Faculty of Design and Technologies of Furniture and Interior

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    Dimensional Stability and Water Absorption of Spruce Wood (Picea Abies Karst.) Impregnated and Coated with Polyurethane and Acrylic Coatings
    (Drvna Industrija, 2018)
    Mihajlovski Nikola
    ;
    Konstantin Bahchevandjiev
    Impregnating materials may affect the stabilization of wood dimensions in two ways: blocking of free water movement paths and chemical connection with hydroxyl groups of wood. The degree of modifi cation depends on the applied material, its penetration and fi xation to the wood. The paper investigates the impact of impregnation and coating with polyurethane and acrylic coatings of spruce wood (Picea abies Karst.) on absorption of water and dimensional stability of wood (anti-shrinking effi ciency) after being immersed in water for a specifi c time. Impreg nated spruce wood absorbs two times less water than untreated wood and it is dimensionally more stable than coated spruce wood. The water absorption of coated spruce wood is low, but it is not dimensionally stable.
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    Surface retention of polyurethane and acrylic coatings on impregnated spruce wood (Picea abies Karst.) and comparison with some wood preservatives
    (Baltic Forestry, 2022)
    Mihajlovski Nikola
    ;
    Konstantin Bahchevandjiev
    The natural spruce wood has low resistance against biological degradation and weather effects, so further protection is required, up to meeting the durability requirements for wood used in exterior classes. According to the wood preservatives standards, coatings as water repellents belong to the group OS (organic solvent) preservatives. The coatings have a water repellent function, and they are not toxic, so these advantages make them usable like impregnation material. The objective of this work is impregnation of the spruce wood (Picea abies Karst.) using the “Double vacuum process” with coating material based on polyurethane and acrylic isocyanate resins and determinate the coatings quantity in wood. The impregnation efficiency is expressed through the retention. The coatings retention is compared with the minimal standard prescribed retention of the preservatives, most frequently used, namely creosote, copper chrome arsenate (CCA) and waterborne copper-rich systems like copper azole (CBA-A, Thanalite E), to show the efficiency of the applied double vacuum process. The coating retention is not significantly different from the minimum prescribed retention of creosote and amounts 118–149 kg/m3 or 32 to 38 times higher than the recommended retention of CCA or CBA-A for wood protection in the exterior use. The polyurethane and acrylic wood coatings can be successfully applied for wood impregnation purposes.
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    Transverse Anisotropy and Dimensional Stability of Thermal Treated Beech Red Heartwood
    (TEM Journal, 2017-02)
    Nikola Mihajlovski
    ;
    Konstantin Bahchevandjiev
    This research is mainly focused on the impact of thermal modification on the transverse anisotropy and dimensional stability of native beech wood (Fagus sylvatica L.) and beech red heartwood. Applied to two time-temperature regimes, the first period of maximum temperature to 180° C and the second to 230° C. The factor of anisotropy in native beech wood is 1.29 and beech red heartwood is 1:24. Dimensional stability of the native beech wood is improved for 33.3% and beech red heartwood for 29.1%. The changing of the volume mass per thermal modification of 6% is too small and does not affect other properties.
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    A review of some factors affecting the accuracy of measuring the geometric characteristics of mortise and tenon joints
    (Faculty of forest industry – University of forestry – Sofia, 2024-10-07)
    Mihajlovski Nikola
    ;
    Gruevski Gjorgi
    The geometric characteristics of mortise and tenon joints represent their ideal shape as well as the permitted deviations from that shape. Measurement accuracy as part of production metrology is of crucial importance for maintaining tolerances and fits as well as quality control in production. The closeness of the measurement results to the actual true value of the measurand depends on many factors. Some factors that affect the accuracy of a measurement are caused by the measuring equipment, the environment in which the measurement is performed, the operator who performs the measurement, the method and procedure of the measurement and the properties of the material. This review paper presents an investigation of the factors and their affect on the accuracy of measurement of mortise and tenon joints while maintaining manufacturing tolerances. The purpose of this investigation is to consider the possibility of their minimization to obtain a more accurate measurement. According to the theoretical analysis, the group of factors that express the heterogeneity and hygroscopicity of wood as a material have a great effect on the accuracy of the measurement.
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    Influence of the window profile on the final quality of the product
    (2023)
    Jevtoska, Elena
    The current product on the market offers a wide range of diverse profiles for producing windows that are made of different materials, width and order of grills depending on the profile. Within the framework of this research the windows with same dimensions shall be elaborated, those which are made of the same production capacity and use the same fittings but different types of PVC profiles. The aim is to prove what kind of influence the used profile has over the final quality of the product. For this research, two groups and six subgroups will be tested. In each subgroup, one tests five windows made of the same profile. The groups are divided according to the used fittings. The testing of the quality shall be conducted in accordance with the European norms EN 1026:2016 (Windows and doors - Air permeability - Test method), EN 1027:2016 (Windows and doors - Water tightness - Test method), EN 12211:2016 (Windows and doors - Resistance to wind load - Test method).
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    INFLUENCE OF MANUFACTURE OF THE WINDOW AND THE FITTINGS USED ON THE FINAL QUALITY OF THE WINDOW
    (2022-11-14)
    Jevtoska, Elena
    The window as a product used in construction aims to provide natural light and the possibility for ventilation in the building where it is placed, but at the same time to protect the room from external influences such as wind and rain and to prevent uncontrolled cooling or heating of the building it is built-in. Given the purpose, a quality window is one that protects against air penetration, water penetration and it ensures wind resistance. The window is a complex product that is composed of different parts that can be made of different materials. As part of this research, windows made by different manufacturers and made from different materials will be tested, but they are with profile identical to the profile used for the frame and the window sash. The main goal is to prove whether the construction of the window and the fittings used have an impact on the final quality of the window. In order to do the research, ten windows will be tested in accordance with the European norms EN 1026: 2016 (test method for air permeability), EN 1027: 2016 (test method for water permeability), EN 12211: 2016 (test method for wind resistance).