Лесотехнически Университет

Summary

Some results, obtained by the work of international research project: Integrated future-oriented management of forest landscapes - INTEGRAL are presented. The decision support system (DSS) SYBILA were partly adapted and used for the first time in Bulgaria. The results of indicators changes model: total volume of standing timber, volume and yield class structure of possible timber cutting volume and total biomass volume under different forest management regimes on the territory of Yundola and Teteven for the period of 50 years are analysed.

Summary

Of the numerous environmental factors affecting tree growth, the relationship between site quality and tree growth seems to be the most important. In this work, the production of fir wood (Abies borisii-regis Mattf.) on quantitative and qualitative basis was investigated in relation to three different site qualities (II, III, IV) at the University forest of Pertouli-Trikala, Greece. For the grading of round timber produced from 268 fir trees, the EN 1927-1:2008 CEN standard was employed. The results showed that the site quality has an influence on both quantitative and qualitative production of fir wood. Higher production and better quality of fir wood were found to be produced in the site quality II, while in the site quality IV, the quantity and quality of wood produced were less and inferior, respectively. In the site quality III, the production and quality of fir wood were at intermediate level.

Summary

Torrefaction is a thermal treatment step in a relatively low temperature range of 210–240˚C, which aims to improve the dimensional stability and durability of wood. The weight loss kinetics for torrefaction of wood samples was studied using equipment specially conceived to measure mass losses during thermal treatment. Laboratory experiments were performed under nitrogen. A mathematical model for the kinetics of the thermodegradation process was used and validated. Measurements of temperature distribution and weight loss were performed sample of poplar wood during pyrolysis in an inert atmosphere at 230°C. The mathematical formulation describing the simultaneous heat and mass transfers requires coupled nonlinear partial differential equations. These unsteady-state mathematical model equations were solved numerically by the commercial package FEMLAB. A detailed discussion of the computational model and the solution algorithm is given. Once the validity of different assumptions of the model had been analyzed, the experimental results were compared with those calculated by the model. Acceptable agreement was achieved.

Summary

The aim of this study was to determine the glue joint shear strength of thermally modified pine (Pinus silvestris) and birch (Betula pendula) in comparison with the unmodified wood and to look at the possibilities of its simultaneous gluing on the same equipment in the same conditions. For the experiments used two types of glue: polyvinylacetate glue (PVAc) Kleiberit 303.0 and polyurethane glue Kleiberit PUR – 501.0. Afterwards glue joint ultimate strength in shear parallel to the grain was measured.

Summary

In this article the, process of longitudinal solid wood profile milling has been studied. In the first part of the article, an analysis is done with regard to: the profile of universal cutterhead used for experimental studies; the characteristics of the chips formation process by longitudinal milling; the influence of the feed per tooth and the accuracy of the cutter teeth placement on the quality of the processed surfaces. The conclusions will be used in the experimental investigation of the milling processes.

Summary

This article presents the results of experimental studies of longitudinal solid wood profile milling. In the present part II, the influence of the cutter rotational frequency and the feed rate on the roughness of the processed surfaces are tested. The studies were carried out in the laboratory of „Cutting of wood and cutting tools“ to University of Forestry. For this purpose universal wood shaper machine, model FD-3 (Bulgaria), with bottom-mounted shaft and mechanical feed of material was used. The results obtained can be used as a basis for the formation of specific recommendations aimed at increasing the reliability of the machine and the accuracy and quality of the production.

Summary

A static analysis of the main shaft of a universal band saw with two bearing supports, a console drive side wheel and console V-belt pulley is carried out by the method of finite elements (FEM) with Autodesk Inventor ProfessionalÒ. The 3D model of the band saw shaft is generated with all elements of the real shaft – keyslot, grooves for clip ring, centre holes, chamfers, filets, and etc. Two variants of loading are set: first for vertical V-belt transmission and second for horizontal V-belt transmission. Stresses, strains, displacements and factor of safety distributions are obtained and visualized in the 3D model of the band saw shaft for these variants. The effected differences in the static strength of band saw shaft are analyzed.

Summary

The proposed study presents a numerical investigation of the forced torsional vibrations in the wood shaper’s saw unit caused by the variable moments on the drive electric motor and the wood shaper’s saw. The influence on the vibrations of the blades’ number of the saw, which really work, is investigated. This research is done on the base of a concrete mechanic-mathematical model for investigation of the torsional vibrations of a wood shaper’s saw developed by the authors. The main features in the construction of this kind of wood shapers are rendered an account in this model. The investigation`s results can be used as a base for making some concrete and well-founded recommendations concerning the operation of these machines. These recommendations are important for increase of reliability of the wood shapers as well as the accuracy and quality of their production.

Summary

The methodology for calculation of the shafts and the axles subjected to deformation taking into account the radial clearance in the bearings is presented in the paper.

Deflection of the shafts and axles is determined for two cases: the first one is when the antifriction bearings are assumed to be perfectly solid supports and the second one is when the above-mentioned are assumed to be elastic.

