热磨机磨片齿形结构的设计及静力学分析

热磨机磨片的齿形结构是磨片和原料间传递能量的主要方式,它与木片原料被研磨时的运动状态和研磨时间,以及纤维制备过程中纤维质量和设备的能耗密切相关。笔者根据磨片破碎区、粗磨区、精磨区的齿形结构、磨齿倾角、周向齿等参数对纤维分离能耗的影响以及磨片的设计要求,设计了一种有利于降低纤维分离能耗的热磨机磨片,并运用ABAQUS软件对磨片进行了静力学分析,分析结果表明磨片受到的静力作用对自身影响很小,设计满足要求。     

林木生物质剪切粉碎特性及其机理分析

为探索林木生物质的粉碎特性和粉碎机理,以林木木屑为研究对象,利用剪切磨在不同给料速度和含水量条件下进行粉碎试验,测量了木粉产品的粒度、密度、均匀性系数、长径比、形貌和能耗;并分析了林木生物质的剪切粉碎机理。结果表明:随着给料速度从26.17 kg/h增加到49.85 kg/h,均匀性从1.63下降为1.34,平均粒径从716.84μm增加为803.73μm,而长径比和单位能耗先降后升;随着木屑含水量的增加,木粉断裂由脆性断裂转变为韧性断裂,最大处理能力逐步下降为19.57 kg/h,产品粒度、长径比和单位能耗逐渐增加。     

Relationship between wood porosity,wood density and methyl methacrylate impregnation rate

Abstract

Mercury intrusion porosimetry (MIP) was used to evaluate the impregnation mechanisms of wood by methyl methacrylate (MMA) through examining the changes in porosity, pore volume, pore size distribution and bulk density of solid wood before and after MMA impregnation. Porosities of MMA-impregnated (hardened) wood samples were lower than those of solid wood samples for six studied species, five hardwoods and one softwood. Densities of hardened wood were enhanced from 45 to 130% depending on the species. The pore volume available for mercury intrusion was shifted from pore d>0.1 µm for solid wood to pore d≤0.1 µm for hardened wood. A pore diameter of 0.1 µm was used as the transition point for MMA impregnation and the increased mercury penetration below this point was attributed to the MMA polymer pore structure. Porosity as an intrinsic property of wood appears to be the main determinant of impregnation rate and polymer retention, especially for porosity with pore diameter >0.1 µm. The results indicate that the MIP technique is an effective tool with which to study the impregnation process.     

数控微米刨切试验台的设计与试验

为解决传统热磨法加工微米薄木片及木纤维中高能耗、工序复杂、加工成本高的缺点,现改变加工方法,采用顺纹纵向刨切木材的方式,研发了数控微米刨切试验台。试验台主要由机架、纵向进给机构总成、工件夹具、控制面板、刨切机构总成、升降机构总成和限位机构组成,可对宽度为50 mm,长度为300～600 mm,高度为20～90 mm的木材工件进行纵向进给、切削量进给和刨切作业。笔者对试验台整机以及各机构进行设计,并通过ANSYSY对刀具进行强度校核。通过试验,确定刨切机构切削角δ取45°,刀刃伸出量h取0.05 mm,刀门宽度d取0.2 mm,刨得的木片平均厚度为18.7μm,最薄为15μm。最后通过显微镜观察发现经过刨切后的刀刃部分出现磨损,可通过表面改性提高刀具的耐磨性。     

Urea-formaldehyde microspheres as a potential additive to wood adhesive

Urea formaldehyde (UF) resins are important for wood industry due to their attractive properties at reasonable price. Particulate fillers added to UF are of interest with regard to improving the functionality of UF and also in terms of reduced UF consumption. To study their potential as filler, solid UF microspheres were synthesized and characterised respecting its morphology, chemical curing and thermal stability. Marigold flower structured spheres with diameters between 5 and 20 µm are presented and application trials demonstrated that high amounts of UF may be replaced by solid microspheres without impairing adhesive bond strength of solid wood bond lines. Fluorescence microscopy showed that microspheres greatly reduce adhesive penetration into the wood substrate, retaining the modified adhesive in the bondline. UF microspheres may thus be considered as viable filler for UF adhesives, particularly with regard to the possibility of endowing them with added functionality like self-healing properties.     

