An analysis of random mechanical failures of bucket wheel excavator

In this article random mechanical failures of bucket wheel excavator at open cast mine "Tamnava Zapad" are analysed. Random mechanical failures of mining equipment may represent an important factor in coal production because these types of failures occur unpredictably. Some of the reasons for the occurrence of such failures are unde-tectable defects, unexplainable causes, and unavoidable failures. In addition, here we have failure of equipment that has a large investment and productivity value. Statistical regularity of the component failure distribution of this system is analysed based on dispatcher's reports about EBS system failures in the period 2003-2011. The proposed distribution is analysed by theoretically, using suitable tests. By using statistical distribution we get the expected uptime of the bucket wheel excavator, for each year, which represents an important factor in maintenance programs and periodic inspections/repairs on bucket wheel excavator and mining components, in general

The Reliability of Bucket Wheel Excavator - Review of Random Mechanical Failures

Statistical regularity of random mechanical failures of the bucket wheel excavator will be considered based on dispatcher’s reports about excavator-conveyors-spreader (ECS-III) on the Tamnava - West Field Open Cast Mine in Lazarevac (Serbia) system failures in the period from 2003 to 2011. This kind of failures happens suddenly due to undetectable defects, unexplainable causes, and unavoidable failures. Reliability functions R(t), failure rate λ(t) and failure density f(t) of the bucket wheel excavator will be empirically determined. It was concluded that the random failures could be well approximated by the Exponential distribution. Below, serial reliability configuration of the BWE subsystem was analysed and the failure frequency as well as the values of the failure rate by subsystems were determined. Finally, proactive maintenance approach, which represents the latest innovation in the field of maintenance, will be presented. This approach to maintenance utilizes various technologies in order to achieve extension of operational life and elimination of reactive maintenance

An analysis of random mechanical failures of bucket wheel excavator

In this article random mechanical failures of bucket wheel excavator at open cast mine "Tamnava Zapad" are analysed. Random mechanical failures of mining equipment may represent an important factor in coal production because these types of failures occur unpredictably. Some of the reasons for the occurrence of such failures are unde-tectable defects, unexplainable causes, and unavoidable failures. In addition, here we have failure of equipment that has a large investment and productivity value. Statistical regularity of the component failure distribution of this system is analysed based on dispatcher's reports about EBS system failures in the period 2003-2011. The proposed distribution is analysed by theoretically, using suitable tests. By using statistical distribution we get the expected uptime of the bucket wheel excavator, for each year, which represents an important factor in maintenance programs and periodic inspections/repairs on bucket wheel excavator and mining components, in general

Životna proizvodnja visokomlečnih krava

Lifetime milk production is a key success factor in fulfilling the production potential of high-yielding cows. Lifetime milk production traits are pronouncedly variable. The life expectancy and the length of productive life of dairy cows are repeatedly limiting factors for improving lifetime milk production. Lifetime milk production is greatly depended on age at first calving and the number of lactations during productive life. Previous researches have implied there are real chances for improving the lifetime milk production of high-yielding cows. The goal of this research was to investigate the significance of key systematic factors on the lifetime production of high-yielding Black-and-White cows. The animals included in the sample had different share of Holstein genes. The researchers determined systematic factors that caused some significant phenotypic variations of the investigated trait. The average lifetime milk production was 25,002.66±7,755.39 kg. When observed by cow genotypes, the mean values of the lifetime milk production varied from 27,061.37 kg ( (lt) 58% HF) and 24,761.26 kg (58-73% HF) to 23,185.36 kg (>73% HF). The differences in lifetime milk production determined among the animals were due to a highly significant (p≤0.01) impact of the bulls - the sires of the cows and the year of culling; the impact of the class of HF genes was significant (p≤0.05), whereas the impact of the reason for culling was non-significant (p>0.05).Osobine životne proizvodnje visokomlečnih krava imaju veliki ekonomski značaj. Crno-bela goveda imaju značajan genetski potencijal za proizvodnju mleka. Visokoproizvodne krave crno-bele rase izložene su tokom produktivnog veka velikom broju složenih uticaja koji intenzivno deluju na nivo relizacije njihovog genetskog potencijala. Uslovi sredine često nisu u saglasnosti sa potrebama ove visokomlečne rase goveda. Povećanjem učešća gena holštajn-frizijske rase, tokom procesa oplemenjivanja evropskog tipa crno-belih goveda, došlo je do povećanja prinosa mleka. Dosadašnja istraživanja ukazuju na mogućnost za značajnije povećanje životne produktivnosti crno-belih krava. Poznavanje broja i nivoa uticaja faktora sredine, na životnu proizvodnju visokomlečnih krava, važno je zbog njihovog uključivanja u model. U skladu sa značajem pojedinih sistematskih faktora u okviru istraživanja je obavljena njihova objektivna procena. Cilj rada je bio da se primenom odgovarajuće metodologije ispita značajnost razlika, u ostvarenoj životnoj proizvodnji mleka kod visokoproizvodnih crno-belih krava, preko najvažnijih sistematskih uticaja. Prosečna životna proizvodnja mleka iznosila je 25002.66±7755.39 kg litara. Posmatrano po genotipovima krava prosečne vrednosti životne proizvodnje mleka iznosile su 27061.37 kg ( (lt) 58% HF), 24761.26 kg (58-73% HF) i 23185.36 kg (> 73% HF). Utvrđene razlike između grla u pogledu ostvarenog nivoa životne proizvodnje mleka nastale su kao posledica visoko značajnog uticaja (P≤0.01) bikova-očeva krava i godine izlučenja krava, klasa HF gena krava imala je značajan uticaj (p≤0.05), dok razlog izlučenja nije imao značajan uticaj (P>0.05)

