Съдържание


Vol. X, Issue 2 2021

PROPERTIES OF WOVEN GLASS FIBER FABRIC REINFORCED POLYPROPYLENE BASED WOOD PLASTIC COMPOSITES

Автори: Sefa Durmaz, Yusuf Ziya Erdil, Erkan Avci

Резюме

Wood-plastic composites (WPCs) have excessively taken place in the construction industry in recent years. The high technological properties are crucial for WPCs when utilized as structural members. In this study, flat-pressed WPCs produced with polypropylene (PP) were reinforced with woven glass fiber fabric to enhance their properties. The effect of intensity of woven fabric (195 gr/m2 and 390 gr/m2) and wood flour content (40, 50, 60%) on WPCs' physical and mechanical properties were investigated. The addition of a coupling agent (CA) positively influenced WPCs' mechanical properties and restricted water absorption. However, water absorption increased with an increase in wood flour content. The increase in water exposure time from 1 day to 30 days increased water absorption up to 37%. In terms of water absorption, there was no significant difference between reinforced WPCs and controls. The reinforcement of WPCs improved mechanical properties significantly; i.e., flexural strength was increased up to 252%, while tensile strength reached up to 667%. As expected, the increase in wood flour content decreased mechanical properties. The incompatibility between wood flour and PP negatively influenced WPCs properties. It could be concluded that, if configured appropriately to the usage conditions, flat-pressed WPCs reinforced with woven glass fiber fabric have a potential for areas where high strength is required.

Ключови думи: Wood-plastic composites, reinforcement, glass fiber, physical properties, mechanical properties

EN Version

ANALYSIS OF ANATOMICAL ELEMENTS AS WOOD TEXTURE CHARACTERISTICS

Автори: Nikolai Bardarov, Nicole Christoff, Vladislav Todorov, Petar Antov, Mariana Kaludova

Резюме

In recent years, more and more systems for computer recognition of tree species are entering, which show good results in solving a certain group of problems. Some of them have already proven themselves in solving such tasks as quality control of wood materials. Studies also show that the classifications of tree species used so far do not allow to solve more general problems of structural wood science. The approaches, methods and means used in computer recognition for modeling the structure of the wood presuppose such a classification of the tree species, which should be based on a more general view on the structure of the wood in comparison with the methods used so far. This would allow to study and describe in a single formalized classification scheme all the anatomical elements that are observed with the corresponding increase in the samples of tree species. In addition, it is necessary to specify the term "texture", applicable in the computer structural anatomy of wood for the purposes of using the methods of computer vision.

The paper discusses the initial results of research related to the application of the requirements of computer modeling in solving some problems of wood anatomy. In particular, recommendations have been made for the quantitative characteristics of the study region in the wood samples and for the description of the anatomical elements making up the wood that will fall into this region and can be examined with sufficient accuracy.

Ключови думи: identification of wood, wood texture, vessels, core rays, annual rings

EN Version

PROPERTIES OF HIGH-DENSITY FIBERBOARDS BONDED WITH UREA-FORMALDEHYDE AND PHENOL-FORMALDEHYDE RESINS

Автори: Viktor Savov, Petar Antov, Neno Trichkov

Резюме

Urea-formaldehyde (UF) resins are the most common type of resins used in the production of wood-based panels. Despite their numerous advantages, the main drawbacks of these thermosetting aminoplastic resins are the deteriorated water resistance, emission of hazardous volatice organic compounds, and to a lesser extent, the reduced strength. Hence, for producing wood-based panels with increased quality, a modification or partial replacement of UF resins should be performed. There are many previous studies on the improvement of UF resins with melamine-formaldehyde (MF) resins. The partial replacement of UF resins with phenol-formaldehyde (PF) resins has been studied to a lesser extent.

The aim of this research work was to investigate the effects of replacing the UF resin with PF resins on the properties of high-density fiberboards (HDF). The panels were produced at a press factor of 15 s.mm-1 and a pressing temperature of 220 °C. The resin content in fiberboards was 6%, based on the dry weight of fibres. A complete replacement of UF with PF resin was performed with an increment of 1%. It was found that at 50% content of PF resin in the adhesive system, the panels meet the strictest requirements for load-bearing applications and use in humid conditions. For achieving further improvement of fiberboard properties, the PF resin content should be increased to 83.3%.

Ключови думи: wood-based panels; high-density fiberboards; adhesive system; urea-formaldehyde resin; phenol-formaldehyde resin

EN Version

ACCESSIBILITY OF THE ENVIRONMENT TO DISADVANTAGED PEOPLE

Автори: Maria Kitchoukova

Резюме

During past years the number of people with temporary and permanent disabilities has been constantly increasing. This trend turns the question for the accessibility of everyday living environment for the disadvantaged people into lively and important topic. This current study is motivated by the relevance of this problem and is based on analysis and comparison of recent and existing regulation in Bulgaria and different countries around the world. In order to support the results obtained and to gather additional information about the current situation, a survey was conducted among people with disabilities, the data from which was analyzed and the relevant conclusions were made.

