Untersuchungen über die Holzeigenschaften von Douglasien aus linksrheinischen Anbaugebieten
The wood-properties of Douglas firs grown on various sites and under different growth conditions on the west-side of the Rhein in the districts Trier and Koblenz (mostly in the Eifel- and Hunsrück-hills) were investigated. Some of the test-trees were grown in pure stands, some in mixed stands between broadleaved species or spruces. Investigations comprehended year ring analysis, percentage of summerwood, thickness of branches, hardness, length of tracheids and wood density (based on volume when green and weight when ovendry). From several stems grown on a good site also the strength properties of wood were tested. For production of timber of high specific gravity and useful for deals and veneer an early limitation of diameter growth is desirable, however on better sites with abundant soil moisture supply is difficult to obtain. The best wood quality was found in densely stocked pure stands, while Douglas firs mixed in wide distance with broad-leaved species were rapidly grown, developed very big crowns with thick branches, conical trunks and broad annual rings. In the examined stands percentage of summer-wood was rather high. The average specific gravity value corresponded exactly with american second-growth stands of coast type. Test-trees from a fully stocked stand showed excellent stress properties, especially high values of bending strength, modulus of elasticity and shock resistance. The quality of the converted lumber cut from test-trees will be discussed in a following essay.
Untersuchung der Schälfurner-Eignung von in Deutschland erwachsenem Douglasienholz
ZusammenfassungEs wurden Versuchsschälungen an insgesamt 54 Blöcken von in Deutschland erwachsenen Douglasien durchgeführt—einerseits unter industriellen, andererseits unter pilotmaßstäblichen Bedingungen. Hinsichtlich der Schäleignung dieses Holzes sind die wichtigsten Problemfaktoren die oftmals vergleichsweise großen Jahrringbreiten, der hohe Dichtekontrast zwischen Früh- und Spätholz, sowie die Blockade der Wasseraufnahme infolge irreversiblen Verschlusses der Hoftüpfel. Lange Dämpf- oder Kochzeiten bleiben deshalb weitgehend wirkungslos. Furniere guter Qualität und mit glatten Oberflächen wurden erzielt beim Schälen von Holz, das im Winter gefällt, nur wenige Wochen naß zwischengelagert und sonst nicht vorbehandelt worden war. Der Keilwinkel des Messers betrug 20°, der Freiwinkel 2°. Der Harzgehalt des Douglasienholzes erwies sich weder beim Schälprozeß noch bei der Weiterverarbeitung der Furniere als störend. Zur Gütebeurteilung der Furnieroberflächen wurde das mechanische Tastschnittverfahren herangezogen. Das aus den geschälten Douglasien-Furnieren hergestellte Sperrholz zeigte sowohl bei der Bindung mit säurehärtenden UF-Harzen als auch mit alkalisch härtenden PF-Harzen gute Bindungsfestigkeit, die sich auch zwischen Kern- und Splintholz kaum unterschied. Die Formaldehydabgabe aus Kern-Sperrholz lag deutlich niedriger als die aus Splint-Sperrholz.AbstractRotary cut veneer was produced on industrial and pilot plant scale from 54 round logs of Douglas fir, grown in Germany. The determinant factors affecting the suitablitity of the wood for the rotary process are the often large ring widths, the big difference in specific gravity between early and late wood and the irreversible blockade of bordered pits. Consequently, long-time steaming or digestion proved to be almost inefficient. Veneer of high quality and surface smoothness has been obtained by peeling of wood felled in winter and stored for some weeks without any further treatment. The grinding and clearance angle were 20° and 2° respectively. Douglas fir was easy to handle during rotary cutting. The characterization of veneers was made according to the profile method. Plywood made from Douglas fir veneers was made using acid cuting urea formaldehyde resins (UF-resins) and alkaline phenolic resins (PF-resins). Plywood from heartwood and spwood was more or less of the same mechanical properties. The formaldehyde release from heartwood plywood was lower than from sapwood plywood.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.