The Effect of Body Mass on Physiological Indicators in the Performance of Forestry Workers

The paper presents the results of research into the effects of body mass (BM) on basic physiological indicators of work capability among forestry workers. The indicators included the maximum theoretical heart rate, the maximum heart rate in exertion tests, and the basal energy expenditure. The effects of the deviation of the actual from the ideal BM values were analysed on a sample of 8 workers. The variables included age, body height and mass. These were used to determine the maximum theoretical heart rate. The maximum heart rate was determined in an ergonomic laboratory in a programmed exertion test on a treadmill. Using standard formulae in work physiology, values of work capability indicators were calculated for the actual and ideal BM of each worker. The results, embracing individual and summary values and their absolute and relative ratios, showed that workers exceeded their ideal BM by an average of 9.9 kg. In all workers, the maximum theoretical heart rate was higher than that achieved in the exertion test. It was also found that even significant deviations of the ideal from the actual BM (the actual BM was more than 20% higher than the ideal BM) did not have any considerable effects on the maximum theoretical heart rate. The analysis of oxygen consumption showed that in relation to physical capability of the ideal BM and the maximal theoretical heart rate, physical capability of each worker was lower by an average of 11.5%. The highest reduction of physical capability was found in those workers with the least favourable ratio between the theoretical and the maximal tested heart rate. It was concluded that on average, the basal energy expenditure in each worker was higher by 7.45% due to the deviation of the actual from the ideal BM. At constant values of other factors, this means an equivalently lower capacity for daily physical performance

Vibracije prenesene na ruke rukovatelja orbitalnim ručnim brusilicama

The paper reports and analyses results of vibration measurement carried out on orbital hand sanding machines. Vibrations were measured on the front and rear handles of the FESTO LRB-W1 and LRB-T1 orbital hand sanding machines and at two points on the holding handle of the FESTO RTL-F1 hand sanding machine. The measured levels of the weighted vibration accelerations were compared to the daily exposure limits according to ISO 5349, ISO/TC 108/SC4/14 and NF E90-402. Daily exposures for each type of sanding machine were determined according to the same standards.Pneumatskim orbitalnim brusilicama, koje se upotrebljavaju u završnoj obradi drva i pri obradi zavarenih spojeva te drugih metalnih površina, na ruke rukovatelja prenose se vibracije. S obzirom na opasnost da se pri rukovanju takvim brusilicama pojave teza oštećenja rukovateljeva organizma istraživane su razine vibracija kojima su rukovatelji izloženi. Mjerenja su obavljena na tri tipa brusilica koje se najčešće rabe za završnu obradu drva: FESTO LRB-W1, FESTO LRB-T1 i FESTO RTL-F1. Mjerenje vibracija na ručkama orbitalnih brusilica obavljeno je u skladu s normom ISO 5349 u normalnim radnim uvjetima. Analiza rezultata mjerenja provedena je u laboratoriju. Mjerenja su obavljena istodobno u sve tri koordinatne osi. Smjer osi, i u skladu s njim položaj akcelerometra, izabran je prema uputama u ISO 5349. Za sve tri osi izračunana je vrednovana vrijednost ubrzanja vibracije. Na osnovi tih vrijednosti izračunan je rezultatni vektor vrednovanih ubrzanja (WAS). Za svaku OS napravljena je i tercna analiza, a rezultati su grafički prikazani. Mjerenja su pokazala da ce 10% rukovatelja brusilicom LRB-W1 zadobiti trajna oštećenja već nakon pet godina rada. Rukovatelji brusilicom tipa RTL-F1 imat će iste probleme za manje od dvije godine rada. Iz rezultata mjerenja se vidi da izmjerena razina vrednovanih ubrzanja vibracija dopušta maksimalno dnevno izlaganje od samo 0.5 sati. Stoga treba organizacijom posla (češćim zamjenama rukovatelja) omogućiti zaštitu rukovatelja i osigurati potrebnu učinkovitost čitavoga proizvodnog sustava

CAN BIOMASS TRIGGER AN ENERGY-WISE TRANSITION IN CROATIA AND REST OF SOUTHEASTERN EUROPE?

