在大潮中搏击——乌奴耳林业局改革纪实

乌奴耳林业局是呼伦贝尔盟地方林区木材生产任务较多的一个林业局。80年代末期,该局大量木材积压,许多木材的外欠款追不回来,应上缴的大量费用、税款无法上缴,职工的工资几个月开不了。内债外债压     

改性木材命名规则探讨

澄清了改性木材的概念,指出其形态限于木材整体和单板;分析了胶压木的特性及名称,认为它不应归于改性木材;通过辨析现有改性木材的类别及名称,发现其存在“命名方法笼统、同物异名或同名异物、归类混乱”等问题;通过分析出现这些问题的原因,对改性木材命名规则进行了初步探讨,以便推动标准化工作和新材料的命名与推广。     

波谱分析在高温高压水蒸汽处理压缩矩形木材中的应用

１ 概述 高温高压水蒸汽处理制造压缩矩形木材（简称压密材）的工艺技术研究，是以高效利用低质木材，提高木材利用率的物理加工手段。它在提高劣质材密度、强度等物理力学性能指标的同时，还可提高压密材尺寸的稳定性，而且在整个制造工艺过程中不进行木材的切削加工，简化了加工工艺、提高了木材的利用率及生产效率，对提高我国木材利用的总体水平，提高产品质量、获得高附加值产品，保障林业可持续发展将产生深远的影响，因此其发展前景十分广阔。对于高温高压水蒸汽处理制造压缩矩形木材工艺技术的研究，目前国内外刊物尚少有公开的报道…     

平压浸注填充PF树脂工艺对杨木增重率的影响研究

为探讨浸注工艺对木材增重率的影响,以PF树脂为浸注材料,以树脂浓度、压缩次数、保压时间、浸渍时间和压缩率为试验因素,采用单因素试验方法在平压浸注装置上对杨木试件进行了浸注填充。结果显示:2次压缩较1次压缩,杨木木材增重率增加了20. 2%;保压时间从0 min延长至10 min,杨木木材增重率增加了11. 5%;浸渍时间从1 h延长至2 h,杨木木材增重率提高了8. 8%;再增加压缩次数、延长保压时间和浸渍时间,杨木木材增重率均变化不大;而杨木木材增重率随PF树脂浓度和杨木木材压缩率增加呈线性增加,PF树脂浓度与压缩率对杨木木材增重率具有显著影响。因此选择压缩次数为2次,保压时间为10 min,浸渍时间为1 h,PF树脂浓度与杨木木材压缩率由改性木材的用途决定。     

木材多尺度孔隙结构及表征方法研究进展

介绍木材中宏观－介观－微观多尺度孔隙的分布、孔隙尺寸、孔隙形貌等孔隙结构,木材自身因素及干燥、热解等加工处理对孔隙结构的影响,压汞法等木材传统孔隙结构表征方法的优缺点,差示扫描热孔计法、核磁共振冷孔计法和超极化129 Xe 核磁共振法等新兴表征技术的基本原理,提出今后应结合多种表征技术重点探索木材介微观孔隙结构,以此为切入点探讨木材的物理力学性能,以期有助于推动木材孔隙结构的深入研究及其在其他领域的应用。     

木材检查应合法执法

木材检查应合法执法方自元木材检查是木材流通管理的一个组成部分，也是整个林业经济管理活动中的一个重要环节。如何做到木材检查执法的合法性，是木材由计划管理走向市场调节过程中的一个重要问题。木材检查是林业主管部门依法对木材运输实行检查、监督和管理，它是一种...     

防火的塑料木材

最近日本的科学家研制出一种新型的人工合成木材。它是用70％的锯木屑和木材的边角废料与30％的耐火惰性塑料,辅以灭火性的化学制剂,经过特殊的辊压工艺制造而成。这种新型的人工合成木材的最大优点,就是耐火性强而不易燃烧,甚至在5分钟之内经受1300     

锯齿压料轴扁面的简易加工法

压料轴扁面(工作面)的形状及其表面光洁度对锯齿质量的好坏有很大影响,而压料质量的好坏又直接影响着锯割质量。在压料过程中,压料轴的扁面对锯齿齿尖起挤压作用。此时,由于锯条硬度较高(HRC43),故压力也较大(σμ=2.55公斤力/毫米~2)。因此,压料轴扁面易出现压痕等磨损现象。为了保证压料质量,就应及时对磨损了的压料轴进行修磨或者更换。从理论上来讲,压料轴扁面的形状只有符合阿基米德螺旋线的变化规律时,才能保证压料质量最佳。故一般木材加工厂都难以自行加工料轴,即或有的木材加工厂修锯工自已磨压料轴的扁面,也都是靠经验而且质量差,其弧面不光滑。鉴于上述情况,我们     