Properties of flat-pressed wood plastic composites as a function of particle size and mixing ratio

This paper presents the effects of particle size and mixing ratio on the properties including physical, mechanical, and decay resistance of wood plastic composites (WPCs). In addition, it also presents the effects of immersion temperatures on water absorption (WA) and thickness swelling (TS) of the WPCs. WPCs with a thickness of 6 mm were fabricated from Albizia richardiana King & Prain wood particles and recycled polyethylene terephthalate (PET) by the flat-press method. To prepare the WPCs, two different wood particle sizes (0.5–1.0 and 1.01–2.0 mm) were used along with four different mixing ratios (w/w). Subsequently, the physical properties include density, moisture content, WA, and TS, and mechanical properties include modulus of elasticity (MOE) and modulus of rupture (MOR) of the produced WPCs was evaluated. Furthermore, decay resistance was evaluated by the weight loss percentage method. Moreover, the effects of immersion temperatures on WA and TS of WPCs after 24 h of immersion in water at three different temperatures, i.e., 25, 50, and 75 °C were investigated. Results showed that the wood particle size had impact on WPC’s density (only 6% decreased with the increase of particle size); however, the density decreased by 29% when the wood particle content increased from 40 to 70%. The WA and TS gradually increased with the increase of particle content and decrease of particle size. In addition, WA and TS increased proportionately with increasing immersion temperature from 25 to 75 °C. Furthermore, the highest MOE (2570 N/mm²) was found for the WPCs fabricated from large wood particles having the ration of 50:50 (wood particle:PET). For decay resistance, WPCs consisted of larger particles and higher PET content showed greater resistance against decay. Therefore, it is comprehensible that fabrication of the WPCs from 50% large particles and 50% PET is technically feasible and further improvement of WPC performance like enhancement of MOE and reduction of density using coupling agent and agricultural waste fibers, respectively, in the WPC formulation is recommended.     

超细木粉的加工原理与运动分析

通过对超细木粉的形态分析,提出了超细木粉颗粒的粒径范围为600～1 500目;介绍了超细木粉加工设备的结构与原理,分析了制备超细木粉的粉碎过程及粉碎力,以及超细木粉的制备方法及所采用的设备对粉体产品的粒度大小、粉体形状及分散性等的影响。提出采用高速旋转搅拌式磨削粉碎方法,将粉碎设备与粉体分级设备连为一体,对未达到加工目数要求的颗粒进行循环式加工,提高了加工效率;在分级装置的不同位置安放两个转速不同的离心风机形成不规则的气流流场,能减少木粉收集时的颗粒团聚,提高了粒度分布的均匀性和木粉质量。     

Convergence of the robust Gaussian regression filter applied to sanded wood surfaces

The quality of a sanded wood surface is represented by its roughness, which can be separated from the originally measured data by a procedure of filtering. Past experience has shown that the robust Gaussian regression filter (RGRF) is suitable for wood surfaces because it does not introduce distortions into the roughness profiles. The filter works iteratively until a user-defined convergence condition is met. The iterations stop when the difference between two consecutive profile median values becomes smaller than a given tolerance. This paper examines the convergence of RGRF when applied to wood surfaces sanded with various grit sizes in order to establish the tolerance value, which leads to convergence with the minimum number of iterations. This study was based on monitoring the variation of roughness parameters with the number of iterations for a range of tolerance values. A tolerance of 0.01 μm was found acceptable for filtering sanded wood surfaces.     

木质复合材料──木材工业的发展方向

本文介绍了木材与塑料、合成纤维及其他非木质材料复合所形成的复合材料及其基本性质、加工工艺和应用前景。木质复合材料是一种很有发展前途的新型材料，此种材料的加工技术扩展了木材的应用领域，亦为木材工业提供了新的发展方向。     

Effect of gap size on mid-rotation stand structure and species composition in a naturally regenerated mixed broadleaf forest

This paper is an assessment of the effect of gap size on stand structure and species composition 48 years following treatment in a mixed broadleaf upland forest. Established in 1960, the study tests three circular openings, 15.2 m (0.02 ha), 45.7 m (0.16 ha), and 76.2 m (0.46 ha). Forty-eight years following treatment (2008) basal area, top height, and quadratic mean diameter were significantly lower in 15.2 m openings. Maple (Acer spp.) species had the highest mean importance value across treatments (0.40). Trends suggest that species composition of dominant and codominant trees among opening sizes may have been influenced by shade tolerance adaptations of the species groups present. Whereas 15.2 m openings were dominated by shade tolerant maple species, 45.7 and 76.2 m openings produced a mixture of commercial species including shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.), trees of intermediate shade tolerance like oak (Quercus spp.), and shade tolerant maple. Data further suggest the density of overstory oak was highest in the intermediate opening size (45.7 m), while yellow-poplar increased in the larger opening sizes. Evaluation of species shifts between 1981 and 2008 showed that relative basal area of maple increased across all treatments. Relative basal areas from 45.7 to 76.2 m openings suggest declines in yellow-poplar and other non-commercial species were balanced by increases in oak and maple.     

Variation in carbon concentration and wood density for five most commonly grown native tree species in central highlands of Ethiopia: The case of Chilimo dry Afromontane forest

ABSTRACT

Information regarding carbon concentration and wood density are lacking in Chilimo dry Afromontane forest.