Šumska biomasa predstavlja važan izvor energije, čijem bi se korištenju u budućnosti trebalo posvetiti znatno više pozornosti. Biomasa u svojim tradicionalnim oblicima je i dalje vrlo važan izvor energije u većini zemalje Jugoistočne Europe, te će u doglednoj budućnosti i dalje biti tako. Međutim, sve se više koristi ne samo za proizvodnju toplinske energije, već za proizvodnju električne i rashladne energije, i to se smatra kao važan dio energijske tranzicije koja je obećavajući model s visokim ekonomskim i ekološkim prednostima. Korištenje energije biomase pruža znatne mogućnosti za otvaranje novih radnih mjesta, te tako može imati znatan pozitivan utjecaj na lokalno i nacionalno gospodarstvo. U radu se opisuje trenutnu fazu energijske tranzicije u zemljama jugoistočne Europe ti ulogu šumske biomase u njegovoj provedbi. Analizirani su primjeri i događanja u Albaniji, Bosni i Hercegovini, Hrvatskoj, Makedoniji, Kosovu i Srbiji. Uporaba biomase kao energenta u ruralnim područjim, potiče stvaranje dodatnih prihoda, povećava proizvodnost te omogućava otvaranje malih seoskih poduzeća. Iz makroekonomske perspektiv, uporaba biomase doprinosi svim bitnim elementima razvoja zemalja jugoistočne Europe.Ključni pokretači, kao i prepreke na koje se može naići pri energijskoj tranziciji u jedinicama lokalne samouprave, mogu se strukturirati kao; poticaj iz potencijala, poticaj od tržišta korištenje trgovačkih i poslovnih veza, biti prvi ili lokalni ponos, zadržati novac kod kuće.U radu je prepoznat velii broj potencijalnih skupina prepreka za korištenje šumske biomase; gospodarska ograničenja, financijska ograničenja kao ozbiljna prepreka za mnoge lokalne samouprave, društvena ograničenja, ograničenja u ljudskim resursima, ograničenja zbog transparentnosti te na kraju tehnička ograničenja.Through the history of mankind, until the mid-19th century, biomass, particularly wood, represented the most important source of energy. In many countries of Europe, the awareness of the importance of forest biomass as fuel has been closely connected to the general understanding and the realization of own and world energetic situation. Forest biomass represents an important source of energy, whose use should be paid more attention to in the future. In its traditional forms, biomass is still a very significant source of energy in most countries of the southeast Europe and it will continue to be so in the near future. However, it is more and more used not just for thermal energy production, but also for the production of electric and cooling energy which is considered as an important part of the energetic transition which is a promising model with high economic and ecological advantages. The use of biomass energy offers significant possibilities for opening new jobs, thus having a significant positive impact on the local and national economy. This paper describes the present stage of the energetic transition in the south-eastern European countries and the role of forest biomass in its implementation. Examples and events in Albania, Bosnia and Herzegovina, Croatia, Macedonia, Kosovo and Serbia are analysed. Rural development projects as well as the use of bioenergy biomass has a great potential for income generation, increase of productivity and opening of small village companies. From the macroeconomic perspective, the use of biomass contributes to all the important elements in the development of the south-eastern European countries.Key drivers as well as the obstacles which can be encountered in the energetic transition in local government units can be structured as follows; potential stimulus, refers to the most south-eastern European countries regarding their significant afforestation and forest biomass potential, market stimulus due to cost-effective accessible plants and equipment for biomass, as well as the adequate support of manufacturing firms, the use of commercial and business connections: where most of biomass trades among the south-eastern European countries and EU is carried out in integration with the forest product trade, to be first or the local pride, is an important driver in the south-eastern European countries to keep money at home is another important link with the positive perception in the use of the forest biomass. The paper recognised a significant number of potential groups of obstacles for using the forest biomass; economic limitations more favourable price of the forest biomass energy in relation to fossil fuels, financial limitations as a serious obstacle for each form of the renewable energy, social limitations are very specific for each form of the renewable energy, human resource limitations since most local governments do not have sufficient human potential, limitations due to transparency are a very frequent problem, primarily depends on the democratic power, technical limitations mostly belong to the fact that most of the equipment for using renewable energy sources and the increase in energetic efficiency from the import, has not been produced on the local level

Determination of Service Life of Sintered Powder Metallurgy Gears in Regard to Tooth Bending Fatigue

The aim of this study is to check the possibility of replacing the pinion gear made of structural steel with the one made of sintered material. The pinion is part of the gear pair mounted in front of the gearbox of the skidder Ecotrac 55V to increase the speed and lower torque. In larger series, powder metallurgy (PM) gears are used as a cost-effective alternative for wrought metal gears in a number of industries including the one producing forest products. The present paper discusses the computational and experimental approach for determining the service life of sintered PM gears in regard to tooth bending fatigue. The proposed computational model is based on the stress-life approach, where the stress field in a gear tooth root is determined numerically using finite element method. The needed material data have been taken from the authors’ previous work. Due to the scattering nature of fatigue, the statistic approach has also been considered by presentation of computational results. The experimental procedure was done on a custom made back-to-back gear testing rig. The comparison between computational and experimental results has shown that the proposed computational approach is an appropriate calculation method for estimating the service life of sintered gears regarding tooth root strength. Namely, it has been shown that, in case of proper heat treatment of tested gears, tooth breakage occurred in the interval with 95% probability of failure, which has been determined using the proposed computational model

