浅谈高频加热在木材胶合中的应用

高频介质加热技术是近三十年来发展起来的一门新技术。它的基本原理是利用高频电场对物质内部分子的反复极化,使分子在这种高频交变电场作用下急剧运动而相互摩擦产生热,从而达到加热的目的。由于它的热量是由内向外传递的,具有加热速度快、加热均匀、加热有选择性、产品质量好等优点,因此应用越来越广。在木材加工中,高频介质加热主要用于木材胶合(如胶接、胶拼、封边、胶合成型、胶合空芯或蜂窝板、家具组合装配胶合、层积材胶合、胶合板以     

高频、微波加热技术在日本木材工业的应用

日本从欧洲引进高频、微波加热技术后,以实用化为目的进行了大量开发研究,并在众多领域推广和应用.本文介绍了高频、微波加热处理技术的原理和方式,以及在日本木材胶合、干燥、可塑化处理、热处理等加工领域的利用现状和应用实例,分析展望了两项技术在我国木材加工领域的应用和发展前景.     

高频对8种泡桐木材介电性质的影响

本文研究了高频电场中频率与8各泡桐木材介电性质的关系；泡桐木材结构对介电性质的影响。得出频率变化对泡桐木材介电常数、电阻率影响很小，对功率损耗角影响较大；密度对泡桐木材介电性能影响不大。建议在高频加热技术的应用中，利用木材功率损耗角极大值和彬小值的频率，以达到良好的加工和节能效果。     

高频介质封边机组的试制

高频介质加热技术已在木材加工行业推广应用,并取得一定效果。但是,将高频介质设备用在板式家具生产流水线还是首次。遵照伟大领袖毛主席关于要把国民经济搞上去的伟大教导,我厂组成三结合会战小组,迅速上马板式家具生产流水线,并在完成封边机组的同时,基本上完成了五板(板式衣柜之柜门二栅、旁身二栅、中身一栅) 连成一条线。一、工作原理高频介质封边机组系采用高频介质加热技术与机械传动相结合完成板式衣柜五栅板的涂胶、封边(胶合)、倒楞、砂光等几道工艺。其中封边(胶合) 是板式衣柜生产线中的关     

低压工业汽水炉供热系统及其在干燥进口地板材中的应用

众所周知，木材干燥是木材加工工业的能耗大户，如何降低木材干燥的能量消耗，以降低干燥成本，是多年来木材干燥技术工作者研究的重要课题之一。南京林业大学干燥技术研究所对木废料为能源的木材干燥方法已有２０多年的研究历史，先后研制开发了炉气直接加热和间接加热木材干燥系统，该系统的优点是投资少、干燥成本低，但不易实现自动控制和现代化管理。燃木废料低压汽水炉供热木材干燥系统不仅具有炉气直接加热或间接加热干燥技术的优点，而且具有适合较大规模的干燥作业和现代化管理的特点，与蒸汽加热相比，还具有运行稳定，便于控制的…     

纪元公司的追求

石家庄开发区纪元电气有限公司于１９９３年在河北石家庄高新技术产业开发区注册，属民营科技企业。１９９５年通过河北省科委认定的“高新技术企业”资质。 纪元公司从成立至今一直从事机电一体化高频介质加热设备的研制与开发工作。先后开发并生产了多种用于木材加工的高频加热木工机械，产品销往全国２０多个省、市、自治区的上百个家具及木材加工企业。特别是高频弯曲木系列液压机组，为我国弯曲木家具的发展起到了重要的推动作用，产品至今畅销不衰，成为公司的支柱产品。目前公司的产品已经有七八个成熟的品种，几十个规格系列。而且…     

微波技术在木材干燥中的研究进展

微波技术以其独特的加热机理和特点为木材快速高效干燥提供了一条新途径。笔者简述了近年来国内外在木材微波干燥工艺方面取得的一些重要的研究进展,主要集中在微波功率、含水率和温度等基本干燥参数的优化及红外摄像技术等先进检测技术的应用等方面。同时指出了在木材微波干燥基础理论、干燥工艺、木材结构特性与微波加热非均匀性等方面缺乏系统性研究的问题。建议今后应加强基础理论研究并结合现代测控技术进行系统研究。     

