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The paper presents a numerical and experimental method for assessing the condition and estimating the residual life of complex large-scale mechanical structures, such as opencast mining and...

Bucket wheel excavators, spreaders, reclaimers etc. are a group of heavy machines commonly used in the mining, power and bulk-handling industry. As machines of this type are used worldwide in various operational conditions, different design and testing approaches were developed. The paper presents and compares the theoretical assumptions stated in most common standards (DIN, AS, ISO, BG…) as well in the technical and scientific literature. Moreover, the paper presents real life application giving this way the opportunity for reliable assessment of the obtained results over the normative theoretical assumptions.

Power and mining industry characterizes with common use of the machines and installations that size and mass exceeds the machinery and equipment used in majority of industries. Due to the scale of those objects, the objects dynamics and external loads characteristics comprises with low frequency, low cycle loads of large energy. The paper presents the objects (bucket wheel excavators, load carrying structures…) which are prone to that type of the loads. Proper loads definition, calculations procedures and the experimental testing and/or validation requires dedicated approach. Improper design and operational conditions assumption, due to the scale of the objects, often leads to the disastrous failures.

The article presents design faults related to the carrying structure of the bucket wheel of the SchRs4600 excavator working in the brown coal mine. The authors analyzed cases of damages of this type of structure occurred in the past in such machines. In order to determine the damage of the carrying structure of the bucket-wheel excavator, non-destructive examinations were carried out using visual and magnetic-particle methods. The real loads occurring during operation of the machine in the case of fatigue were also determined. These measurements were used to verify the numerical model. A strength analysis was carried out using the Finite Element Method. The cause of fatigue cracks was determined by measurements and numerical calculations.

The testing and inspection of fans is a crucial task at the stages of designing and prototyping as well as in terms of future exploitation. In case of machines performing rotational movement, the scope of research is very broad and concerns strength tests, vibration diagnostics, acoustic test, and flow tests. The article presents the issue of studying vibrations of chosen elements of a fan with special regard to the casing and flow tests of the fan itself. The tests were carried out both on the actual object and numerically.

This article describes the methods adopted for determining the stiffness of the bucket wheel boom of the K45 bucket-wheel excavator. Then, the obtained values of deflection of the bucket wheel boom are presented in an experimental and theoretical manner. In the end, the results obtained with both methods are compared.

The aim of the paper is to propose algorithms for suppressing vibrations of massive components of machinery, e.g., operators' cabins in bucket wheel excavators (BWEs). Repetitive perturbations provide the opportunity to learn a control system to suppress or reduce their influence by applying a repetitive control scheme. A new version of the iterative learning control approach, called iterative learning of optimal control (ILOC), is derived. This approach is able to learn a control signal that approximately minimizes the squared acceleration of a system, e.g., the cabin. The resulting algorithms can be used alone or in parallel with a hybrid version of the classic proportional-derivative (PD) controller. The simulations indicate that the ILOC algorithm provides a large improvement in suppressing quasi-periodic disturbances in comparison to the cases of no control and PD control, while the hybrid version provides even slightly better results. The proposed algorithms are intended to be used with magneto-rheological (MR) dampers as semi-active control devices. Subtle properties of MR dampers, such as their hysteresis, are omitted here.

The article presents the results of experimental tests, design work and numerical analyses aimed at optimizing the operating costs of buckets used in the Turow Lignite Mine. The presented approach to designing and optimization takes into consideration the results of tests in real mining conditions as well as modern numerical tools that support the process of designing such structures. The results of the presented work include two buckets with quickly replaceable and permanent teeth, which significantly improve the technical and operational indicators and enable their users to achieve real savings.

On the basis of spreader A2RsB 15400 the method for technical condition state assessment of machines, after many year of operation, in lignite mines is presented. In purpose to identify the structure hot spots and cracks, both numerical and experimental methods were applied. Additionally, the dynamic behavior of the structure was assessed with use of the experimental methods. The paper presents the meaningful results chosen from the assessment procedure.

