Influence of glue-bond on transverse diffusion of water in glued wood

In the wood-glue-wood system, the glue-bond presents an additional resistance,hindering the water transition. The increased resistance of the glued test pieces is the consequence of adhesive being present in the bond, soas of altered wood properties, mainly the increased density and locally decreased wood hygroscopicity, resulting as a consequence of wood exposed to the gluing conditions. Using an unsteady-state method, the diffusion coefficients were defined. The kinetics of absorption of the massive beech test pieces, glued test pieces (PVAc, UF, MUF, PRF and epoxy liquid adhesives and PF film were used), and parallel ones with no glue bonds but exposed to the gluing conditions, were compared. It was established that the thin glue bonds made by using liquid glues do not present a barrier, which could effectively hinder the transition of bound water into the glued piece. A higher resistance was presented just by FF glue film bonds. There exist statistically significant differences among diffusion coefficients, calculatedby analytical solutions and solutions of an equation of the first order model. Transverse diffusion of water vapour and bound water can be described as the first order system

Beech wood - correlations between the quality of trees, logs and sawn wood

V raziskavi smo preučevali količinsko-kakovostni izkoristek bukovine od stoječega drevesa do žaganega lesa. Zanimala nas je ocena kakovosti posameznih dreves in njen vpliv na kakovostne razrede proizvodov iz tega lesa. Pri razvrščanju stoječih dreves smo upoštevali aktualno 5-stopenjsko lestvico ocenjevanja kakovosti Zavoda za gozdove Slovenije (ZGS). Pri ocenjevanju gozdnih sortimentov smo uporabljali standard SIST EN 1316-1:2013, pri ocenjevanju žaganega lesa pa pravila Evropskega združenja žagarske industrije (EOS). Na vzorcu ocenjenih in nato posekanih dreves smo ugotavljali povezave med kakovostjo dreves, iz njih izdelanih sortimentov okroglega lesa in kakovostjo končnih žagarskih izdelkov. V vzorec so bila enakovredno zajeta drevesa vseh petih kakovostnih stopenj. Pri izdelavi gozdnih sortimentov smo dobili največ hlodov B-kakovosti (51 %) in največ žaganega lesa EOS-C-kakovosti (52 %). Iz bukovih dreves odlične kakovosti smo dobili 35 % najkakovostnejših sortimentov in iz teh sortimentov 8 % najkakovostnejšega žaganega lesa. Odločilni kriterij razvrščanja po kakovosti so pri sortimentih okroglega lesa slepice in pri žaganem lesu mrtve in trhle grče.The research addresses beech wood, from a standing tree to sawn wood. It focuses on the quality evaluation of individual trees and its impact on the later products made of the respective wood. For the needs of observing the quality of standing trees, the current 5-class scale for quality evaluation of the Slovenia Forest Service (SFS) was used. To evaluate the wood assortment, the SIST EN 1316-1:2013 standard was applied, while the evaluation of sawn wood was performed as per the rules of the European Organisation of the Sawmill Industry (EOS). On the basis of the sample of evaluated and eventually harvested trees, the correlations between the quality of trees, roundwood products made of them and the quality of final sawn products were established. The sample equally included trees of all five quality classes. The production of wood assortment provided the most logs of B quality (51%) and the highest quantity of sawn wood of EOS-C quality (52%). Beech trees of excellent quality provided 35% of the wood assortment of highest quality and these provided 8% of the sawn wood of the highest quality. The key criteria for the classification by quality were covered knots for forest products and dead and unsound knots for sawn wood

