Utjecaj posmične brzine i vrste drva na hrapavost obrađene površine

In this study, the surface roughness values of planed beech-wood (Fagus L.), oak-wood (Quercus L.) and fir-wood (Abies alba Mill.) specimens were examined. The samples of beech-wood were cut from steamed beech-wood and from thermally modified beech-wood (212oC). The specimens were machined by planing in radial directions with two knives at 6, 12, 18 and 24 m/min feed speed. The cutting depth of 2.0 mm was constant and knife rake angle was 15o. The machining experiments were carried out using a single cutter-block of a Weinig Powermat 400. The cutter-block with a diameter of Ø 125 mm rotated at 6000 revolutions per minute (RPM). Surface roughness was measured from the radial face of each sample according to DIN 4768 (1990) by using Mitutoyo SJ-201 stylus scanner. Comparison between the results of surface roughness of four species showed that surface roughness increases with the increase of feed rate. The surface quality of samples of planed beech-wood, oak-wood and fir-wood were significantly different. The samples of planed surface of oak-wood had the best quality and the samples of fir wood had the highest values of surface roughness. There were no significant differences in the surface quality of thermally modified and steamed beach-wood samples despite the significant difference in mechanical and physical properties of thermally modified and steamed wood.Rad predstavlja istraživanja kvalitete blanjane površine bukovih, hrastovih i jelovih uzoraka. Bukovi su uzorci izrađeni od parene bukovine i termički modificirane bukovine (212 oC). Istraživanja su provedena na uzorcima blistača, koji su blanjani u radijalnom smjeru. Alat za blanjanje imao je dvije oštrice, a blanjano je pri posmičnim brzinama 6, 12, 18 i 24 m/min. Dubina blanjanja bila je konstantna i iznosila je 2,0 mm, a prsni je kut oštrica alata bio γ = 15o. Eksperiment je proveden na četverostranoj blanjalici Weinig Powermat 400. Promjer putanje rezne oštrice bio je 125 mm, a broj okretaja radne osovine 6 000 min-1. Hrapavost površine mjerena je po duljini obrade, u skladu sa normom DIN 4768 (1990) upotrebom elektromehaničkog profilometra Mitutoyo SJ-201. Usporedbom dobivenih rezultata za sve četiri vrste uzoraka može se zaključiti da se s povećanjem posmične brzine povećava hrapavost površine. Kvaliteta blanjane površine za različite je vrste drva različita u jednakim uvjetima obrade. Najmanju hrapavost imali su uzorci hrasta, a najveću uzorci jele. U istraživanjima nije zabilježena značajna razlika između kvalitete površine uzoraka od parene bukovine i termički modificirane bukovine usprkos mnogo lošijim mehaničkim svojstvima termički modificiranog drva u odnosu prema parenom drvu

Izloženost endotoksinu u drvoprerađivačkoj industriji: odnos između razina izmjerenih u zraku i na tlu