Centrifugal fans are widely used in order to move air or other gases in ducts. As exact as possible manufacturing of fan is required in order to ensure long time of operation and desired flow parameters. In the article evaluation of influence of unevenly spaced blades onto flow parameters of impeller is considered. Thanks to usage of numerical simulation, few different configuration of blades inaccuracies could be compared with basic ideal case. Received results suggests that inaccuracies in circumferential blade spacing influences flow pattern across impeller and changes flow parameters of fan. It is interesting that in few cases efficiency of impeller is higher than in basic solution, but in fact such situation cannot been accepted since in these cases non-uniform fluid force distribution can cause higher vibrations of fan. In general, differences of efficiency are small what suggests that influence of unevenly spaced blades onto flow parameters can be in many cases neglected.

The modal analysis of technical objects undergoing variable load intensity is an important task, thanks to which the safety in terms of resonance vibration phenomenon can be measured. This paper concerns the aspects of testing the new WLS series fans, used for local mine ventilation, which provide safer underground conditions resulting in more efficient work. The use of numerical methods in the calculations of natural frequencies and the comparison of numerical and experimental results calculated with the use of operational modal analysis have been emphasized.

The second chapter presents the main types of machines operating in the continuous surface mining industry. Their main mechanical and structural subassemblies are categorized. Readers are acquainted with the main operational issues and the most frequently occurring problems and failures. The chapter presents a general overview of the problems related to designing mega machines and the main guidelines for design—for example, standards—as well as their advantages and disadvantages.

To ensure that mines are operated in a reliable and economically efficient manner, it is necessary to monitor the condition of surface mining machines that have been in use for a long time. However, machine diagnostics is not very popular in the case of such machines, despite the undeniable benefits of collecting data about their condition.

In the paper method for measuring loads acting on excavation unit of bucket wheel and bucket chain excavators is presented. Measurements were performed with the use of strain gauges located on the torque beam of the drive. Analytical and experimental methods were adopted for determination of the torque beam behavior. This method is used for long-term measurements of loads in order to assess remaining life of long term operating excavators.

Chapters 3 and 4 described the methods of assessing the technical condition of surface mining machines and the potential consequences in cases of damage or failure of structural elements. The obtained information about its condition serve as the basis for decisions regarding the future use of the machine. Many machines that are currently in operation are undergoing modernizations. The purpose of such modernizations is to fully restore the functionality of these machines, to extend their lifetime and improve their operational parameters.

The paper presents results of investigations aimed to find relationship between grinding media wear rate and lithology of ores processed in copper production. Laboratory wear tests of grinding media were carried out for “pure” lithological components, natural copper ores and artificial mixtures prepared in the laboratory. Test samples were characterized in terms of lithology, and the results were used for interpretation of results of grinding media consumption. Based on the laboratory tests results a new wear function of grinding media consumption related to lithology of ores was established.

Operation of machines in resonance ranges is a great challenge for design engineers. The paper focuses on the analysis of centrifugal fan casing vibrations which during machine operation, particularly in unsteady states, are very strong. Within a series of investigations performed according to the experimental modal analysis natural frequencies of fan casing vibrations were specified. Additional numerical simulations helped to define theoretical values of the natural vibrations frequency and its mode shapes. The results were analyzed and the numerical model was adjusted. The information was later used in the analysis of vibration measurements in real operating conditions. The results achieved for a nine-blade impeller (new type) were compared to results of an old construction eight-blade fan impeller. New solutions, which shall facilitate casing operation beyond resonance frequencies vibrations areas, were proposed.

The fundamental parameter which determine the design of the structure and proofs its safe operation, is list of dead and live/operational loads together with its distribution. That defines the stability of unit. In case of mining machinery, due to its specific layout and enormous size, occurrence of the stability loss can result in catastrophic failure. In the paper, authors present investigations of the stability loss of discharge bridge operating with bucket wheel excavator. Authors, step by step, present the definition of overturning edges, weighing and balancing process. Moreover, numerical simulations and experimental testing of the structure are presented. On the basis of acquired data, cause of the stability loss and assessment of influence of this incident to the structure is provided.

