Research On Effect Of Pre-treatment On Drying Performance And Quality Of Elm

With the rapid development of furniture industry, the demand of wood resources becoming gradually intensified, excellent manufactured furniture materials become increasingly nervous, which cannot meet the requirement of furniture production and export extremely. Therefore, it is necessary to choose some varieties of trees whose resources is relative richer, which is suitable for the furniture production. Ulmus is ring-porous hardwood, whose heartwood between sapwood is distinguished clearly. Elm is widely distributed in East and North of China, whose texture and pattern is more stout-straight and beautiful compared to Northeast and other origin of China, texture and luster are similar to Ash, and the resources of that are richer. Otherwise, Elm is used to manufacture antique Ming and Qing furniture in East of China for many years in the past, which is more popular around the field of furniture, meanwhile, the serious restrictions of wide application in the field of furniture industry of Elm, however, due to the drying defects of deformation, distortion and shrinkage owing to its high moisture content, large shrinkage rate as well as rough-uneven structure of green wood. According to the current situation, the old Elm is derived from the antiquated houses and furniture that is mostly used for pillar or beams, that is greeted by lots of people contributes to its incomparable advantages such as larger size, straight body, uniform moisture content, better performance of all aspects as well as easy secondary processing of planning and painting, especially the better dimensional stability performance after many years of furnishing and air drying. Unfortunately, the antiquated houses and furniture have been depleted nowadays.Basing on the conventional drying characteristics and technology drying of Ulmus parviflora of Liaocheng, Shandong, the effect of different pre-treated method, temperature and time on the drying speed, drying quality, color as well as the shrinkage and swelling and other dimensional stabilities was investigated in the research, the aim of which is to provide a scientific basis and theoretical support for extending application field of furniture industry of Elm, which, no doubt, has a vital positive significance for achieving transformation of raw materials of furniture industry and technology reform.(1) The research of conventional drying technology and characteristics of Elm by 100℃ test showed that the initial temperature was 65℃, initial depression between dry and bulb was 4℃, the final temperature was 80℃. Then, three drying schedule was selected to conduct comparative experiment, and the results indicated that the drying period of schedule III that the average initial moisture content was 31.5%, the final moisture content was 8.8%, between the schedule I and II, was 177h. Besides, moisture content, deviation of moisture content in thickness and stress index of lumber dropped stably and uniformly during drying process, which created a fine drying condition where had no visible drying defects such as bending, desiccation etc., and the drying consequence of that met the national lumber drying quality examination first-level indicators. In summary, drying schedule III is the best.(2) The research of effect of different pre-treated methods and conditions on drying characteristics showed that the pretreatment before drying would shorten the drying period, at the same time, guarantee the drying quality of Elm. With the pre-treated time prolonging, the drying cycle of 100℃ pre-steamed lumber significantly reduced under the condition of same pretreated temperature, compared to 100℃ pre-boiled ones, the extent of reduction of that was obvious. The drying period of 140℃,6h pre-steamed lumber was 124 hours, which had shorten 29.94% compared to drying schedule III. The drying quality of 100℃ pre-boiled and pre-steamed lumber all met the national lumber drying quality examination first-level indicators, except for the stress index of 100℃,4 and 6h pre-steamed ones that met the third-level indicators. The study of pre-steaming before drying indicted that the drying period of pre-treated lumber dramatically reduced with the pre-treated temperature rising and pre-treated time prolonging. The drying period of 140℃,6h pre-steamed lumber had shorten 41.24% compared to drying schedule III, the drying quality met first-level indicators. Accordingly, the comprehensive conventional drying consequence of Elm had gotten improvement.Meanwhile, the effect of 120℃ and 140℃ pre-steamed on the color after drying was discussed in the research. The result turned out that L* and △E* of pre-treated lumber was significantly declined and increased respectively, however, a* and b* of that reflected a little reduction. The △L* value and △E* value of 140℃,6h pre-steamed lumber of Elm was 15 and 15.58 respectively, the color of that was closed to the old Elm.(3) The research on the effect of different pre-treated methods and conditions on dimensional stability of Elm indicated that the discrepancy of 100℃ pre-boiled and pre-steamed specimens decreased significantly with the pre-treated time prolonging, but the drying shrinkage rate, drying shrinkage coefficient, bulking rate, maximum water absorption rate as well as ASE of that mirrored little extent increase. Simultaneously, compared to 100℃ pre-boiled samples, the increase range of 100℃ pre-steamed ones were larger. The study of effect of pre-steaming on Elm showed that the drying shrinkage rate, drying shrinkage coefficient, bulking rate, maximum water absorption rate of pre-treated specimens markedly decreased with the pre-treated temperature rising and pre-treated time prolonging, the ASE of that obviously improved. For the improvement range of dimensional stability of dry shrinkage, dry shrinkage coefficient etl., the 140℃,6h pre-steaming was the optimal.