木材真空-浮压干燥特性的试验研究

以马尾松为试验材料 ,首先分别以过热蒸汽和空气作为干燥介质 ,在预热阶段通过对木材内部温度场和含水率变化的测定 ,探讨了木材真空 -浮压干燥预热阶段的特性 ;然后 ,通过对干燥介质条件与干燥速率之间影响关系的研究 ,总结出木材真空 -浮压干燥的特性。结果表明 :真空 -浮压干燥预热阶段进行得非常迅速 ,同时其表面水分的凝结量也较空气干燥大 ;木材的浮压干燥速率随着干燥介质温度的增加、绝对压力的减小和浮动频率的加大而增加。上述因素中对干燥速率影响程度从大到小的排列顺序为 :介质温度 (T) >压力浮动频率 (Hz) >绝对压力 (P)     

窿缘桉木材刨削和砂光后的微观破坏形式

以窿缘桉木材为研究对象,对其刨削和砂光处理后的加工缺陷和无缺陷表面采用扫描电子显微镜观察,结果表明:窿缘桉木材刨削加工缺陷处的微观破坏形式为纤维和木射线的撕裂和切断,其中纤维破坏是最主要的破坏形式。而在正常刨削处,主要表现为表层木材组织的大量压溃。砂光后的木材表面,在缺陷处和无缺陷处,其微观表现形式均为组织压溃。     

Effect of thinning on the development of compression wood in stems of Corsican pine

This study considered the effects of thinning on the development of compression wood in stems of 35-year-old stand of Corsican pine (Pinus nigra L.). Part of the stand had been thinned at 5-yearly intervals and part left unthinned. Twenty trees each from the thinned and unthinned stands were randomly selected and felled. Measurements were made on tree height, stem diameter, stem slenderness and canopy depth. Wood samples were removed from the central part of the main log and cross-sectional measurements made on ring width, basic density and compression wood content. Cross-sectional area of compression wood was found to be three time higher in stems from the unthinned trees in comparison with those from the thinned trees. No significant differences in mean radial ring width or basic density were found between treatments. Correlations indicated that, with increasing in stem diameter, compression wood content increased in the unthinned trees, while a decline in compression was observed in the thinned trees. Tree height was also positively correlated with compression wood content in unthinned trees, while no equivalent relationship was observed in thinned trees. Observations from this study, while not conclusive, suggest that phototropic stimulus may be producing stem inclinations in the unthinned stand as trees compete for space in the canopy, whereas crown competition has been largely eliminated in the thinned stand; and that this is responsible for compression wood levels recorded in this study.     

Stem deformation in young plantations of black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) in the boreal forest of Quebec,Canada

Stem deformation has often been observed in young black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) plantations. Whenever important stem deformations are observed at the time of harvesting, timber value is negatively affected especially during the wood transformation process. The present work was undertaken to quantify and qualify the importance of stem deformation of black spruce and jack pine in the boreal forest of central Quebec at the stand and tree levels. In 30 black spruce and jack pine plantations, approximately 22% of spruce trees and 27% of pine trees exhibited stem deformation. The proportion of deformed trees was higher in the youngest plantations and decreased with the age of the plantations. Stem deformation caused the formation of compression wood which is another factor that can reduce the value of wood products. Thirty-nine black spruces and 34 jack pines were analysed at the tree level. On average, compression wood represented 14% and 20% of stem volume in 7- and 10-year old black spruce plantations, respectively. These proportions ranged from 18% in the youngest jack pine plantation to 26% in the oldest one. Stems of both species classified as normal contained a lower volume of compression wood than stems classified as deformed or very deformed. Annual percentages of compression wood and annual shoot length increased significantly with tree age (p < 0.0001 for both variables). Statistically significant correlations were also found between the range of displacement of the stem and the percentage of compression wood. The fewer number of trees with deformed stems in older plantations combined with high compression wood formation suggests that, over time, a deformed tree can become normal and straight in appearance.     

Variations in physical and mechanical properties between tension and opposite wood from three tropical rainforest species

Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization of wood fibres cell wall structure.     

Growth stress distribution in leaning trunks of Cryptomeria japonica

The distribution of growth stresses in leaning trunks of Cryptomeria japonica (L.f.) D. Don was determined by measuring the stresses released by the kerf method with strain gauges glued at specified positions along the trunks. Effects of both tree height and peripheral positions on the surface of leaning trunks on surface growth stress were determined. The inner residual growth strains in leaning trunks were also measured. We found high compression stresses in the lower side of leaning trunks that differed greatly from the tensile stresses in normal erect trunks. However, transverse compression stress was found around the tree trunk in both normal and compression wood. In leaning trees, the distribution of internal stresses in the bent trunk portion differed from that in the erect trunk portion, being compressive on the outside and tensile on the inside. The resistant moment introduced by compression stress generated in compression wood is released by the bending of the leaning trunk. The bending stresses are then superimposed on the original internal growth stress. We demonstrated that Poisson's effect of longitudinal stresses should be considered when evaluating transverse surface growth stresses. The existence and intensity of compression wood development can be assessed by growth stress measurements. We conclude that the compressing force of compression wood functions physiologically to give an upward righting response in a leaning trunk.     

