VOLUME 48, ISSUE 2/2007

The rise of the prices for fossil fuels in the last years and the agreements for the reduction of the greenhouse gas emissions led to an intensified use of wood chips. The range reaches thereby from small wood chip-fired central heating to wood chip-fired combined heat and power plants. Therefore a partial treatment by drying and/or screening of the utilized fuels can be necessary. The drying process can be

carried out naturally or technically (e. g. use of the waste heat of biological gas facilities). Investigations showed that by indoor storage of hardwood-chips a water content less than 30 % can be reached steadily. With the processing of the wood chips into different particle size groups for instance the fine fraction (lead to operating disturbances in larger heat plants) or over sized particles (lead to disturbances with the fuel supply in smaller heating plants) will be removed. This was demonstrated within practice relevant investigations. However, an absolute removal of these particles is not possible, due to technical reasons. Furthermore, the possibilities of wood chips processing and drying are discussed using two practical investigations. The generated actual costs (for Northern Germany) are presented.

Natural constructions rate as optimal regarding their form, function and strength. Investigations of optimization strategies in nature leaded to findings and methods [1], which evoke growing interest in the technical fields and are subsumed today under the term bionic. Solutions based on natural examples do not rest upon the direct usage of these concepts and constructions but on the transfer and adaptation

of their principles. Thus, the usage of curved or branched tree sections as for example in the former ship building trade is not considered anymore. The progress in the field of the information technology, especially the computer aided construction and production as well as the photogrammetry, pave the way first time for an industrial control of complex structures with smallest lot sizes, from which new approaches in civil engineering and architecture follow. In this context, the structural behaviour of codominant branches of deciduous trees, especially ash, is investigated. A new connection concept is motivated in association with textile reinforced wooden tubes, which is treated experimentally and numerically.

The elastic constants of solid wood panels were determined using eigenfrequency and bending tests. The determination of the eigenfrequency offers the possibility of non-destructive testing subsequent to the production. MOE determined by static bending tests correspond with values from eigenfrequency by flexural mode. It was hard to determine a direction depending shear modulus out of torsion swinging with the applied method. Thus a “mixed modulus” was determined, which can only be divided into its components by analysing the distribution of strain. The static bending tests generate clearly repeatable results. The method for determining the bending MOE, as presented in DIN EN 789, also works pretty well for smaller samples. Shear modulus have also been measured by using bending loads perpendicular to plane.

For the investigation of the hardening characteristics of adhesives the ABES system can be used. Investigations were carried out at Institut f
r Holztechnologie Dresden (IHD), using standard UF resins under variation of different technological parameters (temperature, time) and the adhesive formulation (type and amount of hardener). Higher press temperatures or a longer press time always resulted in a better shearing strength. A particleboard production realized parallely showed that there were certain

optima in the production. A direct transfer of the characteristics of surface gluing of veneers to the punctual gluing of particles and wood fibres is not possible. A better suitability of the equipment is given in the case of a comparison of different resin formulations and the influence of certain additives. It is possible to reduce the expenditure of laboratory-scale panel manufacture by the application of the ABES

system.

The series of papers shows new potentialities for the Automation and assurance of efficiency in the machining of shaped wooden parts. These new potentialities are based on the hexapod of simple design. In the first part [3] the relevant spectrum of parts including the requirements to process and motion of the wood machining was initially characterized. Furthermore the hexapod was specified as a flexible and low cost motion system for the economical machining of shaped wooden parts. In this paper the application-project “Parallel kinematic machining centre for shaped wooden parts” [2] shall be introduced. This project was executed together with the Professorship of Wood- and Fibrous Materials Technology (Prof. Wagenführ) of Technische Universität Dresden. The milling machining of a veneer press blank for a seat shell was selected as a concrete example. The automation technological challenge of this example consisted in the efficient connection of the part handling and the machining.

The true surface temperature at the edge of a woodworking tool can not be measured, therefore its value may be underestimated. Theoretical and experimental investigations were performed to establish the effect of cutting speed, chip thickness, tooth angle and edge wear on heat intensity, the zone of heat introduction, convective heat transfer intensity and temperature distribution within the cutting tool. Finite element analysis of the temperature distribution showed that the edge surface may reach high average temperatures (400 to 600 K). In addition, due to a high amplitude cyclic temperature fluctuation, high peak temperatures (more than 1000
C) may develop near the edge for a very short time. Softening may occur in a less than 0.1 mm thick layer near the edge, and the duration of temperatures exceeding the softening limit (around 600
C) is 5 to 8 · 10–4 s within each revolution.

Low-frequency ultrasonic echo technique with longitudinal and transversal waves is well suitable for the non-destructive testing of wood. The anisotropy of wood has a varying influence on the different kinds of acoustic waves, and this influence may under certain conditions be disregarded for transversal waves. Particularly suitable for practical use are point contact probes that do not require coupling agent for

attachment to the surface. The localization of invisible areas with reduced thickness or hidden damage (e. g. interior rot or structurally inaccessible surface rot) is very important. The non-destructive ultrasound echo technique allows the detection of areas with reduced thickness by showing an echo with shorter running time, whereas interior damages are located indirectly through shading of the back wall echo. The efficiency of the ultrasonic echo technique is demonstrated on wooden samples with drilled holes.

Within a research project, thermally modified timber (TMT) of four wood species (Pine, Spruce, Beech, Ash) were investigated and tested, considering the use for playground toys. The material (12 TMT types) was obtained from 9 European manufacturers and 3 process types. The investigations were focussed on assessment of the wood quality an on tests of natural durability (laboratory and field tests), mechanical properties. Furthermore, a study on legal restrictions and conditions (building law) for the use of TMT for playground toys was compiled, also considering load bearing applications.