Monitoring the Quality and Quantity of Beechwood from Tree to Sawmill Product

The analysis evaluates the potential and methods of the respective assessment of beech trees, beech logs and sawn timber. The objective of the study was to assess the impact of the quality of the incoming raw material (tree) on the quality and quantity of products – obtained at the sawmill. The study presents a model that indicates the relations between the assessment of the quality of a standing beech tree and the quality of the sawmill products obtained from its wood. In addition, relations between individual quality classes of sawlogs, pulpwood, energy wood and sawn timber are shown. Standing trees were assessed in three sites according to the national 5-grade quality scale, assortments produced from selected trees pursuant to the EN 1316-1 standard, and sawn timber produced from assortments according to the rules of the European Organisation of the Sawmill Industry (EOS). In total, 87.04 m3 of timber was harvested. In higher quality trees (quality 1 and 2), the shares of sawlogs were between 53% and 72% of gross tree volume, but in the poorest quality trees, the shares were only between 23% and 36%. What remained was pulp and energy wood. In trees of excellent quality (quality 1), sawlogs of the highest quality prevailed (A and B quality grade), while sawlogs of C and B quality prevailed in trees of lower quality. Covered knots and heart defects were typically the decisive criteria for classifying sawlogs quality in all three sites. A total of 30,786 m3 of unedged timber was sawn from the sawlogs, which comprised 35% of the total gross quantity of trees on average. Nine percent of the sawn timber was classified into the A–EOS class (top quality), 27% into the B–EOS class and 47% into the C–EOS class. Seventeen percent of the timber was only suitable for post-processing. The crucial criteria for classifying sawn timber were as follows: dead and rotten knots, heart, curvature and cracks. Above-average sawlogs (A and B quality grade) was mainly obtained from trees of better quality. Relations between the quality of trees, sawlogs and sawn timber indicated the suitability of classifying standing trees and sawlogs, since it was possible to produce sawn timber of higher quality from quality trees or logs. The model presents a rare attempt to establish and monitor quality and quantity from standing tree to end product

Križno lamelirani les – lastnosti in zahteve

Cross-laminated timber (CLT or X-Lam) is a modern building material used for load-bearing construction purposes in residential and non-residential buildings. CLT production has been increasing rapidly in recent years. CLT is suitable for wall, floor, ceiling and roof elements in the construction of houses, multi-family apartment buildings, industrial and storage halls and other buildings and bridges. Manufacturers demonstrate compliance with the essential requirements of the European Construction Products Regulation (CPR) on the basis of an initial type testing and the findings of a factory production control examination. In 2015, a harmonized European standard for CLT was adopted, which defines the requirements for built-in materials, the production and demonstration of constancy of performance, and the CE marking. The article presents the production technology and basic characteristics of CLT and the content of standard EN 16351

Links between beech tree quality and assortments made of them

V raziskavi smo obravnavali stoječe drevo, oceno njegove kakovosti in kakovost iz njega izdelanih sortimentov. Pri tem smo kritično obravnavali različna merila, ki so aktualna v praksi - petstopenjsko lestvico ocenjevanja kakovosti stoječih dreves, ki je v rabi na stalnih vzorčnih ploskvah, in aktualne standarde za ocenjevanje kakovosti izdelanih sortimentov. Na podlagi majhnega analiziranega vzorca ocenjenih in nato posekanih dreves smo ugotavljali povezave med kakovostjo dreves in sortimentov ter podobnosti in razlike, ki nastajajo, če pri presoji kakovosti sortimentov uporabljamo različna merila. Izpostavljamo problematiko različnih standardov, ki so trenutno veljavni pri nas ali pa jih pogosto uporabljamo v praksi.In our research we dealt with the standing tree, estimation of the standing tree, evaluation of its quality and evaluation of quality of assortments made of it. Thereby we critically discussed diverse criteria, currently used in the practice - the five-grade scale for standing tree evaluation, used on permanent sampling plots, and current standards for evaluating the quality of the produced assortments. On the basis of a small analyzed sample of the evaluated and afterwards felled trees we were determining links between quality of trees and assortments as well as similarities and differences occurring when we use different standards for estimation of assortments. We highlight the issues of diverse standards, which are currently valid or most frequently used in practice in Slovenia

The influence of thermal modification on the machining properties of beech wood

The work analyses the influence of thermal modification on the machining properties of beech wood, where the quality of the surface is evaluated after the operation of planing, routing and turning of unmodified and modified beech. After machining, the surface is visually assessed with grades from 1 to 5, with respect to defects of raised, fuzzy and torn grain. As a result an average grade for each type of operation is given, as well as the percentage of each grade. It has been found out that the average grades of thermally modified beech wood in planing were better compared to unmodified beech, but ANOVA analysis did not confirm differences between them. There was also no difference in routing, while in turning the influence of modification was significant, since the surface quality of the thermally modified beech was significantly better compared to that of unmodified beech. From the analysis it can be concluded that thermal modification has a positive effect on the quality of the machined surface

Trajnost i mehanička svojstva različito obrađenih lameliranih nosača tijekom dvije godine izlaganja u eksterijeru