Apical control of branch movements in white pine: Compression wood action

Summary The movements of branches or control stem girdled white pine (Pinus strobus L.) were analyzed using beam theory. The stresses generated in the compression wood (CW) produced bending moments to counter the added bending moments due to new branch growth. The branches on the treated trees produced additional CW after untreated trees stopped elongation and diameter growth. The intensity of the stresses in this additional CW was greater than in the other CW. Thus, branches on treated trees moved up vertically well beyond their initial orientation due to both more CW and more active CW. The branches on untreated trees all deflected downward as branch weight continued to increase after CW production stopped.     

Radial variations of wood properties in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> growing in Bangladesh

Radial variations of wood properties (basic density, fiber length, vessel element length, and compression strength) in plantation-grown Casuarina equisetifolia in Bangladesh were investigated for effective utilization of the wood. Samples disks at breast height were randomly collected from trees in a 10-year-old plantation in Cox’s Bazar Forest Division, Bangladesh. The basic density showed a near-constant value up to 30 mm from the pith and then rapidly increased up to 60 mm from the pith. The fiber length and vessel element length gradually increased from the pith to bark. When radial variation of wood properties was determined according to relative distance from the pith, similar radial patterns were observed among the sample trees, indicating that the wood properties in C. equisetifolia may be related to the growth rate. The compression strength parallel to the grain (CS) increased from the pith to bark. A significant positive correlation was found between the air-dried density and the CS. The results obtained indicated that wood around the pith has a relatively low density, and wood outside the pith area has a relatively high density, suggesting that it could be used as structural lumber. Part of this report was presented at the 58th Annual Meeting of Japan Wood Research Society, Tsukuba, March 2008     

Radial variation in partial compression properties perpendicular to the grain of Japanese larch (Larix kaempferi)

This study investigated the densities, average width of annual rings, and partial compression stresses at 5 % strain perpendicular to the grain of air-dried wood specimens, which were continuous in the radial direction from the pith and were obtained from Japanese larch (Larix kaempferi) trees with different diameters at breast height in the same stand, to evaluate the radial variations in partial compression properties perpendicular to the grain. The air-dried densities of the wood increased with the distance from the pith. The average width of annual rings of the wood tended to decrease with increasing distance from the pith and those of medium- and large-diameter trees seemed to increase near the pith. The partial compression stresses at 5 % strain in the tangential loading direction tended to increase with the distance from the pith and with air-dried wood density. However, in the radial loading direction, this tendency was not observed. The partial compression stresses at 5 % strain in the radial loading direction tended to be low in wood with a small average width of annual rings. These results indicate that the factors affecting the radial variations in the partial compression stress at 5 % strain differ depending on the loading directions.     

Growth strain in the trunk and branches of Chamaecyparis formosensis and its influence on tree form

Distributions of growth strains in branches, straight trunks and basal sweeping trunks of Chamaecyparis formosensis Matsum. trees were measured with strain gauges. Microfibril angles (MFAs) of the S2 layer of the cell wall were measured by the iodine deposition method and their relationships with growth strain examined. The magnitude of the compressive stress on the lower side of trunks with a basal sweep was greater than that of the tensile stress at the surface of straight trunks. However, transverse compressive stress was similar around the trunk regardless of whether normal wood or compression wood was present. The released surface growth strains varied with MFA. At MFAs of 20-25 degrees , growth stress changed from tension to compression, and compressive stress increased dramatically in the compression wood region. Branches suffer bending stress due to self-loading. This stress is superimposed on the growth stress. Growth strains on the upper or lower sides of branches were larger than those in the trunks, suggesting that generation of growth stress on the lower sides of branches with extensive compression wood is affected by the gravitational bending stress due to self-loading. We conclude that branch form is affected by the interaction between the bending moment due to self-loading and that due to the asymmetric distribution of growth stress. Growth strain distribution in a branch differed depending on whether the branch was horizontal, upward bending or downward bending.     

Growth strain in coconut palm trees

Until recently, growth stress studies have been made only on coniferous and dicotyledonous trees. Growth stress of trees is thought to be initiated in newly formed secondary xylem cells. This stress can accumulate for years and is distributed inside the trunk. Major characteristics of the trunk of monocotyledonous trees include numerous vascular bundles scattered inside the ground tissue and the lack of secondary growth for enlarging the diameter of the trunk. We used the strain gauge method to measure the released growth strain of the monocotyledonous woody palm, coconut (Cocos nucifera L.), and to investigate the surface growth strain of the trunk and central cylinder at different trunk heights. The internal strains of both vertical and leaning trunks were measured and compared with those of coniferous and dicotyledonous trees. We found that tensile stress existed longitudinally on the surface of vertically growing trunks, whereas compression stress was found at the bending position of leaning trunks. Compression stress was found in the outer part of the central cylinder, whereas tensile stress is generally found in the outer part of the trunk in coniferous and dicotyledonous trees. The distribution of strain in the palm trunk is similar to that of compression wood of the leaning trunk of a conifer. Specific gravity was greater in the outer part of the trunk than in the inner part of the trunk. This difference may be related to the distribution of growth stress.