Contents


Vol. 1, Issue 2, 2012

REGIONAL ASPECTS OF THE FIRM COMPETITIVENESS IN WOOD HARVESTING

Authors: Nikolay Stoenchev

Summary

An essential part of the logging in Bulgaria is done by private logging companies. From their active participation in the public procurement tenders, from their supplies of personnel and the presence of technical and transport vehicles largely depends on the planned logging – with high quality and in the right time. The peculiarities of the terrain and the different types and maturity plantations, the size of areas designated for logging and other factors cause variations in economic parameters, which they accomplish in different regions of the country. To achieve a reasonable balance between the interests of the owner of forests and the user, these differences must be analyzed, which is devoted to this study.

Keywords: labor productivity, competitiveness, investments

BG Version

PHYSICAL – MECHANICAL AND TECHNOLOGICAL PROPERTIES OF TIMBER OF THE ORDINARY CHESTNUT FROM DIFFERENT SEEDLINGS IN BULGARIA

Authors: Borislav Kyuchukov, Georgi Kyuchukov

Summary

The results from the research on the physical – mechanical and technological properties of the timber of the ordinary chestnut from different seedlings in Bulgaria are announced. Model trees for research have been provided from Belasitsa, Slavyanka, Pirin Mountain and the Western Balkans.

It has been found, that the trees of the ordinary chestnut possess suitable decorative – art, physical, mechanical and technological properties for their use in the construction of furniture, doors, windows and the interior components and monuments of culture and national – historical and decorative – art significance.

It is recommended to organize a selective timber harvest of the oval chestnut materials and purposeful use of their timber.

Keywords: Chestnut wood (Castanea sativa Mill.), physical–mechanical and technological properties of wood

BG Version

EXAMINATION OF THE INFLUENCE OF RIBS ON THE ACOUSTIC PROPERTIES OF THE DECKS FOR GUITARS

Authors: Nikolai Bardarov, Rumena Nistorova

Summary

The quality of musical instruments depends not only on good wood, but the way of construction of oscillating parts. The work examines the impact of size and location of the ribs on the distribution of the resonance of the decks for guitars.

It was tested four decks for classical guitar. Consistently was measuring the acoustic characteristics of each of the boards building decks. It was followed the change of resonances after putting the ribs of the main schemes. It was established the influence of painting on the decks of the frequency and amplitude of the resonance.

Keywords: musical instruments, resonant wood, deck, ribs, resonances

BG Version

EXAMINATION ON THE MODIFICATION OF THE VESSELS WITHIN THE ANNUAL RING IN SEVERAL SPECIES OF THE GENUS OAK (G. QUERCUS)

Authors: Nikolai Bardarov, Rumena Nistorova

Summary

The construction of the ring porous wood species strongly depends on there width of the rings. It has most changing in the size and the location of the vessels. The work examines one of the main representatives of ring porous wood - genus Oak.

It was examined several species of the genus, and it was measured diameter and density of the vessels. It was examined the change of these anatomical features within the annual ring. Made a comparison between values to determine their impact on the use of wood.

Keywords: ring porouse wood, oak, tracheas, annual rings

BG Version

THE WOODWORKING MACHINERY DURABILITY AND METHODS FOR ITS ENHANCING

Authors: Hristo Mihaylov, Neno Trichkov

Summary

On the basis of previous theoretical and experimental studies by the author of this paper, the concept of the woodworking machinery’s durability and methods for its enhancing is theoretically analyzed (presented) as one of the properties for its reliability. The coefficient of the woodworking machinery’s durability - ηт in their lifecycle for the first time is described as a dimensionless value, always less then a unity. This factor takes into account the really accomplished works and the time, needed for repairs and downtime. The ratio ηт can be widely used in theoretical studies, related to kinematics and dynamics of various mechanisms and mechanic systems in the woodworking machinery, in analyzing and working out constructive solutions about the assembly of such machines. The technical resources and exploitation period are the durability’s properties. Due to this methodology, conditions for mathematical description and analysis have been established.

Based on these facts and from the previous theoretical analyses some specific methods for growing the woodworking machinery’s durability are presented, as well as some recommendations for their applications. In theoretical analyses and studies on woodworking machinery mechanical systems this methods will be useful enough in most cases.

