Лесотехнически Университет

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 non-stationary 1D temperature distribution along the thickness of subjected to unilateral heating flat wood details.

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 non-stationary 1D temperature distribution along the thickness of subjected to unilateral heating flat wood details. The paper presents solutions of the model concerning the non-stationary 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 ^oC.

Резюме

Using the explicit form of the finite-difference 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 t₀ = 20 ^oC, during unilateral convective heating for a period of 10 min at t_ha = 100 ^oC, 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.

Резюме

A software program has been prepared in the calculation environment of Visual Fortran for solving of own 1D non-linear model of the one sided heating process of flat wood details. With the help of the program, the 1D non-stationary temperature field in flat oak details with initial temperature of 20 ^oC, 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 ^oC 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.

Резюме

A methodology for the computation and research of the following two mutually connected problems has been suggested: 1D non-stationary 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 1-dimensional 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 1-dimensional non-stationary temperature distribution along the elements’ thickness and of the average mass thermal conductivity for flat oak furniture elements with an initial temperature of 20 ^oC, 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 ^oC, 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 ^oC for the surrounding air near the non-heated 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.

Because of the wide range of applications, the need for paulownia is constantly increasing.

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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%.

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 water-based 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.

Резюме

An approach for computing and research of the duration of regimes for autoclave steaming of non-frozen wooden prisms at limited heat power of the steam generator in cases of dispatching interventions into the regimes in order to obtain a duration that is suitable for the subsequent cutting of the veneer from the heated plasticized wood has been suggested. Using own 2D unsteady model implemented in the approach, calculations of the change of the duration of regimes for plasticizing of beech prisms in an autoclave have been carried out. The variables used during the computer simulation were, as follows: initial wood temperature of 0 °C, wood moisture content of 0.6 kg·kg⁻¹, and cross-section dimensions of the prisms 0.4 × 0.4 m; steaming autoclave with a diameter of 2. 4 m, length of 9.0 m, and loading level of 50% for the cases of lowering by the dispatcher the maximal temperature of the basic steaming regime from 130 ^oC to 120, 110, and 100 ^oC in the 3^rd, 5^th, and 7^th hour of this regime.

Резюме

An approach for computing the average moisture content of the whole quantity of wood materials in given batch subjected to steaming in an autoclave has been suggested. This value of the wood moisture content is needed for calculation and automatic realization of optimal energy saving regime for autoclave steaming of the materials. The approach is based on two own 2D mathematical models: one of the temperature distribution in non-frozen prismatic wood materials during their steaming and other – of the heat balance of the autoclave. The calculated by the models increase in the steaming medium temperature in the beginning of basic regime is compared with the real increase of that temperature, which is measured with a sensor in the automatic control system. After proper processing of the obtained differences between measured and calculated temperatures with the software package Table Curve, an equation for calculating the average moisture content of the wood materials in the batch loaded in an autoclave is derived. The application of the suggested approach for the cases of autoclave steaming of beech prisms in the production of veneer is presented.

Резюме

The transition to a circular bio-oriented industry requires the search for alternative raw materials, sources and binders in producing materials for the furniture industry.

Lignosulfonates (sulphite lignins) are by-products, residues, of cellulose production, and they are bio-based materials with adhesive properties.

This work presents a study evaluating lignosulfonates as binders in the veneering of Medium Density Fibreboards (MDF). An adhesive composition of urea-formaldehyde (UF) resin and ammonium lignosulfonate was used in the veneering. Preliminary experiments have been carried out that show a significant reduction in the adhesion strength when the lignosulfonate content in the adhesive system passes 60%. Therefore, the study used the substitution of UF resin with lignosulfonate from 0 to 60%, with a step of variation from 10%. It is carried out at the gelling time of the various adhesive systems.

An analysis of the adhesive strength in veneering at adhesive systems with different lignosulfonate content was performed. Based on this, conclusions and recommendations were derived.

Резюме

With the help of our own non-stationary model, the defrosting times of frozed beech logs with a diameter of 0.4 m, initial temperature of −10^oC, −20^oC, −30^oC, and moisture content of 0.6 kg∙kg^-1 were determined at water temperatures in the boiling pit equal to 80^oC. Using the determined logs’ defrosting durations, the change in energy required for the entire plasticization process and that for each of the 5 components of the pit’s thermal balance was calculated. Computer simulations were performed for a well-insulated concrete pit with working volume of 20 m³ and degree of filling with logs f equal to 25%, 50%, and 75%. It was found that at f = 75% the total energy consumption of the pit increases from 163.6 kWh.m^-3 to 177.6 kWh∙m^-3 when the initial temperature of the logs decreases from −10^oC to −30^oC. The thermal efficiency of the studied pit decreases almost proportional to the decreasing of f, mainly due to the increase in the specific energy required to heat the water in the pit.

Резюме

With the help of our own non-stationary model, the temperature field and defrosting durations of frozen beech logs with a diameter of 0.4 m, initial temperature of −10 ^oC, and moisture content of 0.4 kg∙kg^-1, 0.6 kg∙kg^-1, and 0.8 kg∙kg^-1 were determined at water temperatures in the boiling pit equal to 80 ^oC. Using the determined durations, the change in energy required for carrying out of the entire defrosting process and that for each of the 5 components of the pit's thermal balance was calculated. Computer simulations were performed for a well-insulated concrete pit with working volume of 20 m³ and degree of filling with logs f equal to 25%, 50%, and 75%. It was found that at maximum possible value f = 75% the total energy consumption of the pit increases from 145.1 kWh.m^-3 to 180.2 kWh∙m^-3, i.e. by 24.2% when the moisture content of the frozen logs increases from 0.4 kg∙kg^-1 to 0.8 kg∙kg^-1. With a decrease in f, the thermal efficiency of the pit decreases almost proportional to f, mainly due to the increase in the specific energy required to heat the water in the pit.

Резюме

A mathematical description of the energy Q_ice-bw required for melting the temperature dependent part of frozen bound water in wood, using a software package Table Curve 2D v.5.01 has been presented. This package allows for the selection of equations, which provide the best similarity between the calculated with them values of Q_ice-bw during thermal treatment of wood containing ice and the respective numerical data obtained with an adequate temperature-energy model of Q_ice-bw. The type and coefficient values of the Table Curve equations for Q_ice-bw in this work have been determined for the case of thermal treatment of frozen beech wood with an initial temperature of −1 ^oC, −10 ^oC, −20 ^oC, −30 ^oC, −40 ^oC and moisture content of 0.4 kg·kg^-1, 0.6 kg·kg^-1, and 0.8 kg·kg^-1. The equations obtained for Q_ice-bw can be used for development and automatic implementation of scientifically based energy-efficient regimes for steaming or boiling of frozen wood materials with different parameters.

Резюме

The scarcity of natural resources and the generation of waste without adequate disposal are worldwide concerns related to the linear production model. The present study is part of a research project to create a technology for the utilization of laminated particleboard cutting waste in furniture element production. A layer of waste details was laminated on both sides with High Pressure Laminate (HPL) with a thickness of 0.8 mm. Polyvinyl acetate adhesive was used for lamination. The influence of the lamination process conditions and the arrangement scheme of the core details on the appearance, bending strength, and processing features in the subsequent technological phases of the manufacturing process has been established.

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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.