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Wood composites produced using aspen flakes have displayed interaction between manufacturing variables and stress-strain consolidation of these mats. This study brings an original approach to the process of wood composites within the analytical nonlinear continuum mechanics based model, developed to predict the consolidation of wood mats during part of the hot-pressing cycle. Consolidation of wood flake mats occurred principally during the closing of the press when the loose mat underwent uniaxial compression along its perpendicular direction. Forming parameters such as mat thickness, and pressing parameters such as press closing rate, were accounted for in a combined viscoelastic model with creep. The stress-strain consolidation model was applied to different formed mat structures using random and oriented layout of flakes, and although slightly higher values were obtained with the model regarding the viscoelastic behavior of the loose mat, the creep model showed a very good agreement with the experience data. These results within a continuum approach, are significant in the manufacturing of wood composites as they would enable optimization of manufacturing processes by integrating the specific conditions of the forming process of wood mats into the pressing strategy.This project is financially supported by a Natural Sciences and Engineering Research Council of Canada Strategic Grant (STR 0167246). 相似文献
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Kohta Miyamoto Shigehiko Suzuki Takayoshi Inagaki Ritsuo Iwata 《Journal of Wood Science》2002,48(4):309-314
Mat consolidation behavior was investigated at various press closing times (PCTs) using hinoki (Japanese cypress) particle mats. The temperature in the core layer of the mat, press pressure, and platen distance were measured. At the plateau stage during hot pressing, the core temperature decreased with increasing PCT. The core temperature did not increase before the platen distance equaled the target board thickness in the PCT range of 4–50 s and rose slightly when the PCT exceeded 100s. There was a linear relation between the logarithm of PCT and the maximum press pressure. The density profile across board thickness was strongly affected by the PCT. As the PCT increased, the position of the peak density (PD) moved toward the core layer as the PD itself decreased. The effect of PCT on the linear expansion (LE) of the board is discussed in relation to the density profile. There was no difference in LE after high relative humidity treatment in the PCT range 4–50s. LE appeared to be related to the low density and the precured region of the board surface. The LE after drying treatment was around –0.1%, and the thickness swelling after high relative humidity and drying treatments increased with increasing PCT.Part of this report was presented at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 1988 相似文献
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ABSTRACTGas permeability and structure of fiberboard mats are essential properties because of their impact on mat internal gas pressure, moisture content and temperature evolution during the hot-pressing process. The objectives of this work were to determine the effect of fiber size and mat density on the intrinsic gas permeability of the mat. For the study of these mat properties, panels with a homogeneous density profile through the thickness were manufactured at five density levels (200, 400, 600, 800 and 1000?kg m?3) for three different fiber sizes. Fiber refining was performed in a disk refiner at three plate spacings. Gas permeability was measured with an in-house built apparatus. The results showed that the fiber sizes studied had no significant effect on the intrinsic permeability. This was likely due to a more significant impact of the internal porous structure of the mat compared to fiber size. Besides, the intrinsic permeability decreased significantly when the panel density increased from 198 to 810?kg m?3. This suggests that the decrease of the intrinsic gas permeability during the last seconds of press closure plays an essential role in the bulk moisture mass transfer through the fiberboard mat. 相似文献
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综述了人造板预热与热压方面的研究现状,分析了人造板尤其是刨花板预热方面研究的不足。阐述了人造板预热的三个主要研究方向:板坯预热过程中的温度场分布、影响板坯温度场变化的因素及其影响规律以及预热对人造板主要力学性能的影响。 相似文献
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竹席/竹碎料新型建筑模板制备工艺研究 总被引:1,自引:0,他引:1
将小径竹及竹材加工剩余物加工成一定规格的竹碎料。以竹碎料为芯层,以竹席为表层组成板坯,通过热压制备竹席/竹碎料新型建筑模板。采用正交试验,选取热压时间、热压温度和施胶量作为工艺因素,对竹席/竹碎料复合新型建筑模板制备工艺进行了研究。研究发现,施胶量对产品的各项性能指标的影响最显著,其次是热压时间和热压温度。通过分析得出优化工艺:热压时间70 s.mm-1,热压温度为170℃,施胶量为10%。 相似文献
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The purpose of this study was to evaluate compression and swelling characteristics of individual furnish elements sampled
through the thickness of lab panels pressed without resin. Commercial southern pine OSB furnish was used to press resinless
mats so individual flakes could be removed from the panel after pressing and evaluated for compression behavior. 19 flake
sets, each set consisting of 15 southern pine flakes with 0.65% wax, were marked and measured for thickness and mass. One
set of marked flakes was randomly distributed in one layer of a mat which consisted of 19 total layers; each of the 19 layers
had 15 marked flakes randomly distributed in the layer. After hot pressing each marked flake was removed from the mat. After
achieving equilibrium at 35%, 65% and 98% relative humidity, each flake was again remeasured for thickness and mass. Experimental
results include flake compaction ratio and its distribution through the mat thickness, flake thickness swelling under different
RH environments, compaction ratio-thickness swelling relationship as well as individual flake compaction ratio and thickness
swelling variations. Comparison is made to adsorption/desorption behavior of pressed flakes. Flakes from surface layers exhibited
compression of 25 to 37%, about double that of flakes in core layers. As expected, flakes from surface layers showed much
greater thickness swell than core flakes and the response was accentuated with higher EMC conditions.
