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VOLUME 61, ISSUE 1/2020

Modelling of wood cutting processes; Part 1: Introduction and basic considerations

Language: German
Pages: 5 - 10
Authors: Christian Gottlöber, André Wagenführ

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Modelling is the base of planning, forecasting and optimizing of wood cutting processes. Since long time ago many researches trying to find effective possibilities to get useful results therefor. Modelling means the finding of a single formula or a set of equations describing the dependency of certain input variables to certain output magnitudes of the process. The more the inputs and the more the variability of the material properties the more difficult and unreliable is the modelling result mostly. Especially the varying properties of wood as a natural, hygroscopic, inhomogeneous and anisotropic material make the modelling of wood cutting processes to a general challenging subject. Within the cutting process some output magnitudes are of interest representing the efforts and the benefits of the process. In terms of wood cutting the cutting quality, the cutting energy respectively the cutting forces, the tool wear and the emissions of noise and dust are the categories of these magnitudes modelling is aiming. Input variables or influencing factors are the geometrical, kinematical and material properties which can be defined for the cutting process e. g. as wood species, moisture content, cutting direction, edge angles, cutting speed and chip thickness. Part 1 of the publication focuses on an introductory description of the situation, a systematic analysis of the machining process on wood and wood-based materials and the identification of levels of consideration for process modelling. In part 2, different modelling strategies and types as well as related model examples and possibilities of determining quantities using available sensors are discussed against the background of future requirements in autonomous, intelligent machines (smart machines).

Utilization of small hardwood for the production of cross laminated timber; Part 1: Log grading

Language: German
Pages: 11 - 15
Authors: Lukas Müller, Sabrina Puttmann, Marcus Müller, Bertil Burian

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As a consequence of climate change and the implementation of natural silvicultural concepts the amount of hardwood in the forests of Germany will increase. Hardwood, especially when coming with small diameters, has been mainly used for energetic purposes so far. For the future new areas for material uses have to be found in order to secure the high value-added production in the timber industry. Therefore, the possibility of using small diameter beechwood in cross laminated timber elements was investigated. Part 1 of the publication deals with the round timber assortment “small beechwood” and the sorting into four quality classes, as well as the influence of different quality characteristics. The study is based on 74 round wood sections of strength classes D 2a to D 3b. The total amount was 18.23 solid cubic meters, of which 92 % were graded in quality class C and 8 % in quality class B. In the second part of the publication, the achieved timber yields and qualities are presented.

The effect of wood alignment in the grinding process – Properties of the resulting ground pulps and fines, and microscopic observations

Language: German
Pages: 16 - 24
Authors: Sabine Heinemann

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During industrial wood grinding, round logs are pressed against a rotating stone, with the logs and fibre (tracheid) axes parallel to the axis of the stone. For this study, wood blocks were fed into a laboratory grinder with various alignments in relation to the surface of the grinding stone. The effects of the alignment on the properties of the pulp, the amount, and the quality of the fines were measured, and a grinding mechanism is proposed. The obtained results show that the pulp quality is highly sensitive to the angle between the stone surface and the log, and different for fatigue-based and force-based grinding. The results are discussed using microscopic techniques. In gentle grinding, the fibre structure is loosened by fatigue before it is bent on the surface, pressure pulses produce fibrillar material. In forced grinding, the process is “violent” and the fibre wears and is crushed immediately on the surface into small particles.

Natural light protection of wood using heartwood extractives

Language: German
Pages: 25 - 30
Authors: Lars Passauer, Christian Walter, Franz Dieringer, Bastian Schubert, Almut Wiltner, Jana Peters

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Decorative wooden surfaces for high-end furniture and interior Fittings are preferentially made of transparently coated intensive or dark coloured wood types and thermally modified timber (TMT). Exposure to daylight often causes intense and unwanted discolouration of the respective surfaces, which cannot sufficiently be stabilised by conventional light protecting systems. In the present paper, novel colour stabilization concepts based on wood extractives are discussed that consider discolouration phenomena of intensive and dark coloured wood species primarily caused by Wood extractives and wood colours/pigments and their sensitivity towards visible light.

Acetylated beech wood in bridges and towers

Language: German
Pages: 31 - 36
Authors: Reiner Klopfer, Jürgen Graf

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The use of beech wood for load-bearing purposes in areas of direct weathering is made possible by chemical modification (acetylation). The European beech can be classified in the durability class DC 1, the shrink-age and swelling behaviour is reduced by approximately 65 % in outdoor areas. Basically, the compressive strength of acetylated boards increases by 30 % (longitudinal pressure) and by 60 % (transverse pressure) compar-ed to native beech boards. The longitudinal tensile strength is reduced by 20 %, the bending tensile strength is reduced by maximum 12 %. Acetylation leads to increased cracking as a result of transverse tension, the spiral grain of beech boards therefore causes large spreads in tensile strength. Laminated beech veneer lumber with vertical acetylated veneers leads to homogeneity of the mechanical properties. The mean value of the bending strength of acetylated beech veneer lumber is approximately the same as that of acetylated solid wood boards. Due to the smaller spread of the individual values around the mean value, the characteristic bending strength increases significantly by 44 %.

Selective hot pressing – a new approach to additive manufacturing with wood

Language: German
Pages: 37 - 40
Authors: Henry Burkhardt

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The subject of a research project at the Institut für Holztechnologie Dresden (IHD) was the investigation of the preconditions for “additive manufacturing” (AF) with a high wood content. For this purpose, concepts for AF with wood were developed, using the known mechanisms from the production of wood-based materials as a reference. A further subject of the project was the testing of different construction materials consisting of wood particles and binding agents with regard to their suitability for AF. A derived method is the “Selective Hot Pressing” (SHP). Here, a mixture of wood particles and binder is pressed layer by layer, whereby the compression and heating is carried out selectively according to the cross-section of each layer. A process has been developed to implement this method in lab scale. With construction materials based on spruce particles, simple geometries could be produced in an additive manner.

Development of a special waste paper digestion and a dry-glue process for waste paper fibres for the production of board in the dry process

Language: German
Pages: 41 - 47
Authors: Tino Schulz, Christoph Wenderdel

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The objective of this project was the development of cardboard produced in a dry process. The new cardboard should be used as potential substitute for traditional cardboard from the wet process. Therefore, the cardboard must meet the requirements for mechanical properties, creasability and foldabaility. For a cardboard production without water, low energy consumption and low costs, processes of the wood-based panel and textile industry were combined. In addition, special raw materials had to be used (e.g. wastepaper, starch). The laboratory cardboard production includes the waste paper digestion with a horizontal turbo-mill, gluing of fibres and fibre mats, mat forming with an air laid system and hot pressing of a mat stack to multilayer cardboards with a basis weight of 220 kg/m² to 840 kg/m². The dry-processed cardboard achieved values for strength, creasability and foldabaility comparable to cardboard. This demonstrates the potential of this new type of material.

Higher Education in Wood Science in Europe and worldwide; Part 30: Mongolia (Part 2)

Language: German
Pages: 48 - 54
Authors: Marius C. Barbu, Bayartsetseg Baasan, Tsedenpuntsag Tsogoo

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In 13 parts were presented the main high educational centers for wood science and technology of 33 European countries. Part 14 to 21 presented an introduction regarding the North American forest and wood industry as well the Canadian and USA institutions for wood science and research. Part 22 to 29 started an overview in Asia (Iran, Japan, Mongolia, Thailand, and Vietnam) and this paper is continuing with aspects of the wood economy, wood research and technology higher education in Mongolia.

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