Bucket Wheel Excavator Research Articles

Iterative learning from suppressing vibrations in construction machinery using magnetorheological dampers

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.

Remaining Lifetime Assessment of Bucket Wheel Excavator’s Boom Structure by Using Non-destructive Method

Abstract The bucket wheel excavators (BWE), when operating in faces with hard intrusions (rock structures with increased cutting resistance) are submitted to loads exceeding those arising during the operation in normal conditions. The most vulnerable structural element of the BWE from the point of view of these loads is the boom. The unexpected occurrence of hard formations produces shocks and vibrations, their unwanted effect being sudden failures of the constitutive elements and, in long term, fatigue, which increases the vulnerability of the mentioned structural element. In the paper we present the results obtained regarding the fatigue and remaining lifetime assessment using a new method, issued from the researches performed in the frame of BEWEXMIN project.

Tie-rods of the bucket wheel excavator slewing superstructure: A study of the eye plate stress state

Tie-rods of the bucket wheel and counterweight booms are vital parts of the bucket wheel excavator slewing superstructure. This paper is dedicated to the problem of identifying the stress state of the critical cross-section ('net section') of the eye plates on these tie-rods. It presents the results of the experimental and numerical investigations carried out on the eyebar model. The results show the appearance of a plastic deformation in the zone near the contour of the hole even when the eye is subjected to the loads within the range of the permissible loads prescribed by the standard DIN 22261-2. Plastification in the eye net section occurs across the full thickness of the plate, but it does not jeopardize the integrity of the structure. The stress value in the eye net section, calculated in accordance with the standard DIN 22261-2, is significantly lower than the actual stress values around the hole and serves only as a comparative value for the static strength proof for the eye.

Analysis of current and voltage harmonics introduced by the drive systems of a bucket wheel excavator

The authors state that this research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Non-destructive testing of welded fatigue specimens

Non-destructive tests were conducted on welded fatigue specimens prepared using the same steel material and welding method as the one used in the manufacture and repair procedures of a KRUPP SchRs 600 bucket wheel excavator to reveal any defects present. The chemical composition, the mechanical properties, tendency to cracks and the microstructure of the bucket wheel material were determined using appropriate tests. The initiation of cracks and their subsequent growth during fatigue testing of the welded specimens was studied using ultrasound testing (UT) and a metallographic examination in order to investigate the causes of failure during service and predict fatigue life of the bucket wheel welded parts. It was found that the welding method used produces welds with numerous discontinuities that can only be detected using ultrasound techniques.

Calculation the capacity of bucket wheel excavator the selective mining of overburden

During open pit coal exploitation inevitably comes to land degradation. The negative changes, processes and consequences impose need for parallel working on sanitation and in general arranging destroyed natural areas. The one of sanitation criterion is implementation of reclamation which has a goal to restore completely or as much as it is possible, the destroyed area to its previous purpose. The priority has consistent conducting of technical reclamation of spoil in accordance with planned landscaping.

Service FMECA of a bucket wheel excavator

Surface mining systems (SMSs) are among the most significant 20th century achievements in mining industry, whose significance to miners is comparable to the invention of dynamite in the 19th century. However, problems of SMS risk assessment are very scarce in relevant literature. For this reason, this paper aims to establish a consistent risk quantification approach for bucket wheel excavators (BWEs), the backbones of these systems. Based on the original structural scheme of a BWE, the risk parameters assessing criteria stemming from multidecadal experience and the database of recorded standstills (in the considered case, one hour of SMS downtime generates indirect financial losses of ≈15000€), a study was conducted applying the Service FMECA technique to the BWE SRs2000 (one of the best-selling models from “Takraf”), with the following conclusions: (a) the material conveying subsystem is the highest contributor in the total number of mechanical and electrical failures, as well as in total downtime; (b) during the monitoring period, there were no extreme risk level failures. Besides, corrective actions for reducing risk levels of the most critical mechanical and electrical failure modes are given in the paper. The presented approach for risk quantification for a BWE can be successfully applied to other SMS subsystems, notably spreaders.

Simulation of the frequency response of the ERC 1400 Bucket Wheel Excavator boom, during the excavation process

Abstract The paper deals with the modal analysis and frequency response analysis of a bucket wheel excavator (BWE) boom, obtained by simulation, based on a virtual model of an existing BWE boom. The boom, which generally is realized as a spatial truss, is the most vulnerable subsystem of the BWE, being submitted to severe operational loads characterized by very pronounced cyclical, dynamic and stochastic variability. This vulnerability is the consequence of its shape and constructive parameters and the nature, source and character of the external exciting loads to which it is exposed. The classical approach recommended by standards and norms cannot predict the occurrence of failures caused by vibration, which produces fatigue due to the load’s cyclical variability and the deformation produced by resonant vibration of some constitutive elements. As exciting load we considered the operational forces acting on the bucket wheel. In this manner we can take into account the constructive features – with modal analysis, and the vibration regime – with frequency response analysis. The proposed method is useful both in the design phase of new load-bearing structures of truss type subjected to high-variability forces, and also in refurbishment or improvement phases of the existing structures of this kind.

