【作者】 杨冬霞；

【导师】 马岩； 杨春梅；

【作者基本信息】 东北林业大学 ， 机械设计及理论， 2013， 博士

【摘要】 木粉在建材、农业、塑胶、化工、冶金和环保等多个领域都广泛应用。木粉的加工原料大都是不同树种的锯屑,而且取材方便、价廉、原料充足,将其超细化后适量添加于复合材料、高分子材料等,会产生各种多功能材料。本文试验加工原料是兴安落叶松锯屑。用显微镜观测锯屑颗粒,其断口形态极不规则,在一些颗粒内存在显著裂纹,而一些锯屑用高倍显微镜观测,会看到微裂纹。这些裂纹出现的原因有,首先锯屑颗粒己受外力作用其内部已存在微裂纹；其次是由于兴安落叶松属于急变材在生长过程中就可能出现微裂纹。根据显微观测结果可将干燥后锯屑假设为脆性板层材料,在受外力作用时木纤维的断裂可分为纵向断裂和横向断裂两种类型。横向受力使管胞间分离直至断裂,破坏针叶材的蜂窝结构；纵向受力则使管胞在长度方向上断裂,减小管胞的长径比。超细木粉的粒径范围小于兴安落叶松管胞的平均弦向直径,所以在进行木粉超细加工时必须进行细胞破壁。用蜂窝结构模拟兴安落叶松的横向管胞结构,模拟兴安落叶松早材管胞径向受力时的拉伸变形直至断裂的过程,应用断裂力学中J积分知识计算出这一过程中细胞壁结构变形直至破坏所需应力大小。将理论计算结果与国内外的不同树种细胞壁断裂实验研究结果相比较,得出早材纤维断裂强度范围。并应用结构力学和有限元的相关知识将兴安落叶松的细胞壁结构模拟成线弹性桁架结构,依据桁架结构特点对杆单元施以压应力进行微观力学模型计算,并将计算结果与传统切削理论相比较,得出细胞壁断裂所需的切削力,为超细木粉机加工刀具、主轴的设计提供了理论参考依据。超细木粉的加工属于纤维类材料的超细化加工,它是超细粉体制备技术的难点,纤维类材料具有很强的韧性,仅靠简单的冲击、挤压、研磨作用力很难将其进行超细化。对于纤维类材料需要施加强剪切力与强研磨力相结合的复合力场才有可能使其达到微米或亚微米尺寸。超细木粉机的设计以机械作用力为粉碎力场,突出剪切和研磨的作用,并与冲击、搅拌、摩擦作用力共同对物料进行粉碎。在超细木粉机的设计上参照国内外粉体制造的先进技术,同时根据纤维类材料加工特点在设计中注重冷却装置的设计,研发的超细木粉机能够实现对较高目数木粉的分离、分级。通过对实验制备出的不同目数木粉的形态尺寸研究,得出加工木粉的目数与时间、刀具、刀片间距之间的关系。对目前的分离、分级设备比较分析并结合木粉自身特点,在分离设备上选择旋风分离器。在旋风分离器的结构设计上依据旋风分离器的经典模型进行设计,依据“平衡轨道”模型对旋风分离器的分离性能进行了理论计算,将计算结果与粉体形状尺寸定义进行比较,所设计的分离设备能够达到预期要求。用经验模型和耗散损失模型对旋风分离器内的压降进行了计算。用计算流体力学软件对旋风分离器内的气体流场和不同粒径的木粉颗粒的运动状态进行了模拟。在木粉的分级上采用干式的气动分级,采用射流预分散离心风机的高速喷射气流使木粉在收集箱中的螺旋分离器中以层流流动,达到木粉的分级。试验制备的不同目数的木粉对其进行粉体物性实验研究后,可得出随着木粉目数的逐渐增加,则木粉的颜色也就逐步加深。这是由于目数越高的木粉其相应的加工时间也就逐渐延长,在加工过程中木粉所受热就越多,碳化现象也就越显著。在加工过程中锯屑颗粒随着加工时间逐渐延长、刀片间距离逐渐减小以及电机转速的增大,颗粒由层状、片状、棒状、针状、丝状直至最后取样观测可以看到球形度较好的木粉颗粒。对不同目数木粉进行试验测定,随着目数的增高密度变大,粉体颗粒间的空隙率变小,颗粒间的配位数增多,粉体的可压缩性变小。在常态下粉体间的主要作用力是范德华力,根据其值大小可计算出木粉的团聚数大小,木粉的目数越高其团聚数也就越大,但在超细木粉定义的目数范围内常态下木粉的性质稳定不易团聚。更多还原

