Лесотехнически Университет

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In this work, the application of a laser drilling technique on fir (Abies borisii regis) and spruce (Picea excelsa) wood and a new approach of improvement the wood permeability is investigated. This technique is focusing on increasing the permeability of wood after surface drilling by a high power laser source. The research was involving the establishment of an effective drilling pattern protocol, which will not substantially affect the mechanical strength of wood and to improve its permeability. All lateral surfaces of the wood specimens, 2 × 2 cm in cross section and 34 cm long, were drilled by laser to a depth of 4 mm (1/5 of specimen thickness) with two drilling patterns (distance between holes 10 × 10 mm and 10 × 20 mm). Preliminary results showed that laser drilling is a promising method for improvement of wood permeability without significant effect on its mechanical strength, and this is very important for an effective treatment of the refractory to impregnation fir and spruce wood.

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Fir (Abies borisii regis) and spruce (Picea excelsa) wood specimens, 2 × 2 cm in cross section and 34 cm long, were prepared with true radial and tangential surfaces. All lateral surfaces of the specimens were drilled by laser to a depth of 4 mm (1/5 of specimen thickness) with two drilling patterns (distance between holes 1 × 1 cm and 1 × 2 cm). ). After drilling, the mechanical strength of wood (MOE, MOR, axial compression, toughness) was determined and compared with non-drilled controls. MOE was not affected by the laser drilling, MOR was significantly increased, axial compression was increased and toughness was decreased but not significantly. The overall results imply that strength properties do not decline by the laser drilling. Furthermore, wood specimens were impregnated with rape oil and CCB preservatives by applying vacuum (0.6 mmHg) and pressure (1,5 bars) for 15 minutes and 30 minutes, respectively. The results showed that both drilling patterns improved the retention and penetration of preservatives in fir and spruce wood specimens and, thus, are encouraging for further evaluating the drilling effects on the liquid permeability of these refractory to impregnation species. This effect was more pronounced in fir than in spruce wood.

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The aim of this paper is to suggest a structure for automatic complex for putting art images on separate details from wood material. For the putting of images is used tampon automatic stamp. The project parameters of the automatic complex are defined. 2D drafts and 3D models of the suggested variants are worked. An analysis and evaluation of the worked variant is made and the optimal was chosen which was projected and researched. The automatic complex was realized and experimental studies were done and part of the results were made in the present study.

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In the present paper, energetic properties of wood chips of the species Robinia pseudoacacia (clones Ambigua, Debrecenyi 2, Göri, Matyasi, Nyirsegi, Rozaszin, Zalyi)  ere determined, relative humidity of chips during a harvest, bulk density, namely the share of bark in chips, chemical composition of combustibles of chips, ash content in dry mass of biofuel, and lower heating value. Green wood chips made of dendromass from plantations consist of juvenile wood and juvenile bark. The share of juvenile bark in green wood chips of the analyzed clones of Robinia pseudoacacia is X_B = 22.97 ± 1.95 %.

The nitrogen content in green wood chips made of Robinia pseudoacacia  trees grown on plantation is 8 times higher than the nitrogen content in the combustibles of fuelwood of broad-leaved tree species, which has negative impact on the production of emissions – concentration of nitrogen oxides NOx in combustion products. The share of inorganic substances determined by the form of ash content A_d = 1.73 % puts the analyzed biofuel into the category of low-ash fuels. The lower heating value of green wood chips of the individual Robinia pseudoacacia  clones analyzed in dry state is Qn = 18.0 MJ.kg^-1.

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The research presented in the paper is directed to creating possibilities for production of multilayered plywood that are resistant to prolonged water impact, as well as to mutual impact of water and heat.

The aim of the conducted research consists of the possibility for production of stable multifunctional plywood made from coniferous raw material. For that purpose experimental multilayered plywood panels are made from peeled black pine veneers bonded with water-soluble phenol formaldehyde resin.

The experimental panels were subjected to standard laboratory tests in conditions of water regimes in order to define the water resistance and dimensional stability under water impact and mutual impact of water and heat, as well as to determine the degree of adhesion between the veneers.

The research showed that panels were characterized by high stability during this kind of treatment. The panels showed consistency in form and dimensions, as well as consistency of the adhesion in glue lines.

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The proposed study presents an investigation of the influence of the wearing and the belt drive parameters’ changes over the forced torsional vibrations in the saw unit of a wood shaper. These changes affect the elastic and damping coefficients of the machines’ elements. The research is done on the base of a concrete mechanic-mathematical model for numerical investigations of the torsional vibrations of a wood shaper’s saw developed by the authors. The main features in the construction of the wood shapers are rendered an account in this model. Work’s conditions in the practice are modeled with the variable moments on the drive electric motor and the wood shaper’s saw. The conclusions based on the numerical investigations are confirmed by the real conditions.

The results of the whole investigation are applicable to the direct well-founded recommendations concerning the operation of these machines. These recommendations are important for the increase of the accuracy and quality wood shapers’ production. At the same time the results of this research are useful for technical diagnostics of the wood shapers.

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In this study are given the results from investigation into stiffness of end corner detachable joints of structural elements made of beech veneer plywood. The stiffness coefficients under compression bending test have been determined. The highest stiffness is characteristic of joints with universal connector and screw for wood ø 6 х 90 and ø 6 х 80 mm while the lowest stiffness is typical of joints with Minifix with bolt, mounting in metal sleeve and direct mounting. The parameters of the screw joints have considerable impact on the stiffness characteristics of the joints.

It is recommended that the comparative data of bending strength be taken into consideration when selecting the type of joints in the construction of furniture made of plywood.

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Thermally modification processes change mechanical properties of wood. These changes depend on the temperature treatment. In this article are reported mechanical properties changes in spruce, beech and poplar wood, modified in temperature 200 °C sunflower oil. It is determined: density, bending strength, compressive strength on fiber direction, sharing strength on fiber direction, splitting strength on received wood according to BDS 16987:89. About comparison are studied mechanical properties of untreated samples. It is proven that the modified wood in sunflower oil has lower density and lower bending strength in parallel comparing with untreated wood.

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Basic aspects and innovations in concurrent engineering and its major place in the production of furniture in our days are represented. The main advantages and the main differences between concurrent and traditional furniture engineering are analyzed. Examples of using 2D and 3D models made by CAD-based programs in the production of furniture, with the help of CNC machines and 3D printers are considered. The new technology for 3D printing and its using for production of wood elements and furniture are presented, which leads to establishing the idea for „Smart wood materials”. The opportunities to use these technologies to make easier the work of designers and adapt them in everyday life, which make them more available to the customer are discussed.

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At the Faculty of Forest Industry, seemingly for the first time in the bandsaw studies history, the statically indeterminate problem of spring mechanism tension in bandsaw blade sections was set up and solved. The solution, transferred and generalized for a horizontal bandsaw, was defended in a Ph.D. thesis. Questions and discussions arose necessitated additions and details to the solution spared in previous papers for their limited volume. Now, the following points are detailed: the concentration of distributed loads, the subcritical friction, and the application of L'Hôpital's rule for obtaining the tension of the blade in the state of idle running (without cutting).

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The behaviour of wooden, aluminium and various types of PVC joinery has been studied in extreme conditions with a testing device. The resistance of different types of joinery has been determined in occurrence of wind, air and water influence. The sound insulation and heat transfer properties of the double glazing windows made of different materials or a different design have been compared. Based on the studies conducted, the systems with the most stable performance have been established.