Vibration analysis of a bucket wheel excavator boom using rayleigh’s damping model

Abstract For the ERc 1400-30/7 type bucket wheel excavator (BWE) used in various Romanian open pit mines, a virtual model of the boom was constructed in SolidWorks. On this model, the variable in time forces acting during the excavation process were simulated, and the time history analysis (time response) was performed. This dynamic time response analysis was performed for excavation of homogenous material only, considering the damping as being of Rayleigh’s type, where the damping matrix is a linear combination of the mass and stiffness matrices. Based on the conducted analysis, the displacements of the boom during excavation were observed.

Investigation of the failure of the bucket wheel excavator bridge conveyor

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.

Simulation of the Time Response of the ERc 1400-30/7 Bucket Wheel Excavator’s Boom during the Excavation Process

The sustainability of lignite production requires, among other factors, cost reduction, high efficiency, as well as the increase of the production capacity. In order to rationalize and increase the efficiency of lignite mines, the optimization of the production process is necessary. In this respect, equipment revitalization and modernization is a key issue. This paper deals with the analysis of the time response of the boom structure of a bucket wheel excavator (BWE) during operation. For this, we propose a virtual model of the boom, on which a variable-in-time force generated by the bucket wheel acts. The kinematic drive chain of the bucket wheel and the conveyor belt, which are also vibration generators, were simulated only by the static load produced on the excavator’s boom. Thus, it is possible to highlight the time response of the load-bearing structure (the boom) of the bucket wheel to the action of forces resulting from the cutting of the face under pretensioning conditions. The forces generated by the excavation process have high values and a slow variation over time, depending on the bucket wheel’s rotation speed and the number of buckets installed on the wheel. The dynamic time response simulation was performed considering the global damping variation as dependent on frequency. The simulation was done for both the excavation of a homogeneous material and for the case of the sudden appearance of a hard material inclusion (boulder) during homogenous material cutting.

Impact of the Length of Manoeuvering Roads of a Bucket Wheel Excavator for Working Times in the Shortwall

The article presents one of the possibilities of using a bucket wheel excavator technology (with a daily capacity of over 100,000 m3) when removing an overburden on the stabilised front in the opencast lignite mine. The influence of excavator manoeuvring movements on the choice of parameters of operational floors is discussed. The assessment of the efficiency of the work process was made, among other things, while maintaining the required safety conditions and geometric parameters of the working front. It has been shown that in the bucket wheel excavator’s over-elevation work with variable variants of vertical and horizontal division (for a given floor height), the length of manoeuvring roads on the operational front is more favourable than the working technology of the entire height of the floor.

Integrity assessment and determination of residual fatigue life of vital parts of bucket-wheel excavator operating under dynamic loads

In this paper are presented results of tests and analyses of complex dynamic loads carried out on the bucket-wheel excavator SchRs 650/5 × 24 Krupp, as well as assessment of service life of vital welded structures of a bucket-wheel excavator boom subjected to cyclic loading with a variable amplitude through the use of experimental tests carried out in order to determine operational strength and growth of a fatigue crack for one structural part. Bucket-wheel excavator was built by “Thyssen Krupp” company, Germany. Outer loads, or in other words digging forces for the overburden and coal have been calculated on the basis of measured values of actual current intensity of the bucket-wheel drive and recorded output values of changeable loads. Correlations between the power of the bucket-wheel drive system and adequate hourly production, depending on the overall digging resistance which affects the stress condition of the bucket-wheel, were also determined. Results of the theoretical and experimental analysis of natural and forced oscillations of the support structure for various exploitation conditions are presented in first part of the paper. Deformations εi determined by tensometric measurements on the rotating shaft of the bucket-wheel were converted into tangential stresses through the introduction of the modulus of elasticity and Poisson's ratio, which, along with the polar moment of inertia of the cross-section, define the moment of rotation on the bucket-wheel shaft. Through the use of the load - strength comparison method (maximization of the ratio of load and strength indicators) the application factor of the gear with the largest number of turns KA has been determined.In the second part of the paper methodological approach for the assessment of service life of vital welded structures of a bucket-wheel excavator boom was presented. Assessment was done in order to determine operational strength and growth of a fatigue crack, through the use of experimental tests. Realized researches and results presented in this paper offer great possibilities for the analyses of behaviour of vital welded structures of the bucket-wheel boom. By the application of the measurement device with 8 channels for registration and processing of electric signals HBM Spider 8 and measurement tapes HBM 6/350 × XY31 deformations were measured at vital welded structures of the boom in the area of the bucket-wheel. The objective of the test is to determine if there is a possibility of occurrence of plastic deformations or initial cracks due to fatigue at vital welded structures and to obtain data which define crack growth.

