Rastislav Igaz

This paper presents an experimental evaluation of the thermal performance of a wood–aluminum window installed in a timber building exposed to real climatic conditions. The assessment is based on long-term in situ measurements of heat flux and temperature variations. The aim of the research was to determine the thermal transmittance of individual parts of the window assembly, analyze their dynamic thermal behavior, and identify critical areas in terms of heat losses. The results revealed a spatially heterogeneous distribution of heat fluxes through the window structure. The center of the glazing achieved values close to the declared U_g parameter, whereas the edge regions of the glazing and the window frame exhibited a significant increase compared with the declared values. The time-dependent analysis confirmed a distinct diurnal cycle of heat flux and a phase shift between the glazing and frame components. Furthermore, it was demonstrated that the accuracy of local U-value determination is significantly affected by the magnitude of the temperature difference, with the stability and repeatability of the calculated U-values improved at higher ΔT values, particularly above approximately 10–15 K. The findings highlight the need for detailed, spatially resolved assessment of window structures and emphasize the importance of experimental verification of their thermal performance under real conditions.

This paper discusses cutting beech wood (Fagus sylvatica L.) using a CO₂ laser and optimising its feed speed and laser power concerning the roughness of the cut surface and the kerf width. The roughness, defined by the parameters Ra, Rz, Rv, and Rp, and the kerf width changed with varying technological parameters of the CO₂ laser—feed speed and laser power. The lowest roughness was achieved at 50% laser power and a 15 mm·s⁻¹ feed speed, while the highest roughness was reached at 50% and 30 mm·s⁻¹. The lowest kerf width was achieved at 50% laser power and a feed speed of 15 mm·s⁻¹ on both the upper and lower sides and vice versa. The result of the experiment was the creation of second-degree polynomial regression models, from which the optimal values of the technological parameters of the CO₂ laser for cutting wood were determined for surface roughness and kerf width. The achieved accuracy of the models was 98.01% for the kerf width on the upper side, 95.95% for the kerf width on the lower side, 82.71% for the Ra parameter and 85.44% for the Rz parameter.

The paper deals with the acoustic and thermophysical properties of selected materials created from the recycling of newsprints with potential applications in the structural components of timber buildings. The samples for the study were produced by recycling paper in three forms: as pure paper, then with the addition of used coffee grounds, and then with the addition of rubber from crushed automotive tires. Based on the measurement of the Sound Absorption Coefficient (SAC) and Noise Reduction Coefficient (NRC), it can be concluded that these materials are among the less absorptive in terms of acoustics. The best results were achieved by the material made from newspaper mixed with coffee grounds (NRC is equal to 0.30), which can be classified into sound absorption class D. The other studied materials fall into class E, with an NRC of 0.20. From the perspective of thermophysical properties, the tested materials exhibit thermal conductivity coefficient values ranging from 0.083 to 0.103 W·m-¹·K-¹, indicating that they do not meet the thermal insulation properties commonly associated with standard insulating materials.

In this work, we focus on the prediction of the influence of CO₂ laser parameters on the kerf properties of cut spruce wood. Laser kerf cutting is mainly characterized by the width of kerf and the width of the heat-affected zone, which depend on the laser power, cutting speed, and structure of the cut wood, represented by the number of cut annual rings. According to the measurement results and ANN prediction results, for lower values of the laser power (P) and cutting speed (v), the effect of annual rings (ARs) is non-negligible. The results of the sensitivity analysis show that the effect of v increases at higher energy density (E) values. With P in the range between 100 and 500 W, v values between 3 and 50 mm·s⁻¹, and AR numbers between 3 and 11, the combination of P = 200 W and v = 50 mm·s⁻¹, regardless of the AR value, leads to the best cut quality for spruce wood. In this paper, the main goal is to show how changes in the input parameters affect the characteristics of the cutting kerf and heat-affected zones for all possible input parameter values.

The present paper deals with the analysis of cross-section surface irregularities after CO₂ laser cutting. The surface irregularities of beech (Fagus sylvatica L.), oak (Quercus petraea), and spruce (Picea abies L.) wood were quantified by primary profile parameters using a digital microscope. The arithmetic mean height (Pa), used as the basic parameter, was supplemented by amplitude parameters (Pv, Pp, Pz) and the Psm parameter, through which the shape of the irregularity was specified in more detail. A statistically significant change was demonstrated when changing the values of the feed speed and the power of the CO₂ laser. The results of this article confirm that the surface irregularities increased with an increasing laser power and decreasing feed rate. The scanned topographic images also provide a more detailed explanation of the measured P-parameters and point out the risks associated with the evaluation of the cross-section with the primary profile.

The operation of CNC machining centers, despite their technological progress, can still be affected by undesirable events associated with the technological parameters of their operation. The minimization of these risks can be achieved via their adaptive control in the process of operation. Several input parameters for adaptive control are still the subject of research. The work aimed to find out the influence of the change in feed speed, revolutions, and radial depth of cut on the noise and temperature of the tool during the milling of wood-based composite material particleboard. At the same time, it was evaluated whether it is possible to use the measured values of these parameters in the future in the process of an adaptive control of the CNC machine with the minimization of their negative influence. The methods of measuring these parameters were chosen based on valid legislation and previous research. The results of the research show that all parameters influence both the noise and temperature of the tool, while the rate of the radial depth of cut has the greatest influence on the increase in temperature, and the noise is most affected by the revolutions. The effect of temperature during woodworking can also be characterized in terms of the potential long-term wear of the cutting tool. The setting of optimization algorithms of monitored parameters in the adaptive control of the CNC machining center will be the subject of further research.

In addition to traditional chip methods, performance lasers are often used in the field of wood processing. When cutting wood with CO₂ lasers, it is primarily the area of optimization of parameters that is important, which include mainly laser performance and cutting speed. They have a significant impact on the production efficiency and cut quality. The article deals with the use of an artificial neural network (ANN) to predict spruce wood cut characteristics using CO₂ lasers under several conditions. The mutual impact of the laser performance (P) and the number of annual circles (AR) for prediction of the characteristics of the cutting kerf and the heat affected zone (HAZ) were examined. For this purpose, the artificial neural network in Statistica 12 software was used. The predicted parameters can be used to qualitatively characterize the cutting kerf properties of the spruce wood cut by CO₂ lasers. All the predictions are in good agreement with the results from the available literary sources. The laser power P = 200 W provides a good cutting quality in terms of cutting kerf widths ratio defined as the ratio of cutting kerf width at the lower board to the cutting kerf width at upper board and, therefore, they are optimal for cutting spruce wood at 1.210⁻² ms⁻¹.