Faisabilité du déroulage du bois assisté par infrarouge.

Abstract : In the wood-products industry ‘peeling' is the process of converting a log into a continuous thin ribbon of green wood (from 0.6 to more than 3 mm thickness) termed veneer. Veneers are mainly used for manufacturing light weight packaging and Engineer Wood Products (EWP) such as plywood, Laminated Veneer Lumber (LVL) and Parallel Strand Lumbers (PSL). These three latter EWPs manufactured from veneers glued and pressed together, are amongst the most used wood products. That is the reason why the production of veneer plays an important role in the wood-products industry. For certain species, the peeling process requires the prior heating of round green-wood to temperatures ranging from 30 to 90 °C. This treatment is necessary to increase wood deformability, to reduce the severity of lathe checking in the veneers and to reduce cutting forces. It is usually done by immersion in hot water or by steam treatment. However it has many disadvantages amongst which are the duration of treatment (12 to 72 hours), the washing out of polyphenolic extractives - which causes water pollution and can affect wood's natural durability - low yield and energy losses.The goal of this PhD thesis was to develop a heating system embedded on the peeling lathe to circumvent many of these disadvantages. Infrared technology appears to be the most promising solution because of the ease of integration into the peeling process and of the power it offers, enabling the required heating temperatures to be achieved quickly and follow the highly demanding peeling speeds in use in the industry (from 1 to 5 m.s-1). This new technology, using radiant energy to heat green-wood prior to peeling, would be a major innovation for the industries involved in the production of plywood, Laminated Veneer Lumber (LVL), etc.The plan to achieve this goal consisted of:- Creating a model of infrared heat transfer in green wood while peeling it, with the characteristics of wood (moisture content, thermal properties) being amongst the input variables,-Investigating the thermal and optical characteristics of green wood (in terms of penetration depth and infrared absorption by green wood) to feed the model,-Validating the model with experimental peeling tests assisted by an infrared heating system.One of the main outputs of this study was to demonstrate that the penetration depth of infrared radiation into green wood is limited to several tenths of micrometers. Heat transfer into green wood up to the cutting plane (located several millimeters underneath the surface) is by conduction, which is slow due to the insulating properties of wood. Heating green wood with infrared radiation is therefore unable to match the highly demanding peeling rates in use in the industry today. However, the use of an embedded heating system in the case of slicing and the potential impact on improving veneer quality (colour, surface quality) remain open for further research.
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Anna Dupleix. Faisabilité du déroulage du bois assisté par infrarouge.. Autre. Ecole nationale supérieure d'arts et métiers - ENSAM, 2013. Français. ⟨NNT : 2013ENAM0044⟩. ⟨pastel-00999086⟩

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