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以压缩杉木为研究对象,采用热处理和蒸汽处理两种方法,在不同温度条件下(160、180℃和200℃)对其进行压缩变形固定处理,分析不同处理工艺条件对压缩杉木回复率、残余应力和力学性能的影响,并探究压缩杉木变形固定机理。结果表明:热处理和蒸汽处理都可以降低压缩杉木的回复率和残余应力。随着处理温度的升高、处理时间的延长,压缩杉木的水煮回复率和吸湿回复率均减小。与热处理相比,各温度条件下蒸汽处理的压缩杉木水煮回复率和吸湿回复率均较小。随着处理温度的升高和处理时间的延长,热处理和蒸汽处理均可减少残余应力。在相同处理温度和处理时间条件下,蒸汽处理对压缩杉木的残余应力有更好的消除效果。热处理和蒸汽处理对压缩杉木力学性能都有一定的削弱作用,特别当处理温度达到200℃时,力学性能下降幅度较大。热处理和蒸汽处理改变了压缩杉木中C元素和O元素含量,O/C值分别降低了5.88%和7.84%;不改变压缩杉木纤维素结晶区的晶胞构造,但相对结晶度分别减小了5%和3%。综合考量,对压缩杉木采用蒸汽处理(180℃)进行变形固定是较好的选择。 相似文献
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氧化反应对热处理固定杉木压缩木材的影响(英文) 总被引：5，自引：0，他引：5
该研究的目的是明确氧化反应对热处理固定杉木压缩木材的影响 .首先 ,饱水状态的杉木试件在热压机中被径向压缩约 50 % ,然后压缩试件被分别放在一个普通烘箱 (有氧热处理 ,空气的压力为大气压 )和一个真空干燥箱中 (真空热处理 ,空气压力很低 ,约 0 .0 75MPa)进行热处理 ,两种热处理都设置了 5种温度包括 140 ,160 ,180 ,2 0 0 ,2 2 0℃以及不同的时间 .同时进行热处理的还有一些绝干的对照试件 ,用来测定不同热处理过程中的重量损失率 (WL)和抗收缩率 (ASE) .研究结果如下 :( 1)热处理过程中氧气的存在大大提高了热处理的效率 ,在 2 2 0℃时有氧热处理约 2 .5h后 ,压缩木材的RS(回复率 )达到 0 ;但在真空热处理时 ,在 2 2 0℃时加热约 30h后 ,压缩木材的回复才能基本被固定 .( 2 )氧化并不是压缩变定的固定、木材重量的损失或尺寸稳定性提高的必不可少的条件 ,氧气的存在几乎对RS和WL以及ASE和WL间的关系没有影响 ,但对RS和ASE间的关系有一些影响 .( 3)T T平面中的RS等值线 ,Δt一定回复率和温度下两种热处理所需时间的差值 )和温度间的关系 ,以及由于氧化反应而引起的热处理效率增加的系数 η清楚地反映了氧化反应对热处理固定杉木压缩木材的效率的影响 相似文献
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家具和地板用浸渍改性杉木研究进展 总被引：2，自引：0，他引：2
《林业工程学报》2016,(5)
杉木是我国南方重要的速生林树种之一,但其木材存在诸多缺陷,极大地限制了其在家具、地板中的进一步开发利用。将杉木进行浸渍改性以提高综合利用率是解决全球木材的供需矛盾和家具、地板用材短缺的重要手段之一。浸渍改性目前主要应用的树脂有UF树脂、PF树脂、聚乙烯醇缩甲醛、MF树脂等,其中以PF应用较常见,其改性效果较为显著。浸渍改性过程中,主要有真空处理、真空加压、抽提后常压浸渍或真空浸渍等浸注方法,辊压浸注作为常温常压条件下高效快速浸注处理木材的方法也可用于杉木的浸渍改性,真空-叠压法既能保证改性药剂完全渗入杉木木材,也能防止杉木试材在压力下被压溃。不同的浸渍工艺参数和树脂固化条件对改性后杉木性能影响不同:浸渍时间对浸渍材的吸水率及吸水厚度膨胀率影响较大,热压温度、热压时间与压缩变形恢复率、静曲强度密切相关,各工艺因素间存在一定的相互关系和影响。最后讨论了浸渍改性杉木在家具、地板业中的发展方向与应用前景,为杉木浸渍改性的进一步研究和应用提供参考。 相似文献
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γ射线辐射杉木压缩木材的固定和蠕变(英文) 总被引：1，自引：0，他引：1
为了探讨木材压缩变定固定的机理 ,该研究对杉木压缩木材进行γ射线辐射处理 ,射线辐射剂量分别为 0 (作为对照试材 ) ,10 3 ,5× 10 3 ,10 4 ,5× 10 4 ,10 5,5× 10 5,10 6,5× 10 6Gy ,然后测定和讨论了γ射线辐射杉木压缩木材的重量损失率、平衡吸湿含水率 (EMC)、吸湿回复率 (RSA)和吸水回复率(RSW )、绝干状态下和吸湿解吸过程中的蠕变。该研究表明 :γ射线的辐射剂量对杉木压缩木材的重量损失率、EMC、RSA、RSW有重要的影响 ,当辐射剂量超过 10 6Gy后 ,试材的重量损失率和EMC显著增大 ,RSA和RSW显著下降 ;另外 ,随着γ射线辐射剂量的增大 ,绝干状态和吸湿解吸过程中杉木压缩木材的瞬时柔量和蠕变柔量均呈增大趋势 .从该研究结果可以推测 ,当γ射线辐射剂量较大时 ,特别当辐射剂量在 5× 10 6Gy左右时 ,杉木压缩木材的细胞壁中发生了降解反应或非结晶化反应 .而且 ,该研究证明了压缩木材细胞壁主成分发生的降解反应能够使木材压缩变定得到一定程度的固定 相似文献
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本试验以杉木中龄林为供试对象,采取N、P、K三因素三水平正交试验设计、方差和协方差分析、回归显著性检验等方法对林地施肥效应进行研究.试验分析表明,氮肥对杉木中龄阶段的树高生长有促进作用,但施肥对杉木中龄阶段的胸径生长和材积生长无显著差异,杉木中龄林的材积生长速度依赖于进入中龄阶段前的生长速度,施肥效果不显著. 相似文献
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为拓展竹基纤维复合材料的应用领域,对慈竹纤维化单板进行热处理,探讨蒸汽压力和热处理时间对竹基纤维复合材料性能的影响.结果表明:经过热处理,竹基纤维复合材料的尺寸稳定性改善；随着蒸汽压力的增大和热处理时间的延长,材料的静曲强度和水平剪切强度显著降低,弹性模量则呈现先增后减的趋势.在保证材料性能的前提下,建议根据产品需求来选择适宜的热处理工艺. 相似文献
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《中南林业科技大学学报(自然科学版)》2017,(12)
本研究以脲醛(UF)树脂改性杉木为研究对象,采用高温过热蒸汽对其进行热处理,系统研究了热处理温度和时间对UF树脂改性杉木力学强度的影响规律。结果表明:与杉木对照材相比,UF树脂改性杉木力学强度显著提高;高温热处理使杉木浸渍材的力学强度降低;随着温度升高和时间延长,杉木浸渍材的抗弯弹性模量和强度、顺纹抗压强度和横纹抗压比例极限应力均呈明显下降趋势;经热处理后,UF改性杉木抗弯弹性模量、抗弯强度、顺纹抗压强度最大分别可降低11.4%、65.1%和17.3%,横纹全部弦向和径向抗压比例极限应力最大分别可降低60.9%和59.6%,横纹局部弦向和径向抗压比例极限应力最大分别可降低36.5%和56.5%。 相似文献
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王赛南 《中南林业科技大学学报(自然科学版)》1995,(1)
本文针对现有喷雾机存在皮碗容易损坏、易跳闸熄火的原因进行了分析，提出了用液压控制自动卸压装置取代原手动机控卸压的设想．并对此自动卸压装置的工作原理及设计计算进行了探讨．证明此改进设计可行，可以应用于生产实践． 相似文献