Multi-Criteria Approach for Selecting Optimal Dozer Type in Open-Cast Coal Mining

In a continuous system of production in open-cast coal mining, in addition to the basic machinery which consists of highly productive machines (bucket-wheel excavators, bucket-chain excavators, spreaders, conveyor-belt transporters, etc.) that provide an uninterrupted exploitation of mineral ores, the usage of auxiliary machinery is also necessary. The auxiliary machinery provides the possibility of using the capacities of basic machinery adequately and timely. Further, it must be mentioned that the auxiliary machinery generates up to 20% of the total mining expenses. Dozers are the most commonly used machines. Choosing the adequate dozer of the right type and manufacturer is of great importance and can be made easier by carrying out an analysis of the existent operational-exploitative parameters. In this paper, the method of grading the operational-exploitative parameters of dozer is defined. The choice of the optimal type of dozer was conducted by using the analytical hierarchy process (AHP).

Evaluation and Risk Analysis of Open-Pit Mining Operations

Mining of raw materials is a process that consists of several stages. In open-pit mining, material with high compressive strength is extracted by drilling and blasting and material with low compressive strength is extracted by e. g. a bucket wheel excavator. Most important influencing factors for crusher decision are compressive strength, moisture content, capacity of crusher, abrasiveness, and feed size. Depending on sequence of mining, fixed, semi-fixed, semi-mobile, or fully-mobile crusher stations can be applied. Compressive strength, tensile strength, cleavage, fracture behaviour, and stickiness are the most significant influencing factors for bucket wheel excavator selection. The waste removal and dumping associated with mining must be handled very well, so that the environmental impacts are as low as possible and dump stability is guaranteed. Essential are dump foundation properties, design of dump, and construction of dump. Open-pit mining operations harbour risks which can lead to project delays, operation standstill, injury to personnel, damage to equipment, or negative impacts on the environment. Therefore, risk identification and prevention of risks is essential.

A New Method for the Calculation of Energy and Power Requirements of Bucket Wheel Excavators

Abstract The bucket wheel excavator (BWE) is a continuous working rock harvesting device which removes the rock by means of buckets armoured with teeth, mounted on the wheel and which transfers rock on a main hauling system (generally a belt conveyor). The wheel rotates in a vertical plane and swings in the horizontal plane and raised / descended in the vertical plane by a boom. In this paper we propose a graphical-numerical method in order to calculate the power and energy requirements of the main harvesting structure (the bucket wheel) of the BWE. This approach - based on virtual models of the main working units of bucket wheel excavators and their working processes - is more convenient than those based on analytical formulas and simplification hypotheses, and leads to improved operation, reduced energy consumption, increased productivity and optimal use of available actuating power.

Exploring the effect of physical, human and technical factors on bucket wheel excavators' efficiency: a fuzzy cognitive map approach

Several parameters, e.g., characteristics of the excavated material, number and thickness of lignite layers, bucket wheel capacity, experience of personnel, etc., affect the efficiency of bucket wheel excavators (BWEs). In this paper, the fuzzy cognitive map (FCM) approach is used to explore the factors affecting the efficiency of BWEs as well as their interlinkages and interdependencies, based on an extensive review of scientific literature and expert intervention. The main goal is to provide a transparent and flexible model and propose a different simulation approach for complex mining systems that can interconnect the factors influencing system's behaviour. The implementation of the proposed model revealed significant differences in BWEs' efficiency under favourable and hostile conditions. This is a first step towards simulations intended to help mining practitioners, bridging the gap between 'pure' qualitative and quantitative approaches.

Analysis of the cause of the girth gear tooth fracture occurrence at the bucket wheel excavator

Abstract Premature damages and fractures of components and structures of bucket-wheel excavators at open-pit mine often occur in exploitation, caused either by inadequate design or insufficient knowledge of the material properties, welded joints and flaws in component production technology. The bucket-wheel excavator, TAKRAF SRs 2000 × 32/5.0 was employed on the excavation of barren soil for 5.000 h (a few weeks more than a year after the assembly) when the fracture of the tooth of the girth gear, which enables the circular motion of the upper structure of the bucket-wheel excavator, occurred. The gear was, according to the manufacturer’s certificate, made of the cast steel GS 40 MnCrSi3 V. The paper presents calculations of the stress variations cycles’ number for one tooth, as well as of the fracture mechanics parameters – the critical stress intensity factor and critical crack length. It was established that the fracture of the tooth occurred due to an initial crack existing in its base, which originated during the gear’s manufacturing, i.e. due to the so-called manufacturing-in defect.

Aspects relating to the reliability calculation of the cutting-teeth mounted on the bucket wheel excavators used in lignite mining

The paper deals with the calculation of the operational reliability for the cutting-teeth mounted on bucket wheel excavators used in lignite extraction in the Oltenia Basin. Based on the data recorded for three types of cutting-teeth used in production, a reliability study has been carried out which determines the main reliability indicators of the quality level of these cutting-teeth. The study compares the constructive and functional characteristics of the three types of cutting-teeth, which is the basic criterion for purchasing a certain type of cutting-tooth, as well as for the supply of spare parts.

Exploring the effect of physical, human and technical factors on bucket wheel excavators' efficiency: a fuzzy cognitive map approach

Exploring the effect of physical, human and technical factors on bucket wheel excavators' efficiency: a fuzzy cognitive map approach