The aim of this study was to estimate carbon concentration and wood density for Allophyllus abyssinicus, Olea europaea, Olinia rochetiana, Rhus glutinosa, and Scolopia theifolia. A total of 105, 30–50 mm thick wood discs were collected and oven dried at 102°C and 67°C to constant weight, chopped and finally grinded into 0.2 mm with a grinding mill. Carbon concentration was analyzed using the ash method, while wood density was estimated using the water displacement method. The highest carbon concentration (57.12%) was found for O. rochetiana, however, the lowest carbon concentration (56.43%) was found for A. abyssinicus. Stem parts had higher carbon concentration (56.98%) than branch (56.74%) and leave (54.53%) parts. O. europaea exhibited the highest wood density (0.67 g cm^?3) value than other species. However, the lowest wood density (0.42 g cm^?3) was exhibited for A. abyssinicus. Wood density was also showed a decreasing trend along with increases in stem height and maximum wood density (0.62 g cm^?3) was found under stump position, while, the minimum wood density (0.4 g cm^?3) was found under tree commercial height.     

超细木粉原料粉碎机的设计

介绍了一种超细木粉加工设备的总体布置及工作原理,阐述了该设备筛箱的出料机构设计。应用粉碎力学原理估算木粉粒径,根据粒径要求进行参数选择与动力学设计,并用试验结果验证理论分析的正确性。     

Integrated harvesting for conventional log and energy wood assortments: a case study in a pine plantation in Western Australia

Biomass or energy wood harvesting can be integrated with conventional log harvesting (saw log or pulpwood production) to allow more cost-effective energy wood supply. The efficiency of an integrated energy wood harvesting system was evaluated and compared with conventional log harvesting in a 32-year-old Pinus radiata plantation (radiata pine) located in south-west Western Australia. The harvesting system consisted of a harvester and a forwarder. The study included two treatments: a conventional log-harvesting operation where merchantable sawlogs and pulp logs were produced at the stump by the harvester and extracted by the forwarder; and an integrated energy wood operation where the harvester produced sawlogs, pulp logs and energy wood at the stump that were extracted by the forwarder. In the integrated energy wood harvesting plot, 37 m3 ha?1 of energy wood was extracted in addition to the sawlog and pulp log volumes. Extracting the additional energy wood reduced the productivity of the forwarder and increased the cost of extraction (AU$2.7?m?3) compared with the control plot (AU$2.2?m?3). Harvesting system cost was not significantly impacted, with a cost of AU$3.18?m?3 in the control plot and AU$3.23?m?3 in the integrated energy wood harvesting plot. Diameter at breast height (DBH) was a significant factor influencing the working time of the harvester, whereas load volume, extraction distance and extraction type (sawlog, pulp logs, and pulp log/energy wood) significantly impacted forwarding time. Increasing DBH resulted in longer working cycles for the harvester. Heavier loads and longer forwarding distances increased forwarding cycle time, while extracting sawlogs was least expensive and energy wood extraction was the most expensive. The marginal cost of the energy wood was approximately AU$10.2?m?3 (AU$7.0 extraction and AU$3.2 harvesting), which is about double the cost of the sawlogs. Additional material recovered in the integrated energy wood plot resulted in less residual residues on the plot (103.2 green metric tonnes per hectare [GMt ha?1]) than the control plot (144.2 GMt ha?1).     

Impacts of fiber orientation and milling on observed crystallinity in jack pine

Influences of fiber orientation and milling on wood cellulose crystallinity were studied using jack pine wood. The fiber orientation effects were measured by sampling rectangular wood blocks in radial, tangential, and cross-sectional orientations. The influence of milling was studied by analyzing the unsieved and sieved milled wood fractions (all <1,000 μm). Fiber orientation effect was manifested in both X-ray and Raman measurements and was dependent upon the orientation of the sampled wood blocks. In Raman, the observed crystallinity was similar between the blocks sampled on the tangential and the radial faces. However, the estimated values were 5.5 % lower compared to that measured in a powdered sample pellet. Moreover, in these sampling modes, the orientation of the block with respect to the direction of the electric vector of the laser made a difference only for the tangential mode of sampling. When a wood block was sampled on the cross-sectional face, the observed Raman crystallinity was 3.9 % higher from that of the pellet. The observed crystallinity did not significantly differ with change in sample orientation with respect to the electric vector direction. In contrast, the Segal-WAXS study of the blocks indicated that compared to the pellet, the estimated crystallinities in the radial, tangential, and cross-sectional sampling modes were 5, 2, and 11 % lower, respectively. This suggested that the radial and the tangential faces of the blocks can be used to estimate the crystallinity of wood. With regard to the effect of milling on Raman and Segal-WAXS estimates, the wood crystallinity did not depend upon the particle sizes of the fractionated samples and was similar to that of the original unfractionated ground wood.     