Keywords: durability, woodworking machinery, products, technical resources and lifecycle

BG Version

SYSTEM FOR AUTOMATIC CONTROL OF THE ROTATION FREQUENCY OF AN ELECTROMOTOR OF THE CUTTING MECHANISM OF MACHINE FOR PRODUCTION OF SLICE VENEER

Authors: Peter Petrov, Nencho Deliiski, Veselin Brezin

Summary

This paper presents the structure and functions of system for automatic control of the rotation frequency of an alternating current powerful electromotor of the cutting mechanism of machine for slice veneer production. In the system a microprocessor programmable frequency regulator for the supplying of the controlled electromotor have been inbuilt.

There is already the automated system integrated, as a result of which the productivity of the veneer slice machine has improved significantly, the specific energy consumption has reduced and the intellectual pressure of the operator has decreased.

Keywords: slice veneer, veneer cutting machine, automatic control, frequency regulator

BG Version

THE EFFECT OF FILTRATION SPEED AND INITIAL DUST CONTENT OF THE WOOD DUST ON THE FILTER FABRIC’S RESISTANCE

Authors: Petar Nikolov

Summary

The study was conducted using filter fabric Filtertex A. The fabric’s resistance at different speeds and for different dust concentrations of filtered air was calculated.

Keywords: wood dust, dust content, filtration speed

BG Version

ENERGY CHARACTERISTICS OF BIO-FUEL – CHIPS OF ROBINIA PSEDOACACIA – CLONE NUIRSEGI, GROWN ON PLANTATIONS

Authors: Ladislav Dzurenda, Miroslav Dzurenda

Summary

In this paper, there are presented the results of experimentally determined chemical composition of the combustible in dry mass of energy chips made of the wood species Robinia Psedoacacia – clone Nyirsegi grown on plantations.

The average chemical composition of the combustible of chips of Robinia Psedoacacia – clone Nyirsegi is: carbon Cdaf = 49,45 %, hydrogen Hdaf = 5,84 %, oxygen Odaf = 43,37 % and nitrogen Ndaf = 1,33 %. In comparison with combustibles of wood of fully-grown broad-leaved trees, the combustible of chips of Robinia Psedoacacia on plantations is characterised by markantly higher share of nitrogen. The share of nitrogen in the combustible of chips of Robinia Psedoacacia – clone Nyirsegi is 6,5 times higher than the content of nitrogen in the combustible of chips of Fagus sylvatica. From the environmental aspect, this fact manifests itself in the increased production of emission – concentration of nitrogen oxides NOx in combustion products, which is 4 times higher, than the valid value of emission limit in Slovakia for nitrogen oxides from the process of biomass combustion.

Keywords: bio-fuel, energy chips, Robinia Psedoacacia clone Nyirsegi, combustible fraction, emission, nitrogen oxides NOx

BG Version

THE ROLE OF POSITIVE TEMPERATURE GRADIENT IN WOOD DRYING

Authors: Teodor Lulchev, Christophоr Videlov

Summary

This study investigates the theoretical and technological aspects of concrete methods for wood drying in positive temperature gradient condition. Accelerated water movement from central wood layers to surface creates conditions for faster and better quality drying. It was explained four events when is possible benefit a similar condition: high-frequency drying, microwave drying, vacuum drying and by cyclic convective regimes.

Keywords: regimes of drying, positive temperature gradient, high-frequency drying, microwave drying, vacuum drying, cyclic convective regimes

BG Version

INITIAL STUDY ON VARIABLE TENSILE STRESS IN BAND-SAW BLADE WITH REGARD TO FATIGUE STRENGTH CALCULATION

Authors: Stefan Stefanov, Petya Koleva, Zoya Vasileva, Trayanka Gavrilova, Nikola Nikolov, Kamen Getsov