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分析了汽车发电机抛负载电压的形成过程及其与发电机的相电动势、激磁电流和转速之间的关系.汽车发电机抛负载电压包含两个部分,且均由定子绕组本身产生.其一为定子绕组中负载电流突变产生的自感电动势,其特点是持续时间短,危害较小;其二为在激磁磁场作用下定子绕组产生的感应电动势经整流后得到的电压,其特点是电压持续时间长,危害较大.最后推导了发电机磁路在未饱和及饱和时抛负载电压的计算公式,并给出了相应的实例分析. 相似文献
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本文根据在湖南省会同县杉木人工林定位研究站测定的数据,对林分内的各和湿度参数,包括降水量、蒸发散量、水汽压、绝对湿度、饱和水汽压、饱和水汽压差、比湿和相对湿度等因于的年变化、日变化及其垂直分布规律进行了分析。结果表明,优越的湿度环境适于杉木喜温暖、湿润的习性,有利于杉木的生长,是当地成为杉木中心产区的重要原因之一。 相似文献
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Summary The preservative treatment of four different wood based board materials using an esterified borate applied in the vapour phase was investigated. Under optimum conditions complete impregnation via the board faces was achieved in all boards treated. Board moisture content and treatment time had a major influence on retention and depth of penetration of the borate vapour. 相似文献
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A. J. Hunter 《Wood Science and Technology》1994,28(3):185-188
Summary When lines of constant moisture content (isosteres) are plotted on axes of In r (r, relative humidity) versus In ps (ps, pressure of water vapour at saturation), approximately straight lines result. Other axes with the same property are discussed. The slope of lines of constant Gibbs free energy of water vapour is derived for the above chart and it is shown that the basic equation of sorption is represented by this slope and that of the isostere. 相似文献
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Preparation of active carbons from a commercial holm-oak charcoal: study of micro- and meso-porosity 总被引：1，自引：0，他引：1
We studied the influence of the degree of gasification and the choice of activating agent (carbon dioxide, water vapour, or both carbon dioxide and water vapour acting successively) on the activation of samples of a commercial holm-oak wood (Quercus rotundifolia) charcoal. To this end, we prepared the active carbon samples using the activating agents at 800, 850, 900, and 950°C for the time required to gasify 20, 40, or 60% of the mass of the charcoal at the moment when the set gasification temperature had been reached. The active carbons were characterised by physical gas adsorption and densimetry. Those prepared with carbon dioxide or water vapour alone had textural characteristics that were better than those of the precursor charcoal. The micropore volume was greater in the samples activated with carbon dioxide than with water vapour. The activation with both carbon dioxide and water vapour successively led to a major increase in porosity, taking into account that these samples presented a 40% burn-off percentage which endowed them with good textural characteristics. In general, as the burn-off percentage increased, so did the micropore and mesopore volumes.To sum up, holm-oak wood is a good raw material, not only to get barbecue coal, which has been used as a precursor to obtain activated coal, but it also allows the activated coal to develop its microporosity and mesoporosity in a good way, which is suitable for new applications as it is absorbent in liquid phase, gas absorbent, is a constituent part of combustible batteries, etc.The main interest of this research is the preparation of activated coal and the determination of the size pore distribution obtained, given its great influence in the quality of the activated coal obtained starting from holm-oak wood, what gives a great economic and industrial value in the Southwest of Spain for this raw material. 相似文献