Wood processing is usually performed in environments with large amounts of endotoxin-rich bioaerosols that are associated with a variety of health effects. The aim of this preliminary study was to assess the relation between endotoxin levels in settled and airborne dust in wood-processing industry. Ten pairs of airborne and settled dust samples were collected in a sawmill and parquet manufacture of two wood-processing plants in Croatia. Endotoxin was assayed with a chromogenic end-point LAL (Limulus amebocyte lysate) method. The results showed that endotoxin levels in airborne respirable dust were above the proposed occupational exposure limit of 125 EU m-3 and could be considered hazardous for the respiratory system. In settled dust they ranged between 229.7 EU mg-1 and 604.3 EU mg-1 and in airborne dust between 166.8 EU mg-1 and 671.6 EU m-3, but there was no signifi cant correlation between them (Spearman’s rho=0.358, P=0.310). This study points to sawmill settled dust as endotoxin reservoir and suggests that it may add to already high exposure to airborne endotoxins associated with wood processing. Investigations of the relation between settled and airborne endotoxin levels should be continued to better understand the sources and sites of endotoxin contamination in wood-processing industry.Drvoprerađivačka industrija radna je sredina s izloženošću velikim količinama bioaerosola bogatog endotoksinom, što je povezano s učincima na zdravlje izložene radne populacije. Cilj ove studije bio je procijeniti odnos između razina endotoksina u sedimentiranoj prašini i zraku (aerosoliziranoj prašini) drvoprerađivačkih radnih prostora. Deset parova uzoraka zraka i sedimentirane prašine skupljeno je u dvije tvornice za preradu drva (pilanama i pogonima za proizvodnju parketa) u Hrvatskoj. Endotoksin je izmjeren kromogenom “end-point” LAL (Limulus amebocitni lizat) metodom. Rezultati su pokazali da razine endotoksina u aerosoliziranoj respirabilnoj prašini drvoprerađivačkih pogona prelaze preporučene granice izloženosti za radne prostore od 125 EU m-3, pa se mogu smatrati štetnima za dišni sustav izloženih radnika. Razine endotoksina izmjerene u sedimentiranoj i aerosoliziranoj prašini kretale su se u sličnu rasponu [(229.7 do 604.3) EU mg-1 i (166.8 do 671.6) EU m-3], ali nije utvrđena značajna korelacija razina endotoksina između parova uzoraka sedimentirane i aerosolizirane prašine (Spearman rho=0.358, P=0.310). Ovi rezultati upućuju na to da uz velike količine proizvedene i aerosolizirane drvne prašine u sklopu radnih operacija u pilanama, razini endotoksina u aerosoliziranoj respirabilnoj prašini može pridonijeti i uskovitlana sedimentirana prašina koja je dodatni rezervoar endotoksina. Istraživanje odnosa između razina endotoksina u sedimentiranoj i aerosoliziranoj prašini treba nastaviti kako bi se bolje defi nirali izvori i mjesta kontaminirana endotoksinom u pilanama

Correction factor for real-time determination of wood dust mass concentration by photometric method

U pogonima za mehaničku obradu drva skupljani su uzorci drvne prašine iz zraka u radnom okružju radi određivanja korekcijskog faktora uređaja za kontinuirano mjerenje masene koncentracije lebdećih drvnih čestica fotometrijom. Prema normi NIOSH 0600 i NIOSH priručniku analitičkih metoda o fotometrijskome mjerenju, korekcijski je faktor potrebno odrediti prije mjerenja za svaku vrstu prašine posebno, i to kao omjer masene koncentracije čestica određene gravimetrijskom metodom i masene koncentracije određene fotometrijom. Korekcijski faktor treba odrediti zbog utjecaja fizikalnih svojstava čestica različitog materijala (vrste, veličine i oblika čestice te njezina indeksa refleksije) na učinkovitost fotometrije. Istraživanje je provedeno s ciljem ispitivanja mogućnosti primjene fotometrijske metode za određivanje masene koncentracije inhalabilne drvne prašine u zraku. Uzorkovanje je provedeno pri obradi sirove i suhe bukovine, sirove i suhe hrastovine, sirove jelovine i iverice. Rezultati mjerenja fotometrijom u signifikantnoj su korelaciji s mjernim rezultatima dobivenim gravimetrijskom metodom (R2=0,88), što je temeljni uvjet za mogućnost upotrebe fotometrije pri mjerenju masene koncentracije drvnih čestica u zraku. Rezultati istraživanja upozorili su na nužnost određivanja korekcijskog faktora za mjerenje masene koncentracije drvne prašine pri obradi različitih vrsta drva i drvnih materijala, ali i istih vrsta drva s različitim sadržajem vode. Za uzorke uzete pri obradi jelovine dobiveno je najbolje slaganje rezultata gravimetrijske i fotometrijske metode (ksr=1), a najveći korekcijski faktor treba primijeniti pri određivanju izloženosti radnika drvnoj prašini suhe hrastovine (ksr=4,4) i iverice (ksr=4,5). S propisanim graničnim vrijednostima izloženosti radnika drvnoj prašini usporedive su samo gravimetrijski određene masene koncentracije iz osam sati skupljanog uzorka. S obzirom na kancerogenost bukovine i hrastovine i njihovu veliku zastupljenost u domaćoj drvnoprerađivačkoj industriji, fotometrijska metoda određivanja masene koncentracije drvnih čestica, osim za određivanje kratkotrajne izloženosti može poslužiti, i kao vrlo korisna metoda u analizi vremenskog profila izloženosti na radnim mjestima tijekom radnog dana. Osim toga, fotometrijska metoda omogućuje istodobno određivanje masene koncentracije inhalabilne, torakalne i respirabilne frakcije lebdećih čestica.Samples of wood dust were collected in the working environment of wood machining processes for the purpose of determining correction factors for measuring mass concentration of wood dust by photometric method. According to the NIOSH 0600 Norm and NIOSH Manual of Analytical Methods for photometric measurement, correction factor must be determined before measuring mass concentration of different types of dust. The correction factor is defined as the ratio of mass concentration obtained by the gravimetric method and mass concentration obtained by the photometric method. The correction factor should be determined because of the influence of particle size distribution, density, particle shape and refractive index on values obtained by the photometric method. The aim of the research was to investigate the possibility of using photometric method for the determination of mass concentration of inhalable fraction of airborne wood dust. Sampling was conducted in several woodworking plants during the machining of wet and dry beech-wood, wet and dry oak-wood, wet fir-wood and particleboard. There is a significant correlation between the results obtained by the photometric method and values obtained by the gravimetric method (R2=0.88) and this is the base for using the photometric method in determining mass concentration of airborne wood dust. According to the results of this research, correction factors must be determined and used for measuring mass concentration of inhalable wood dust during the machining of different wood species and wood with different moisture content. The best corresponding results of photometric and gravimetric methods are obtained for the samples collected during machining of wet fir-wood (k=1). The largest correction factor should be used in determining workers exposure to wood dust during machining of dry oak-wood (k=4.4) and particleboard (k=4.5). Only the results of 8-hour measurements of mass concentration by gravimetric methods can be compared with limit values of aerosol mass concentration. However, the determination of mass concentration of wood dust by photometric method may be applied not only for short-term exposure measurements but also for additional measurements within the analysis of exposure time profile at workplaces during the working day. Additionally, photometric method is very useful for simultaneous collection of samples of the respirable, thoracic and inhalable fractions of airborne particulate matter

