Welding temperature is an important factor of rotary welding and affects the strength of the joint or the embedded force. This research focused on the parameters that affect the welding temperature ...and the effect of welding temperature on the embedded force of the dowel. Welding temperature was measured using measuring probes that were moved away from the dowel being welded. The results indicate that the speed of the dowel feed (duration of the welding process) influenced the welding temperature; the embedded force was then determined. With increased rotation frequency with the same duration of the welding process, there was a slight increase in the welding temperature. The influence of the rotational frequency on the extraction force was not unambiguously determined, because the rotational frequency is related to the duration of the welding process. As the welding temperature increased, the embedded force decreased. To avoid difficulties in contact measurement of welding temperature, it is necessary to develop a mathematical model of heat transfer to more accurately determine the welding temperature.
The increasing use of wood leads to the need for a better understanding of its thermal properties with the aim of quantitatively identifying the exchange of thermal energy between wood and the ...surrounding solar radiation as precisely as possible. Reliable and rapid measurement of thermal conductivity is one of the most important current industrial requirements. The aim of this study is to examine the validity of using the modified transient plane source method (MTPS), which uses the principle of one-sided heating of the sample, and is defined by the ASTM D7984-21 (2021) standard, for determining the thermal conductivity of complex biocomposite composite materials such as wood. The analysis of the available literature shows a lack of data on the thermal conductivity of the type of wood originating in Croatia. In this study, the thermal conductivities of beech and fir wood samples in the longitudinal direction was determined by the MTPS method depending on the temperature and moisture content in the samples. Measurements were made on samples with a moisture content of 0%, 10%, and 20% in the temperature range from 20 to 80 °C.
Biomass Pelletizing Process Dujmović, Marin; Šafran, Branimir; Jug, Matija ...
Drvna industrija,
03/2022, Volume:
73, Issue:
1
Journal Article
Peer reviewed
Open access
A review paper was designed as a lab-scale start-up guideline for general pelletizing process and technologies for biomass feedstock. The main body consists of summarized published research on the ...topic of all main parts of the biomass pelletizing process and technology, including machinery and their parts, optimal feedstock conditions as well as pellet forming processes and principles. This paper is more focused on the specific parameters necessary to obtain optimal pelletizing process that results in desired pellet quality, and less on feedstock preparation, final product post-treatment (e.g. cooling), handling (storage, transportation) or exact quality specifications. A summary of the suggested feedstock, technological and other parameters for the purpose of easier lab-scale start-up of biomass pellets production, which is based on the cited literature throughout this paper, is given in the last section.
Pregledni rad pripremljen je kao laboratorijski priručni materijal za osnovne procese i tehnologije peletiranja biomase. U njemu su sistematizirane spoznaje iz dostupnih izvora literature o temi glavnih dijelova procesa i tehnologije peletiranja biomase, uključujući strojeve i njihove pripadajuće dijelove, optimalne ulazne parametre sirovine, kao i načela i procese izrade peleta. Ovaj je priručni materijal više usmjeren na specifične parametre nužne za optimalan proces peletiranja radi dobivanja peleta željene kvalitete, a manje na pripremu sirovine, tretiranje proizvedenog peleta (npr. hlađenje), rukovanje peletima (skladištenje, transport) ili na određena kvalitativna svojstva peleta. Sažetak preporučenih tehnoloških parametara i ulaznih parametara sirovine, koji se temelji na informacijama iz navedene i citirane literature, nalazi se na kraju ovoga preglednog rada.
Specific Heat Capacity of Wood Radmanović, Kristijan; Đukić, Igor; Pervan, Stjepan
Drvna industrija,
01/2014, Volume:
65, Issue:
2
Journal Article
Peer reviewed
Open access
Specifi c heat capacity is defi ned as the amount of heat that a kilogram of a given substance is required to absorb in order to increase its temperature by one degree. The temperature of a given ...substance can change either at constant pressure or at constant volume, so we differentiate between specifi c heat capacity at constant pressure (cp) and specifi c heat capacity at constant volume (cv). When doing research into the heat propertiesof wood, the quantity that most frequently remains constant is pressure, thus restricting our study on specifi c heat capacity to cp. This paper provides an overview of the research that has so far been carried out into the specifi c heat capacity of wood depending on the temperature and moisture content. An analytical and graphical comparison has been performed of the results published in the Wood Industry Manual (1967) (DIP), Wood Handbook (1999) (WH) and work published by Deliiski (2012) (DEL).
Activation spectra of wood under natural irradiation were investigated in detail in this work. The main purpose was to study colour changes on the wood surface over time and into the depth during ...natural light exposure and thus to further contribute to the optimization of surface-protecting treatments. In a natural weathering test, three 80-μm-thick strips of fir wood forming the surface layer of a wood composite were exposed to light under a series of glass cut-off filters. Samples were withdrawn at intervals and tested for colour changes. Identification of the most detrimental wavebands of light causing photodegradation was performed based on recorded colour changes. With chronological development of exposure, the colour changes shifted ever deeper into the surface and further into the visible region of the spectrum. A relatively narrow waveband from 360 to 435 nm was identified in the activation spectra to be the most active band, causing the greatest proportion of recorded colour changes. However, also visible light of wavelengths up to 515 nm significantly contributed to colour changes of the surface layers.
Because of its hardness, wear-resistance, strength, and bending capabilities, beech wood is a widely-used hardwood in Europe. It is mainly used for furniture, floors, construction, veneer boards, and ...laminated wood. For such uses, the mechanical properties are very important, especially in cases of impact loads. The aim of this work is to analyse the mechanical properties of beech wood samples exposed to compressive force in the longitudinal direction based on different loading rates (in the range from 10 mm/min to 500 mm/min). Stress–strain diagrams were made with the experimental data, and mathematical functions were fit to them. Using the fit functions, the following properties of beech wood samples were determined: the stress and strain at the elastic limit; the maximum stress and associated strain; the modulus of elasticity; the tangent modulus; the specific energy of elastic strain; and the specific energy of plastic strain. The results showed that by increasing the loading rates, the elastic properties of beech wood increase, while the analysed plastic properties do not show a clear tendency of changes with increase of the loading rates.
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.
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 angustifolia
Vahl.), 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.
The paper discusses various methods of measuring the width of unedged sawn boards with nominal thickness of 50, 60 and 80 mm, as well as the importance of measuring methods for the calculation of ...their volume. The starting point in determining the method of measuring the width of the boards were Croatian and European regulations as well as common methods of measuring used in Croatian sawmills. Experimental measurements were performed in a sawmill in Croatia. Based on the research results, it was concluded that there is a difference in the calculation of the volume of the unedged sawn boards as a result of the different methods used to calculate their width. For 50 mm thick sawn boards, the highest values of the measured volume were obtained by applying a measurement method common in Croatian sawmills, labelled as P2. This was followed by measurement methods according to HRN2, EN, and another method used in Croatian sawmills, labelled as P1, and finally by the HRN1 method; however differences in this case were not statistically significant. The EN method of measuring the width of sawn boards of 60 and 80 mm thickness resulted in the highest value of volume, followed by the HRN2 method, and finally methods used in the sawmills labelled as P2, P1 and HRN1; however differences were statistically signifi cant only with 80 mm sawn boards. For all the observed widths, measurement methods according to EN, HRN2 and the sawmill method, labelled as P2, resulted in smaller mutual deviations. With an increase of thickness, an apparent increase in volume was observed; however it was statistically signifi cant only for the planks with a thickness of 80 mm.
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