木质粉尘燃爆的爆炸指数理论评估

从燃烧化学反应动力学出发,结合热力学原理以及气体分子动理论,提出了木粉燃爆的动力学理论模型,对木粉燃爆试验的测量数据进行了理论计算。在不同木粉浓度以及不同木粉粒径下,将本模型的计算结果与已有模型的理论计算结果对比。结果表明:本模型的理论结果更接近试验测量结果,最大爆炸压力以及最大压力上升速率理论计算值与试验数据的平均偏差仅为9%。此外,利用本理论模型计算了最大压力上升速率随连续木粉浓度的变化曲线,得到在木粉质量浓度845 g/m3附近,爆炸指数的极大值为14.57 MPa·m/s。爆炸指数大于10 MPa·m/s的木粉质量浓度为330～1 945 g/m3,在此区间,利用本理论模型可以对不同浓度木粉的爆炸指数进行理论估算。研究得到的相关结果对试验测量以及实际生产中的燃爆防控技术均有理论指导意义。     

保山市高黎贡山周边社区森林能源现状与供需对策

通过对保山市高黎贡山周边社区森林能源现状调查分析 ,结果表明 :该区现有森林资源 192 3万m3 ,每年的薪材消耗量为 16万m3 ,占总资源量的 0 83%。目前可能提供的薪材量为 7 6万m3 ,仅为需求量的 4 7 5%。作为主要薪材来源的杂灌木林 ,每公顷产柴量只有 4m3 ,仅为一般薪炭林产量的 4 3%。依据该区的经济及资源状况、消费结构、薪材供需和经营现状认为 ,要解决社区薪材供需矛盾 ,需要增加科技投入 ,加大低产林分改造力度 ,提高单位面积产柴量 ,限额开山采樵利用 ,加强经营管理技术     

欧洲木质颗粒燃料产业发展现状与启示

欧洲是全球木质颗粒燃料产业发达地区.文中介绍欧洲木质颗粒燃料市场总体情况、生产特征、消费特征和价格体系, 分析其为规范和引导发展木质颗粒燃料产业而在原料收集、燃料燃烧、能源服务等3个环节采取的政策措施, 从统筹环境保护与经济发展角度提出对我国发展木质颗粒燃料产业的启示.     

Preparation of acetylated wood meal and polypropylene composites II: mechanical properties and dimensional stability of the composites

Acetylated wood meals of Sugi (Cryptomeria japonica D.Don) wood were prepared by mechanochemical processing using a high-speed vibration rod mill. Weight percent gain (WPG) of the acetylated wood meals ranged from 7.0 to 35.5 %. Wood–plastic composites (WPCs) containing 50 % acetylated woods were produced by an injection molding technique. The polymer matrix used was polypropylene homopolymer. Maleic anhydride-grafted polypropylene (MAPP) was also used as a compatibilizing agent. The mechanical properties of WPCs in bending and tensile tests were independent of WPG of acetylated wood meals, and the test values for WPCs containing acetylated wood meals were lower than that of unmodified wood meal. The use of MAPP increased bending and tensile strength, but no effect on bending modulus was found. An increase in WPG significantly decreased water absorbability and thickness swelling of WPCs as measured by dimensional stability tests. These results demonstrated that mechanochemical processing is a promising technique for preparing WPC material with improved dimensional stability. The future challenge is to inhibit the decreases in mechanical properties of WPCs containing acetylated wood meals.     

椴木除湿干燥的能耗分析

描述了椴木除湿干燥过程中干燥室内空气温度、相对湿度及木材含水率的变化曲线。着重分析了椴木除湿干燥过程中除湿量及能耗的变化规律。实验结果显示,除湿干燥各阶段的除湿量和节能效果有较大的差异。干燥初期的除湿量大,开除湿机的节能效果最好;干燥中期的节能效果变差;干燥后期则不宜开除湿机。建议除湿干燥用于木材预干或作为联合干燥的第一阶段。     

Dynamic Mechanical Properties of Wood Powder /Polypropylene Composites

The dynamic mechanical properties of wood powder/polypropylene composites with different wood content treated and untreated with the compatibilizer have been studied. It has been found that addition of wood powders and the compatibilizer can both improve the viscoelasticity of composites. Glass transition temperature (Tg) of appropriate wood powder-filled composites decreased. The value for the storage modulus (G') increased gradually with increasing wood powder content. The addition of the compatibilizer made glass transition temperature shift to a higher temperature. DSC (Differential Scanning Calorimetry) results showed that, for pure PP, the addition of the compatibilizer decreased its melting point, and increased its Calorie of Melt at the same time. For the composite with 50 % wood powder treated with the compatibilizer, the melting point was almost unchanged, but its Calorie of Melt decreased.