Received April 26 1999 相似文献
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微波预热MDF板坯的实验研究 总被引:2,自引:0,他引:2
利用微波对MDF板坯进行预热处理的研究结果表明,微波预热处理不仅能够在很短时间内提升板坯的温度,还能使板坯内的水分重新分布。通过处理,板坯表层的水分得到了提高,芯层水分被降低。这一结果有利于板坯在热压时热量从表层向芯层传递,从而缩短热压时间,提高生产效率。 相似文献
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从胶水类型、施胶方法以及关键工艺参数等方面探讨了竹木复合刨花板的生产工艺,综合结果表明,竹木复合刨花板批量生产的工艺参数为:低摩尔比环保树脂胶、搅拌气流式喷胶法、竹刨花比例40%~60%、用胶量70 kg(干胶)·m-3、热压压力2.0 MPa、热压温度170℃、热压时间20 s·mm-1、刨花颗粒(芯层)0.5~1.0 mm、板厚8.8 mm。生产的竹木复合刨花板产品质量执行国家标准,质量可以达到国标A类刨花板一等品标准。 相似文献
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对三种竹碎料板的物理力学性能进行了比较分析。板材弹性模量:竹席增强竹碎料板〉竹碎料/木纤维复合板〉普通竹碎料板;静曲强度:竹席增强竹碎料板〉竹碎料/木纤维复合板〉普通竹碎料板;吸水率:普通竹碎料板〉竹碎料/木纤维复合板〉竹席增强竹碎料板;吸水厚度膨胀率:普通竹碎料板〉竹碎料/木纤维复合板〉竹席增强竹碎料板;内结合强度:竹碎料/木纤维复合板〉竹席增强竹碎料板〉普通竹碎料板。 相似文献
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采用常规热压法对刨花板板坯进行热压,探讨热压时中心层温度变化规律与板坯含水率、板厚、板材密度及热压温度等的关系.结果表明:在快速升温段,升温速度随板厚的增加而明显减小,随热压温度的提高而加快;在慢速升温段,升温速度随板厚的增大而显著加快,随热压温度的升高而明显加速,升温速度受目标密度和板坯含水率影响很小;板坯内水分蒸发所需时间随板厚、板坯含水率、热压温度、板材密度的增长而增加;板坯内水分蒸发温度随板材密度的增加而升高,随板厚的减少而升高,热压温度和板坯含水率对其几乎没有影响;加入胶粘剂会使快速升温段的升温速度有所加快,而使恒温段的水分蒸发温度有所降低. 相似文献
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Xiang-Ming Wang Bernard Riedl Robert L. Geimer Alfred W. Christiansen 《Wood Science and Technology》1996,30(6):423-442
Summary To better understand the curing and bonding behavior of phenol-formaldehyde (PF) resin under dynamic conditions, flakeboards were manufactured either by conventional pressing at 7% or 12% mat moisture content or by steam injection pressing with 10 or 20 seconds steaming duration. Resin-impregnated glass-cloth samples and lap-shear tension specimens were embedded in the core of each flakeboard. After the flakeboards were pressed for various periods of times, the samples and specimens were quickly retrieved. The degree of resin cure was determined on the resin-impregnated glass-cloth samples by dynamic mechanical analysis. The bond strengths were measured from the lap-shear tension specimens on a mechanical testing machine. The results of resin curing and bonding were then correlated to the performance of the resin-bonded boards, which were evaluated by internal bond, modulus of rupture, modulus of elasticity, and thickness swelling. Resin curing and lap-shear bonding did not proceed simultaneously. In conventional pressing, the mat moisture content (MC) at 12% favored resin curing, but slightly retarded lap-shear bonding, as compared to 7%MC. In steam injection pressing, the rates of resin curing and lap-shear bond strength development were much faster for 20 seconds than for 10 seconds of steaming duration. Longer press times were needed to obtain boards with maximum strength in the 12%MC conventional pressing and the 20-s steam duration steam injection pressing than in those conditions where moisture content was lower or steam time was less. The need for longer press times must be attributed to higher internal vapor pressures and/or lower wood and resin component strengths, rather than to incomplete cure or bonding.This material is based on work supported by the Ministry of International Affairs, Quebec Government, the Natural Sciences and Engineering Research Council of Canada, and Laval University (Quebec City). The work was also supported by the U.S. Department of Agriculture under research joint venture agreement FP-92-1835 相似文献
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Muhammad Navis Rofii Satomi Yumigeta Yoichi Kojima Shigehiko Suzuki 《Journal of Wood Science》2013,59(5):402-409
