Orthogonal cutting forces in juvenile and mature Pinus taeda wood

Abstract

The distinct characteristics of juvenile and mature woods, which are observed particularly in softwoods, have an influence on processing due to their different mechanical resistance properties in relation to cutting operations. In the past, when most of the wood used industrially came from adult trees of natural forests, little importance was given to a distinction between different zones of the tree stem. At present, however, as the supply of mature trees with large diameters from native forests is constantly decreasing, the use of short-cycle trees has become a common practice, through the adoption of species that grow relatively fast, such as pines and eucalyptus. In both softwoods and hardwoods, juvenile wood cells are generally smaller and thinner than in mature wood, and this reflects on their density and mechanical resistance, which should have an effect on the cutting forces developed during processing. The main object of this research was to evaluate orthogonal cutting forces in juvenile and mature Pinus taeda woods. Cutting force magnitude differences were observed for those two regions of the trunk, with parallel cutting forces being 33.4% higher, on average, at the mature wood region for 90-0 cutting, and 12% higher for 90-90 cutting. This result is consistent with the distinct anatomical structures of the material, since the forces developed during machining depend directly upon its properties. Key words: wood machining, softwood, plantation wood, cutting optimization FORÇAS DE CORTE ORTOGONAL NA MADEIRA JUVENIL E ADULTA DE PINUS TAEDA RESUMO: As características distintas dos lenhos juvenil e adulto, existentes principalmente na formação das coníferas, influenciam na usinagem devido às diferentes propriedades de resistência mecânica ao corte. No passado, quando a maior parte da madeira utilizada industrialmente era proveniente de árvores adultas de florestas naturais, pouca importância era dada à diferenciação de zonas no tronco. Atualmente, no entanto, com o decréscimo constante do suprimento de árvores adultas de grandes diâmetros, provenientes de florestas nativas, tornou-se comum o aproveitamento da madeira de ciclos curtos, através da adoção de espécies de crescimento relativamente rápido, como exemplo os Pinus e os eucaliptos. Tanto nas coníferas quanto nas dicotiledôneas, as células da madeira juvenil são, geralmente, menores e mais delgadas do que na madeira adulta, refletindo em sua densidade e resistência, o que deverá afetar as forças de corte desenvolvidas durante o processamento. O objetivo principal desta pesquisa foi avaliar as forças de corte ortogonal nas madeiras juvenil e adulta de Pinus taeda. Houve diferenças de magnitude das forças de corte nessas duas regiões, sendo as forças de corte paralela, em média, 33,4% maiores na zona de madeira adulta, no corte 90-0, e 12% maiores no corte 90-90. Esse resultado é coerente com a diferenciação da estrutura anatômica do material, uma vez que as forças geradas durante a usinagem dependem, diretamente, de suas propriedades. Palav...

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