Съдържание

Vol. XIV, Issue 1 2025

HOW TO FIND RESONANCE WOOD?

Автори: Nikolay Bаrdarov, Nikolai Minkovski

Резюме

Wood is widely used to produce sound emitters (decks) of musical instruments. This wood is called resonant. Although this name does not accurately reflect the physical nature of the phenomena occurring in wood when used in musical instruments, it is widely used in practice and in technical literature. 
The article examines the parameters that make a wood resonant. It is suggested that wood should be tested only when it meets part of the requirements and does not have good sound qualities. In this way, the influence of one or several factors can be isolated, and their importance on the quality of the wood can be determined. 

Ключови думи: resonance wood, spruce, musical instruments

EN Version

ANALYSIS OF DIAMETER TAPER IN FIR (ABIES ALBA Mill.) AND SPRUCE (PICEA ABIES L.) SAWLOGS FROM 1ST AND 2ND QUALITY CLASS

Автори: Ana Marija Stamenkoska

Резюме

The success of sawmill capacities mainly depends on the rational use of raw materials, specifically the logs for sawing. The rational use of sawmill logs is primarily influenced by quantitative yield. The quantitative yield is a complex matter influenced by several parameters, with the main ones related to the sawmill logs. The key parameters include the diameter of the logs, their length, and the diameter taper. This study focuses on analyzing the diameter taper of fir (Abies alba Mill) and spruce (Picea abies L.) sawlogs from 1st and 2nd quality class. Taper, which represents the gradual reduction in log diameter from the base to the top. By examining 80 selected logs from the sawmill company in Berovo, Republic of North Macedonia, this study identifies patterns in taper rates across eight diameter groups. The results show the impact of taper on log utilization, highlighting the implications for sawing efficiency and wood quality. 

Ключови думи: diameter taper, fir, spruce, log geometry, log volume, mean diameter, quality class, sawmill

EN Version

OPTIMAL PRETREATMENT CONDITIONS OF INDUSTRIAL HEMP RESIDUES TO GLUCOSE

Автори: Vencislav Blyahovski, Stoyko Petrin, Ivo Valchev, Vesislava Toteva

Резюме

Hemp (Cannabis sativa L.) is an annual herbaceous plant with excellent agrarian and economic characteristics and has been used since ancient times as a raw material for making fabrics. Industrial hemp, with its high biomass yield per hectare, has great potential for the production of biofuels and valuable products. Regulatory documents in Bulgaria allow the cultivation of cannabis plants only if they are intended for fibres, seeds for animal feed or sowing if they have a content of less than 0.2% tetrahydrocannabinol. The residue of hemp after such processing is characterised by a hardwood-like content of cellulose, hemicellulose and lignin but with a very low bulk density. The specificity of the biomass residues and the woody structure of hemp stalks requires an additional mild, wet beating prior to enzymatic hydrolysis.  
The present work aims to investigate the effect of mechanical treatment of steam-exploded hemp residues on glucose yield after enzymatic hydrolysis and to determine the optimal pretreatment conditions. The classic steam and CO2 steam explosion methods are used as the first pretreatment step in this investigation. It has been found that the mechanical processing of hemp pulp leads to higher glucose yields after enzymatic hydrolysis, and this effect is reduced by increasing the steam explosion temperature. 

Ключови думи: hemp, mechanical treatment, enzymatic hydrolysis, glucose

EN Version

SATURATED WATER STEAM CONSUMPTION STANDARD FOR THE PROCESS OF STEAMING BEECH WOOD WHILE ELIMINATING DIFFERENCES IN THE COLOR OF SAPWOOD AND FALSE HEARTWOOD

Автори: Ladislav Dzurenda

Резюме

The article presents the normative values of the consumption of saturated water steam for steaming beech lumber with false heartwood wood of thickness h = 40 mm by a volume of 16 m3 in pressure autoclave AZ 240 for the purpose of eliminating colour differences between sapwood and false heartwood by steaming modes I. and II. The norm of water steam consumption for the steaming process of beech wood using mode I, uniting the wood to a light brown colour, is mH2O-I = 2637.6 kg. Normative heat consumption for the process of steam mode II. to dark brown-gray coluor is            mH2O-II = 3051.9 kg.  
The discontinuous process of steaming wood in an autoclave is characterized by uneven consumption of saturated water steam, the largest consumption is at the beginning of the technological process when heating the steamed wood and the autoclave. In the heating phase, in the most demanding mode of steam consumption, mode II, mH2O = 856.4 kg.h-1 steam is consumed. After heating, the consumption of saturated steam drops significantly to mH2O = 6.1 kg.h-1. The practical benefit of specifying the consumption of saturated water steam in the process of steaming wood in a steam autoclave is when planning the production of heat in the heat source – the boiler room of the plant and the capacity load of the waste water treatment plant. 