重齿铁线子木材高频真空干燥工艺研究

高频真空干燥有效集成了高频快速加热与真空下水沸点降低的双重优势,能够使木材在低温下快速干燥,在干燥名贵和大断面木材上具有综合优势。探讨了高频真空干燥工业生产中干燥工艺参数的计算方法和选用原则,并对重齿铁线子(Manilkara bidentata)木材进行了生产试验验证。结果表明:单位体积输入功率(Pu)及脱水量的确定是干燥工艺实施及干燥过程控制的前提,Pu可以通过调整高频发振设备的电流(IP)、电压(EI)及发振率(R)来设置;干燥后期通过下调IP降低极板间的电压来避免干燥过程极板放电;干燥后木材含水率及干燥缺陷满足国标二级要求;干燥速度为1.2%/d,且随含水率的下降而减小。含水率在20.9%~10%之间,脱水效率与材温呈正相关。此外,脱水效率与含水率呈二次抛物线关系,在含水率为14.5%时取得峰值;材料升温能耗占全部能耗的11.2%,全部过程高频加热能耗占比为71.7%;升温阶段能量转换效率为44.5%,干燥阶段为27.7%,升温及干燥时间计算时应该考虑能量转换效率。干燥工艺参数计算方法、选用原则及试验结果可为高频干燥工业生产提供技术参考。     

木材湿热软化压缩技术及其机制研究进展

木材压缩是提高软质木材密度、强度和硬度,改善木材物理力学性能,扩大木材应用范围的有效方法。本文针对湿热软化下的木材压缩问题,从木材软化机制、软化特性、软化点的确定、热板加热下的传热传质特性、层状压缩的形成和压缩变形固定等方面分析木材压缩技术的研究现状、进展以及存在的问题。木材细胞壁的成分和组织构造是影响木材软化和压缩变形的主要内在因素,而湿和热则是影响木材压缩变形的外在因素。木材是一种具有弹塑性的天然高聚物。干燥木材缺乏塑性,水分和热量都能对木材组分起到增塑作用,特别是在湿热共同作用下增塑作用更加显著。木材细胞壁主要成分纤维素、半纤维素和木质素的特性及所占比例直接影响木材的可塑性,其中木质素的含量和软化特性是木材软化的主要影响因素。玻璃化转变温度和应力屈服点是表征木材软化最常用的参数。在木材弹塑性分析中,应力屈服点控制了木材在塑性区域的应力-应变关系,同时也决定了塑性变形潜能,但由于木材成分和结构非常复杂,应力-应变关系的拐点并不明显,因此应力屈服点和屈服应力的确定是木材塑性变形表征的关键点,也是一个难点。木材的组织构造主要影响木材的传热传质过程。利用木材3个断面渗透性的显著差异,通过干燥、浸水、放置、热板加热等处理,可使木材内部各个层面上形成差异显著的含水率梯度分布和屈服应力差,压缩后形成层状压缩木材。层状压缩木材压缩层的密度可达0.8 g·cm-3以上,未压缩层仍然保持原有的密度,而且压缩层的形成部位是可控的。层状压缩技术可以解决整体压缩木材损失大的问题,但目前木材压缩变形机制的研究都是围绕木材整体压缩开展的,缺乏木材软化点和屈服应力随含水率变化规律以及热板加热下木材内部屈服应力差变化规律的基础研究。要实现层状压缩的可控性,还需要在热板加热下的传热传质规律及木材湿热梯度分布的形成与调控等方面开展深入研究。     

木材微波加热厚度的确定

较之传统加热方法,微波加热是一种新型加热技术,在简述木材微波加热的机理上,阐述了影响木材介电特性的因素,指出其中木材含水率和温度是影响木材节电性质的两个最重要的因素.通过理论计算确定微波在木材中的穿透深度.计算表明:随着木材含水率和微波工作频率的增加,微波在木材中的穿透深度减少;当用频率为915 MH z和2 450 MH z的微波加热或干燥具有高含水率的木材时,木材的最大厚度应分别控制在16 cm和6 cm左右.     

地暖供热的发展空间和应用

随着社会的发展及人们对节能低碳生活的重视，大量的新技术在越来越多的行业应用起来，供暖行业也不例外。在供暖形式上人们改变了传统的散热器供暖方式，而是采用地暖供热。地暖供热：即将加热管安装在地板以下，用热媒不高于60℃的热水使地板循环加热。以辐射和对流的方式通过地面向室内供暖的供热方式。该文从地暖供热的优势、应用发展前景及使用时的注意事项几方面进行了综合论述。     