Research of fir-wood dust concentration in the working environment of cutters

This paper shows the results of measurement of daily exposure of cutters to respirable particles and total fir-wood dust during cutting and processing of dead standing fir-trees. The separators of non-respirable fraction (cyclones) are designed so as to imitate the separation of respirable particles in the respiratory system of a healthy adult person, with a medium efficiency (50 %) with aerodynamic diameter of 5 μm. The mean value of mass concentration of total fir-wood dust was (1.29 ± 0.419) mg/m3 and of respirable fraction (0.564 ± 0.154) mg/m3. The results of this research show that no measured value (N = 26) in cutting and processing fir-trees exceeds the Croatian limit values (maximum permissible concentrations) for wood dust of softwood broadleaved species and conifers

Correction factor for real-time determination of wood dust mass concentration by photometric method

Samples of wood dust were collected in the working environment of wood machining processes for the purpose of determining correction factors for measuring mass concentration of wood dust by photometric method. According to the NIOSH 0600 Norm and NIOSH Manual of Analytical Methods for photometric measurement, correction factor must be determined before measuring mass concentration of different types of dust. The correction factor is defined as the ratio of mass concentration obtained by the gravimetric method and mass concentration obtained by the photometric method. The correction factor should be determined because of the influence of particle size distribution, density, particle shape and refractive index on values obtained by the photometric method. The aim of the research was to investigate the possibility of using photometric method for the determination of mass concentration of inhalable fraction of airborne wood dust. Sampling was conducted in several woodworking plants during the machining of wet and dry beech-wood, wet and dry oak-wood, wet fir-wood and particleboard. There is a significant correlation between the results obtained by the photometric method and values obtained by the gravimetric method (R2=0.88) and this is the base for using the photometric method in determining mass concentration of airborne wood dust. According to the results of this research, correction factors must be determined and used for measuring mass concentration of inhalable wood dust during the machining of different wood species and wood with different moisture content. The best corresponding results of photometric and gravimetric methods are obtained for the samples collected during machining of wet fir-wood (k=1). The largest correction factor should be used in determining workers exposure to wood dust during machining of dry oak-wood (k=4.4) and particleboard (k=4.5). Only the results of 8-hour measurements of mass concentration by gravimetric methods can be compared with limit values of aerosol mass concentration. However, the determination of mass concentration of wood dust by photometric method may be applied not only for short-term exposure measurements but also for additional measurements within the analysis of exposure time profile at workplaces during the working day. Additionally, photometric method is very useful for simultaneous collection of samples of the respirable, thoracic and inhalable fractions of airborne particulate matter