Summary

The closed contour of a band-saw blade is a bright example to the theme of the internally statically indeterminate schemes in the Strength of Materials syllabus of the students in Wood Technology at Sofia University of Forestry. An original model is proposed aimed at strength and deformation calculations of the blade which embraces the two wheels of the band-saw. The internally statically indeterminate structure problem is solved in a way in which the students are taught. At an instant position of the blade, the tensile stress is determined at various blade’s points taking into account the assembly pre-tension, the cutting force, the bending of the blade at the wheel periphery, and the heating. The stress at any point, while traveling onto the blade contour, varies and follows an oscillogram with complicated, random variations. Under such conditions, the blade is threatened by metal fatigue. A basic, approximate oscillogram has been theoretically obtained which will be complicated with additional waves in next studies. Application of the Integration of Damage Differentials (IDD) method is envisaged for fatigue life assessment as developed in the Faculty of Forest Industry. As well, the study done is envisaged to continue into possible diploma and doctoral theses of the students instructed also by professors in next school subjects. Then, additional dynamic phenomena can be involved in the calculation model, and loading spectra under different regimes of cutting can be built, etc.

Keywords: band-saw blade, statically indeterminate closed contour, metal fatigue, integration of damage differentials (IDD)

BG Version

BANDSAW BLADE STRESS ОF PORTABLE SAWMILLS

Authors: Valentin Atanasov

Summary

Studies have been done for the different stresses acting on the bandsaw blade of portable saw mills. The methods for their determination and their impact on the quality of processed surfaces are analyzed. The relationship between technical parameters of the basic machine units and bandsaw blade are investigated, as well as their impact on the magnitude of stress. The general guidelines for further research in this area are formulated.

Keywords: portable sawmill, band saw blade, stress

BG Version

STUDY ON SHARPENING OF NARROW BAND SAW BLADES

Authors: Zhivko Gochev

Summary

Sharpening and smoothing of cutting tools are basic and final stages in their preparation as well. Moreover, in these processes can not always get a edge with the necessary quality. This requires engineering and technical staff directly involved in the maintenance of the instruments to have good depth knowledge and practical skills.

The article presents results of experimental studies of narrow band saw blades sharpening with abrasive tools with ceramic and organic bond. The indicators of performance and quality of abrasive tools are defined. The durability of sharpened band saw blades was determined.

Keywords: narrow band saw blades, abrasive tools, grinding

BG Version

WOOD-POLYMER COMPOSITES BASED ON A MIXTURE OF RECYCLED POLYOLEFINS

Authors: Petar Velev, Stanislava Kovacheva

Summary

Polyolefins are among the most widely used polymers. This leads to accumulation of huge quantities of used mixed polymers, which can hardly be separated and reprocessed. Using a mixture of recycled polyolefins for preparing wood-polymer composites is one of the options for improving the properties and utilization of mixed polyolefin materials. The influence of modification of maleated polypropylene and SBR on the physical and mechanical properties of composites made from wood flour and recycled polyolefin.

Keywords: recycling, polyolefins, wood polymer composites; extrusion

BG Version

OPTIMISATION OF THE COMPOSITION OF BOARDS MADE FROM WHEAT STRAW AND SAWDUST FROM THE WOOD OF BEECH AND SPRUCE

Authors: Lillyana Valcheva, Lilia Lozanova, Todor Todorov

Summary

The utilization of wood waste for the production of boards or other composite products and their combination with different agricultural lignocellulosic raw materials has become more and more popular.

For the purpose of this study, boards were produced from mixtures of wheat straw and sawdust from the wood of beech and spruce. The following properties of the boards have been determined: bending strength, perpendicular tensile strength, water absorption and swelling in thickness. The method of SHEFFE simplex grid plans has been used for the optimisation of boards’ composition and graphs ‘composition-property’ have been drawn up.

Conclusions about the possibilities for inclusion of up to 33% wheat straw in the composition of particleboards, produced from waste raw material while maintaining the quality of the end products, have been summarized on the basis of the results from the carried out planned experiments.

Keywords: optimization, particleboards, sawdust, wheat straw, swelling in thickness, bending strength, perpendicular tensile strength

BG Version

STUDY ON INFLUENCE OF RESIN CONTENT OVER MAIN PROPERTIES OF DRY-FORMED HARDBOARDS

Authors: Viktor Savov

Summary

Fiberboards are homogeneous wood-based composite material with dispersion phase – wood fibers and matrix of adhesion and cohesion binders formed between the elements. The importance of this two binder types for board’s properties depends from manufacturing processes. The adhesion binders have main significance at dry-processes manufacturing.

