DHS3665香蕉筛设计【含9张CAD图纸、说明书】
中国 xx 大学毕业设计任务书任 务 下 达 日 期 : 20* 年 3 月 10 日毕业设计日期:20* 年 3 月 10 日至 20*年 6 月 10 日毕业设计题目:DHS3665 香蕉筛毕业设计主要内容和要求:DHS 香蕉筛设计:了解振动筛的工作过程及原理。对比各种振动筛的工作原理,设计一台香蕉筛 。参数:处理量:1500t/h; 双振幅:911mm; 给料粒度:0300mm振动频率:15Hz; 筛分粒级:50mm1.根据相关参数完成香蕉筛设计的总体设计;2.完成振动筛结构设计、激振器的设计;3.完成振动筛主要传动组件、零件图的设计;4.完成振动筛运动学参数的确定;5.根据设计要求,完成工艺参数的确定;6.编写完成整机设计计算说明书。院长签字: 指导教师签字:英文原文Modal Characteristics and Finite Element Analysis of Screen Box forUltra-heavy Vibrating ScreenGuo Nianqin Luo LepingSchool Of Mechanical and Electronic EngineeringJiangxi University Of Science And TechnologyGanzhou, Jiangxi, China 341000Email:nfgnq126.comAbstractThe model of ultra-heavy vibrating screen has been established by using finite element analysis software ANSYS,the stress distribution of the screen box has been revealed under static load, meanwhile, analyses dynamic characteristics of the screen box structure for ultra-heavy vibrating screen,then, has gotten the low order natural frequency and vibration mode of the screen box, and the stress distributions and deformation in various parts of the screen box under rated load, which provided a necessary basis for the design improvement and dynamic strength study about the screen box. In allusion to the cracks of the bottom screen frame and side panels, according to the stress analysis conclusion,improve the screen box structure and change the original welding connection of the bottom screen shelf steel pipe with the side panels into flange, and this improvement gets good results in the field.Keywords- Ultra-heavy vibrating screen, screen box, FEM,Modal characteristics.I. INTRODUCTIONThe ultra-heavy vibrating screen consists eccentric-block exciter, screen box, motor, base plate and support device, which have the characters of simple structure, smooth operation, reliable work and so on. The Screen box structure takes the welding connection which is strong and reliable. It is showed in Figure.1.Besides eccentricity in the central part, each ends of the main axis are fixed with eccentric wheels. Through triangular belt, the motor rotates the exciter eccentric block at a high speed. The rotator eccentric block generates a great centrifugal force, exciting the screen box to do circular movement with certain amplitude. The spring is used to support the screen box and reduce the power passed to the base while the screen is in operation 1. II. SCREEN BOX MODELModel the 2YAC2460 ultra-heavy vibrating screen as the research object. There are two ways to establish finite element model of the screen box: model in CAD, then lead the solid model into ANSYS, which not only needs a long time to model, but also takes a long time to compute, and even could not get results; The other is modeling in ANSYS unit to establish the finite element model of screen box. This method can build models quickly, compute fast and accurately23. A. The finite element model of screen box In order to accurately and reasonably simulate the screen box, shell63, beam188, combin14, mass21 are used tosimulate side panels, up screen frame, bottom frame, springs and exciter respectively. The Unit selection is showed in Table 1. To note that, after finished the cell division of the grid, there must be common nodes to transfer load between the junction of different thickness side panels, the junction of the side panel with the beams and the side panel with the strengthening sinew, otherwise, the locations between the plate elements as well as between the plate element and the beam element will occur separation in calculation process, leading to inaccurate results, and the failure of model establishment. Side panel is formed by a number of surfaces, and the boundary line between surfaces is the strengthen beam. The boundary line intersection of surfaces is the connecting point of the beam to the side panels. After this cell divisionof the grid finished in the model establishment, no matter through the welding connection or flange connection, in this model there are public nodes to represent them. In the side panel model of the screen box, the bolts and flange whose quality and stiffness have very small influence to the sieve box system, if established in the model, would bring much trouble in cell division of the grid, and effectively increase the number of units, therefore ignore them. After the model handle, we get the finite element model of screen box as showed in figure 2: B. Calculating conditions and screen containers force analysis In the course of work, the screen box bears gravity, the exciting force, the spring restoring force and damping force. As for the vibrating screen is an inertia