The bucket wheel boom tie-rods are vital structural parts of the bucket wheel excavators (BWE). Their failures inevitably cause BWE collapse and are followed, among other things, by a substantial ...financial loss (millions of €). Non-destructive testing revealed a flaw in the butt welded joint of the body and eye-plate of the bucket wheel tie-rod. Its size exceeds the level allowed by current technical regulations. An integrity assessment of the bucket wheel tie-rod has been carried out, i.e. the remaining fatigue life has been determined based on the stress-state characteristics in the welded joint and defined by experimental research in real working conditions. The calculation results show that despite the excessive size of the internal flaw the welded joint integrity is not compromised. During periodical inspections of the welded joint in the past two years (BWE was put into operation in December 2007) changes that could compromise the structural integrity were not observed. In this way, by using a “fail-safe” philosophy design, a considerable financial saving (ca. 1,600,000 €) was achieved while at the same time there was no threat to the worker’s safety and life, the safety of the machine and the production process in the open pit mine.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Tie-rods are vital parts of the bucket wheel excavator slewing superstructure.•Experimental and numerical investigations are carried out on the eyebar model.•Plastification occurs across the full ...width of the cross-section near the hole.•DIN yields the results much lower than the actual stress values around the opening.•Nevertheless, DIN criterion is sufficient for the preservation of the eye integrity.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We discuss dynamic system performance evaluation in the river port utilizing queuing models with batch arrivals. The general models of the system are developed. This system is modelled by MX/M/n/m ...queue with finite waiting areas and identical and independent cargo-handling capacities. The models are considered with whole and part batch acceptance (or whole and part batch rejections) and the interarrival and service times are exponentially distributed. Results related to the batch blocking probability and the blocking probability of an arbitrary vessel in nonstationary and stationary states have been obtained. Numerical results and computational experiments are reported to evaluate the efficiency of the models for the real system.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
A cradle-to-gate LCA analysis of a small belt conveyor was conducted. Manufacturing stage was analysed from the aspects of environmental impacts and energy consumption. The biggest environmental ...impact in majority of baseline impact categories is obtained from low-alloyed steel production and electricity consumption during the manufacturing stage, followed by impact of the transport. Ways for possible energy savings regarding manufacturing practice and technologies were proposed later on.
Intermodal freight transportation refers to a multi-modal chain of container-transportation services which usually links the initial shipper to the final consignee of the container (door-to-door ...service) and takes place over long distances. Container transportation is a major component of intermodal transportation and international commerce. Container flow should be optimal to ensure proper resource utilization and profitability to players. Various multi-objective evolutionary algorithms have been developed to efficiently solve optimization problems in container flows. This paper presents a short review of optimization problems in intermodal transport using sea and land legs together regarding three mostly observed objectives (transport cost, transit time and CO2 emissions).
The last decade brought the blooming of the shuttle-based automated storage and retrieval system (SBS/RS) in many industrial applications. They proved the superiority over the mini-load automated ...storage and retrieval system mainly due to higher throughput capacity, high flexibility of future extension, much better energy efficiency resulting from lower energy consumption and high energy regeneration capability. A comprehensive literature review on SBS/RS given in the paper pointed out main specifics and crucial approximations and assumptions of the developed system performance estimation models or control strategies, as well as the main conclusions resulting from the obtained results. Presented modeling approaches could be a valuable tool for SBS/RS designers and other related decision makers to estimate the system efficiency in the starting phase of SBS/RS design activities.
With the efficient influence on making an adequate and prompt managing decision it is possible to improve operation of any system. This study presents one of the possible ways of exerting influence ...on the information and material flow so that the management could make optimal decisions in the system of parts regeneration which exists in a multilevel system of supplying the spare parts. The optimization process consists of generating functional variants in the system of supply with regenerated parts, then determining the values of characteristics of these variants and forming the model of multi-criteria decision making. Flow variants were determined by using modelling and simulation and the method of multiple attribute decision (Analytic Hierarchy Processes-AHP in this case). Variants were analyzed and after that, some conclusions were adopted. This is an example of how it is possible to make right decisions with the purpose of getting the user's satisfaction and on the other hand also reducing the costs within the system, direct or indirect ones.Original Abstract: Efikasnim utjecajem na donosenje odgovarajucih i blagovremenih upravljackih odluka moguce je unaprijediti funkcioniranje bilo kojeg sustava. Ovaj rad predstavlja jedan od mogucih nacina utjecaja na tokove informacija i materijala kako bi uprava mogla donijeti optimalne odluke u sustavu regeneracije dijelova koji postoji u viserazinskom sustavu snabdijevanja rezervnim dijelovima. U postupku optimizacije navednih tokova utvrduju se moguce varijante funkcioniranja sistema snabdijevanja regeneriranim dijelovima, zatim se odreduju vrijednosti karakteristika funkcioniranja tih varijanti i formira se model visekriterijskog odlucivanja. Varijante tokova u sustavu odredene su primjenom modeliranja i simulacije, a odabranom metodom operacijskih istrazivanja analizirane su, u ovom slucaju metodom viseatributnog odlucivanja (AHP metoda), nakon cega su usvojeni zakljucci. Na ovaj nacin mogu se donositi prave odluke u cilju zadovoljenja korisnika, a na drugoj strani takoder i smanjenje troskova u sustavu, bilo direktnih ili indirektnih.
► Concept of leaning and badly shaped junctions were the cause of cracks appearance. ► The intuitive attempt to reinforce the girders was unsuccessful. ► The solution to the problem was found in the ...redesign of the junctions. ► After the presented reconstruction no damages of the structure were observed.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Stacker ARs 2000 presents the final link in the system for continuous overburden removal in the open pit mine “Kostolac” – Serbia. Its superstructure leans on three crawlers of the same length, width ...and height. During the stacker's travel from the erection site to the open pit mine, three crawler chain links fractured, presenting an indication of the problems that were to occur during exploitation. In fact, after only 1000 working hours (about three months), 30 chain links sustained fractures resulting in direct and indirect costs due to the downtime that substantially diminished the effects of the overburden removal system. The goal of the study presented in the paper was to diagnose the cause of chain link breakdown occurrence. Working stresses in the chain link are defined by applying FEM. Experimental investigations define the chemical composition, the tensile properties, the impact toughness and the macro and microhardness. Metallographic examinations are conducted additionally. Based on the results of the numerical-experimental analysis, it can be concluded that chain link breakdown is predominantly caused by (a) substantial deviation of the mechanical properties of the material with respect to those prescribed by the standard and (b) the existence of macro and microcracks in the material structure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Failures of the cranes’ structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or ...crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (xl425C) counterjib. The crane is used for assembly works at the hydropower dam. The counterjib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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