The purposes of this study were to examine the use of furniture mill residues containing high-density raw materials in particleboard production and to evaluate the effect of mixing several types of furnish on board performance. Wood wastes collected from the furniture industry in Japan containing matoa (Pometia pinnata), Douglas-fir (Pseudotsuga menziesii), and sugi (Cryptomeria japonica) with different particle shapes were prepared as raw materials for use in the manufacture of experimental particleboards. Seven board types and three mixed boards were manufactured with three replications. Methylene diphenyl diisocyanate (MDI) resin was applied at 6 % content in mat preparation. The pressing conditions were temperature of 180 °C, initial pressure of 3 MPa, and pressing time of 5 min. The target density was 0.72 g/cm³. This study showed that matoa particleboard had properties suitable for use in interior applications, although its properties were considered inferior compared with other particleboards. Improvement of matoa particleboard could be achieved by mixing with higher quality wood particles such as those from sugi or Douglas-fir. The furnish type used in this study affected board performance. All residues from furniture mills have the potential to be used for particleboard production, even when they contain different furnish types and wood species. 相似文献
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Summary A procedure is presented to estimate the relative vapor pressure, equilibrium moisture content, average flake temperature, and average flake moisture content in a flakeboard mat during hot-pressing. This method is based on measurements of temperature and total gas pressure in the mat during hot-pressing. A heat and mass transfer model was adapted from the literature to predict the temperature and moisture content inside an individual flake. Significant moisture gradients are predicted to develop within flakes. Convective heat transfer appears to control the change of moisture content within a flake. Thermodynamic equilibrium between the gas phase and the wood component is not achieved during hot-pressing.This work was funded by the USDA Competitive Grant Program for Forest and Rangeland Renewable Resources, Project No. 85-FSTY-9-0106 and 87-FSTY-9-0253 相似文献
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Fatemeh Bavaneghi 《Wood material science & engineering》2016,11(1):57-61
In this study, the effects of acetylation and press time on the heat transfer from the surface to the core on the particleboard mat, springback, internal bonding, modulus of elasticity, and modulus of rupture were determined. Particles were soaked in the acetic anhydride for 24 h and heated in an oven at 120°C for 40 minutes, 3 h and 6 h to achieve three weight gain levels of 8%, 12%, and 17%, respectively. Acetylated and control boards were produced with 10% melamine urea formaldehyde (regarding the particles dry weight) and pressed for 5, 6, and 7 minutes. During the pressing process, the heat transfer to the core layer of the mat was measured by thermocouple made of Cr-Ni wires. It was found that the increase of acetylation level leads to significant reduction in heat transfer during manufacture process and develops springback which in turn, results in density loss. Findings indicated that these defects were correlated with the press time and compensated by the press time prolongation. Strength loss of the acetylated boards was due to debonding of the constituent that compensated somewhat with increasing press time. 相似文献