The deflection of the antifriction bearings is a sum of the initial clearance and the elastic deformations of the antifriction bodies and their rings.

The aim of the present work is to determine the elastic deformations of the antifriction bodies and the rings of the bearings.

Summary

In spite of the different diameter and density of the vessels of diffuse porous species, they can be more or less similar in these characteristics. This study discusses the differences of the vessels in several Bulgarian local growing tree species which have only single row core rays.

There are measured the average diameter and density of the vessels. Using them, the area of the individual anatomical components is calculated. The mean and the variance are determined in order to be used as diagnostic indicators. An examination of the statistical significance of the samples is made in order to determine which of the anatomical features can be used to identify the wooden species.

Summary

For use in this search, was realized thermally treatment by temperature 210ºC on spruce, beech and poplar wood in sunflower oil and glycerol environment. Thermally treated wood have some differences from natural, like colour, odor, density and other physical and mechanical properties. From this wood was produced samples with measure 30х30х10mm (last one in longitudinal direction). In parallel with this was produced control samples from same wood dried to constant weight by temperature 102±3ºC. It was determinate water vapour adsorption of samples according to BDS 16987-89.

Summary

Wood machining through milling is one of the wide-used cutting processes in woodworking and furniture industry. It is also one of the noisiest, due to the high noise immission levels that often exceed the accepted sanitary standards.

In this work the influence of the feed rate, the speed of the working shaft (or cutting speed) and the thickness of the out cut layer on the noise levels, measured at work place, generated during Pinus silvestris L. milling process has been evaluated.

Summary

A mathematical model of the specific heat energy, which is needed for defrosting of wood materials in the hygroscopic range, qbfr, has been suggested. The specific heat energy qdfr consist of two parts: the energy needed for heating of the frozen wood until melting of the ice in it, qwfr, and the energy needed for the melting of the ice formed from the bound water in the wood, qbw. Using the suggested model computations have been carried out for the determination of qwfr, qbw and qdfr = qwfr + qbw during defrosting of oak, pine, beech, and poplar frozen wood with moisture content from 0.2 kg·kg-1 up to the border of the hygroscopic diapason and with initial temperature in the range from −20 oC to −2 oC, at which the thawing of the ice formed from the bounded water is completed.

Summary

During DAAD 2013 research stay of the first author in Rosenheim Faculty of Wood Technology, joint research started into dynamics and strength of bandsaw blades. This paper is, in fact, the first one under the above title resulting from cooperation with Professor Scholz and his team. They have dealt with problems concerning dynamic instability of new sawblades with special crowned tooth shape. Studies had been carried out under various blade-tensioning and guide-system conditions. Now, FE analysis has been involved by means of Autodesk Inventor software. An approach has been proposed and developed for FE modelling the complicated buckling of bandsaw blades by substituting it with a sufficiently equivalent eccentric compression. Research results and conclusions on the reasons for the instability of blades with crowned tooth shape are presented.

Summary

The problem of the internal forces and stresses in the blade of a horizontal band-saw is statically indeterminate in the case of pre-tensioning by a spring. After our solution in a preceding article, in this paper the internal forces and stresses in the different parts of the blade are considered. Some remarks are addressed to the interpretation of such stresses in the bandsaw references reviewed. As well, stresses are analyzed relating to bending the blade over the wheel contours. Additional stresses are also outlined: at the guide rollers, other more bending stresses, as well as stresses due to torsion of the blade, etc.

Summary

The paper presents basic energy characteristics of wood pellets from different producents. We took the samples from producents in Bulgaria and in Slovakia. Energy characteristics of the pellets, such as their dimensions, moisture content, content of ash, gross and net calorific value were estimated in accordance with European technical standards. We used the standard STN EN 14961-1:2010, Solid biofuels as a basic platform for estimation. Values of net calorific value belonged to interval between 16,103 MJ.kg-1 and 17,120 MJ.kg-1, moisture content values were in interval 7,2÷12 %. We observed ash content of the samples from 0,43 to 1,47 %. All of tested samples met the requirements of the standards for ecological biofuel.
 

Summary

Тhe aim of the research presented in this paper is to study the water resistance of experimental plywood bonded with alcohol-soluble phenol-formaldehyde resin. The evaluation of water resistance is made on the basis of the obtained data for the changes of the physical properties of plywood after exposure to prolonged water treatment. Tests for the thickness swelling, volume swelling and water absorption are made after immersion in water for prolonged period in controlled laboratory conditions. The measuring of thickness, length, width and mass of plywood specimens for determination of these properties is made after immersion in water for the period of 1 day (24 hours) to 52 days (1248 hours).

The experimental plywood model was made from peeled beech veneers. Pure alcohol-soluble phenol-formaldehyde resin is used as plywood binder.