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木材微波干燥内部压力对水分移动的影响 总被引：1，自引：0，他引：1
在微波干燥过程中,能量是以电磁波的形式直接渗透到木材的内部,并通过微波电磁场与水分子及木材中极化分子(羟基)的相互作用而迅速产生大量的热,导致木材内水分移动机理与常规干燥很大的不同。实验结果表明:微波干燥过程中,存在内高外低的压力场,内中蒸汽压力是水分移动的驱动力。 相似文献
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Recent investigations on friction-welded wood-to-wood connections have shown interesting capacities of these adhesive-free joints for further development towards constructional elements. This paper addresses challenges and technical requirements for the enhancement of this technology from small specimens to samples of structural scale. Inhomogeneities in bonding quality and joint strength, herein referred to as scale effects, become relevant with an increase in size of the welded interface. It is assumed that the water vapour and smoke that evolves during the welding process by evaporation of moisture within the cell structure is a reason for these inhomogeneities. In order to achieve a better understanding of these effects, the influence of the water vapour on welded spruce (Picea abies) boards was investigated. It was shown that the vapour increases the internal gas pressure within the welding zone. Thus, it strongly influences the welding process and the quality of the joint. The results of these investigations lead to technical solutions, permitting a significant attenuation of the negative effects and improvement in quality and joint resistance. 相似文献
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The response of photosynthesis to temperature is a central facet of plant response to climate. Such responses have been found to be highly variable among species and among studies. Understanding this variability is key when trying to predict the effects of rising global temperatures on plant productivity. There are three major factors affecting the response of leaf net photosynthesis to temperature (A(n)-T): (i) photosynthetic biochemistry, (ii) respiration and (iii) vapour pressure deficit (D) and stomatal sensitivity to vapour pressure deficit during measurements. The overall goal of our study was to quantify the relative contribution of each of these factors in determining the response of A(n) to temperature. We first conducted a sensitivity analysis with a coupled photosynthesis-stomatal (A(n)-g(s)) model, using ranges for parameters of each factor taken from the literature, and quantified how these parameters affected the A(n)-T response. Second, we applied the A(n)-g(s) model to two example sets of field data, which had different optimum temperatures (T(opt)) of A(n), to analyse which factors were most important in causing the difference. We found that each of the three factors could have an equally large effect on T(opt) of A(n). In our comparison between two field datasets, the major cause for the difference in T(opt) was not the biochemical component, but rather the differences in respiratory components and in D conditions during measurements. We concluded that shifts in A(n)-T responses are not always driven by acclimation of photosynthetic biochemistry, but can result from other factors. The D conditions during measurements and stomatal responses to D also need to be quantified if we are to better understand and predict shifts in A(n)-T with climate. 相似文献