Veneer stiffness predicted by NIR spectroscopy calibrated using mini-LVL test panels

Pinus radiata D. Don) veneers. Spectral data obtained from 1.2×2.4 m veneer sheets was corellated against stiffness data obtained from 6-ply mini-LVL panels prepared from the sheet. This paper describes the method used to prepare the mini-LVL test pieces and the results of multivariate regression of NIR spectra with the test piece stiffness. The results show the potential for using NIR spectroscopy for on-line assessment of veneer stiffness prior to layup of plywood or LVL panels. Selection of high stiffness veneers for layup would enable engineered panels of high uniform stiffness to be produced.

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Pinus radiata D. Don.) wurde unter Verwendung von NIR Spektroskopie vorhergesagt. Spektroskopische Daten von 1.2×2.4 m grossen Schichtholzfurnieren wurden korreliert mit der Elastizit?t von 6-schichtigen mini-Furnierschichtholzplatten, welche aus diesen Schichtholzfurnieren hergestellt worden waren. Dieser Artikel beschreibt die Methode, mit welcher die mini-Furnierschichtholzplatten hergestellt wurden, und die Ergebnisse der multivariaten Regression von NIR Spektren und der Elastizit?t der Proben. Die Methode zeigt, da? eine prinzipielle M?glickkeiten besteht, NIR Spektroskopie für eine on-line Beurteilung der Furnierelastizit?t zu verwenden, bevor diese zu einer Sperrholzplatte geschichtet werden. Eine Auswahl von Funieren mit geringer Elastizit?t vor der Schichtung würde es erm?glichen, Platten mit geringer, einheitlicher Elastizit?t herzustellen.

     

The potential of phenol–formaldehyde as plasticizing agent for moulding applications of wood veneer: two-dimensional and three-dimensional moulding

Two phenol–formaldehyde resols, namely a low and a medium molecular weight phenol–formaldehyde, were investigated for their applicability as plasticizers in moulding of European beech veneer (Fagus sylvatica L.). Therefore, beech veneers specimens were impregnated with both phenol–formaldehyde resol types in various concentrations. Subsequently, two-dimensional mouldability of the veneer was tested in a three-point-bending test along and perpendicular to the grain. Additionally, three-dimensional moulding of the phenol–formaldehyde impregnated veneer was tested throughout a modified Erichsen cupping test, where the veneer is pressed through a circular shaped coining die. The obtained results indicate a significantly improved mouldability of the treated beech veneers compared to untreated, water-saturated control specimens. Even at low phenol–formaldehyde concentrations plasticizing effects were detected in longitudinal direction and perpendicular to the grain. These findings are substantiated by results from three-dimensional moulding. Furthermore, the low molecular weight phenol–formaldehyde treated veneers displayed a higher mouldability than medium molecular weight phenol–formaldehyde specimens at similar phenol–formaldehyde concentration.     

Effect of laminated structure design on the mechanical properties of bamboo-wood hybrid laminated veneer lumber

The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a one-piece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (B-bamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.     

The mechanical behaviour of veneer subjected to bending and tensile loads

Bending and tensile tests were carried out on veneer of beech (Fagus sylvatica L.) and European oak (Quercus robur L./Quercus petraea Liebl.) with a thickness between 0.35 mm and 0.5 mm. The tests were done on veneer in two test series, one parallel to the fibre and the other one perpendicular to the fibre. Mechanical properties and bending radiuses were measured and evaluated. It could be concluded that the bending properties of the veneers not only depend on the bending stiffness but also the mechanical strength and structure of the material. During the tests it could be shown that the 3-point bending test procedure is not a suitable method for determining the bending modulus of rupture.     

高含水率染色、固色桦木单板的胶合性能探讨

高含水率染色、固色单板的胶合质量是制造人造薄木的关键技术之一。试验比较、分析了不同含水率条件下,素板、染色、固色单板的胶合强度。结果表明：随着含水率的升高,素板、染色和固色桦木单板胶合强度均呈下降趋势,并且其湿状胶合强度均明显低于各自的干状胶合强度;素板的干湿状胶合强度均明显大于染色和固色单板。     

Natural decay resistance of LVL made of veneers from durable and non-durable wood species

Laminated veneer lumber (LVL) was laboratory manufactured using veneers from decay and non decay resistant species in order to evaluate changes in the durability as a result of the LVL manufacturing process, and to test if the mixing of decay resistant species and non decay resistant species can improve durability. Laboratory soil block test and field test were conducted. The durability of solid wood was comparable to that of LVL made using the same species. For LVL made using veneer from durable and non-durable wood species, durability was improved when two faces and one core veneers were from decay resistant species.     

