Study On Drying Properties And Technology Of The Russian Pinus Sylvestris Sawn Timber

As the studying object of the Russian Pinus sylvestris sawn timber, we do some researches about drying properties of Pinus sylvestris and the timber drying technology. Through a series of tests with 100℃drying test method, we learn that the Moisture content, density, size stability of pinus sylvestris with time variation, during the process of drying, then trying to define the schedule of suiting for Pinus sylvestris . In order to study the changes in water transport, this paper studied on the change of the Pinus sylvestris water transverse relaxation time T2 in different stages of water moisture content .at 120℃high temperature drying process, using the low-field nuclear magnetic resonance analyzer. This research aims to provide theoretical proof for the further study on the factors of stress relaxation under different conditions. In this study, Pinus sylvestris was used as the experimental materials and dynamic stress-strain test system was used as experimental instrument. Stress relaxation was not only affected by the temperature, but also affected by the moisture.We press the lumbers in tangential, and then dry them by conventional drying kiln with foot-fan. We study the velocity and quality influence about the precompression of square lumber, thus determine the best precompression ratio. The square timber of Pinus sylvestris, with routine and high temperature drying schedule, the drying speed of the square wood influence by different diameter of aperture, two surface or four surface aperture, or by one surface notch. The general results were as follows:1. Pinus sylvestris belongs to the wood drying classification of "easy to dry"。The grades of the initial check, the honeycomb, the cross section deformation, the twist deformation, the drying rate are 3, 1, 2, 2, 3 for Pinus sylvestris. Based on the grades of drying defects and corresponding drying conditions, the drying schedules for Pinus sylvestris var. mongolic were established, and can keep the drying quality under 120℃。2. Through analysis of various parameters about water transverse relaxation time, we can determine the transport and distribution of water in sawn during high-temperature drying process. The results suggest that transverse relaxation time is an efficient method for determination of water mobility and distribution capacity in wood during the dying process.3. The temperature and moisture content on the stress relaxation have a significant impact. Stress relaxation dramatically increased and the residual stress rapidly decreased with temperature enhancing or moisture content rising. In other words, the initial stress decreased gradually and the relaxation rate was on the rise. It was also found that, under the same conditions, compared with the tangential section of the Pinus sylvestris, the radial section has the larger initial stress and smaller stress relaxation rate. Besides, the initial stress of late wood is larger than early wood and the stress relaxation rate of late wood is smaller than early wood.4. By 13.2% and 26.2% compression ratios compress in tangential, the destructiveness is small to pit, but works as in drying in transit moisture content when 30% - 12%, drying velocity distinct enhancement. When the moisture content is lower than 12%, the drying velocity is not distinct enhancement. Theoretically, tangential compress them to compression ratio of 36.4%, the cell cavity were closed. Pits were partial destructed, but the cell walls almost are perfect, it can enhance the drying velocity in a great degree. Compresses the square lumber to the compression ratio about 13.2% and 26.2%, and then dry them by conventional drying kiln with foot-fan. There have not the surface check and internal ruptures finally. The moisture content deviation obviously reduces, the dry uniformity is very good, the drying quality distinct enhanced. G1 and G2 were compressed by 13.2% and 26.2% compression ratios compressions in tangential. After drying, the moisture content windage is 1.71% and 1.73%, it is lower than the lumber that was not compressed.5. Whether in the condition of routine or high temperature drying schedule, the speed of Perforated and slotted timbers are faster than general timbers .At the same time, the Numerical MOR and MOE relationship between the processing timber is: general timbers>timbers with￠1mm hole >timbers with￠2mm hole >timbers with notch . Compared with the routine drying schedule timbers, the high-temperature drying of timbers has higher CrI.