Louis Denaud

Wood peeling process monitoring: a comparison of signal processing methods to estimate veneer average lathe check frequency

Experienced peeling operators are able to adjust the settings of their device by hearing the sound coming from the process. Based on this idea, a research program was undertaken to evaluate the possibility of using acoustic or vibration measurements supplying a support decision system to assist untrained operators.The present paper deals with lathe check phenomenon which is one of the most critical defects of veneer (leading to handling difficulties, excess of glue consumption, poor veneer surface quality, etc.). Several signal processing techniques giving a spectral representation of sensors measurements are compared. Finally, an original procedure based on Power Spectral Density ratio is proposed to measure the average lathe check frequency of the veneer during the process.ZusammenfassungErfahrene Schälmaschinenführer können die Maschineneinstellungen nach Gehör vornehmen. Davon ausgehend wurde ein Forschungsprogramm initiiert, in welchem untersucht werden soll, ob Schall- oder Schwingungsmessungen als Entscheidungshilfe für unerfahrene Arbeiter genutzt werden können.Die vorliegende Studie beschäftigt sich mit Schälrissen, einem der kritischsten Mängel bei Furnieren, die zu Schwierigkeiten bei der Bearbeitung, wie z. B. übermäßigem Klebstoffverbrauch oder schlechter Qualität der Furnieroberflächen führen können. Verschiedene Signalverarbeitungsverfahren, die eine spektrale Darstellung der Sensormessungen liefern, werden verglichen. Abschließend wird ein neues Verfahren zur Messung der mittleren Rissfrequenz bei Furnieren vorgeschlagen, das auf dem spektralen Leistungsdichteverhältnis (PSD) basiert.

Analysis of chip formation mechanisms and modelling of slabber process

During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability. Thus, this study aims at better understanding and predicting chips production in wood milling. The different mechanisms of their formation were studied through orthogonal cutting experiments at high cutting speed for beech and Douglas fir. Under these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on beech. As previously seen in quasi-static experiments, chip thickness is proportional to the nominal cut thickness. Moreover, the grain orientation has a great influence on the cutting mechanisms, so as the nominal cut and the growth ring widths. This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling. In order to optimize machine design as well as cutting geometry, a geometrical model of a generic slabber head was developed. This model allows the study of the effective cutting kinematics, the log-cutting edges interactions and the effective wood grain direction during cutting. This paper describes the great influence of the carriage position on cutting conditions. The results obtained here can be directly used by milling machine manufacturers.

Modelling the effects of wood cambial age on the effective modulus of elasticity of poplar laminated veneer lumber

Key messageA modelling method is proposed to highlight the effect of cambial age on the effective modulus of elasticity of laminated veneer lumber (LVL) according to bending direction and veneer thickness. This approach is relevant for industrial purposes in order to optimize the performance of LVL products.ContextLVL is used increasingly in structural applications. It is obtained from a peeling process, where product’s properties depend on cambial age, hence depend on radial position in the log.AimsThis study aims to highlight how radial variations of properties and cambial age impact the mechanical behaviour of LVL panels.MethodsAn analytical mechanical model has been designed to predict the modulus of elasticity of samples made from poplar LVL panels. The originality of the model resides in the integration of different data from the literature dealing with the variation in wood properties along the radius of the log. The simulation of the peeling process leads to veneers with different mechanical properties, which are randomly assembled in LVL panels.ResultsThe model shows a correct mechanical behaviour prediction in comparison with experimental results of the literature, in particular with the decrease in MOE in LVL made of juvenile wood. It highlights that the bending direction and veneer thickness have no influence on the average MOE, but affect MOE dispersion.ConclusionThis paper proposed an adequate model to predict mechanical behaviour in the elastic domain of LVL panels based on the properties of raw wood material.