Furnierverarbeitung in der Türen-, Paneel- und Möbelindustrie

True wood vencers are nowadays gaining increasing importance in varous fields of wood industry. The processing of veneers with suitable machinery is of special interest for the manufacture of doors and panels, as well as for furniture. This paper describes the preparation of veneers by smoothing (“ironing”) by means of special hot presses and trimming by vencer seissors. Further attention is given to three veneer jointing procedures at present in use: the respective equipment, its functions and capacities, are described. With respect to costs the three systems are compared and, finally, evaluated.     

Influence of the slicing technique on mechanical properties of?the?produced veneer

The aim of this investigation was to compare the mechanical behaviour of lengthwise and plain sliced veneer of the species beech (Fagus sylvatica L.). Therefore, tension tests parallel and perpendicular to the grain were carried out. The results were evaluated using the variance analysis (ANOVA). As a result it can be stated that lengthwise sliced veneers exhibit significantly higher strength and better mechanical characteristics than plain sliced veneers. The checks parallel to the grain which occurred by manufacturing at that side of the veneer leaf which faces the cutting edge and which is stressed in tension are to be considered as reason therefore. In contrast to the tests parallel to the grain the modulus of elasticity perpendicular to the grain shows significantly lower values for lengthwise sliced veneers than for plain sliced veneers. Due to their higher strength values lengthwise sliced veneers are considered better base materials for engineered wood products than plain sliced veneers.     

Perpendicular to grain and shear mechanical properties of veneer-based elements glued from single veneer sheets recovered from three species of juvenile subtropical hardwood plantation logs

This paper quantifies the mechanical properties perpendicular to the grain and in shear of glued rotary peeled veneers, as would be encountered in veneer-based structural products (i.e. by including both the effects of hot pressing the veneers and the glue used during the manufacturing process), of three species recovered from juvenile (early to mid-rotation) subtropical hardwood plantation logs. This underutilised resource has currently little to no commercial value in Australia but proven potential to produce attractive veneer-based structural products. Determining these unknown properties is important as they constitute essential input data to ultimately predict the behaviour and design properties of veneer-based structural products in cost-effective numerical simulations. Two species planted for solid timber end-products (Gympie messmate—Eucalyptus cloeziana and spotted gum—Corymbia citriodora) and one species traditionally grown for pulpwood (southern blue gum—Eucalyptus globulus) are considered in the paper. The dynamic modulus of elasticity, compressive and tensile strengths perpendicular to the grain of veneer-based elements, each manufactured from single veneer sheets, were experimentally measured and are analysed herein. These properties are found to have no to weak correlation to the parent veneer sheet dynamic modulus of elasticity parallel to the grain, a value which is commonly measured in line to grade veneers. The shear modulus (in the longitudinal-tangential plane), also referred to as “modulus of rigidity”, through-the-thickness and rolling shear strengths were also experimentally measured, and the results are discussed in the paper. Little to no correlation to the veneer sheet dynamic modulus of elasticity parallel to the grain was found for these properties. Weibull distributions are fitted to all test results and presented to probabilistically consider the investigated properties in numerical simulations of veneer-based structural products.     

Ultrasound evaluation of lathe check depth in birch veneer

In this study, the lathe checks in birch veneer were examined with contact ultrasound and a preliminary study for the measurement with air-coupled ultrasound from green birch veneer (moisture content 60–75%) was carried out. The contact measurements were conducted from dry veneer and then from moistened veneer. Several ultrasound parameters measured from dry veneers were related with lathe check depth, e.g. correlation between ultrasound transit time and lathe check depth was 0.63 (p<0.001, N=30) when measuring perpendicular to grain from unchecked face of the veneer. The same correlation for moistened veneers was 0.74 (p <0.01, N=12). Furthermore, air-coupled reflection and through-transmission measurements were carried out with green veneer samples. In air-coupled through-transmission measurements, it seemed that moisture content dominated the measurement when measuring parallel to checks. There was also positive correlation between energy-related parameters in through-transmission and reflection measurement, which could be utilised to measure the properties of veneer with transducers on one side.