The purpose of this research is to investigate the acoustic properties of natural fibres and compare them with the values achieved by common insulation materials used in the construction of buildings. Three materials based on biomass were used for testing, namely cork, hemp and fibreboard. From the group of conventional materials, mineral wool, propylat and polyurethane foam were selected. For the purpose of determining the values of the sound absorption coefficient (α), the absorber specimens were tested using the impedance tube and two microphones method, according to standard ISO 10534-2. The measurement was performed for thicknesses of 20, 40, 60, 80 and 100 mm. The highest sound absorption of all materials was measured with a hemp sample at a frequency of 2000 Hz (α = 0.99) and a thickness of 20 mm. The lowest performance was achieved by cork at the same thickness and frequency of 100 Hz (α = 0.02). Among biomass materials, hemp dominated in the entire frequency range and at all thicknesses. The lowest values were for cork, from 160 to 500 Hz with a tendency to exceed the values of the fibreboard sample. Among conventional materials, mineral wool achieved the best results, while the lowest values were recorded for propylat with the occasional exception of the highest frequencies from 1600 to 2500 Hz.

The contribution deals with the laser marking as one of the progressive and environment friendly technologies with utilisation in many branches of industry. Engraving and other types of laser marking of different types of materials are very actual technologies these days. Laser marking decreases the waste creation in comparison with the other classical marking technologies, which use paintings or created chips. In this experimental investigation the laser marking surface texturing of material AL99,7 according to STN 42 4003:1993-08 (STN EN 573) has been conducted. The laser marking machine TruMark 6020 and software TruTops Mark were used. Laser surface texturing after laser marking has been realised under different combinations of process parameters: pulse frequency, pulse energy and laser beam scanning speed. The morphological characterization of engraving or annealing surfaces has been performed using scanning electron microscopy (SEM) technique. The evaluation of roughness of engraved surfaces has been realized according to STN EN ISO 4287 by using Surftest SJ 301. The aim of the contribution was to show how different laser parameters affect the surface texture and colour change of metallic materials while creating minimal waste.

Industry and industrial complexes are often located in the proximity of people’s homes. One of the negative effects of industry is noise emissions into the surrounding environment. With the increasing concentration of the human population and the increase in industrial production, more and more people are exposed to the negative effects of noise. This article discusses a comprehensive approach to reducing noise emissions from industrial operations, and the subsequent impacts on surrounding villages and human health. The first step of the whole process is to understand the current state of the acoustic situation in industrial operation and in the nearby villages, an important part of which is the identification and localization of dominant noise sources. For this purpose, a unique noise visualization tool was used, namely, an acoustic camera. The next important step is to propose a technical solution and measures to reduce the noise of the individual source. Consequently, it is necessary to create a mathematical model, i.e., noise maps, in order to verify whether the proposed measures will be sufficient. Once the proposed measures have been implemented, verification of the effectiveness of these measures needs to be carried out through repeated noise measurements in nearby villages and also on the site of the industrial installation. The above procedure was applied to the operation of a wastewater treatment plant that was causing noise exceeding the permissible levels in the surrounding villages. The application of this approach, the implementation of the proposed measures, and the subsequent verification confirmed a significant reduction in the noise levels in the affected villages, and the measures implemented were assessed as highly effective.

The contribution examines the effects of the electrolyte chemical composition on the resulting AAO layer thickness, which is one of the main indicators of corrosion protection of aluminium parts and which also favourably affects mechanical properties of component surfaces. For comparison purposes, there were selected the electrolytes comprising sulphuric acid, oxalic acid, boric acid and sodium chloride. Anodizing time for all specimens was 210.00 minutes. At the same time, equal electrolyte temperature 22.00°C ± 13.64% as well as equal magnitude of the applied voltage 12.00 V ± 4.17% were determined for all specimens. The results obtained lead to the assumption that it is possible to replace conventional electrolytes by those that are more environmentally friendly, reduce the costs of their disposal and allow obtaining oxide layers of the same thickness. The admixture of sodium chloride plays here the crucial role and its effect on the thickness of the formed oxide layer has not been published yet in any study.