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.
Impact of spacing and pruning on quantity, quality and economics of Douglas-fir sawn timber: scenario and sensitivity analysis
Controlling the long-term effect of management on the quantity and properties of individual boards is a fundamental challenge for silviculture. Within this basic study on Douglas-fir, we have investigated the sensitivity of the net present value (NPV) to three most common planting densities and a prominent pruning strategy. We therefore have applied an individual tree growth model, which represents intrinsic stem structure as a result of crown competition. The model extrapolated board strength development to the rotational age of 70 years, starting from real and comprehensive data recorded from experimental Douglas-fir plots at the age of 20 years. Total volume production increased from about 1600 m 3 ha −1 for 1000 and 2000 trees ha −1 to 1800 m 3  ha −1 for 4000 trees ha −1 . The economic superiority of the lowest density stands increased considering the NPV at inflation-adjusted interest rates of 0%, 2% and 4%: Given an interest rate of 2% and no pruning, the NPV at 2000 was at about 50% of the one at 1000 trees ha −1 . The NPV at 4000 trees ha −1 was even negative. Generally, artificial pruning was not effective. The revealed financial trade-off between growth and timber quality in young stands underlines the importance of silvicultural guidelines, which quantify the effect of management on yield per strength class and financial outcome.
Determination of Optimal Ball-Burnishing Parameters for Plastic Injection Moulding Steel
The objective of this study is to determine the optimal plane ball-burnishing parameters for plastic injection moulding steel PDS5 on a machining centre by utilising the Taguchi’s orthogonal array method. The design and manufacture of a burnishing tool are described. Four burnishing parameters, namely the ball material, burnishing speed, burnishing force and feed, were selected as the experimental factors in Taguchi’s design of experiments to determine the optimal burnishing parameters which have the dominant influence on surface roughness. The optimal burnishing parameters were found after carrying out the experiments specified by Taguchi’s L18 orthogonal table, by the analysis of variation, and by a full factorial experiment. The optimal plane burnishing parameters for the plastic injection moulding steel PDS5 were a combination of a tungsten carbide ball, a burnishing speed of 200 mm/min, a burnishing force of 300 N and a feed of 40 μm. The surface roughness Ra of the specimen can be improved from about 1 μm to 0.07 μm by using the optimal burnishing parameters for plane burnishing.