Автор: Dimitar Angelski
Статии
 COMPUTATION OF THE AVERAGE WOOD TEMPERATURE AND THE RATE OF ITS CHANGE DURING UNILATERAL HEATING OF FLAT SPRUCE DETAILS BEFORE THEIR BENDING

Резюме
An approach for the computation of the average mass temperature of the wood and the rate of its change during unilateral heating of flat wood details aimed at their plasticizing in the production of curved outside parts for corpses of stringed music instruments, has been suggested. The approach is based on the numerical integration of the solutions of a linear model for the calculation of the nonstationary 1D temperature distribution along the thickness of subjected to unilateral heating flat wood details.
Ключови думи: average mass temperature, rate of change in average temperature, spruce details, unilateral heating, plasticizing
 COMPUTATION OF THE HEAT FLUX NEEDED FOR UNILATERAL WARMING UP OF FLAT SPRUCE DETAILS BEFORE THEIR BENDING

Резюме
An approach for the computation of the heat flux, which is needed for warming up of flat wood details during unilateral heating aimed at their plasticizing in the production of curved outside parts for corpses of stringed music instruments, has been suggested. The approach is based on the numerical integration and differentiation of the solutions of a linear model for the calculation of the nonstationary 1D temperature distribution along the thickness of subjected to unilateral heating flat wood details. The paper presents solutions of the model concerning the nonstationary change in the specific heat flux needed for warming up of flat spruce details with thicknesses of 6, 8 and 10 mm during their unilateral heating at temperatures of the electrically heated metal band equal to 100, 120, and 140 ^{o}C.
Ключови думи: unilateral heating, flat wood details, heat flux, plasticizing, bending
 TRANSFORMATION OF TWO MUTUALLY CONNECTED MODELS FOR CONVECTIVE HEATING OF WOOD DETAILS BEFORE THEIR LACQUERING IN A FORM, SUITABLE FOR PROGRAMMING

Резюме
Using the explicit form of the finitedifference method, two suggested by the authors mutually connected mathematical models have been transformed in a form, suitable for programming. For the numerical solution of the transformed models, a software program has been prepared in the calculation environment of Visual Fortran Professional. With the help of the program, the 1D distribution of the temperature along the thicknesses of flat oak details and of their carrying transport rubber band with h_{w} = 16 mm, l_{w} = 0.6 m, u = 0.08 kg.kg^{1}, h_{B} = 4 mm,
b_{B} = 0.8 m, and t_{0} = 20 ^{o}C, during unilateral convective heating for a period of 10 min at t_{ha} = 100 ^{o}C, v_{ha} = 2 m·s^{1}, 5 m·s^{1}, 8 m·s^{1}, and t_{nha} = 20 ºC in order to ensure suitable thermal conditions for the subsequent details’ lacquering has been calculated, visualized and analyzed.Ключови думи: oak details, unilateral convective heating, lacquering, carrying rubber band
 COMPUTATION OF THE ENERGY CONSUMPTION FOR WARMING UP OF FLAT OAK DETAILS BEFORE THEIR BENDING

Резюме
A software program has been prepared in the calculation environment of Visual Fortran for solving of own 1D nonlinear model of the one sided heating process of flat wood details. With the help of the program, the 1D nonstationary temperature field in flat oak details with initial temperature of 20 ^{o}C, moisture content of 0.15 kg.kg^{1}, thickness of 12 mm, 16 mm, and 20 mm during their 30 min one sided heating at temperature of 80 ^{o}C of the heating metal body has been calculated. After integration of the temperature field, the energy consumption for warming up of the details before their bending in the production of curved back parts of chairs has been calculated. The obtained results are graphically presented and analyzed.
Ключови думи: oak details, one sided heating, bending, energy consumption
 COMPUTATION OF THE AVERAGE MASS THERMAL CONDUCTIVITY OF OAK FURNITURE ELEMENTS SUBJECTED TO CONVECTIVE HEATING BEFORE LACQUERING

Резюме
A methodology for the computation and research of the following two mutually connected problems has been suggested: 1D nonstationary temperature distribution in subjected to unilateral convective heating process of flat wooden furniture elements before lacquering and change in their average mass thermal conductivity. For the realization of the methodology, created earlier by the authors 1dimensional nonlinear mathematical model has been solved for the transient heat conduction in the furniture elements during their unilateral convective heating. The model contains a mathematical description of the average mass thermal conductivity of the elements and their surface layer, which is intended for lacquering. For the numerical solution of the model with the aim of applying the methodology a software program has been prepared and input in the calculation environment of Visual FORTRAN Professional. Using the program, computations have been carried out for determination of the 1dimensional nonstationary temperature distribution along the elements’ thickness and of the average mass thermal conductivity for flat oak furniture elements with an initial temperature of 20 ^{o}C, moisture content of 8 %, thickness of 16 mm, width of 0.6 m, and length of 1.2 m during their 10 min unilateral convective heating at temperature of the processing air medium of 100 ^{o}C, which circulates above the elements with a velocity of 2 m·s^{1}, 5 m·s^{1}, and 8 m·s^{1} aimed at improvement of the conditions for the subsequent lacquering. During the computations a temperature of 20 ^{o}C for the surrounding air near the nonheated surface of the carrying rubber band has been used. The change in the average mass thermal conductivity of the studied furniture oak elements and also of their heated surface layers during the heating is graphically presented and analyzed.
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Ключови думи: oak furniture elements, one sided convective heating, lacquering, thermal conductivity
 SURFACE SMOOTHING OF THE SIDES OF PRISMSHAPED BEECH WOOD DETAILS VIA LAPPING WITH FASTROTATING METAL CYLINDER

Резюме
The article presents and analysis the results from laboratory experimental researches over opportunity for effective surface smoothing of cutterprocessed or initially sanded surfaces of prismshaped 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.min1; q = 6÷8 kN.m1; 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 SOME FACTORS ON ADHESION STRENGTH IN THE FORMATION OF WATERBASED FINISHES ON BEECH PLYWOOD

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 waterbased 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, waterbased finishes, coating