Analysis of the Drive Shaft Fracture of the Conveyor Belt for Transport of Coal

The conveyor belt for slag and coal transport in the open mine pit "Kolubara" - Serbia is driven by means of two drive drums : attached on separate shafts. Each shaft is driven by two electric motors on both sides. During exploitation, the conveyor belt drive shafts are subjected to torques and transverse forces due to belt tension. The gearboxes and the bearing units on both sides of the drive drum support each shaft. A fracture of one of the drive shafts of the conveyor belt occurred at its connection point with the gearbox. The first part of the paper defines the loads relevant for shaft calculation, based on measurements in different phases of operation and the manufacturer's data. It is followed by the FEM analysis and fatigue analysis, for the most unfavourable load case. It has been established that the critical stress value has occurred near the connection point between the shaft and the gearbox, in the fracture zone. The second part of the paper presents chemical composition and mechanical properties of material, as well as metallographic examination of fracture surface. The experimental test procedure shows that the fracture has occurred not because of an error in the material but as a consequence of the inadequate heat treatment. Superposition of two negative influences: material fatigue and inadequate heat treatment, expressed in the cross section at the point of fracture is the main case of the conveyor belt shaft fracture

THE NORTH ATLANTIC OSCILLATION (NAO) AND THE WATER TEMPERATURE OF THE SAVA RIVER IN SERBIA

The data on the water temperature of the Sava in Serbia (hydrological stations Šabac and Belgrade, period 1961–2015) were used for the research, as well as the data on the surface air temperature. The temperature trends were determined and the significance (at p≤0.05 and p≤0.01) was established on the basis of the t-test. The Pearson correlation coefficient (R) was used for the calculation of the correlation. Increasing trends of the water temperature of the Sava were recorded in all cases at both stations. However, in the case of the HS Šabac, the trends for 6 months (February–April and September–November) were not statistically significant. In the case of the HS Belgrade, all the calculations (except for April) showed statistically significant increasing trends, which can be explained by anthropogenic influence. High level of correlation between the surface air temperature and the water temperature was also determined. In this research, the lowest values of R were recorded for October (0.561 for Belgrade), and on the seasonal level, for autumn (0.625 for Šabac). The research on the correlation between the water temperature of the Sava River and the NAO index showed the highest values of R for January (0.512 for HS Šabac and 0.528 for HS Belgrade). On the seasonal level, the highest values were recorded for winter (0.422 for HS Šabac and 0.432 for HS Belgrade)

Analysis of the Drive Shaft Fracture of the Conveyor Belt for Transport of Coal

The conveyor belt for slag and coal transport in the open mine pit "Kolubara" – Serbia is driven by means of two drive drums, attached on separate shafts. Each shaft is driven by two electric motors on both sides. During exploitation, the conveyor belt drive shafts are subjected to torques and transverse forces due to belt tension. The gearboxes and the bearing units on both sides of the drive drum support each shaft. A fracture of one of the drive shafts of the conveyor belt occurred at its connection point with the gearbox. The first part of the paper defines the loads relevant for shaft calculation, based on measurements in different phases of operation and the manufacturer’s data. It is followed by the FEM analysis and fatigue analysis, for the most unfavourable load case. It has been established that the critical stress value has occurred near the connection point between the shaft and the gearbox, in the fracture zone. The second part of the paper presents chemical composition and mechanical properties of material, as well as metallographic examination of fracture surface. The experimental test procedure shows that the fracture has occurred not because of an error in the material but as a consequence of the inadequate heat treatment. Superposition of two negative influences: material fatigue and inadequate heat treatment, expressed in the cross section at the point of fracture is the main case of the conveyor belt shaft fracture

Development of the mathematical model for surface topography quality determination at the end milling process