Specialised mining and material handling equipment such as stackers, reclaimers, bucket wheel excavators, etc. require special attention during the design and manufacturing stages. The third party audit conducted by independent expert plays an important role in the entire delivery process. Although the use of a third party auditor is recommended by different standards, it is not a mandatory step that will ensure a design and manufacturing crosscheck. It appears, however, that more and more complex industrial projects utilise this process, which may consist of design and manufacturing check, erection and performance tests supervision and final approval of the equipment. Although it may slightly increase the initial costs of the project, it is beneficial as it decreases future investments and downtimes of equipment. In this paper, the authors present recommended scope of third party audit of mining and material handling equipment and their experiences gained during many projects completed in this field.

In this paper, studies into the causes of fatigue cracks of a jaw crusher supporting structure are presented. The problems appeared after short time of operation at a new crushing facility. A large number of fatigue cracks with a high growth rate and bolt failures were observed in the crusher supporting structure. Considering the high dynamic forces that occur during the operation of such equipment, an investigation into the problem was undertaken in order to prevent catastrophic failure of the crushing station. A specially developed, combined numerical and experimental method was used to determine the reasons for the problems and to solve them.

Some of the most serious problems related to the reliability of cement kiln are bearings failures and damages to the roller carrying surface, both of which often occur without apparent warnings. Although the root causes of these problems can be understood, their on-time detection still remains a problem. This paper presents a new methodology for proactive monitoring of such machines and provides on-line information pointing to potential failure. Both, theoretical and practical considerations are discussed.

This paper presents a method of determining modal characteristics of surface mining machines, which was used to establish the optimal number of buckets based on experimental studies of an existing machine. An experimental and operational modal analysis was implemented to determine the dynamic characteristics. Based on the technical requirements of the excavator, the quantity of buckets was set so as to avoid resonance during operation.

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.

The estimation of the lifetime of high pressure and high frequency loaded components by testing is very costly and time-consuming. The simulation of fatigue life is an important design step in the fast moving and competitive automotive industry, where the steady rise of engineering components and the demand for lightweight construction concurred with enhanced reliability require an optimized dimensioning process. The paper presents the chosen problems of 3D numerical strength and fatigue simulation of a rotary screw compressor of a liquid cooler. The presented results of the FEM mechanical calculation based on a real components. The fatigue analysis were executed using the criterion of critical plane. Local multi-axial state of stresses and deformation has been calculated based on Hooke’s law with simultaneous consideration of kinematics hardening rule of material according to Jiang’s model.

The paper presents selected aspects of stress analysis of eccentric press. This approach is based on the assumption that fractures can be present in the analyzed constructions. Calculations define the current state of the component with respect to fracture mechanics. Reported research work was performed using analytical, numerical and experimental methods in order to evaluate durability of the considered structural element.

In this paper the character of loads exerted on bucket wheel was evaluated. The places of maximal stresses were determined by using finite element analysis. After this operation, a new wheel hub design was initiated. The first phase was related to development of new conceptions of the hub. The proposed conceptions were rated with respect to mass and total length of welds. This procedure led to selection of the most suitable design, which was optimized in order to minimize stress. The work at this stage consisted of continuous modification of the geometrical form, meshing of finite element model and structural analysis thereby providing information about stresses and deformations. The workmanship of the structural component and welded joints were defined according to DIN 22261 2:2006 standard.

The main purposes of the paper are to discuss designing problems of machines used in underground mining and investigation of its reasons based on cracked boom of underground mine machine. Numerical and experimental approach was considered. The finite element method was used for numerical simulation. Fractographic and microscopic evaluation, chemical analysis, hardness tests were used to perform material evaluations. The objectives are achieved by numerical simulation of cracked loader boom, material evaluations of specimens and comparison of results achieved from both approaches. These were determined through a numerical experiment, based on a discrete model of the jib boom and predefined boundary conditions. The finite element analysis for the jib boom provided information about stress distribution for extreme load conditions. The study included macroscopic and fractographic inspection, microscopic evaluation as well as hardness tests of the material used for the jib boom. Conclusions from both approaches were drawn then.

This chapter presents application of FEM as a supporting tool for condition monitoring of existing equipments (technical assessment of condition, determination of best monitoring parameters, setting limits for early corrective actions).