Uticaj energetskog dodatka u ishrani na koncentraciju tireoidnih hormona, insulinu sličnog faktora rasta-i i njegovih vezujućih proteina u krvi krava tokom rane laktacije

The objective of this study was to examine the effect of dietary energy supplementation on hormones that are considered to be the main signals of a shift in energy balance around parturition. Sixty dry cows, 15 days before calving, were chosen and divided into two eaqual groups: control and experimental (GLY). Both groups were fed a standard ration balanced in accordance to the stage of the productive reproductive cycle. Additionally, each cow in the GLY group was given glycerol based dietary energy supplementation (250 mL daily during the dry and 300 mL daily during the lactation period), which provided additional 9.30 MJ NEL during the dry and 13.95 MJ NEL during the early lactation period. Milk production was measured on days 30 and 60 of lactation and milk production was significantly higher in GLY compared to control group at day 60 of lactation (p lt 0.05). Service period and insemination index were used as reproductive outcome parameters. Average service period in the control group was significantly longer than in the GLY group (p lt 0.05). Average insemination index in the control group was not significantly different than the index obtained for the GLY group. Blood samples were taken before the begining of the experiment (15 days before parturition), and at days 7, 30 and 60 of lactation. Concentrations of thyroid hormones, IGF-I, relative abundance of IGFBP-2, IGFBP-3 and IGFBP-4, concentrations of total protein and albumin in the blood were measured. Results showed that at days 7 and 30 after parturition, T4 concentrations were significantly higher (p lt 0.001, respectively) in GLY than in the control group, while T3 concentrations were significantly higher in GLY group only at day 7 after parturition (p lt 0.001). IGF-I concentrations and IGFBP-3 abundance were significantly higher in the GLY compared to the control group in all three examined postpartum periods. IGFBP-2 and IGFBP-4 concentrations were higher in GLY compared to the control group in all three examined postpartum periods, but the difference was significant only on day 60 after parturition (p lt 0.01, respectively). Concentrations of total protein and albumin were significantly higher in GLY compared to the control group in all three examined periods after parturition. Based on these results it can be concluded that peripartum dietary energy supplementation prevent cows' exposure to severe negative energy balance, preserves synthetic activity of hepatocytes and consequently has a positive impact on milk production and reproductive performances in dairy cows.Cilj ovog rada je bio da se ispita uticaj energetskog dodatka u ishrani krava na koncentraciju hormona u krvi koji su u periodu oko teljenja glavni pokazatelji promena u energetskom statusu. U tu svrhu, petnaest dana pre teljenja odabrano je 60 krava koje su podeljene u dve jednake grupe: kontrolnu i oglednu (GLY). Obe grupe krava su dobijale identičan obrok usklađen sa proizvodno reproduktivnim ciklusom. Dodatno, kravama GLY grupe je tokom poslednje dve nedelje zasušenja i do 60. dana laktacije dodavan energetski dodatak na bazi glicerola (250 mL dnevno tokom zasušenja odnosno 300 mL nakon teljenja), obezbeđujući dodatnih 9,30 MJ NEL tokom zasušenja, odnosno 13,95 MJ NEL tokom rane laktacije. Kod svih krava je izmerena prosečna dnevna proizvodnja mleka 30. i 60. dana lakatcije, koja je kod GLY grupe bila značajno viša 60. dana (p lt 0,05). Kao pokazatelji reproduktivnog statusa koriščeni su servis period i indeks osemenjavanja. Servis period je bio značajno duži kod kontrolne u odnosu na GLY grupu (p lt 0,05), a vrednost indeksa osemenjavanja se nije značajno razlikovala između grupa. Uzorci krvi krava uzeti su neposredno pre početka ogleda, odnosno 15 dana pre teljenja, kao i 7, 30. i 60. dana laktacije i u njima je određivana koncentracija tireoidnih hormona, IGF-I, relativna zastupljenost IGFBP-2, IGFBP-3 i IGFBP-4, koncentracija ukupnih proteina i albumina. Rezultati su ukazali da je 7. i 30. dana nakon teljenja GLY grupa imala značajno višu koncentraciju T4 (p lt 0,001, pojedinačno) u odnosu na kontrolu, dok je koncentarcija T3 bila značajno viša kod GLY grupe 7. dana nakon teljenja (p lt 0,001). Koncentracija IGF-I i zastupljenost IGFBP-3 je bila značajno viša u krvi krava GLY grupe u odnosu na kontrolu u sva tri ispitivana perioda posle teljenja. Zastupljenost IGFBP-2 i IGFBP-4 je bila viša u krvi krava GLY u odnosu na kontrolnu grupu u sva tri ispitivana perioda postapartalno ali je ova razlika bila značajna jedino 60. dana lakatcije (p lt 0.01, pojedinačno). Koncentracija ukupnih proteina i albumina je, takođe, bila značajno viša u krvi krava GLY grupe u odnosu na kontrolnu grupu u sva tri ispitivana perioda posle teljenja. Na osnovu dobijenih rezultata može se zaključiti da energetski dodatak u ishrani sprečava izloženost krava izrazitom negativnom energetskom bilansu, održava sintetsku funkciju hepatocita i posledično ima pozitivan uticaj na mlečnost i reproduktivne pokazatelje