The performance of the composites is influenced by the service life of input raw wood material and used adhesives. The aim of the study was to assess the durability and mechanical performance of glulam beams treated in a different way (thermally modified and/or treated with copper-based wood preservative) and exposed in an outdoor application. Glulam beams (83 mm × 68 mm × 1100 mm), made of three layers of Norway spruce (Picea abies) with PUR adhesives used have been exposed in use class 3.2 in a horizontal position since 4th November 2016. Part of the specimens was equipped with MC sensors. Every year, the degradation was evaluated visually. The dynamic modulus of elasticity was determined by longitudinal vibration, and the static modulus of elasticity using a 4-point bending test. On the smaller specimens, cut from glulams, compressive strength, delamination, and shear strength of adhesive bonds were determined. After two years of exposure, the results indicate that the performance of glulams is determined by the wood modification and applied wood preservative.Na svojstva kompozita utječu trajnost sirovine i svojstva primijenjenih ljepila. Cilj ovog istraživanja bio je procijeniti trajnost i mehanička svojstva različito obrađenih lameliranih nosača (toplinski modificiranih i/ili impregniranih bakrom) izloženih u eksterijeru. Lamelirani nosači (83 mm × 68 mm × 1100 mm) izrađeni su od tri sloja smrekovine (Picea abies) koji su slijepljeni PUR ljepilom. Nosači su prema klasi uporabe 3.2 izloženi u vodoravnom položaju od 4. studenoga 2016. u trajanju od dvije godine. Na dio uzoraka postavljeni su senzori za mjerenje sadržaja vode u njima. Svake je godine vizualno ocjenjivano propadanje uzoraka. Dinamički modul elastičnosti određen je longitudinalnom vibracijom, a statički modul elastičnosti savijanjem u četiri točke. Na manjim uzorcima ispiljenima od nosača određena je tlačna čvrstoća, delaminacija i čvrstoća lijepljenog spoja na smicanje. Nakon dvije godine rezultati izlaganja pokazali su da svojstva lameliranih nosača ovise o toplinskoj modifikaciji drva i sredstvu za impregniranje

Vpliv sušilnega postopka na kakovost in izkoristek bukovega žaganega lesa

We estimated the quality of beech (Fagus sylvatica) sawn timber before and after the industrial normal-temperature convection kiln drying and after air drying. We analysed 42 mm thick and 2.6 m to 5 m long boards, where we measured the number and size of end- and surface cracks, and fissures close to the knots. The orientation and direction of the wood grain, the number and size of knots as well as occurrence of red-heart and twisting were also determined. We ranked the boards using these criteria before and after the end of the drying processes in accordance with the standard of the European Organization of the Sawmill industry (EOS). We found a significant effect of drying on the occurrence of drying defects, but differences between the two procedures were not confirmed. The increase in the number and size of the surface and end cracks, especially in the boards assessed to lower B- and C-classes was obvious. The latter mainly contributed to the lowering of the quality of the sawn timber after drying from the A- to B- or lower class. After the kiln and air drying 20 % and 33 % of the sawn timber quality was degraded, respectively. The presented research was part of a larger study where we followed the quality of the beech timber from the forest to the final product

Visual grading of structural sawn timber

Masivni žagani les, ki se uporablja v nosilnih gradbenih konstrukcijah, mora ustrezati zahtevam harmoniziranega standarda SIST EN 14081-1. Standard dopušča vizualno in strojno razvrščanje lesa. Pri strojnem razvrščanju uporabljamo nedestruktivne metode testiranja (NDT). Les na podlagi izmerjenih indikacijskih vrednosti razvrščamo v vnaprej definirane trdnostne razrede. Pri vizualnem razvrščanju ocenjujemo vidne značilnosti lesa. Upoštevamo značilnosti lesa, zaradi katerih je zmanjšana njegova nosilnost, ter značilnosti, ki so povezane z geometrijo in biološko razgradnjo lesa. Na podlagi primerjave izmerjenih značilnosti z mejnimi vrednostmi, ki so podane v standardih, lahko les razvrstimo v t.i. sortirne razrede. Če poznamo drevesno vrsto in izvor hlodovine, lahko sortirne razrede preko povezav iz standarda SIST EN 1912 prevedemo v trdnostne razrede. Od 1.9.2009 lahko vizualno razvrščanje konstrukcijskega žaganega lesa v Sloveniji izvajamo po standardu SIST DIN 4074-1:2009.Sawn timber used in load-bearing building structures shall comply with the requirements given in harmonized European standard SIST EN 14081-1. Timber shall be either visually or machine graded. Machine grading is based on non-destructive testing (NDT) methods. Considering so called grade indicating properties measurements, timber pieces are graded into previously defined strength classes. Through visual grading each piece of timber is evaluated based on visual parameters. Visual grading rules consider the conformance of surface strength reducing, geometrical and biological characteristics to limitations established within each grade category. On that basis, so called visual strength grades (Sortierklassen) are assigned. Considering visual strength grades, species and sources of timber, strength classes can be assigned according to SIST EN 1912