At the report is presented study on influence of resin content over main properties of dry formed hardboards, produced from hardwood on the base of phenol-formaldehyde resin. For the purpose is implemented experiment in laboratory conditions. The correlation coefficient and functional subjections of fiberboard’s properties from resin content are determinate. It is conducted analyze of the results and proper conclusions are made.

Keywords: dry-formed hardboards, resin content, phenol-formaldehyde resin, correlation

BG Version

COMPARATIVE CARRY OUT OF ADHESION OF THE ADHESIVE FILMS FORMED BY CARBAMIDEFORMALDEHYDE AND ACETATE POLYMER ADHESIVES

Authors: Panayot Panayotov, Galina Saykova

Summary

This report experimentally examined adhesion of adhesive films formed by carbamideformaldehyde and polyvinilacetate adhesives to wood. It is influence of some factors (roughness gluing surfaces, specific pressure, temperature) on the values of adhesion. For this purpose used test fixtures from beech wood, glue carbamidformaldehyde PREFERE 4114 and polyvinilacetate polymer adhesive Jowacoll 124.00. Strength of adherence was defermined under the regulation of EN 302 and BS EN 205.

Keywords: gluing; adhesion, wood, reactive glues; PVAc adhesives

BG Version

NORMS FOR ULTIMATE BENDING MOMENTS OF SOME MAIN TYPES OF GLUED CORNER JOINTS OF STRUCTURAL ELEMENTS OF ONE-LAYER PINE WOOD BOARDS

Authors: Assia Marinova

Summary

The main factors concerning the strength and shape stability of the case furniture are the strength and stiffness of the joints between the furniture’s structural elements. Presently, there is high interest in furniture made of solid wood boards. This requires new studies for evaluating the strength and stiffness characteristics of corner joints of structural elements made of solid wood boards.

In this study the data are given about the experimentally established ultimate bending moments of some of the most frequently used glued corner joints of structural elements made of one-layer solid pine wood boards under compression bending test. On this basis norms for ultimate bending moments are propounded.

It was established that the type of the joints has a significant influence on their strength under bending loading. The determined ultimate bending moments and their normative values of the tested glued corner joints of one-layer solid wood boards of Scots pine under bending loading can be used by furniture designers in strength investigations of solid wood furniture, as well as for the quality assurance control in manufacturing.

Keywords: case furniture, one-layer solid wood boards made of Scots pine wood, glued corner joints, strength characteristic, ultimate bending moments, compression bending test, norms

BG Version

DURABILITY OF PROTECTIVE DECORATIVE COATINGS FORMED ON THERMALLY MODIFIED WOOD PANELS

Authors: Zhivko Georgiev

Summary

The durability of polymer coatings, formed on thermally modified spruce wood articles outdoor exposed was investigated. It was applied two regular coating systems (alkyd system; waterborne acrylate system). It was made some marks on destructions in wood and coating during four year outdoor exploitation. It is discover that after four years exploitation waterborne acrylate protection have a local destruction in crater form in the beginning and totally removed in these zone after, while alkyd system is practically destructed in zone near to end. Thermally modified wood without coating become grayish and cracked in the ends. This tendency is also valid for alkyd protection, but not really valid for waterborne acrylate. The coatings do it with alkyd system protection has character destruction in zone of summer timber, which is more underlined for tangential samples.

Keywords: thermally modified spruce wood, alkyd coatings, acrylate coating, coating destruction

BG Version

USE OF FMEA METHOD IN MANUFACTURE OF CABINET FURNITURE TO INCREASE QUALITY

Authors: Julia Mihaylova, Diyana Mladenova

Summary

Quality of products manufactured takes an extremely important position in all types of manufacture today. This is necessitated by the continuously growing competition at market level – customers value more and more quality products and turn to those companies that can give them the necessary thing according to their requirements. This applies especially to furniture-manufacturing companies.

That is why of extreme importance is to find the exact approaches and methods for quality management and assurance. One of those methods is the FMEA (Failure Mode and Effect Analysis) method that is an analytical engineering method used to examine and eliminate potential discrepancies, problems, faults and errors.