Contribution to the research on wood pellet characteristics from Turopolje area

U ovome radu analiziraju se kvalitativna svojstva peleta izrađenih iz vrsta drva turopoljskog kraja – sadržaj pepela, ogrjevna vrijednost, gustoća peleta i tlačna čvrstoća. Prikupljeni su uzorci hrasta lužnjaka (Quercus robur L.), običnoga graba (Carpinus betulus L.), poljskog jasena (Fraxinus angustifolia Vahl.), crne johe (Alnus glutinosa L.) i crne topole (Populus nigra L.). Prikupljeni i okorani uzorci usitnjeni su na mlinu s noževima na granulaciju 2,00 mm. Na uzorcima je ispitan sadržaj vode, pepela i ogrjevna vrijednost. Sadržaj pepela određen je zasebno za koru i drvo. Sadržaj pepela u kori pokazuje visok udio kod hrasta lužnjaka koji iznosi 13,64 % i graba sa 11,91 %, dok je kod ostalih vrsta udio pepela u kori između 7 i 10 %. Sadržaj pepela okoranog drva pokazuje vrijednosti 0,63 % za hrast, 0,50 % za jasen, 0,46 % za grab. Vrijednosti sadržaja pepela kod johe i topole bile su oko 0,4 %. Rezultati ukazuju na potrebu okoravanja u proizvodnji peleta s ciljem postizanja kvalitete peleta klase A1 i A2. Određivanjem ogrjevne vrijednosti najbolji rezultati utvrđeni su kod uzorka drva crne topole koja iznosi 19,63 MJ/g, a najmanja vrijednost izmjerena je kod uzorka graba 18,94 MJ/g. Nadalje, navedeni uzorci pomiješani su te su fomirane 3 grupe mješavina. Udio tvrdih vrsta listača hrasta, graba i jasena u svakoj pojedinoj mješavini bio je 60 % dok su u preostalom udjelu od 40 % jednoliko sudjelovale joha (20 %) i topola (20 %). Formirane mješavine materijala JTJ (jasen 60 : topola 20 : joha 20), HTJ (hrast 60 : topola 20 : joha 20) i GTJ (grab 60 : topola 20 : joha 20) prešane su u pelete uz pomoć hidrauličke laboratorijske preše pri 2 veličine sile (3,0 i 6,0 kN) i 2 temperature (150 i 200 °C). Po isprešanju, peleti su ostavljeni 15 dana da se dimenzijski stabiliziraju te su im određene dimenzije i gustoća. Peleti su potom ispitani na tlačnu čvrstoću u radijalnom smjeru pomoću kidalice. Peleti iz svih mješavina, prešani silom 6,0 kN kod temperature 200 °C pokazali su visoku gustoću koja je bila u rasponu 1 207 – 1 234 kg/m3. Peleti osnovne mješavine jasena dali su kod sile 3,0 kN i temperature 200 °C vrlo visoku gustoću od ≈ 1200 kg/m3, dok su općenito najmanju gustoću imali peleti osnovne mješavine graba kod svih režima prešanja. Rezultati tlačne čvrstoće u radijalnom smjeru pokazuju najbolje rezultate kod peleta prešanih pri 6,0 kN i 200 °C i to 13,59 MPa kod osnovne mješavine jasena, 11,1 MPa mješavine hrasta i 9,06 MPa mješavine graba.Ako se tlačna čvrstoća peleta promatra zbirno prema mješavini, značajno bolje rezultate daju peleti izrađeni iz mješavine jasena, topole i johe u usporedbi s ostale dvije mješavine.The paper deals with some quality characteristic of wood pellets from Turopolje area. The samples of pedunculate oak (Quercus robur L.), European hornbeam (Carpinus betulus L.), narrow-leaved ash (Fraxinus angustifoliaVahl.), European alder (Alnus glutinosa L.) and black poplar (Populus nigra L.) were collected. Collected and debarked samples were crushed by a mill with knives to 2.00 mm granulation. The content of water, ash and calorific value were examined on samples. The ash content was determined separately for the bark and the wood. The ash content in the barks shows a high rate in pedunculate oak which is 13.64 % and hornbeam with 11.91 %, while in other species the ash content in a bark is between 7 and 10 %. The ash content of a debarked wood shows the following values: 0.63 % for the oak, 0.50 % for the ash, 0.46 % for the hornbeam. Values of the ash content in the alder and the poplar were 0.4 %. Results indicate the need for debarking in pellet production in order to obtain the quality of class A1 and A2 pellet. By determining the calorific value the best results were determined in the black poplar sample which is 19.63 MJ/kg, and the lower value was measured in hornbeam sample 18.94 MJ/kg. Furthermore, the mentioned samples were mixed and 3 mixture groups were formed. The share of hard broad-leaved trees of oak, hornbeam and ash in each individual mixture was 60 %,while in the remaining 40 %,alder (20 %) and poplar (20 %) equally participated. Formed material mixtures APA (ash 60 : poplar 20 : alder 20), OPA (oak 60 : poplar 20 : alder 20) and HPA (hornbeam 60 : poplar 20 : alder 20) were pressed into pellets by hydraulic laboratory press in 2 forces (3.0 and 6.0 kN) and 2 temperatures (150 and 200 °C). After pressing, pellets were left for 15 days to stabilise in dimension and their dimension and density were determined. Then, pellets were checked for pressure strength in a radial direction by a testing machine. Pellets from all the mixtures, pressed by a force of 6.0 kN at 200 °C showed a high density in the range from 1 207 – 1 234 kg/m3. Pellets of basic ash mixture at force of 3.0 kN and at 200 °C gave high density≈ 1200 kg/m3, while the smallest density was generally given by pellets of basic hornbeam mixture in all pressing regimes. The results of pressure strength in radial direction give best results in pellets pressed at 6.0 kN and 200 °C which is 13.59 MPa with the basic ash mixture, 11.1 MPa with the basic oak mixture and 9.06 MPa of basic hornbeam mixture.If the pressure strength of a pellet is considered collectively according to the mixture, pellets made from the mixture of ash, poplar and alder give significantly better results in comparison to other two mixtures