【Abstract】 Wood flour is widely used in a number of areas such as building materials, agriculture, plastics, chemical, metallurgical and environmental. Wood flour processing raw materials are different species sawdust. They are easily obtained, cheap and abundant raw materials. If added the amount to ultrafine composite polymer materials, they will produce a new multifunctional materials.Used the microscope to observe the larch sawdust, the fracture shape is very irregular. After amplification observations, we observed significant cracks within some of the particles. After high magnification observation, observed micro cracks in some sawdust. These cracks appear related to two factors, one is the test materials is larch, is a radical change material, micro-cracks may occur in the growth process; another sawdust has been processed, in the process had been cause internal micro cracks by the external forces. According to the observation results, the dried sawdust can be assumed to be a brittle laminate. The fracture mode of the wood fibers is separation until fracture between the tracheid, can destroy the honeycomb structure transverse of the softwood transverse, and another is that the tracheids is fracture in the longitudinal direction, so that the tracheid shorter. Based on the microscopic structure of the larch to superfine processing must do cell wall broken. Knowledge of fracture mechanics, structural mechanics and finite element theory calculate the size of the force of the wood cell wall, provides a theoretical basis for the ultra-fine wood flour machining tool spindle design. Available cellular structure to simulate the softwood tracheid structure, application of J integral in the fracture mechanics theory, simulation of Xingan Larch earlywood tracheids tensile deformation of radial force until fracture process and calculate the force in the process of cell wall structure deformation and damage. Compared the theoretical calculation results with the domestic and foreign different species of cell wall fracture experimental study results, obtained the early wood fiber breaking strength range. And apply the structural mechanics and finite element related knowledge in Xingan Larch cell wall structure to model as linear elastic truss structure. According to the structure characteristics of truss with rod unit to compressive stress, calculate the micro mechanics model, and cpmpard the calculation results and the traditional cutting theory, drawed the cutting force of cell wall fracture, provided the theoretical reference for the superfine wood powder machine tool, spindle design.Superfine wood flour processing belongs fiber materials the superfine processing, it is the difficulty of ultrafine powder preparation technology. Fiber material toughness, impact alone, extrusion, grinding force is difficult to ultrafine. The composite force field applying strong shear force and strong grinding force combining for the fiber material needs to be possible to reach the micron or submicron size. Superfine wood flour machine design mechanical force to crush the force field, the prominent shear and the role and impact of grinding, mixing, friction force interaction crushed materials. Based on advanced manufacturing technology of powder in the domestic and foreign about Superfine wood flour. And according to the characteristics of wood flour processing, paid attention to the design of cooling equipment. Research and development of superfine wood powder machine can realize the high mesh wood powder and grade separation. Conclude the wood flour processing relationship among mesh, time, cutter and cutter spacing.Current separation, grading equipment comparative analysis and test characteristics of the preparation of ultra-fine wood flour, cyclone separation equipment, it mainly collected powder dry powder-based, low manufacturing costs, easy maintenance, inactivity member, pressure drop constant, the main disadvantage is the presence of the particle separation efficiency of the small particle size is low. Design in cyclone structure design based on the classic model of the cyclone, the theoretical calculations based on the equilibrium orbit model of cyclone separation performance, comparing the calculation results with the powder shape and size of the definition, the design a separating apparatus is able to achieve the desired performance. Empirical model and dissipation loss model and the calculation of the voltage drop across the cyclone separator and the use of computational fluid dynamics software to simulate the gas flow field in the cyclone separator and the state of motion of the particles of different size of wood flour. The high-speed jet stream so that the flow of the laminar flow in the spiral separator of the wood meal in the collection box, dry-type pneumatic classifier used in the wood flour grading jet pre-dispersed centrifugal fan reaches the classification of the wood powder.Test preparation different mesh wood flour powder physical properties of experimental study it, can be drawn with the gradual increase of wood flour mesh, wood flour color will gradually deepen. This is its corresponding processing time also gradually extended due to the higher the mesh number of the wood powder, wood flour in the process to heat the more carbonization more remarkable. Sawdust particles during processing as the processing time by laminar, sheet, rod, needle, until the results of the last observed filamentous. Different mesh wood flour test measured with the higher density of the mesh becomes large, the porosity of the powder particles becomes small, between the particles increased coordination number, powder compressibility becomes small. The main force under normal powder van der Waals force, its magnitude can calculate the size of the reunion of wood flour, wood flour mesh greater the higher the number of its reunion, but defined in superfine wood flour stable under normal conditions within the mesh wood flour reunion is not easy.更多还原