As a metal machining process, end milling is the most widely used processes in industry. One of the most important indicators of success in finishing operation is the estetic quality of the surface that is directly connected to the maximal height of uneven surfaces, namely rougness. In process of milling the quality of the machined surface depends of many factors, for example, tool geometry, cutter parallel axis offset and cutter axis tilt, tool deflection due to cutting forces, tool and work piece vibrations etc. This paper presents the development of mathematical model for the determination of the quality of the machined surface topography. The model starts from an ideal trochoid point trajectory on the cutting edge tooth end mill, and then inserts the deviations due to cutter parallel axis offset and cutter axis tilt and gives instructions for the input of other factors that influence on the machined surface quality. Also it compares the values of maximal roughness height with different mill axis positions, and on different mill cross section heights, as well as the differences at up and down milling

Planning aspects of solar parks – experience of Germany and Serbia

Solarna energija predstavlja čist, besplatan i praktično neograničen izvor energije. Tehnička i tehnološka rešenja kojima trenutno raspolažemo dovoljna su da se prikupi mnogo više elektične energije, od one koju trošimo. Solarni parkovi, odnosno fotonaponske elektrane su postrojenja namenjena za proizvodnju velike količine električne energije koja se, uglavnom, isporučuje u elektro mrežu. Za razliku od solarnih sistema koji koncentrišu sunčeve zrake, fotonaponske elektrane, pored direktnog koriste i difuzno zračenje, kao važan izvor energije za oblasti na većim geografskim širinama. Stoga, ne začuđuje činjenica da je Nemačka među prvim zemljama u svetu po proizvodnji električne energije dobijene od Sunca sa instalisanim fotonaponskim kapacitetom od 39,7 GW. Iako je potencijal globalnog zračenja u Srbiji oko 30% veći od Nemačke, ukupan fotonaponski kapacitet, od svega 10 MW, je neuporedivo manji. Troškove koje iziskuje eksploatacija solarne energije, mogu se lakše prevazići uz dobro osmišljene mere i instrumente. U ovom radu je prikazano nekoliko uspešnih projekata u Nemačkoj, poput solarnog parka Finstervalsde, koji mogu obezbediti bolju osnovu za planiranje sličnih projekata u Srbiji. Suština ovog rada je da pruži uvid u dosadašnje rezultate Srbije na polju solarne energije, kao i da odgovore na pitanja koja se tiču održivog planiranja solarnih parkova.Solar energy is a clean, free and virtually unlimited source of energy. Technical and technological solutions that are available right now are sufficient to collect much more electrical energy than we consume. Solar parks or photovoltaic power plants are facilities that produced large amounts of electricity which is mainly supplied to the electrical network. Unlike concentrated solar power systems, photovoltaic power station apart from direct radiation is using diffuse radiation, as an important source of energy for areas at higher latitudes. Therefore, it is not surprising that Germany is top-rated country in the world by production of electricity from the sun, with an installed PV capacity of 39.7 GW. Although the potential of global solar radiation in Serbia is about 30% greater than Germany, the total PV capacity of only 10 MW, is much smaller. Expenses for exploitation solar energy, can be overcome much more easier with well designed incentive measures and instruments. This paper describes some successful projects in Germany, such as a solar park Finstervalsde, which can provide a planning solution for similar projects in Serbia. The essence of this paper is to provide overview of current results of solar energy sector in Serbia, as well as to answer the questions that are related to sustainable planning solar parks

Forest fires threaten biomass production in the EU: experiences from Portugal, Spain and France impose Preventive measures for Serbia