Ключови думи: beech wood, sapwood colour, false heartwood color, steaming of wood, consumption of saturated water steam

EN Version

MACHINES FOR PRIMARY LOG CUTTING: PART II – COMPARATIVE ASSESSMENTS AND ANALYSIS

Автори: Valentin Atanasov

Резюме

In the paper a developed methodology is presented, which will be useful in a comparison between individual machines for primary cutting of logs – a vertical band saw machine with a carriage feed mechanism (Üstünkarli – Turkey), circular saw machine for logs (Kallion Konepaja Oy – Finland) and a mobile horizontal band saw machine (Arsov 90 Ltd. – Bulgaria). On the basis of the obtained experimental results, which are presented in the first part of the current study and the technical parameters of the machines, the following evaluation indicators were selected: productivity, dimensional accuracy, roughness of the obtained surfaces, width of the cut, required power, cutting tools, etc. The obtained quantitative results were transformed into point scores. For each of the indicators, a weighting coefficient is also selected, depending on its importance. The advantages and disadvantages of the studied machines are indicated and an analysis of the results is carried out. 

Ключови думи: log cutting band saw, log cutting circular saw, mobile horizontal band saw, productivity, dimensional accuracy

EN Version

WOOD-BASED BUILDING MATERIALS WITH A THERMAL ENERGY STORAGE FUNCTION

Автори: Meysam Nazari, Mohamed Jebrane, Nasko Terziev

Резюме

Encapsulating of phase change materials (PCM) in ceilings, floors and walls improved energy storage in buildings. The results show 10% saving of thermal energy by using bio-based, building materials with added functionality. 
The environmental impact of fossil-based materials on the construction industry and significant energy consumption in housing have driven the production of bio-based, renewable and sustainable materials for building applications. This is achieved by incorporating bio-based PCM into wood materials for thermal energy storage in residential buildings. 
Phase change materials absorb and release heat when changing from a solid to a liquid state. Organic PCM in form of fatty acids or esters produced from renewable resources, e.g., vegetable oils are suitable for the purpose. PCM can be impregnated in solid wood, wood fibers or sawdust and in the developed wood-based composite materials.  
The bio-composites store and release heat energy in the human comfort temperature range of 18–21°C. A step in the technology is the development of a bio-composite consisting of sawdust impregnated with ethyl palmitate (EP) as PCM and linseed oil as bio-based binder. The composite consists of 25% ester and has 50 J/g latent heat while being thermally stable up to 200°C.  
The new building materials are exposed in models for long-term monitoring and data collection for material behaviour and LCA. The thermal energy saving after 1 year of exposure was 10% and the model house had a better climate performance with 5.4% lower impact during its lifetime in comparison to the model house without PCM.  

Ключови думи: bio-based phase change materials, bio-based composites, building materials, impregnation, wood materials, thermal energy storage

EN Version

EFFECT OF STAINING ON THE ROUGHNESS OF BEECH FURNITURE SURFACES

Автори: Krasimira Atanasova, Dimitar Angelski

Резюме

Staining is a process of transparent wood surface colouring. Stains are liquid systems that wet and penetrate treated surfaces, changing their properties, including their roughness. The article presents research on the surface roughness change of beech, beech plywood, and beech veneered wood-fibre boards after treatment with waterborne and solvent-based stains and waterborne stains with PVA resin additive. Before staining, the surfaces were sanded with P150-grain sandpaper. A contact roughness tester model SJ-210 and a standard Gaussian filter were used to evaluate the roughness. The influence of the substrate structure, the stain dilution and the type of thinner on the surface roughness were determined. The parameters Ra, Rpk, Rk, Rvk and the composite parameter Rpk+Rk+Rvk were analysed. The results are presented graphically and also in tables. 