Ключови думи: standards, accessible environment, disadvantaged people

EN Version

INFLUENCE OF SOME FACTORS ON ADHESION STRENGTH IN THE FORMATION OF WATER-BASED FINISHES ON BEECH PLYWOOD

Автори: Dimitar Angelski, Krasimira Atanasova

Резюме

Adhesion strength is an indicator of the coating’s detachment resistance from the base. The magnitude of the adhesion strength depends on the nature of the lacquer system, the type and state of the substrate, and the film formation conditions. In this study, a water-based varnish system was applied to beech plywood. The influence of а sandpaper grit size used and the time between а sanding and coating processes has been determined.

Ключови думи: adhesion strength, plywood, sanding, water-based finishes, coating

EN Version

A STUDY ON THE EFFECT OF THE BEARING CLEARANCE OF THE WHEELS ON THE MOVEMENT OF THE BAND SAW BLADE

Автори: Valentin Atanasov, Petar Nikolov

Резюме

The present work refers to verification of the axial run-out of the band saws blades in band saw machines, as their geometric accuracy. It has been determined that the axial force is applied when rotating the wheels by hand, which, in the presence of bearing clearances, results in a displacement of the band saw blade in one direction for each complete rotation which does not allow its geometric accuracy to be determined.

The effect of the bearing clearances of the wheels on the trajectory described by the back part of the band saw blade is studied. The deflection of the crown of the guide wheels when applying a force of 150 N in the direction of feed for worn and new bearings was measured, as well as the displacement of the back of the band saw blade in this direction for these two bearings. Displacement of 0.2 – 1.1 mm of the band saw blades in one direction has been detected for each complete rotation which depends on the condition of the bearings. It is recommended that such verification should be carried out on relatively new bearings and that no axial force will be applied to worn ones.

Ключови думи: band saw machines, band saw blades, run-out of band saw blade, frontal run-out

EN Version

FORCED SPATIAL VIBRATIONS OF A WOOD SHAPER CAUSED BY THE WEAR OF THE CUTTING TOOL

Автори: Georgi Vukov, Valentin Slavov, Pavlin Vitchev, Zhivko Gochev

Резюме

This study presents the results of conducted investigations of the forced spatial vibrations of a wood shaper, caused by the wear of the cutting tool. The paper is based on a specific mechanical – mathematical model, developed by the authors, which allows studying of vibrations of this type of machinery. In this model the wood shaper is regarded as a system of three rigid bodies, which are connected by elastic and damping elements with each other and with the motionless floor. This study renders an account the mass, inertia, elastic and damping properties and geometric parameters of the machine. A necessary system of matrix differential equations is compiled and analytical solutions are presented. The results of the numerical investigations are presented. They are obtained through modern software and by using parameters of a particular machine. The results show that the amplitudes of the body’s vibrations are relatively small but the amplitudes of the spindle’s vibrations are significant especially at resonance zones.

Ключови думи: forced spatial vibrations, cutting tool, woodworking shaper

EN Version

MODEL FOR TRAINING ENGINEERING DESIGN STUDENTS BY USING METHODS FROM HUMANITIES AND SOCIAL SCIENCES

Автори: Pavlina Vodenova, Ophelia Kaneva

Резюме

This article presents a successful model of training practice as part of the student’s education in "Engineering Design" (Interior and Furniture Design) Program at the University of Forestry. Stimulation and emphasizing the strengths of the learners by provoking a new teaching style for the traditional training of designers and engineers is the main accent of this model. The model itself is not just conceptual, but also applied in the training of students in design programs and could be also successfully implemented in a wide range of cross-disciplinary platforms in the training of designers and engineers (and not only). At the same time, this innovative approach highlights new forms of support for students' learning progress, expanding the operationalization of their involvement in direct work with clients with diverse status and needs.

Ключови думи: design, project week, design project, rehabilitation through design, educational management, students’ potential, universal design

EN Version

EXPERIMENTAL STUDY IN PRIMARY WOOD CUTTING WITH CIRCULAR SAW AND BAND SAW MACHINE

Автори: Valentin Atanasov

Резюме

Experimental research on some performance indicators of a circular saw machine (Kallion Konepaja Oy – Finland) for longitudinal cutting of logs were performed. The accuracy of the machine operation and the roughness of the boards were measured successively. For this purpose, the feed speed vf was varied widely, from 4 to 100 m.min-1. The test specimens are of beech wood (Fagus silvatica L.). The research place was the manufacturing facility of Pentop Ltd. – Varshets. The results were analyzed and compared with those obtained previously with а band saw machine.

Ключови думи: circular saw machine, logs, surface quality, productivity

EN Version

EXPERIMENTAL APPLICATION OF THE METHOD OF FOCAL OBJECTS IN DESIGN EDUCATION

Автори: Desislava Angelova

Резюме

This article discusses the practical application of the Method of Focal Objects in the learning process of students in the Engineering Design (Interior and Furniture Design) Program at the University of Forestry, Sofia, Bulgaria. The experiment has been conducted in studied course Innovative and Strategic Design with the students of the first course from the Master Degree Program. The experiment's main objective is to examine what influence the Method has on students' creativity. The methodology of the experimental conducting of the Method and the way of work have been described. Based on the obtained results, analyses have been made for the Method's application in students' learning process to develop their non-standard and analytical thinking.

Ключови думи: design methods, design education, creative and associative thinking

EN Version