Uticaj genetskih i negenetskih faktora na proizvodne osobine krava simentalske rase

This study covered 737 controlled first calving Simmental cows with, lactations concluded within one year. All first calving animals were on the farms of individual farmers in the municipalities of Kragujevac and Mladenovac. The research included the influence of bull sires, year and season of calving on milk yield and fertility. Least squares method was used to determine the average duration of lactation of 323.74 days. For a period of 305 days, heifers produced 3701.67 kg of milk, or 3644.58 kg of 4% FCM. The average production of milk fat was 144.26 kg and milk fat content was 3.88%. The interval from calving to first insemination lasted in average 124.19 days, and the animals were first calved at the age of 789.95 days. The bull sires had a highly significant effect (P (lt) 0.01) on the duration of lactation, milk yield and 4% FCM, milk fat yield and content and age of cows at first calving. The duration of service period was not under significant effect (P>0.05) of bull sires. Year of calving had a significant effect (P (lt) 0.01) on the duration of lactation, production of milk, milk fat and 4% FCM. Milk fat content, service period and age at first calving did not show significant variation due to the impact of different years of calving (P>0.05). Season of calving of cows demonstrated highly significant effect (P (lt) 0.01) on the production of milk and 4% FCM, and significant (P>0.05) on the production of milk fat, however it had no effect (P>0.05) on the milk fat content, duration of lactation and service period and age at calving.Ovim istraživanjem je obuhvaćeno 737 kontrolisanih prvotelki simentalske rase, sa laktacijama zaključenim u toku jedne godine. Sve prvotelke su se nalazile na imanjima individualnih poljoprivrednih proizvođača. Istraživanja su obuhvatila uticaj bikova očeva, godine i sezone telenja na osobine mlečnosti i plodnosti. Metodom najmanjih kvadrata ustanovljeno je prosečno trajanje laktacije od 323,74 dana. Za vremenski period od 305 dana prvotelke su proizvele 3.701,67 kg mleka, odnosno, korigovano na 4%MKM 3.644,58 kg. Prosečna proizvodnja mlečne masti iznosila je 144,26 kg a sadržaj mlečne masti 3,88%. Interval od telenja do prve inseminacije trajao je u proseku 124,19 dana, a grla su se prvi put telila u uzrastu od 789,95 dana. Bikovi-očevi su imali visoko signifikantan uticaj (P (lt) 0,01) na trajanje laktacije, prinos mleka i 4%MKM, proizvodnju i sadržaj mlečne masti i uzrast krava pri prvom telenju. Na dužinu servis perioda bikovi-očevi nisu ispoljili značajnije dejstvo (P>0,05). Godina telenja imala je visoko značajan uticaj (P (lt) 0,01) na trajanje laktacije, proizvodnju mleka, mlečne masti i 4%MKM. Sadržaj mlečne masti, trajanje servis perioda i uzrast pri prvom telenju nisu pokazali značajnija variranja usled uticaja različitih godina telenja (P>0,05). Sezona telenja krava je visoko značajno uticala (P (lt) 0,01) na proizvodnju mleka i 4%MKM, značajno (P>0,05) na proizvodnju mlečne masti, a na sadržaj mlečne masti, trajanje laktacije i servis perioda, uzrast pri telenju nije imala značajnijeg uticaja (P>0,05)