国内外软木研发进展与我国对策

软木是以栓皮栎的栓皮为原料,具有弹性、保温隔热、防滑耐磨、消音减震、安全无毒等特性的一种可再生绿色材料,产品广泛用于国计民生等重要行业和领域。文中介绍了世界软木资源分布情况、软木用途和产业趋势,综述了国内外软木细胞结构、化学成分、工艺与产品研发等概况,在比较欧美各国与我国软木产品标准制定/修订现状的基础上,概述了我国对现行软木纸标准LY/T 1320-2010和软木纸试验方法LY/T 1321-2013的修订研究过程。提出了加强我国软木研发的建议,即紧跟软木脂研究国际前沿,加大软木脂基础与应用技术研究;加强软木行业标准建设,实现软木产品标准国际化、单项化、功能化;加强软木产品开发利用以及软木资源的培育以提升我国软木产品竞争力,促进我国软木行业健康快速高效发展。     

The mechanical and physical properties of strand boards treated with preservatives at different stages of manufacture

The physical and mechanical properties of boards treated with a preservative at different points during the manufacture process were evaluated to determine the best stage for the application of preservative. A copper boron tebuconazole amine water-based preservative was used in 3% PF-bonded strand boards to achieve five different retentions. Preservative addition was examined at different stages of the manufacture cycle, namely, green strand diffusion, dry strand vacuum treatment, glue-line spray addition, heat and cold quench of manufactured board, and by post-manufacture vacuum treatment. The treatment methods had marked effects on the mechanical properties of some of the boards when the boards with the highest preservative retention were compared with their respective untreated controls. The best results were achieved where the preservative was applied by vacuum treatment of dry strands or by diffusion of green strands before board manufacture. Increasing preservative retention had minimal effects on board properties with these two methods but significant deterioration was noted when the preservative was applied by spraying dry strands or by post-board-manufacture heat and cold quench. An increase of pressing temperature resulted in significant improvements to the mechanical properties of the spray-treated boards. Post-manufacture vacuum treatment of boards caused excessively high losses in internal bond strength.     

Calculation models of pressure and position of curved laminated veneer lumber in molds during pressing

Curved laminated veneer lumber (LVL) for use in furniture-making was produced from glue-coated pieces of rotary-cut veneers that were assembled and pressed between molds. Pressure was applied until glue-lines were set and finally held in an assembly of the desired curvature. Pressure was an important factor during pressing of curved LVL. In this study we deduced some equations for designing the shape of molds and calculating the total pressure from the mechanics. The results are summarized as follows: (1) The position angle of every section of curved LVL assembly in molds on the horizontal and the total pressure during pressing can be calculated in relation to the shapes and dimensions of the curved LVL. (2) The pressure distributions in the glue-line measured using pressure-sensitive film were in good agreement with the glue-line unit pressure provided for the experiment and calculation. Therefore, the equations deduced in this study were suitable for calculating the position angle and pressure of curved LVL in molds. (3) The total pressure on curved LVL was greater than the pressure on straight LVL. The total pressure consisted of the pressure on the glue-lines of straight LVL with the same length and width as curved LVL plus the supplementary pressure needed to bend the veneers. (4) The total pressures and position angles of curved LVL in molds were affected by the shape, bent angle, and length of each section of curved LVL.The outline of this study was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 3, 1998     

微波处理中木材内温度分布的数学模拟

从热传导的物理规律出发,建立微波加热过程中木材内部热传导模型,并通过理论模拟揭示不同微波加热方式对预处理中木材内部温度分布的影响规律。结果表明:微波处理过程中,木材内部的温度分布规律及均匀性与微波加热方式直接相关;当采用单向微波辐射的方式进行加热时,沿着微波入射方向,木材温度逐渐降低,木材内部温差较大,且温度分布均匀性较差;当使用双向微波辐射的方式进行加热时,木材内能形成内高外低的温度梯度,且温度分布均匀性较好。     

Seasonal variation in photosystem II efficiency and photochemical reflectance index of evergreen trees and perennial grasses growing at low and high elevations in subtropical Taiwan

Three pines species, three evergreen broadleaf trees, one C(3) and two C(4) perennial grasses of subtropical Taiwan were studied to elucidate the correlation between photosystem II (PSII) efficiency and photochemical reflectance index (PRI = (R(531) - R(570))/(R(531) + R(570))). Measurements were made at two sites differing in altitude (800 and 2600 m) over several growing seasons. At high elevation, potential PSII efficiency, measured by chlorophyll fluorescence (the ratio of variable to maximal fluorescence; F(v)/F(m)) at predawn, decreased with decreasing air temperature and varied greatly among species. At the lowest air temperature (-3 degrees C) studied, variation in F(v)/F(m) among species ranged from 0.33 to 0.72. In contrast, at low elevation where air temperature was moderate, seasonal variation in F(v)/F(m) was small in all of the study species. When species, elevation and season data were pooled, despite the high variation in F(v)/F(m) among species, a good correlation between F(v)/F(m) and PRI was observed. When compared at the same value of PRI, F(v)/F(m) of evergreen trees was higher than that of perennial grasses; however, when the minimum temperature on the measurement day was below 0 degrees C, F(v)/F(m) was underestimated relative to PRI. We conclude that PRI could be used as a remote indicator of photosynthetic function when air temperature is above 0 degrees C.     

