The subject of this paper is to analyse the drying process of oak lamellas, which are the solid wood top layer of engineered wood flooring. The focus of the first part of the paper is on dehumidification kilns. Drying in a dehumidification kiln is an interesting alternative to conventional drying of thin solid oak wood with the aim of reaching high drying quality in a reasonable time. Drying tests were done in an industrial dehumidification kiln, and drying parameters were compared with the drying in the conventional kiln. Simultaneously, a drying test at a higher temperature was done in the programmable climate chamber. It was demonstrated that thin oak lamellas (approx. 5 mm thick) could be successfully dried in a dehumidification kiln in a relatively short time and with high drying quality. With the applied drying schedule (initial temperature of 36?C, final temperature of 46?C), the drying cycle will last 2 to 5 days, depending on the amount of wood and the initial MC. Due to the high rate of water evaporation and the inability of the kilns to remove it fast enough, the drying of lamellas in both dehumidification and conventional kilns takes place at a higher equilibrium moisture content than the set values.
др. Здравко Поповић, редовни професор, Универзитет у Београду-Шумарски факултет др. Небојша Тодоровић, доцент, Универзитет у Београду-Шумарски факултет др. Горан Милић, ванредни професор, Универзитет у Београду-Шумарски факултет Извод: Предмет овог рада је анализа квалитета природног и конвенционалног сушења субфосилног дрвета храста. Поред ква литета сушења, испитана је и боја овог материјала, као и утицај процеса сушења на промену боје. У експерименту је коришћено субфосилно дрво храста које потиче из централне Србијe. Грађа је након изрезивања сушена природним путем до око 20% влажности, а затим вештачки до влажности од 9,5%. Испитивањем квалитета природног сушења утврђено је велико присуство пукотина, као и непрецизност мерења влажности помоћу електровлагомера. Шаржа за вештачко сушење се састојала од 24 даске, од којих су 4 коришћене за праћење влажности и профила влажности у току сушења. На крају процеса одређена је коначна влажност, разлика влажности по дебљини грађе и скорелост. Иако је коришћен благ режим вештачког сушења, размак је, као мера скорелости, код субфосилног храста био већи од очекиваног за уобичајено дрво храста исте дебљине. Утврђено је да процес сушења нема значајног утицаја на промену боје субфосилног дрвета. Очекивано, боја субфосилног дрвета храста је била значајно тамнија у односу на уобичајено дрво храста, а утврђена је и разлика у боји централног и спољашњег дела трупца субфосилног храста.
The subject of this paper is the analysis of the influence of higher initial temperatures during the drying of oak lamellas on the final quality and wood colour. Two different drying schedules (initial temperature: 45?C and 50?C; final temperature: 55?C) were used and then the drying quality and wood colour were determined. The colour change was expressed by parameter ?E but also by the corrected parameter ?E00. It was shown that the drying quality was very high in both cases, and that the colour change that occurred during drying was invisible to the naked eye. The application of higher temperatures does not pose a risk to the drying quality due to the small thickness of the wood and the short drying process. In industry, a higher initial temperature is justified in situations where sufficient quantities of (cheap) thermal energy are available. The results confirmed that the percentage of lamellas? deformation was reduced when the load was applied while drying.
This study aimed to compare two thermal modification (TM) schedules—with short and long heating phases—and their influence on the properties of maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) wood. Two TM runs were conducted in industrial conditions (open system, steam atmosphere; substantially longer method compared to the processes usually described in the literature), with the same peak phase (200 °C, 3 h), but with different heating rates—slow (1.1 °C/h) and fast (2.5 °C/h). The results revealed that both TMs significantly reduced hygroscopicity and swelling of wood, but the influence of slow heating rate—through prolonged exposure of wood to relatively high temperatures—on dimensional stability was more pronounced. The modulus of elasticity, compressive strength and Brinell hardness remained mostly unchanged after TM (except for fast-modified maple), while the modulus of rupture was strongly reduced by TM in both species. It is assumed—at least in the case of maple wood—that a combination of initial moisture content above 8% and fast heating rate during TM can cause more intensive degradation of wood polymers. Relatively small differences in colour between slow- and fast-modified wood were found. The results confirmed the hypothesis that the heating phase is an important part of the TM schedule, and it can directly affect (together with peak temperature and time) certain wood properties.
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