excavator slewing platform

This paper discusses the results of the investigation of occurrence of cracks in the structure of bucket wheel excavator (BWE) slewing platform, the repair procedure and the reconstruction of the slewing platform. The results of the finite elements analysis (FEA) point out the pronounced stress concentration in the zones of crack occurrence. The values of calculated stresses in the said zones exceed the yield stress of the material. The design solution for the slewing platform reconstruction is chosen based on the comparative analysis of stress–strain states of alternative solutions. The adopted solution enabled the repair and reconstruction in field conditions, without previously dismantling components of the BWE superstructure. Moreover, the regular maintenance procedure has not been impeded. Experimental analysis of the stress state of the reconstructed slewing platform in regular working conditions has confirmed the validity of the reconstruction design. After the reconstruction the BWE has dug up more than 2.9 × 10⁶ m³ of overburden. Visual inspection of slewing platform proved that there are no defects in the structure.     

Failure analysis of gas turbine buckets

The failure of a gas turbine first stage bucket was investigated by visual inspection and finite element analysis. The failure of a major bucket cooling passage was a critical cause of the separation of a bucket segment and caused microstructural deterioration of the neighboring regions by serious thermal load. Changes of microstructural morphologies of the damaged buckets under the thermal and mechanical stress were observed. After coating stripping, the bucket surface condition was evaluated through visual inspection and finite element analysis. The TMF (thermal-mechanical fatigue) cracking of surface coatings on the suction and pressure sides of the bucket was described.     

WK-75型矿用挖掘机斗齿的磨损分析

为了从物料粒度和物理特性方面探究WK-75型矿用挖掘机斗齿的磨损规律,采用UG软件建立铲斗和斗杆装配后的三维参数化模型,并将其导入离散元软件中,对铲斗沿理想挖掘轨迹挖掘进行了磨损仿真分析,找出了铲斗的主要磨损部位,与实际结果相符,验证了模型的正确性.并从物料的密度、硬度、大小和形状等方面探究了斗齿的磨损规律.研究表明,斗齿的平均磨损深度随着物料的密度、硬度、粒径和棱角尖锐度的增加而增大,为后续从减少斗齿磨损方面优化铲斗结构提供了一定的参考.     

具有复杂内腔和外形的斗齿快速逆向设计

为了获得某型挖掘机斗齿点云逆向造型的实体化模型和CAD工程图样,研究了斗齿点云快速实体化的方法.采用基于“曲面重构-实体化-工程图”的逆向设计途径,提出把对精度要求高的内腔和销孔部位及对精度要求一般的斗齿外形分别用Imageware及Geomagic Studio软件完成曲面重构和基于Pro/E软件完成曲面合并和实体化的逆向策略,介绍了斗齿点云的数据分割、曲面重构与合并、实体化以及其工程图获取过程中的主要过程和方法.研究结果表明：对于型面数量多而复杂的斗齿,曲面逆向工具的选取及点云的数据分割方法是否得当是决定曲面和实体模型重建效率和成败的关键,通过恰当选择逆向策略和工具,合理简化点云的分割、曲面重构与合并以及实体模型的建立等,可显著提高逆向设计效率.     

Failure investigation of crown wheel and pinion

The crown wheel and pinion are the critical components in the transmission system of an automobile. Failure of these components has drastic 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 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 the vital component of transmission system in a vehicle.     

Failure analysis of an abrasive cut-off wheel

The relationship between composition, structure, properties and performance is central to the design, use and failure analysis of engineering components. Thermogravimetric analysis (TGA) and wavelength X-ray fluorescence (WRXF) were applied in evaluating the elemental composition and thermal properties, respectively, of a failed abrasive cut-off wheel. The cutting tool, consisting of a bonded abrasive disc, failed prematurely during the routine sectioning of a steel member. The operator was injured as a result. Analysis indicated an improper mixture of the organic constituents comprising the wheel bonding material. Instead of the uniform wear anticipated under normal cutting conditions, the improper mixture resulted in a degradation of the wheel’s mechanical properties, and catastrophic brittle fracture.     

Failure analysis of a cast steel railway wheel

The failure analysis of a broken railway pearlitic cast steel railway wheel, which was involved in a train derailment, has been investigated. The fractographic results near the fracture origin of the wheel have been compared to the regions of stable (fatigue) and unstable crack propagation of cast steel fracture toughness samples. The macro and microfractographic features of the broken wheel did not show any evidence of the occurrence of a fatigue mechanism, indicating that its fracture was caused by transgranular cleavage fracture, as a consequence of the train derailment.     

微弹性啮合轮的传动力及失效分析

 根据大变形梁原理推导出微弹性啮合轮传动力的计算公式,结合计算和实验结果研究弹性杆的传动力与变形程度、啮合深度之间的关系,分析微弹性啮合轮发生传动失效的原因.计算结果表明,传动力的大小随弹性杆倾斜变形角度的增大而增加;实验表明,弹性杆啮合越深,机构产生的传动力越大;失效分析表明,微弹性啮合轮传动失效的主要影响因素包括变传动力、振动冲击和弹性啮合轮的微细制造工艺等.     