Sorption of Cu2+ and Co2+ from aqueous solutions onto sepiolite: an equilibrium, kinetic and thermodynamic study

The efficiency of natural sepiolite for the removal of Cu2+ and Co2+ from aqueous solution was determined using the batch method. The sorption experiments were performed as a function of the initial metal concentration, the equilibration time and temperature. Thermodynamic parameters, such as enthalpy, free energy and entropy, were calculated from the temperature dependent sorption isotherms and these values showed that the sorption of the investigated metals onto sepiolite was endothermic. The pseudo-second order kinetic model provides the best correlation of the experimental kinetic data

Growth of common beech (Fagus sylvatica L.) saplings under the impact of suboptimal mineral nutrition

U ovome radu prikazani su rezultati rasta bukovih sadnica pod utjecajem suboptimalne ishrane s dušikom (N), fosforom (P), magnezijem (Mg) i željezom (Fe). Cilj rada bio je približiti ovu problematiku šumarskoj praksi kroz raspravu dobivenih rezultata u kontekstu dosadašnjih spoznaja o rastu biljaka pod utjecajem suboptimalne ishrane s mineralnim hranivima. U rano proljeće 2019. godine 30 bukovih jedinki u razvojnom stadiju ponika, porijeklom iz jedne prirodne mješovite sastojine hrasta kitnjaka i obične bukve, presađeno je u sterilni supstrat (agroperlit). Nakon presadnje tijekom sljedeće tri godine po šest presađenih biljaka redovito je zalijevano (tretirano) s kompletnom hranjivom otopinom (KO tretman), odnosno hranivim otopinama u kojima su izostavljeni dušik (-N tretman), fosfor (-P tretman), magnezij (-Mg tretman) ili željezo (-Fe tretman). Prema tomu, na šest biljaka unutar svakog od pet prethodno opisanih tretmana bilježeni su početak i trajanje razvoja lišća (2020. i 2021. godine), broj listova te prosječna i ukupna površina lišća (2019., 2020. i 2021. godina). Promjer stabljike na vratu korijena i visina stabljike mjereni su u proljeće 2019. i jesen 2021. godine, na temelju čega je izračunat debjinski i visinski prirast bukovih sadnica, te njihova vitkost na početku i na kraju pokusa. Uz to, tretiranim sadnicama utvrđena je masa suhe tvari lišća, stabljike i korijenja te ukupna dužina krupnog i sitnog korijenja, kao i broj račvanja i vrhova sitnog korijenja, što je obavljeno u jesen 2021. godine nakon njihova vađenja iz agroperlita. Na temelju usporedbe dobivenih rezultata između biljaka u kontrolnom i ostalim tretmanima bilo je moguće zaključiti da je pod utjecajem suboptimalne ishrane bukovih sadnica s P došlo je do odgode proljetnog otvaranja pupova i početka razvoja lišća. Najsporiji razvoj lišća zabilježen je pod utjecajem suboptimalne ishranjenosti s N i Mg. Prosječna površina lišća nije bila značajnije utjecana suboptimalnom ishranjenošću niti s jednim hranivom. Smanjenje broja listova i njihove ukupne površine pod utjecajem suboptimalne ishranjenosti sa svim hranivima zabilježeno je tek u posljednjoj godini provedbe pokusa. Debljinski i visinski prirast stabljike također su bili negativno utjecani suboptimalnom ishranjenošću sa svim hranivima, a smanjena vitkosti sadnica zabilježena je samo pod utjecajem suboptimalne ishranjenosti s Fe. Ukupna, duljina krupnog i sitnog korijenja također je bila negativno utjecana suboptimalnom ishranjenošću sa svim hranivima, izuzev N. Pod utjecajem suboptimalne ishranjenosti s N došlo je do povećanja ukupne dužine sitnoga korijenja, kao i do povećanja broja račvanja i vrhova sitnog korijenja. Unatoč tomu, na masu suhe tvari krupnog i sitnog korijenja suboptimalna ishranjenost sa svim hranivima imala je negativan utjecaj, uključujući i N.This paper presents the results of beech seedling growth under the influence of suboptimal nutrition with nitrogen (N), phosphorus (P), magnesium (Mg) and iron (Fe). The aim of the paper was to bring this issue closer to forestry practice through the discussion of the obtained results in the context of current knowledge on plant growth under the influence of suboptimal nutrition with mineral nutrients. In the early spring of 2019 year, 30 beech seedlings originating from one natural mixed stand of sessile oak and common beech were transplanted into a sterile substrate (agroperlite). After transplanting, over the next three years six transplanted plants for each treatment were regularly watered (treated) with a complete nutrient solution (KO treatment), or nutrient solutions in which nitrogen (-N treatment), phosphorus (-P treatment), magnesium (-Mg treatment) or iron (-Fe treatment) was omitted. Therefore, the beginning and duration of leaf development (2020 and 2021), the number of leaves and the average and total leaf area (2019, 2020 and 2021) were recorded on six plants within each of the five previously described treatments. The root collar diameter and the height of the stem were measured in spring 2019 and autumn 2021, based on which the diameter and height increment of beech seedlings and their slenderness at the beginning and end of the experiment were calculated. In addition, on the treated saplings we determined the dry mass of leaves, stems and roots, and the total length of coarse and fine roots as well as the number of forks and tips of fine roots, which was done in autumn 2021 after their removal from agroperlite. Based on the comparison of the obtained results between the plants in the control and other treatments, it was possible to conclude the following. Under the impact of suboptimal nutrition of beech saplings with P there was a delay in spring bud burst and the beginning of leaf development. The slowest leaf development was observed under the impact of suboptimal nutrition with N and Mg. The average leaf area was not significantly affected by suboptimal nutrition with any nutrient. The decrease in the number of leaves and their total area under the impact of suboptimal nutrition with all nutrients was recorded only in the last year of the experiment. Stem diameter and height increments were also negatively affected by suboptimal nutrition with all nutrients, and reduced saplings slenderness was observed only under the impact of suboptimal Fe nutrition. The total length of coarse and fine roots was also negatively affected by suboptimal nutrition with all nutrients except N. Under the impact of suboptimal N nutrition, there was an increase in the total length of the fine roots as well as an increase in the number of forks and tips of the fine roots. Nevertheless, suboptimal nutrition with all nutrients had a negative effect on the dry mass of coarse and fine roots, including N

