Utjecaj parametara CNC obrade na kvalitetu površine drvnih ploča koje se upotrebljavaju u industriji namještaja

The processing of wood-based panels such as plywood, particleboard and fiberboard, which are widely used in the furniture industry, with CNC (Computer Numerical Control) milling machines has been increasing recently. Even though CNC milling machines have many advantages for furniture producers, it is difficult to set process parameters to obtain the desired surface quality of the material. Therefore, it is necessary to determine the most suitable of these parameters for the surface quality of each wood-based panel. This study aimed to determine the effects of processing parameters on the surface quality of plywood, particleboard and medium density fiberboard (MDF) panels processed in CNC milling machines. Furthermore, the average surface roughness values of these panels were compared after CNC processing. Three spindle rotational frequencies (10.000, 14.000 and 18.000 rpm), three feed rates (5, 7, and 9 m/min) and two cutting tool diameters (2 and 5 mm) were selected as CNC processing parameters. To determine the surface quality of wood-based panels, the surface roughness measurements were performed according to DIN 4768 standard and three surface roughness parameters (Ra, Rmax and Rz) were determined. According to the results of this study, it can be concluded that the surface roughness values of wood-based panels decreased with increasing spindle rotational frequency and feed rate, while they increased with increasing cutting tool diameter. Among the wood-based panels used in this study, the lowest average roughness values were obtained for plywood samples.Za obradu ploča na bazi drva kao što su furnirske ploče, iverice i vlaknatice, koje imaju široku primjenu u industriji namještaja, u posljednje se vrijeme sve češće primjenjuju CNC (Computer Numerical Control) glodalice. Iako CNC glodalice imaju mnoge prednosti za proizvođače namještaja, teško je odrediti parametre procesa za postizanje željene kvalitete površine obrađivanog materijala. Stoga je potrebno odrediti najprikladnije parametre obrade za svaku vrstu ploče na bazi drva. Cilj ovog istraživanja bio je utvrditi utjecaj parametara obrade CNC glodalicama na kvalitetu površine furnirske ploče, iverice i ploče vlaknatice srednje gustoće (MDF ploče). Nadalje, uspoređene su srednje vrijednosti hrapavosti površine tih ploča nakon CNC obrade. Kao parametri CNC obrade odabrane su tri frekvencije vrtnje vretena (10 000, 14 000 i 18 000 okr./min), tri posmične brzine (5, 7 i 9 m/min) te dva promjera reznog alata (2 i 5 mm). Za određivanje kvalitete površine ploča na bazi drva provedena su mjerenja hrapavosti površine prema normi DIN 4768, a hrapavost je iskazana trima parametrima hrapavosti površine (Ra, Rmax i Rz). Prema rezultatima ovog istraživanja može se zaključiti da su se vrijednosti hrapavosti površine ploča na bazi drva smanjivale s povećanjem frekvencije vrtnje vretena i posmične brzine, dok su se povećavale s povećanjem promjera reznog alata. Među pločama na bazi drva na kojima je provedeno ovo istraživanje najniže srednje vrijednosti hrapavosti dobivene su za uzorke furnirske ploče

Usporedba ekonomskih i tehnoloških svojstava brezovine i bukovine za proizvodnju furnirske ploče