Bucket chain excavator: Failure analysis and redesign of the counterweight boom supporting truss columns

The supporting truss of the counterweight boom is a vital part of the bucket chain excavator’s (BCE) superstructure. The occurrence and propagation of cracks in the supporting truss columns’ heads may lead to BCE collapse. The goals of the study presented in this paper were to: (a) diagnose the cause of cracks occurrence; (b) define the reconstruction design of the supporting truss columns and (c) validate the reconstructed structure by numerical–experimental analysis. In order to clarify the causes of cracks occurrence, experimental investigations were performed with the purpose of defining the chemical composition, tensile properties, impact toughness and macrohardness of the columns’ material. Metallographic examinations were also conducted. Based on the results of finite elements analyses (FEA) and experimental analyses it can be concluded that cracks are caused by the ‘design-in’ defects. The redesign solution enabled repair and reconstruction in field conditions, without previously dismantling any substructure of the BCE superstructure. Thereby the time required for performing reconstruction is shortened and indirect costs due to the BCE downtime are considerably diminished. Both the experimental analysis of the stress state of the reconstructed columns in regular working conditions and the failure-free exploitation have confirmed the validity of the reconstruction design, while the BCE excavated approximately 8.5 × 10⁶ t of coal and 1.8 × 10⁶ m³ of overburden after the reconstruction.     

Failure analysis of gas turbine last stage bucket made of Udimet 500 superalloy

ABSTRACT This study presents the failure analysis of the 37.5 MW gas turbine third stage buckets made of Udimet 500 (U-500) superalloy. The buckets experienced repetitive integral tip shroud fractures assisted by a low temperature (type II) hot corrosion. A detailed analysis of all elements which had an influence on the failure initiation was carried out, namely: the commensurate loss of a load bearing cross-sectional area of the bucket tip shroud by the conversion of metal to the corrosion product (scale) and related increase in stress; the influence of the tip shroud microstructure, e.g. a presence of equiaxed and columnar grains, their distribution and orientation; evidence of the transgranular fracture initiation and intergranular creep mechanism fracture propagation. Finally, the most probable mechanism for bucket damage, conclusions and recommendations to prevent failures of the buckets are presented.     

Failure analysis of gas turbine last stage bucket made of udimet 500 superalloy

This article presents a failure analysis of 37.5 mW gas turbine third stage buckets made of Udimet 500 superalloy. The buckets experienced repetitive integral tip shroud fractures assisted by a low temperature (type II) hot corrosion. A detailed analysis was carried out on elements thought to have influenced the failure process:

Failure of an Al-alloy tail wheel trunion of a combat vehicle

Systematic material failure of wheel suspension assemblies was observed on several combat vehicles after about 10 years of continuous operation under severe cross-country route and environmental conditions. The present study focuses on the failure of the trail wheel trunion, cast from an Al-alloy. Visual inspection, macrographic examination and microscopic observations revealed that cracking was initiated at the inner micromachined surface of the alignment lugs and propagated towards the external surface, during long term vehicle operation. Similar findings were observed on the conjugate trunion piece, where intergranular cracking was extended in a significant depth beneath the fracture surface. Failure is attributed to the existence of a stress gap, due to the different fixation configurations of the attachment pin on the alignment lug.     

Failure analysis of a gear wheel of a marine azimuth thruster

A failure analysis of two helical gear wheels of a ducted azimuth thruster is presented. The research work consisted of a fracture examination of the material in order to determine the damage root causes. The samples for the failure analysis were obtained from two broken teeth of two helical gear wheels. An analysis through the scanning electron microscope (SEM) was carried out close to the crack initiation. It was found that the damage in the bevel gears were by the fatigue fracture mode. The SEM analysis showed that the gear teeth were under severe contact stress during the operation aggravated by an inappropriate lubricating. A possible misalignment between the pinions and the gear wheels teeth could also contribute for the premature failure.     

Failure analysis of cracking in wheel rims – material and manufacturing aspects

Manufacturing of wheel in automotive industries demands no-flaw wheels. However, process as well as material deficiency in varying ratios of influence has been the counteracting factors in producing flawless wheel components. Tube and tubeless wheels for light and medium commercial vehicles are manufactured by cold forming of slit hot rolled strips from low carbon steel with or without micro alloying. During manufacturing and forming of the strips, cracking of wheel rims is a major problem at the production line. The paper discusses about one of the failure types in wheel rims, where the wheel rim thins down locally and cracks at the weld.     

Safety analysis of autonomous excavator functionality

This paper presents an account of carrying out a hazard analysis to define the safety requirements for an autonomous robotic excavator. The work is also relevant to the growing generic class of heavy automated mobile machinery. An overview of the excavator design is provided and the concept of a safety manager is introduced. The safety manager is an autonomous module responsible for all aspects of system operational safety, and is central to the control system's architecture. Each stage of the hazard analysis is described, i.e. system model creation, hazard definition and hazard analysis. Analysis at an early stage of the design process, and on a system that interfaces directly to an unstructured environment, exposes certain issues relevant to the application of current hazard analysis methods. The approach taken in the analysis is described. Finally, it is explained how the results of the hazard analysis have influenced system design, in particular, safety manager specifications. Conclusions are then drawn about the applicability of hazard analysis of requirements in general, and suggestions are made as to how the approach can be taken further