Lifetime production of high-yielding dairy cows

Lifetime milk production is a key success factor in fulfilling the production potential of high-yielding cows. Lifetime milk production traits are pronouncedly variable. The life expectancy and the length of productive life of dairy cows are repeatedly limiting factors for improving lifetime milk production. Lifetime milk production is greatly depended on age at first calving and the number of lactations during productive life. Previous researches have implied there are real chances for improving the lifetime milk production of high-yielding cows. The goal of this research was to investigate the significance of key systematic factors on the lifetime production of high-yielding Black-and-White cows. The animals included in the sample had different share of Holstein genes. The researchers determined systematic factors that caused some significant phenotypic variations of the investigated trait. The average lifetime milk production was 25,002.66±7,755.39 kg. When observed by cow genotypes, the mean values of the lifetime milk production varied from 27,061.37 kg (73% HF). The differences in lifetime milk production determined among the animals were due to a highly significant (p≤0.01) impact of the bulls - the sires of the cows and the year of culling; the impact of the class of HF genes was significant (p≤0.05), whereas the impact of the reason for culling was non-significant (p>0.05)

Housing conditions and welfare of dairy cows in Serbia

Research conducted on 16 dairy farms in Serbia has shown that poor housing conditions represent one of the major dairy cows’ welfare problem in our country. This is also an area of animal welfare in which the greatest difference in relation to the situation in EU countries can be observed. Poor comfort conditions are estimated based on a high share of cows that lie outside their lying area (36.5%) as a consequence of inadequate or insufficient size of lying areas. Investigated the farms showed a very poor state of hygiene of dairy cows, with a high percentage of cows with the contaminated lower parts of the legs (84.6%), rump (71.3%) and udder (60.0%), which indicates the inadequate hygiene of lying areas and facilities, insufficient amount of bedding but also disorders of rumen digestion. The biggest welfare problems are present on farms with tied system, also the presence of grazing in our conditions, unlike the EU, is also insufficient from the standpoint of ensuring the welfare of dairy cows