Vpliv velikosti bukovega iverja, uporabljenega v zunanjem sloju na upogibno trdnost trislojne iverne plošče

Znano je, da vrsta lesa in velikost iverja vplivata na upogibno trdnost trislojnih ivernih plošč. Namen posebej zasnovane raziskave je bil ugotoviti, kako velikost bukovega (Fagus Sylvatica L.) iverja vpliva na upogibno trdnost trislojnih ivernih plošč, če je velikost bukovega iverja spremenjena samo v zunanjem sloju. Uporabljeno je bilo bukovo iverje petih različnih velikosti. Iverje je bilo oblepljeno z UF lepilom. Rezultati meritev so pokazali, da upogibna trdnost ivernih plošč narašča z naraščanjem specifične površine iverja, faktorja zgostitve zunanjega sloja in prostorninske mase zunanjega sloja, medtem ko z naraščanjem oblepljenosti upogibna trdnost pada.It is well known that wood species and particle size used influence the bending strength of the three-layer particleboard. The purpose of this research was to determine how the size of beech (Fagus sylvatica L.) particlesinfluences the bending strength of the three-layer particleboard, where size of particles used was altered in surface layer only. Beech wood particles of five different sizes were used and blended with UF adhesive. The results show that the bending strength of boards increases with increasing particle specific surface area, increasing surface layer compaction ratio and surface layer density, while bending strength decreases with increasing surface covered with adhesive

Influence of thermal treatment temperature on the dielectric properties of wood

The effect of thermal treatment temperature on the dielectric properties of beech (Fagus sylvatica L.) and spruce (Picea abies L.) was investigated. Wood disks with a diameter of 45 mm and a thickness of 5 mm were thermally treated at seven different temperatures (50 to 200 °C) before measurements were performed. Dielectric properties of the wood disks were measured at nine various frequencies (2 to 10 MHz) at room temperature. The impedance analyzer HP 4191A RF and the micrometer screw method with circular aluminum electrodes were used. The results indicate that the dielectric constant and the loss tangent of wood decrease as the temperature of the thermal treatment increases, provided the temperature is higher than 100 °C. The dielectric constant also decreases with increasing weight loss of the specimen

Influence of thermal treatment temperature on the dielectric properties of wood

V prispevku so predstavljeni rezultati vpliva temperature termične obdelave nadielektrične lastnosti bukovine (Fagus sylvatica L.) in smrekovine (Picea abies L.). V eksperimentu smo uporabili diskaste preskušance premera 45 mm in debeline 5 mm, ki smo jih termično obdelali pri sedmih različnih temperaturah (50 do 200 °C). Dielektrične lastnosti preskušancev smo ugotavljali pri devetih različnih frekvencah (2 do 10 MHz). Vse meritve smo opravili pri sobnitemperaturi z impedančnim analizatorjem HP 4191A RF po metodi z mikrometrom, na katerega sta bili pritrjeni diskasti aluminijasti elektrodi. Na osnovi dobljenih rezultatov smo ugotovili, da se dielektrična vrednost lesain izgubni kot zmanjšujeta z naraščajočo temperaturo obdelave, če je le-tavišja od 100 °C. Dielektrična vrednost lesa je nižja pri večji izgubi mase preskušanca.The effect of thermal treatment temperature on the dielectric properties of beech (Fagus sylvatica L.) and spruce (Picea abies L.) was investigated. Wood disks with a diameter of 45 mm and a thickness of 5 mm were thermally treated at seven different temperatures (50 to 200 °C) before measurements were performed. Dielectric properties of the wood disks were measured at nine various frequencies (2 to 10 MHz) at room temperature. The impedance analyzer HP 4191A RF and the micrometer screw method with circular aluminum electrodes were used. The results indicate that the dielectric constant and the loss tangent of wood decrease as the temperature of the thermal treatment increases, provided the temperature is higher than 100 °C. The dielectric constant also decreases with increasing weight loss of the specimen

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

High-frequency Heating of Wood with Moisture Content Gradient

The influence of moisture content (MC) gradient on the development of a temperature gradient in wood heated in a high-frequency (HF) electromagnetic field was investigated. Fifteen layers of 1.6-mm-thick beech veneer (Fagus sylvatica L.), with dimension 400 X 400 mm, were used to simulate a moisture content (MC) gradient. A uniform MC of 5, 10, 15, and 20%, and two MC gradient schemes ranging from 20% to 5%, were used in the experiment. The dielectric constant and loss tangent were measured before HF heating at 6.3 MHz. During HF heating of wood, the magnitude of the MC, the shape of the MC gradient, and the potential for thermal losses influence the development of the temperature gradient. An MC gradient in a laminated composite could be used to control the shape and severity of the temperature gradient during HF heating

Utjecaj tehnologije lijepljenja na fizikalna i mehanička svojstva lamelirane drvne građe

This paper presents the analysis of the influence of conventional hot (CH) and high frequency (HF) gluing on relevant physical and mechanical properties of Laminated Veneer Lumber (LVL) made from beech peeled veneer with the thickness of 2.1 mm. Student’s T-test was applied to determine the signifi cance of differences between mean values of results obtained for the two different treatments. A significant difference has been determined for the thickness loss, density, moisture and bending strength, while no statistically significant difference has been established for the modulus of elasticity and shear strength of gluing between the means of the tested samples.U radu je istraživan utjecaj klasičnoga vrućeg (KV) i visokofrekventnog (VF) lijepljenja na neka relevantna fizikalna i mehanička svojstva uzoraka lamelirane drvne građe (LVL) dobivene od listova ljuštenoga bukova furnira debljine 2,1 mm. Prikazani su i analizirani dobiveni rezultati. Primijenjen je T-test za određivanje značajnosti razlike artimetičkih sredina dvaju skupova uzoraka. Za smanjenje debljine, gustoću, sadržaj vode i čvrstoću na savijanje utvrđena je signifikantna razlika, a za modul elastičnosti i čvrstoću lijepljenja nije utvrđena signifikantna razlika artimetičkih sredina ispitivanih uzoraka izrađenih primjenom različitih tehnologija lijepljenja

Influence of beech particle size used in surface layer on bending strength of three-layer particleboard

It is well known that wood species and particle size used influence the bending strength of the three-layer particleboard. The purpose of this research was to determine how the size of beech (Fagus sylvatica L.) particlesinfluences the bending strength of the three-layer particleboard, where size of particles used was altered in surface layer only. Beech wood particles of five different sizes were used and blended with UF adhesive. The results show that the bending strength of boards increases with increasing particle specific surface area, increasing surface layer compaction ratio and surface layer density, while bending strength decreases with increasing surface covered with adhesive