The research results showed that the plywood model has uniform density; it is dimensionally stable during and after prolonged water treatment, without any deformations of the shape of the test specimens. The changes of the values of thickness and volume swelling, as well as the values of water absorption in the analyzed period are proportional to change of the duration of the period of water treatment. According to the obtained data from the tests of these properties the plywood model meets the requirements of the standard for load-bearing plywood for use in construction.

Summary

Subject of the investigation is the prognostication of the resistance of structural three- and multilayer particleboards (SPB) to continuous static bending load under the conditions of relatively dry environment. The theoretical prerequisites of the development are the rheological model of SPB and the schematic diagram of their deformation during continuous load, the algorithm and the nomogram to determine the stiffness of SPB on the basis of their simulation model of a “double T-beam” and the regression dependences of the moduli of elasticity of SPB with various thicknesses on their volumetric density.

An algorithm and a nomogram to determine the continuous load factor of SPB to prognosticate their resistance as structural elements in furniture and building structures have been proposed. The creep coefficient of composite particleboards under operating conditions has been determined.

Summary

On the basis of performed literature overview and analysis of the effect of production modes on physical indices of fibreboards, following variable factors were determined: pressing temperature, board thickness and binder content.

In this paper, the results of the performed analytical and empirical investigations with respect to the effect of pressing temperature, board thickness and binder content on physical properties of MDF-type boards (medium-density fibreboards manufactured after the dry method) made of hard hardwood species are presented. Regression models showing the effect of variable factors on board indices were derived. The changes in the values of those indices in case of combinations of levels of production factors were examined. Analysis of the result was made, with the respective conclusions having been drawn.

Summary

Determination of quality of production of the same kind is performed in its predominant part by means of sampling test. This also applies to manufacture of particleboards (PBs). Statistical methods allow assessing and comparing the quality of products. To assess and compare the quality of individual manufacturers with respect to standard requirements, an interval estimate of the arithmetic mean value of indices has been used, and to compare the quality between different manufacturers, a test of hypothesis with respect to mean values of two samples has been used.

After performed tests of laminated particleboards (LPBs) of different manufacturers, statistically significant differences in the quality level between individual manufacturers have been established.

The aim of the investigation is approval of methods for application of statistical methods when selecting a manufacturer / supplier of PBs according to objective criteria related to production quality.

Summary

The role of driver tracing is significantly expanded by identifying drivers unrelated to the volume of product produced. The use of both unit- and non-unit-based activity drivers increases the accuracy of cost assignments and the overall quality and relevance of cost information. Such cost accounting systems are called an activity based cost (ABC) systems. In woodworking exist a great deal of auxiliary processes which require specific costs drivers due to precise the cost allocation. In this paper is made an attempt of modeling and testing of such a methodic for costs tracing and allocation in lumber production.

Summary

The paper illustrates the potential for application of constructive-building components made of glued laminated timber, as alternative to traditionally used elements of solid wood. An example is proposed to demonstrate the promise of these structures by the use of finite element method. The comparison of the stress - strain state between structural element of solid wood and glulam is described in the paper, based on calculations, made according to the national regulations.

Results and the comparison between them gives hope to expand the opportunities for effective application of glued laminated timber structures in the Bulgarian construction practice, as well as, for engineers, designers and architects, and with more complicated shapes and longer supporting distances.

Summary

The manufacture of curved wooden details is a technological process with long duration. Repeatedly reducing the time needed for plasticizing and drying the wood may be performed by its high-frequency heating. The basic regime parameters that control the production of curved detail in high frequency electromagnetic field are: the frequency of the electricity (respectively of the field power), the water content in the material, the duration of the process (plasticizing, bending and stabilization), the relationship between the anode and grid current (Ip/Ia). Drawing up a regime for faultless performance of the operation is a difficult task with multiple alternatives. However, there are insufficient data and research upon that issue, especially for a comprehensive regime including consistent implementation of the phases of plastification, bending and drying of wood. In this connection, some regimes of high frequency plasticizing, bending and drying were carried based on beech details. The conducted regimes were assessed by the duration of the production cycle and the final production waste.

Summary

The traditional forms of education used to answer the needs of the young people at a time when it was possible with a relative certainty to foresee the knowledge and skills from which they are going to need in the years of their mature life. Today it is not like this. The young people cannot expect already to spend their whole life in one and the same sphere of activity and even at one and the same place; their professional way is about to change in a way could not be foreseen, and they need a broad circle of common skills, which will let them adapt. In a more complex and globalized world the creative skills, the ability to think in a multifunctional way, the skills in different fields, and their adaptability as a tendency are valued more than the specialized knowledge.

To answer these needs, it is necessary as part of the syllabuses on the disciplines, apart from the knowledge, which should be taught, to be given the results (the skills and the habits which are expected to be developed from the educated at different stages of their education).

In the present research a theoretical framework for electronic education is introduced and the issue for discussion is: Could the modern systems for electronic education provide the young people with skills and motivation for the turning of education into a whole life activity?