This chapter describes the basics of maintenance management systems and key factors for successful organization and performance. It also points out the main characteristics of major maintenance strategies with their advantages and disadvantages.

Review of condition monitoring techniques for low-speed machines is given describing their possible usage. Good practices for monitoring and technical assessment of new and already in use equipment for most frequently used low-speed machines in heavy-duty industry are given. How to obtain information for proactive actions from the listed techniques is explained. Special focus is paid on vibrodiagnostics as condition monitoring tool.

Condition monitoring of low-speed machines differs from medium to high-speed machines mainly due to misunderstanding of the condition changes and due to low energy emitted when certain damages happen in the moving components. Failures develop slowly and they stay latent till some critical point of their development interval when it is usually too late to act on prevention. Therefore, special considerations must be taken when deciding on data collection and special measuring systems employed for condition monitoring of machines with low cycles of operation. These considerations are presented in the chapter in order to assist technical teams to successfully implement effective maintenance systems to such machines.

Brief review of the condition, the new developments and trends in industry and related researches is given. Difference of today’s maintenance process and system with the adequate systems only a decade ago is given appointing to the fast-growing demands and responsibilities. The main reasons for the development of separate condition monitoring systems for low-speed machinery are given. A short intro of the contents of next chapters is also given.

Surface mining machines are the largest mechanical engineering structures. Bucket wheel excavators operating in lignite mines are continually exposed to dynamic loads. Moreover, nearly all structures are over 10 years old. The methods used in design and construction did not cover the dynamic behavior of machines, which resulted in problems in their operation and decreased durability. The tendency to optimize and increase the operational time of machines is currently also visible in the field of surface mining. As a result the machines which have been operating for many years are subject to investigation. The SchRs (Schaufelradbagger auf Raupenschwenkbar) 4600.50 excavator, which is over 120 m long, 64 m high and weighs approximately 5,000 tons (excluding the dumping bridge), was investigated with regard to vibrations. Operational modal analysis was performed with 15 measurement points in different directions. This approach allowed to determine the variability of the dynamic characteristics of the machine in terms of operational conditions. Simultaneously a numerical model was prepared. Eventually, it was possible to compare and correlate both the numerical and experimental models and to establish the differences based on the operational load acting on the structure.

The condition of headframes in underground mines has a substantial effect on the proper operation and safety of hoisting equipment. One of the potential problems that might occur during operation is the tilting of these structures, which can lead to difficulties in operation and, in extreme cases, to failures. The paper presents an original method of evaluating the technical condition of headframes, estimating the remaining operating time and finding the causes of irregularities in the operation of this kind of structures. To show this, a series of experimental studies and structural analyses were conducted on a model headframe. Based on experimental tests and numerical calculations, the operational safety of the structure was established along with limit values of operational parameters and possible preventative measures were proposed.

In many industries, there are ventilation systems equipped with large scale industrial fans of high power up to or even higher than 3 MW. These are both axial and radial, which in most cases play a key role in the production process like in underground mines ventilation systems or power blocks of power plants. Operation of this type suffers of many vibration problems, resulting from the large-scale (large rotating masses) as well as the complex flow phenomena. Emerging negative phenomena, mainly in the form of excessive vibration, they are often difficult to identify and eliminate. The paper presents examples of such events present in the operation of large scale fans along with numerical and experimental methods for their identification and subsequent elimination.

The subject of this paper is a vibration analysis of an exhaust fan in a power plant unit. Excessive vibrations were observed during the exploitation of the fan, preventing it from proper operation. In order to identify the causes of excessive vibrations, FEM calculations of the vibrations of flue gas ducts, shaft assembly, and measurements on the actual object were conducted. Based on the numerical vibration analysis, the occurrence of resonant vibrations of the flue gas duct and the shaft assembly was demonstrated. Calculations carried out with the use of a laser vibrometer confirmed the occurrence of vibrations with frequencies similar to the frequency forced by the movement of the exhaust fan’s rotor. The results of the analysis contributed to the modification of the shaft assembly and to the introduction of additional stiffening to the walls of pressure and suction ducts.