Thermo-hydro and thermo-hydro-mechanical wood processing: An opportunity for future environmentally friendly wood products

Abstract

This state-of-the-art report presents the basic concepts of some of the thermo-hydro (TH) and thermo-hydro-mechanical (THM) wood processes that are in use today, i.e. heat treatment, compression of wood in the longitudinal or transverse direction and wood welding. The reasons for the growing interest in TH and THM techniques are discussed, and the development of the different concepts, from first ideas to current status, is briefly presented. The physical and chemical changes that occur in wood during TH and THM processing according to the latest research are also presented. Finally, developments that are close to or already have an industrial application are presented, and the challenges for further development of the heat treatment, compression and wood welding processes are discussed. The TH processing of wood is based entirely on water and heat, and a THM process incorporates an additional mechanical force. The purpose of wood transformation by a TH or a THM process is to improve the intrinsic wood properties, to acquire a form and functionality desired by engineers without changing its eco-friendly characteristics or hindering its further use in the total material life cycle. Only a few of the recently developed techniques, e.g. heat treatment, wood welding and various densification applications, have been industrialized to some extent. There are many reasons for this relatively low transfer of the research results to a full up-scaled industrial production. Some of them are related to unsolved problems at the laboratory level on small-sized samples and others are related to the scaling-up processes in industry. Furthermore, the ageing of heated wood leads to deterioration with time, in some cases there is an unpleasant odour, the strength of the wood decreases substantially and the wood becomes more brittle. These are new challenges which need to be resolved by the collaboration of researchers from the different scientific domains of academia, research institutes and industry.     

纤维板热磨机磨片材质开发与研究

Defibrator is a very important machine in the wood industry for producing fiberboard.The refiner plates are the key parts of defibrator that directly act with the wood,and broken easily.The working life of the refiner plates is of significance to the wood industry.It may affect refining quality,production efficiency,and power consumption.In this paper,the abrasion resistance of the refiner plate made of different materials,the stainless steels and high chromium cast irons,were tested and compared.The results showed that abrasion resistance of refiner plate made of high chromium cast irons was better than that of the stainless steel materials.Although the two kinds of materials have the same compositions,their abrasion resistances have apparent difference.The main reason is that the material microstructures have very important effects on their performance.The refiner plates made of developed high chromium cast irons don‘t demand the complex heat treatment.This can simplify the producing process,save the cost of production,decrease labor strength,and increase the production efficiency.     

我国暖通、空调系统设备的发展趋势

我国空调设备具有多样性和复杂性,应在空调冷源、空气处理设备、空调末端产品、控制系统、机房专用机、家用空调、通风设备等方面开发新技术,新产品,在引进和消化国外技术的基础上,大力保护和发展民族产业。供热设备应开发适用性广的散热器,发展低温地板辐射供热方式和远红外辐射供热设备,研制适合中国国情的热计量手段。     

Selection strategy for a seedling seed orchard design based on trait selection index and genomic analysis by molecular markers: a case study for Eucalyptus dunnii

Molecular genetic analysis was applied to 162 individuals of 37 half-sib selected families belonging to six provenances of Eucalyptus dunnii Maiden in a provenance/family trial. The individuals were selected by a trait selection index and genetic diversity criteria were later applied for designing seedling seed orchards. Genetic diversity and its distribution, as well as relationships among individuals, were assessed on the basis of nine microsatellite loci and 243 amplified fragment length polymorphism markers. High diversity was found with both kinds of markers. Clear-cut genomic patterns of identification (fingerprinting) were obtained for each individual. Genetic differentiation estimates consistently showed low differentiation among provenances (R(ST1) = 0.069, theta(P) = 0.026 and F(CT) = 0.035) and great differentiation among families (R(ST2) = 0.223, theta(S) = 0.174 and F(SC) = 0.164). A high proportion of the total variation was observed within families (around 80% by both marker analyses), suggesting that orchard design should be based on individual or family selection rather than on provenance selection, and that individual ranking by both trait selection index and molecular genetic diversity criteria should be considered. A selection procedure for a seedling seed orchard design is proposed.