Автор: Vladimir Mihailov
Статии
- INFLUENCE OF THE APPLIED PRESSURE ON FINGER JOINED END-TO-END WOOD
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Резюме
In the production of finger-jointed details, it is most important to provide the required applied pressure to achieve the desired adhesion strength of the joint. The results of the study of beech wood elements (Fagus Sylvatica) are presented, with applied different pressure for the face ends of the details (0,4 and 0,7 N/mm2). The following properties have been determined of the tested samples: bending strength, modulus of elasticity and the density of wood. The pneumatic-piston system also provided for securing the bonding pressure in the longitudinal direction of the wood. In the carried – out experiments, it was used a polyvinyl acetate adhesive with a class of water resistance D3. The mechanical properties of the glued elements depend on their structure, the type of adhesive and the type of wood. The paper presents the values of strength and modulus of elasticity in static bending of elements derived from beech wood.
Ключови думи: beech wood, finger-joint, polyvinyl acetate adhesive, pneumatic-piston system
- SURFACE SMOOTHING OF THE SIDES OF PRISM-SHAPED BEECH WOOD DETAILS VIA LAPPING WITH FAST-ROTATING METAL CYLINDER
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Резюме
The article presents and analysis the results from laboratory experimental researches over opportunity for effective surface smoothing of cutter-processed or initially sanded surfaces of prism-shaped steamed beech samples with grit number of a sandpaper № 80. The lapping is executed by a special work instrument – cylindrical steel circlet, loaded on the milling spindle. Upon handing over and further pressure of a detail to the smooth polished surrounding surface of the rotating bushing, the lapping that occurs results in smoothing of the detail’s surface that has been in contact. It is also due to the partial heating, densification, decrease and rounding of the tops of the microgrades remaining after sanding. The purpose of the research has been to evaluate the degree of smoothing, by checking the multiple influence of the major factors on which it depends. In this particular case, we have chosen to vary the following factors: feed speed of detail U; radially directed force of pressing to the spindle q; number of impacts over the same surface n. The research results show that a quality smoothing, equal to the traditional one that is double sanded with sandpaper №180 or №240, can be reached at values of the variable factors, as follows: u = 8÷10 m.min-1; q = 6÷8 kN.m-1; n = 1÷2 impact. Apart from the quality smoothing, this lapping method results in further economy of sandpaper and lacquer of up to 20%.
Ключови думи: surface smoothing, lapping, beech, lapping regime
- INFLUENCE OF THE TYPE OF ADHESIVE ON THE PHYSICO-MECHANICAL PROPERTIES OF BEND FURNITURE BOARDS
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Резюме
In the manufacture of furniture structural elements from folded glued thin furniture panels, it is important to determine the parameters affecting the performance of the finished wood composite panels. The purpose of the study was to determine the effect of the type of adhesive used on laminated high-density laminated wood fiber boards (HDF) and poplar plywood. The test specimens are made of five layers of 2.8 mm thick HDF slats and 4 mm thick plywood with 260/100 mm glued plate dimensions. For bonding, three types of adhesives were used - polyvinyl acetate (PVA) dispersion adhesive Jowacoll 103.05, polyurethane (PU) dispersion adhesive - Jovapur 150.50 and polyurethane wood adhesive - SOUDAL 66A. Bending and gluing were performed in a laboratory vacuum press with a rubber membrane and a template with a radius of curvature of 150 mm. The time to achieve minimum technological adhesion strength, vacuum velocity and minimum bending radius are determined. Samples were tested by standard bending with shoulder collection. The results obtained are analyzed and presented graphically.
Ключови думи: glued bent furniture panels, HDF, polyvinyl acetate (PVA) dispersion adhesive, polyurethane (PU) dispersion adhesive, bending strength, vacuum presses
- INVESTIGATION OF ATMOSPHERE SUSTAINABILITY OF PROTECTIVE- DECORATIVE COATINGS
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Резюме
The strength of bonding between protective-decorative coatings and the surface of wood materials, plays a major role in the durability of the wooden products, exposed to atmospheric conditions in the open area. This article analyzes the effects, that has the protective-decorative coatings, like durability of the natural oils and synthetic lacquer products used for protective layer of wood and the surface condition, after stay under the environmental impacts. To achieve this aim, an experimental stand was built according to standard EN 350:2016 and mounted in the territory of Yundola, Velingrad municipality. By the determined 12 months under review time period it is followed the change of surface of different types of natural oils and synthetic lacquer products used for protection of wood exposed to open area. The change in color is reflected, the damage to the surface of the used protective-decorative coatings, the mold formation, and the moisture resistance of the protective coatings. The results are analyzed and graphically presented.
Ключови думи: atmosphere sustainability, lacquer gloss, wood protection, coatings, oils, aging
- PRESSURE EFFECTS ON POLYVINYL ACETATE JOINTS IN HEMP-SHIVE PARTICLEBOARDS – A COMPARATIVE STUDY
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Резюме
This work presents one of the first systematic, ISO-aligned assessments of PVAc-bonded joints in laboratory-made hemp shive particleboards, benchmarked directly against industrial P2 particleboard under identical processing conditions (adhesive type and spread, surface preparation, and three nominal pressing pressures). By holding all bonding variables constant and varying only the substrate and pressure, the study isolates the effect of the substrate on shear strength. It offers actionable data for furniture construction with emergent hemp-based panels.
The key achievement is a consistent approximately 45% increase in PVAc shear strength for hemp shive panels across the tested pressures, with mean values rising from 1.23 to 1.53 N/mm², compared to 0.68 to 0.83 N/mm² for P2 (ISO 6237:2017). This result demonstrates that hemp shive particleboards can deliver markedly stronger adhesive joints without changing adhesive type or application rate, directly supporting their use as a higher-performance alternative in PVAc-bonded furniture assemblies. The observed variability at the highest pressure level highlights a practical optimization window for balancing pressure with adhesive spread and substrate permeability.Ключови думи: hemp-shive particleboards; shear strength; furniture joints; PVAc bonding; ISO 6237