The aim of this study was to investigate the use of birch wood, one of the most important wood species used in the plywood industry, especially in Europe, the Nordic countries, Poland, Belarus and Russia as an alternative to beech wood. For this purpose, comparison was made of their economic and technological properties. In five-ply plywood manufacturing, beech (Fagus orientalis Lipsky) and birch (Betula pendula) veneer sheets were used with melamine urea formaldehyde (MUF) and urea formaldehyde (UF) resins. Some mechanical properties such as shear strength, bending strength and modulus of elasticity of plywood panels were conducted according to EN 314-1 and EN 310, respectively. Mean mechanical strength obtained for birch plywood panels was quite above the limit values specified in the related standards. When taking into consideration the annual increment of beech and birch trees in 1 ha and the time they need to reach suitable diameters for the manufacturing of rotary cut veneers, it was calculated that birch trees provide 2.46 times more physical harvesting than beech trees.U radu je istraživana uporaba brezovine kao jedne od najvažnijih vrsta drva koja se upotrebljava kao alternativa bukovini za proizvodnju furnirskih ploča, posebice u Europi, u nordijskim zemljama, Poljskoj, Bjelorusiji i Rusiji. Za potrebe rada uspoređivana su njihova ekonomska i tehnološka svojstva. U proizvodnji furnirske ploče od pet slojeva upotrijebljeni su listovi furnira od bukovine (Fagus orientalis Lipsky) i brezovine (Betula pendula), koji su slijepljeni ljepilom na bazi melamin-urea-formaldehidnih (MUF) i urea-formaldehidnih (UF) smola. Ispitana su mehanička svojstva furnirskih ploča prema normi EN 314-1 i EN 310, i to čvrstoća na smicanje, čvrstoća na savijanje i modul elastičnosti. Dobivene srednje vrijednosti čvrstoće brezovih i bukovih furnirskih ploča bile su znatno iznad graničnih vrijednosti navedenih u normama. Kada se u obzir uzme godišnji prirast bukve i breze na 1 ha šume i vrijeme potrebno za postizanje odgovarajućih promjera za proizvodnju ljuštenih furnira, izračunano je da breza osigurava 2,46 puta više raspoložive količine za sječu od bukve

Swimming training and pulmonary variables in women

Most spirometry testing is done for patients with pulmonary problems not for general population samples (Enright et al., 2004) and not for the effect of training. Evaluation of the effect of exercise on diffusing capacity would be helpful to evaluate the ability of the pulmonary capillary bed to expand and increase its capacity to transfer gas during exercise (Wang, 2004). The purpose of this study was therefore to examine the effects of swimming technical skill training on pulmonary variables such as FVC (forced vital capacity), FEV1 (forced expiratory volume in one second), FEF25–75 (forced expiratory flow from 25% to 75%), MVV (maximal voluntary ventilation), ERV (expiratory reserve volume), VC (vital capacity), PEF (peak expiratory flow) in women. Nineteen women (swimming trained group= 11, control inactive group= 8) participated in this study. All the subjects with the exception of inactive control group participated in swimming technical skill training, three times a week for 12 weeks. Measurements were made before and after the swimming training for each subject with spirometer (Sensormedics Vmax 29 C). The swimming training program was designed on the basis of swimming skills including: breathing in water, sliding the body in water, free style and backstroke foot drills, arm-foot and breathing coordination drills with and without swimming board, free style and backstroke drills. It was found that swimming has a positive effect on FVC (forced vital capacity), FEV1 (forced expiratory volume in one second), MVV (maximal voluntary ventilation) (Akgün, 1986). According Khosravi et al. (2013) endurance training combined with resistance training has greater effect on VC, FVC, FEF rating at 25%-75%, and also on PEF except MVV. The following variables exhibited significant difference after the 3 months swimming technical skill training: MVV and PEF. Results indicated that swimming technical skill training during 12 weeks training had a significantly positive effect on pulmonary variables such as MVV, PEF but no significant changes were observed in FVC, FEV1, FEF %25-75, ERV, VC. Efficacy of respiratory and pulmonary functions has a direct relationship with general health. Exercise training improves endurance and strength of athletes’ respiratory muscles; it also causes resistance reduction in respiratory canals, and increases lung elasticity and alveolar expansion as studies have supported the expansion of pulmonary volumes and capacities (Khosravi et al., 2013). As a conclusion of the present study suggest that swimming technical skill training can improve pulmonary function of women. According to a study (Armour et al., 1993) the increased lung volumes in swimming were not due to an increase in alveolar distensibility and may, therefore, have been due to an increased alveolar number. Our study was conducted in healthy subjects. In the future, it may be of value to investigate the effects of the swimming in people who have airway problems or the other health problems like obesity and also in athletes