Energy Analysis of Pellets Made of Wood Residues

The use of high technology in the manufacture of pellets and their use in modern furnace chambers of boiler plants for remote heating and heating of family houses, are the reason why pellets as the energy source find an ever increasing application. The biggest problem and obstacle for increasing their use is the starting investment in the boiler and pellet tank, which is considerably higher than the heating oil installation. In order to obtain the best possible indicators on economic feasibility of manufacturing wood pellets, a comprehensive research has been carried out in a wood processing plant. Pellets are manufactured from beech and oak residues. Beech accounted for about 90%. In order to get a complete picture of the consumption of electrical power per unit of manufactured pellets and of required power, the operating and idle power was measured at measurement sites during operations of individual electromotors. The measuring results were stored directly into computer and analysed later by a softwarepackage LabVIEW. The machines’ consumption of electrical power in the observed period was derived from the measuring results by numerical integration, based on which the average electrical power was then determined. Regarding the results of measuring carried out on four groups of electromotors, the highest consumption of electrical power has been measured during pressing, and then on electromotor group for the preparation of chips for pelleting. The highest consumption of electrical power has been recorded for the manufacture of one ton of pellets in pressing 138.98 kWh/t and transport system 74.25 kWh/t, which makes a total of 213.23 kWh/t or almost 95% compared to total consumption of electrical power. The measured electrical power for the manufacture of one ton of pellets in pressing hardwood residues, (in this research – beech), is by 100% higher than the electrical power referred to in literature, which relates to softwood. Consequently, the difference should be made in each study between the consumption of electrical power in pressing softwood and hardwood. Lower consumption of electrical power has been recorded with chippers with sharpened knives amounting to 24.3% compared to unsharpened knives

Study of Processes in Critical Operating Conditions of Sliding Pairs

The occurrence of working irregularities in journal bearing such as loss of geometry correctness, sudden failure of lubrication, overloading, etc., requires that serious damage of journal bearings have to be overcome in a short period of time. In such cases, it is important that the applied combinations of materials and lubricants do not have a tendency to seizure. Such critical conditions were simulated in this work for various combinations of materials and lubricants. Model research was carried out using the adapted Timken device and results were compared with the real loaded bearing. Data for nominal working conditions has shown relatively good agreement with calculated values whereas maximum frictional moment was significantly higher for the real bearing. This difference was explained as a consequence of different lubricating conditions. Nevertheless, a profile of the frictional moment was qualitatively similar compared to a model testing for equal combination of material and lubricant, thus confirming initial assumptions