The aim of the paper is to establish the possibility of application of the FMEA method in increasing the quality of cabinet furniture manufactured, with following tasks having been carried out: an assessment of the risk of allowing potential discrepancies, problems, faults and errors during manufacture of cabinet furniture in specific company has been performed, by characterising the reasons leading to them by means of application of the FMEA method; the necessary actions for improvement have been determined; a new assessment of the risk of potential discrepancies, problems, faults and errors after performance of the outlined improvements by means of the FMEA method has been made.

Keywords: quality, FMEA, risk assessment, cabinet furniture

BG Version

CORPORATE DESIGN. ELEMENTS AND DEVELOPMENT STRATEGIES

Authors: Jancho Genchev

Summary

The development of design and manufacturing companies follows different stages. In the conditions of continuous competition, the contemporary world features increasing and developing globalization and internationalization of economic processes in the conditions of information and telecommunication revolution. In the paper, the basic elements of corporate design are considered, as the basis of creating an integral concept of corporate identity. A special attention is given to the choice of strategy for the design of serial and individual pieces of furniture.

Keywords: corporate design, design methods, furniture

BG Version

HOUSING STOCK IN BULGARIA. CURRENT STATE AND TRENDS

Authors: Maria Marinova

Summary

During the years of transition housing stock has changed rapidly. Social changes have led to changes in the material world. The new way of life implies a different perspective on the living environment, which acquires a new appearance. It is of interest to note the dynamics of differentiation in the type and quality of housing in our country. The purpose of the present work is to determine the housing stock current state and the trends in its development.

Keywords: housing stock, changes, trends

BG Version

STUDY OF ARCHITECTURE IN BULGARIA DURING THE 19TH TO MID 20TH CENTURY

Authors: Aleksandrina Parvanova

Summary

In the article, the development of Bulgarian architecture from the Revival period to the mid-20th century is considered. An analysis is performed of existing historical patterns in the residential and public architecture. Their development is traced over the time. The research aims to show how eclectical European style of this period leaves a mark on Bulgarian architecture. The purpose of this study is to explain the variety of styles in interior and furniture, using basic architectural elements as a source.

Keywords: architecture, Bulgarian architecture, historical patterns, Revival architecture

BG Version

ECO?!?

Authors: Pavlina Vodenova

Summary

In the vast variety of different products today demand adequate sources of inspiration for designers every day has become increasingly challenging. Very recently become fashionable all new products carry the label „eco“ or „bio“, but whether this is just a way to attract consumers' attention to them, or rather – is building a new behaviour, oriented towards the establishment of responsibility to the planet and its precious resources – that's the issue, seeking the answer to the author. Looking at the recent past, and tracking the development of different labels until today concludes that the name „green“ or „organic“ must not be used for its own sake, that no longer have a product to be produced only by the fact that economy has a need for it – rather in its design to be rationalized each country, the author adds a new - namely – to consider the so-called. „Second life“ of the product, and how important is the current life cycle of products „from cradle to grave“ to be replaced by a new – „cradle to cradle.“ This should become the responsibility of many people, including designers.

Keywords: ecological, bio, design, harmless

BG Version

SOLAR THERMAL SYSTEMS' SIMULATION PROGRAMS

Authors: Maya Stoyanova, Liliana Takeva, Rumen Stoykov

Summary

The optimum utilization of the renewable energy potential is one of the priorities of the Bulgarian economy and energetic. Investors and engineers increasingly often face questions connected with taking the best solutions concerning solar thermal systems, solar yield and the quantity of delivered energy. World market offers a great number of simulation programs for solar thermal energy assessment: yield prognosticating ones, others for solar thermal system sizing, process optimization, etc. A comparative analysis has been made in the present study of the stimulation programs for solar thermal systems. A classification is suggested according to the process of programming and examination made of models representing the classification. Each of the instruments is described in short together with an account of its good and weak points. A table presents information for the different model comparison based on users’ necessary qualification, number of program users, users’ category, the computer platforms needed, program language, prices, etc. The information presented can serve a substantial advantage for engineers, constructors, university lecturers and students working in the field of RES.

Keywords: renewable energy sources, solar thermal systems, simulation programs, models, energy assessment

BG Version

TECHNOLOGIES FOR THE BIO FUELS PRODUCTION FOR ENERGY PURPOSE FROM WOOD WASTE

Authors: Nikolay Vangelov

Keywords:

EN Version