【作者】 杜红光；

【导师】 董玉平；

【作者基本信息】 山东大学 ， 机械设计及理论， 2011， 硕士

【摘要】 秸秆固化成型技术能使松散的秸秆致密化,提高秸秆能量密度和燃烧特性,使其可作为清洁能源直接替代煤用于生产生活各个领域,同时也能解决秸秆储存、运输困难问题,是实现秸秆综合化、规模化利用的重要技术手段。但是目前该技术尚需在成型过程特性及成型摩擦热方面加深理论研究,揭示秸秆成型粘结机理,为成型制品品质预测和控制、设备优化提供理论依据。本文通过对秸秆化学组成、物理特性及常温成型机理的分析,得出影响秸秆常温固化成型品质的关键因素是压缩力和成型过程中的摩擦热。基于该结论,根据活塞式成型技术间歇式生产的特点,对活塞一次冲压成型中成型力变化和物料移动进行实验研究,提出适合活塞式成型技术的“半闭式”成型模型,即成型过程未达到推移阶段前,物料相当于在由模具和靠摩擦力作用下保持静止的已成型制品组成的闭式环境中进行压缩。运用弹塑性力学、接触力学、粘弹性和有限元理论对秸秆固化成型主压缩阶段进行限元分析,研究主压缩阶段物料形变规律、应力分布及接触应力情况,为模具设计和成型工艺改进提供方法指导和依据。基于摩擦学、传热学原理,结合秸秆活塞式常温成型技术的特点,对成型过程中的摩擦热问题进行研究,通过引入平均压力、当量速度等物理量推导成型过程中摩擦热产生方程,将成型过程摩擦热问题转化为第二、三类边界条件的无内热源的非稳态传热问题；建立成型摩擦热有限元分析模型,对摩擦热引起的温度场分布进行研究,并通过实验验证有限元模拟的正确性,得出摩擦热引起的温度场变化规律；通过对实验样机在不同生产率条件下的摩擦热模拟分析,研究表明模具在摩擦热作用下,温度随着时间升高并稳定在一定温度,其增长速度和稳态温度随着生产率的提高而提高。在摩擦热引起的温度场规律研究基础上,针对目前秸秆类生物质材料的热物性参数欠缺的现状,进行了秸秆物性参数的实验研究,得出秸秆导热系数、比热随含水率、温度和密度的变化规律,为本文研究摩擦热引起的温度场在成型制品的传导提供数据支持的同时,也能为秸秆类材料热相关的技术研究提供依据；建立秸秆成型过程中摩擦热传导模型,分析不同条件下摩擦热在制品内的分布及对木质素粘结作用进行分析,研究表明制品内温度场分布是由模具温度和制品在模具内滞留时间共同决定的；对于本文实验样机,虽然当生产率为60kg/h时,摩擦热引起的温度场能达到220～230℃,生产率为50kg/h时温度场为180～190℃,但是由于制品在模具内滞留时间的影响,生产率为50kg/h,制品中心木质素也能达到软化温度,成型品质较高；该研究能为成型生产工艺改进、提高成型品质和设备设计提供理论依据。更多还原

【Abstract】 Straw curing briquetting technology can densify unconsolidated straws, increase the energy density, improve the combustion properties, replace coals as clean energy used in every field of production and living, and solve storage and transportation problems. It is an important technical method of integrated and large-scale use of straws. However, it still needs to be deepened on the theoretical research of briquetting process properties and briquetting frictional heat, so as to reveal briquetting adhesive mechanism of straws, and provide theory support for predicting and controlling quality of briquetting products and optimizing equipments.Through the analysis of chemical compositions, physical properties and normal temperature briquetting mechanism of straws, it can be concluded that the key factor of impacting curing briquetting qualities under normal temperature is compression force and frictional heat in the briquetting process. Based on this conclusion, changes of riquetting forces and transportation of materials in the piston one-time stamping molding process are studied according to properties of piston-type briquetting technologies. Semi-closed briquetting model that suits to the piston-type briquetting technologies is built:materials are compressed in the closed environment equivalent to be made up of mould and briquetted products which remains stationary by the action of friction. The finite element analysis method is established in the primary compression stage of straw curing briquetting using the plastoelasticity, contact mechanics, viscoelastic and finite element theory. With this method, material deformation law, stress distribution and contact stress situation in the primary compression stage are studied, which provides method guideline to mold design and briquetting process improvement.Research on frictional heat in the briquetting process is carried out combing with piston-type nomal tempreture briquetting technologies based on tribology and heat transfer theroy. By introducing physical quantity such as average pressure and equivalent velocity, the equation of the frictional heat generation in the briquetting process is derived, which converts the frictional heat problem in the briquetting process into transient heat transfer problems without inner heat source under the second and third boundary condition. The finite element analysis model of briquetting frictional heat is built, and then the temperature field distribution caused by frictional heat is researched. The rule of temperature field variation caused by frictional heat is drawn through validating the correctness of finite element simulation by experiments. Based on the frictional heat simulation and analysis of prototype under different productivities conditions, it is shown that the tempreture of the mould is increasing and remain stable at a certain tempreture over time under the action of frictional heat, and the growth rate and steady temperature go up with the increasing productivities.On the basis of research on the rule of temperature field distribution caused by frictional heat, the experimental study of straw thermophysical parameters is carried out according to lack of thermophysical parameters of biomass materials currently. The change rule of thermal conductivity and specific heat with the changes of moisture content, tempreture and density is obtained. It can not only provide data support for the research on conduction of temperature field caused by frictional heat in briquetting products, but also provide basis for research on technologies related to heat of straws. The model of friction heat transfer in the straw briquetting process is built. And the distribution of frictional heat in briquetting products under different conditions is analyzed; aslo the cohesive action of lignin is studied. It is revealed that temperature field distribution in briquetting products is determined by both mold temperature and residence time that the briquetting products stay in the mold. With regard to the prototype in this paper, when the productivity is 60kg/h, the temperature field caused by frictional heat can reach 220-230℃, and when the productivity is 50kg/h, the temperature field is 180～190℃. However, because of the impact of residence time that the briquetting products stay in the mold, when the productivity is 50kg/h, the lignin in the center of briquetting products can also be softened, and the briquetting quality is high. This research can provide theoretical basis for improving briquetting process, briquetting quality and eqipment design.更多还原