Title: Physical properties of juvenile fir-wood [Abies alba Mill.) from Gorski Kotar
Author: Tomislav Sinković
Felling of small-diameter trees has posed a threat to fir (Abies alba Mill.) in the Gorski Kotar region. In logs obtained from small-diameter trees the share of juvenile wood has been increasing. It is therefore important to be aware of juvenile fir-wood properties in order to be able to define the processing modes. This research has covered the properties of ring width, oven dry wood density, basic density, longitudinal, radial, tangential and volumetric shrinkage, and fiber saturation point for juvenile and mature fir-wood. The research has been carried out on ten fir trees at breast height (breast height diameter being 25-30 cm for four trees, 31-40 cm for two trees, 41-50 cm for two trees, 60 cm and more for two trees). Juvenile and mature wood were distinguished on the basis of the radial shift in the trend of physical properties distribution. Such a method does not grant the establishment of a firm line between juvenile and mature wood. Juvenile fir-wood covers the inner part of a trunk, 30-40 rings from the pith. This has been concluded on the basis of the radial shift in ring width distribution trend, in density of oven dry wood and in tangential and volumetric shrinkage trends. The other physical properties have been neglected in final consideration because of the great variation in data. Under the assumption that juvenile wood encompasses the thirty innermost rings, the density of oven dry wood mean value is 0.3976 g/cm3 for juvenile wood and 0.4977 g/cm3 for mature wood; the tangential shrinkage mean value is 7.7% for juvenile wood and 8.8% for mature wood; the volumetric shrinkage mean value is 11.8% for juvenile wood and 13.6% for mature wood. If juvenile wood is assumed to spread over the forty innermost rings, the mean values are: 0.4083 g/cm3 (juvenile wood) and 0.4512 g/cm3 (mature wood) for oven dry wood density; 8% (juvenile) and 8.9% (mature) for tangential shrinkage; 12.3% (juvenile) and 73.7% (mature) for volumetric shrinkage. It can be generally stated that juvenile fir-wood has larger ring breadth, lower oven dry wood density, lower tangential shrinkage and lower volumetric shrinkage than mature fir-wood.
Title: Research of noise levels emitted by two-spindle moulders
Author: Vlado Goglia, Ružica Beljo
The protection of work environment from emitted noise, vibrations, gases and dust is nowdays the production process designers\' main concern. This problem is gradually winning adequate attention in Croatia, too. Work environment protection problems are particularly emphasized in woodworking industry. At the Faculty of Forestry in Zagreb protection from noise and vibration has been systematically studied for more than 20 years now. The paper presents the results of routine measurements regularly carried out at wood-working plants by researchers of the Department for Mechanical Engineering of the Faculty of Forestry, University ofZagreb. Presented are the measured noise levels emitted by two-spindle moulders. Because of the high level of the emitted noise, the moulders were placed in a separate room. But, the small room volume and the proximity of reflecting surfaces resulted in a noise level significantly above the noise level limits. The measurements covered all operator positions. According to the results of the measurements the operators, depending on the position, should not be exposed for more than 1/4 to 1 hour without adequate personal protection. In order to optimize personal protection the octave band analysis was carried out.
Title: Application of Hamm’s approximate method of electric power determination for transport means research
Author: Ružica Beljo, Jaromir Malek
This paper presents Hamm\'s approximate method of determination of the consumed electric energy in three-phase asynchronous induction electric motors. The method gives brief and sufficiently exact information for a selection of advisable technical factors in working conditions. The basis of this approximate method is dependence of power factor cos φ upon electric motor load. Using empiric data, Hamm has developed a diagram for determination of electric power on the basis of measured current for three characteristic values of the power factor (cos φ = 0.7; cos φ = 0.8; cos φ = 0.9). The method is illustrated with a practical example where specific consumed electric energy of a pneumatic and a mechanical conveyor is determined. Results of the research have confirmed that mechanical conveyor is more favourable than pneumatic conveyor with respect to power.
Title: Wood preservation and European regulations
Author: Božidar Petrić, Radovan Despot, Jelena Trajković
Wood, being a product of a living tree, is liable to deterioration due to abiotic and biotic factors. The rate of wood degradation is dependent on its natural durability which varies from species to species. Those of poor natural durablility have to be chemically protected to prolong their time of service. Intensity of protection depends on the environmental conditions in which the wood is used. Various European regulations are made concerning the ways of choosing the wood species, chemicals and intensity of protection, all depending on the place of use. In view of the intention of Croatian economy to participate on the European market, this article wants to review European regulations in the field of wood protection, and thus help Croatian regulations to be in keeping with the European ones. The first part of the article describes mechanisms of the most important wood deteriorating factors, while the second one presents European regulations in the field of wood protection.