Države Evropske unije u poslednje vreme ulažu sredstva u obnovljive izvore energije, što se posebno odnosi na šumsku biomasu. U Portugaliji, Španiji i Francuskoj se povećava broj termoelektrana i kogenerativnih CHP postrojenja za sagorevanje i gasifikaciju šumske biomase. Sagorevanjem tradicionalne biomase oslobađa se količina CO2 koja je prethodno uzeta iz atmosfere, tako da je nivo emisije gasova sa efektom staklene bašte niži u poređenju sa tradicionalnim elektranama na ugalj. U Portugaliji najveći deo šumske biomase dobija se iz borova i eukaliptusa. Pri tome, više od 50% šumske biomase je iz proreda i čišćenja kultura borova i eukaliptusa. Potrugalija, Španija i Francuska su države Evropske unije koje su posebno pogođene šumskim požarima. U periodu 1980-2014. godine zabeležen je trend porasta ukupne godišnje opožarene površine u Portugaliji, dok je u Španiji i Francuskoj konstatovan trend smanjenja. Naročito velike štete zabeležene su u Portugaliji 2003. godine, kada su požari zahvatili oko 5% teritorije ove države i kada je opožareno 280.000 hektara šuma. U ovom slučaju, problem takođe predstavlja i prisustvo lako zapaljivih vrsta drveća.The EU states have been recently investing in the funds for renewable energy sources, especially for forest biomass. In Portugal, Spain and France, the number of thermal power plants and cogenerative CHP plants for combustion and gasification of forest biomass is increasing. By combustion of traditional biomass, the amount of CO2 that has been previously taken from the atmosphere is released, so the level of greenhouse gases emission is lower in comparison with conventional coal power plants. In Portugal, the biggest part of forest biomass is obtained from the pines and eucalyptus. In addition, more than 50% of forest biomass originates from thinning and cleaning of pine and eucalyptus plantations. The EU countries especially affected by forest fires are Portugal, Spain and France. In the period 1980-2014 increasing trend of the total annual burned area was recorded in Portugal, while decreasing trend was registered in Spain and France. Particularly great damage was recorded in Portugal in 2003, when fires covered about 5% of state territory and 280,000 ha of forest were burnt. In this case, the problem is also the presence of flammable tree species

Climatic and anthropogenic impacts on forest fires in conditions of extreme fire danger on sandy soils

Forests on sandy soils are particularly vulnerable to fire. The study area in this research was Deliblatska peščara (the Deliblato Sands), one of the most endangered areas in Serbia. The linear trends, the polynomial trends and the Pearson correlation coefficient (r) were applied. Statistically significant decrease in the number of forest fires was found, while the increasing trends of the burned area and burned forest area were not significant. There was also an increase in the air temperature during the same period. In a study of the connection between forest fires and the Atlantic Multidecadal Oscillation (AMO), significant values of r were statistically observed only for the annual number of fires. The highest values were recorded for June (-0.373) and July (-0.375), and for summer r = -0.374 (statistically significant at p ≤ .01). As for the AMO in the main fire season (February-August), r = -0.331 (statistically significant at p ≤ .01). In settlements in Deliblatska peščara area, there were trends of the decreasing number of inhabitants, agricultural population, and agricultural households in the investigated period. These trends contribute to the reduction of fire risk. The r value between the dynamics of the number of fires and the population is .50 (statistically significant at p ≤ .01). The reduced agricultural activity contributes to the reduction of fire risk, while increased tourist presence is a risk factor

Comparative phenotypic and metabolic analysis of Helianthus species for improve stress resilience

The species of the genus Helianthus have very broad spectrum of life forms since they occupy diverse habitats. Cosmopolitan distribution of these species could be explained by a number of anatomical and physiological mechanisms that create the basis for survival of the plants in a wide variety of habitats. At the Institute of Field and Vegetable Crops (IFVCNS), Novi Sad, there is one of the largest collection of annual and perennial sunflower species, interspecific hybrids, sunflower varieties, lines and hybrids worldwide (http://www.nsseme.com/about/inc/oilcrops/wild.php). This collection has been actively used in breeding as a source of disease resistance and abiotic stress resistance genes. Within the framework of ongoing projects, we have started to perform comparative phenotypic and metabolic analysis of genotypes chosen from IFVCNS collection in order to identify morphological and metabolic parameters of various plant organs that could be useful tools for detection of genotypes tolerant to different environmental stresses. This will be further complemented by molecular analyses for identification of QTLs correlated to abiotic and biotic stresses. The final aim of this combined approach to stress resilience study in sunflowers is to identify genotypes with desirable traits that could be further included in sunflower breeding programs and creation of highly productive stress resistant hybrids, as well as to create an ideotype specific for certain agro-ecological conditions