共查询到19条相似文献,搜索用时 156 毫秒
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刘恩永 《林业机械与木工设备》2002,30(8):36-37
蒸汽喷蒸热压是近年来研究开发的一种热压新技术,它可以提高中密度纤维板和刨花板的生产效率,保证产品质量,减少能耗,降低成本,在中密度纤维板和刨花板生产中具有广阔的应用前景.1蒸汽喷蒸方法简介 运用蒸汽喷蒸技术的热压机具有较特殊的结构,即热压机的压板表面上钻有直径为3mm左右且按一定规律排列的蒸汽喷射孔.为防止细小纤维和刨花堵塞蒸汽喷射孔,压板上垫有防腐蚀、防氧化的金属网垫.网垫的边部用橡皮密封,以防止蒸汽泄漏(见图1). 当压机闭合且板坯被压缩后,通过压板上的蒸汽喷射孔向板坯内喷射具有一定温度和压力的水蒸汽,水蒸汽从板坯表面冲向芯层,对纤维和刨花加 相似文献
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国外人造板喷蒸热压新工艺 总被引:3,自引:0,他引:3
国外人造板喷蒸热压新工艺王国超喷射蒸汽热压工艺(SteamlnjectionPre-esing),是近年来兴起的一种新工艺。从压机上、下压板或侧面向板坯(刨花板、纤维板等人造板)喷射高温高压水蒸汽,喷蒸时机一般控制在压板已经闭合,板坯被充分压缩,压缩... 相似文献
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论述了国内外人造板在常规热压、喷蒸热压、高频热压和板坯表面喷水热压条件下传热规律研究的现状,指出了目前研究存在的问题及其进一步改进的设想. 相似文献
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研究了高频电场中板坯厚度方向温度分布规律以及制板工艺因素(包括原料含水率、板材厚度和板材密度)对轻质稻秸保温材料板坯内部温度的影响,试验采用荧光光纤温度测定仪自动准确测定高频热压时板坯内部温度。结果表明:板坯升温过程分为快速升温、水分排出、慢速升温三个阶段,板坯内部温度在厚度上存在差异.温度分布总体表现为芯层高表层低。与常规热压相比,高频热压大大缩短了热压时间,且板坯厚度方向温度均匀性大大优于常规热压。在快速升温阶段,在一定范围内提高含水率能加快板坯的升温速度;在水分排出阶段,通过减小原料含水率能缩短水分汽化时间;原料含水率对慢速升温阶段基本没有影响。在整个升温阶段,板材密度越低,其升温速度越快;在水分排出阶段。板材密度越低,水分汽化时间越短。板材厚度的影响作用与板材密度类似。 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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To improve the understanding of strawboard manufacturing processes, mat pressing behaviour of wood particleboard and strawboard bonded with urea formaldehyde resins were experimentally investigated and compared in terms of mat compressibility, transverse permeability, mat pressure, core temperature, core gas pressure and vertical density profile. The results have shown that straw particles are much more compressible and therefore require less platen pressure for pressing. Compared to wood particle and refined straw particle mats, hammer milled straw mats have low permeability and subsequently show high core gas pressure and high maximum core temperature during hot pressing, in addition to large differential densities between surface and core layers in the final pressed boards. It is recommended that a slower press closing rate and longer press opening time be used to develop the strawboard pressing schedule. 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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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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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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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