Ключови думи: waterborne stain, solvent-based stain, roughness, beech, beech plywood

EN Version

INCORPORATING SOCIAL DESIGN FOR DISABILITY-INCLUSIVE SOCIAL ENTREPRENEURSHIP: A CATALYST FOR SOCIETAL TRANSFORMATION

Автори: Maria Kitchoukova, Emil Kitchoukov

Резюме

This study uses the potential of social design as a tool to promote social entrepreneurship involving people with disabilities. Social design, with its human-centered, empathic and collaborative approach, is being explored as a key strategy for creating business models that effectively meet the needs and aspirations of people with disabilities. 
This article uses social design principles and explores how they can be incorporated into social entrepreneurship to promote disability inclusion, improve accessibility and generate socio-economic impact. This approach highlights the need to further explore the unique experiences and requirements of people with disabilities, thereby promoting the development of innovative, tailored solutions. 

Ключови думи: social design, social entrepreneurship, people with disabilities

EN Version

PRODUCTION AND TRADE OF WOODEN PRODUCTS IN BULGARIA FOR THE PERIOD 2007–2021 – QUANTITATIVE ANALYSIS AND FACTORS OF INFLUENCE

Автори: Nikolay Neykov, Radostina Popova-Terziyska

Резюме

This analysis covers Bulgaria’s wood product industry over a period of 14 years. It uses quantitative techniques to assess production volumes, export and import trends and trade balance of wooden products. Certain key aspects such as the shift in economic policy or the change in market demand have also been examined in terms of their effects on the sector’s performance. Multiples methods of statistics are also used to detect the production and trade anomalies over time, and also major domestic and international events that may have caused a great shift in production dynamics. In mapping the development of Bulgaria’s wood product industries, the analysis identifies both the main’s determinants and constraints within the industry that can be used in strategic decision-making in the future by the stakeholders. 

Ключови думи: wood products, market demand, trends

EN Version

MODELING INNOVATIVE PRODUCTS THROUGH DESIGN THINKING

Автори: Gergana Ivanova Koleva, Diana Ivanova Georgieva

Резюме

"Design thinking" (DТ) is an innovative concept for making and implementing new business solutions (products, services, processes), contributing to an increase in their quality according to the expectations and requirements of their users. His methodology involves thorough research and understanding of stakeholders, as well as qualitative changes to the outcome with rapid implementation of corrective actions. 
"Design thinking" is also a modern tool for achieving innovation through creative co-creation of the final solution by working in teams together with customers. Because of this, this methodology is increasingly used in making management decisions of a different nature, especially in product management – the area in which the goal is to create quality product innovations.
In connection with the practical interpretation of the DТ methodology in product management, in making operational management decisions related to innovation and modelling of innovative products, the authors also created a short-term training course program for specialists in the field of standardization and quality management, members on "Club 9000". 
The purpose of the training is to present the methodology of DТ, its algorithm and the possibilities of its use as an innovative tool in the process of creating new products while minimizing risk. At the same time, it is aimed to support through interactive training the building of practical skills for work, using tools from the specially created Manual for the application of DТ in modelling innovative products in a specific sector (Woodworking and furniture industry). 

Ключови думи: design thinking, innovative products, product management, innovation, innovative programs, training

EN Version

CHALLENGES IN THE CIRCULAR ECONOMY OF BULGARIA

Автори: Todor Stoyanov, Nikolay Neykov, Emil Kitchoukov

Резюме

The transition towards a circular economy presents a transformative challenge with the potential to yield extensive economic, environmental, and societal benefits. In Bulgaria, the shift from a traditional linear economy to a circular one is fraught with a unique set of challenges, which this paper meticulously examines. Through qualitative and quantitative analysis, the paper identifies the primary barriers impeding the adoption of circular economy practices, including inadequate regulatory frameworks, insufficient technological infrastructure, and the entrenched habits of consumption and production that resist change. It explores the role of government policy, business innovation, and consumer engagement in fostering a conducive environment for the circular economy. The paper also discusses the potential for economic growth and sustainability that a circular economy can offer within the Bulgarian context, suggesting strategic approaches to leverage indigenous resources, and encouraging collaboration between sectors. Through this exploration, the paper provides valuable insights and proposes actionable recommendations that aim to guide policymakers, business leaders, and civil society in overcoming these challenges and achieving a sustainable circular transition in Bulgaria. 

Ключови думи: circular economy, challenges, success factors

BG Version