喷蒸真空热压技术

喷蒸真空热压系在板的热压周期中,通过向板坯内部注入高温高压蒸汽以加速热固性树脂固化,并借助真空处理帮助残余蒸汽和其它有害气体排除、降低板鼓泡发生率的一种热压方法。该技术可有效缩短厚板的热压时间,并改善板的尺寸稳定性、控制板的密度分布、减少砂光损失。喷蒸真空热压技术有望成为木质刨花板和木质复合板热压的发展方向。     

纤维板喷蒸热压传热传质规律研究

采用喷蒸热压方式对中低密度纤维板坯进行热压,测定并记录热压过程中板坯中心层开始升温的时间、达到100℃的时间、稳定温度及达到稳定温度的时间、热压结束后板坯的含水率;分析蒸汽压力、目标厚度、目标密度、热压温度及板坯含水率对其影响,得出了中低密度纤维板喷蒸热压传热传质的基本规律.     

科技开发信息

喷蒸压机喜获国家专利最近 ,由南京林业大学与江苏省建湖县轻工业通用机械厂共同研制的“喷蒸及真空处理装置”获得国家专利 ,专利号为ＺＬ99 2 2 941 0。该设备是一种具有表面、侧面喷蒸及真空处理装置 ,是生产刨花板、纤维板、麦秸板、稻草板的关键设备 ,其优点 :一是节能降耗 ,能缩短热压时间 ,比常规压机提高工效 2～ 5倍 ;二是提高产品质量 ,通过喷蒸热压新技术 ,使具有一定压力的饱和蒸汽从板坯的上下两面注入 ,保证板坯表芯层同时加热 ,胶粘剂同时固化 ,提高了制品的内部结合强度和侧面握钉力 ;三是有效地解决了超厚草木轻质墙…     

刨花板喷蒸热压

刨花板喷蒸热压王洁瑛，刘正添（北京林业大学北京１０００８３）热压是刨花板生产的关键工序。热压的间取决于板坯芯层的升温速度及胶粘剂的固化速度。传统的热压方法依靠热压板（或垫板）向板坯的接触传热，芯层升温慢，尤其是在生产厚板的情况下，单纯依靠提高热压温度...     

采用喷蒸热压技术提高中纤板和刨花板的热压效率

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     

国外人造板喷蒸热压新工艺

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...     

人造板在不同热压条件下传热的研究现状

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.     

轻质稻秸保温材料高频热压板坯内部温度的研究

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。     

单板层积材喷蒸热压的初步探讨

探讨了喷蒸热压制作杉木单板层积材的工艺。研究了热压温度、热压时间、喷蒸时间和涂胶量对单板层积材性能 的影响。结果表明,喷蒸热压可有效缩短杉木单板层积材的热压时间,且制品性能较好。     

喷蒸-真空热压技术在厚型中纤板制造中的应用

针对传统热压法生产厚型MDF板存在板坯芯层升温速度慢、热压时间长等问题,研究成功以喷蒸-真空热压技术为核心的厚板制造技术,并用于国产多层普通MDF生产线的改建.采用该技术,制板热压时间大大缩短,生产能力显著提高.改建线生产的厚度为30、35 mm的中纤板,经检测可达到GB/T 11718-1999的要求.     

微波预热MDF板坯的实验研究

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。     

Comparison of the pressing behaviour of wood particleboard and strawboard

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.     

湿地松制造中密度纤维板工艺的研究

以湿地松（Ｐｉｎｕｓｅｌｉｏｔｉ）为原料制造中密度纤维板工艺的研究,采用正交试验方法,分析了施胶量、板坯含水率、热压温度及热压时间对中密度纤维板物理力学性能的影响。试验结果表明：板坯含水率及热压时间对试验板质量影响较大,热压温度及施胶量的影响较小。采用适宜的工艺,即板坯含水率在１０％、热压温度１６５℃、热压时间５ｍｉｎ,施胶量可以降至８％～９％,试验板的各项物理力学性能可以达到国标特级品的要求。     

刨花板常规热压传热研究

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.     

A continuum model of the interaction between manufacturing variables and consolidation of wood composite mats

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).     

Flake compression behavior in a resinless mat as related to dimensional stability

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     

Phenol-formaldehyde resin curing and bonding under dynamic conditions

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