screen, in the vibration mainly the inertia force generated from the exciter eccentric mass when rotating is playing the leading role. Spring restoring force and damping force are negligible, therefore, in case of the screen Strength analysis, the screen box suffers a payload of gravity and the exciting force. The exciting force generated by eccentric block rotation:2()ijFMrWhich is equivalent to concentration acting on both sides of the side panel, then decomposed in x, y direction, the exciting force was gotten: For the simulation of the exciter, it make use of the rigid regional set in ANSYS, regard the exciter as a point mass element, and respectively establish point quality unit in the rotation center of the four groups of eccentric wheels, then use these four-point quality unit modules to stand for each eccentric quality, and take it as the master node, set 16 nodes at the location on the side of the screen box where the exciter is installed, simulate the exciter and the flange on the side panels as the slave nodes. Through establishing rigid region command in the ANSYS, connect the master node and the slave nodes. The two excitation eccentric shafts of the circular vibrating screen move with same rotation speed, and its resultant force fit sine. Then decomposed the exciting force along horizontal and vertical directions and calculate the quality of eccentric shaft, apply these averagely to the nodes around connected holes through which the exciter is connected with the side panels.The angular velocity of vibration is determined by the motor and the transmission ratio of the size pulley:Where Eccentric distance: r=107.5mm, Eccentric weight: m=209Kg.C. Boundary condition When conducting finite element analysis for the screen box, in order to gain a accurate result, it is necessary to bound the boundary conditions. For example, simplify the coil spring for supporting as the boundary element for tension and compression spring, sequentially determine the boundary conditions to the computational model. Besides use the spring-damper element in ANSYS to simulate rubber springs, the unit connect with a short screen box beams node at one end while is fully constrained at the other end. III. SCREEN BOX STATIC ANALYSIScos,inxyFttminax286140/min5283.7/60dyorrsIn the ANSYS software, when set the type of analysis to be static, the Solver program will automatically solve the model4, and the results of solving will be showed in the post-processor post1. According to the shaker stress cloud figure under static load, we get known the bending stress which the steel pipe of the under beam of the vibrating Screen beams bear is the maximum stress of the whole screen box. The location on the side panels where bear the greatest force are the bottom around the hole of exciter, the sinew junction and the junction of the bottom beam pipe and the side panel respectively, and the maximum stress is 31.7Mpa. From the actual running situation of the vibrating screen, it would generate crack in the bottom of the exciter, sometimes in the connections of the side panels with the beams. Under the eccentric excitation force, it creates concentrated stress between the pipe and the cross piece, therefore, crack was crated under the work of welding residual stress, which is fit for the actual situation.IV. SCREEN BOX MODAL ANALYSISAs the vibrating screen depends on the rapid vibration screen body to carry out work, therefore, there is an operating frequency. If the frequency happens to be at or too close to the natural frequency, it would occur Resonance phenomenon.When the resonance occurs, theoretically the amplitude is infinite, in that case, the vibrating screen structure would be destroyed quickly, and also create a great noise. Besides, under the action of the exciting force with cyclical changes, the screen body would have changes in isplacement and stress response. Some locations, in the operating frequency, may bear a great response or excess stress, and became vulnerable to fatigue or failure. For example, through the field experience of using large-scale vibrating screen, it can be found that the main fault of the vibrating screen is the rupture of the cross piece, therefore, it is not enough to only do the static analysis for the screen. When do the dynamics analysis to the large screen, it should be conducted in three areas. Firstly, do the modal analysis and in accordance with its natural frequency and shape mode, evaluate the vibrating screen and modify it to avoid its natural frequency is equal to or near the operating frequency. Then do dynamic stress analysis, through the cloud chat of the Stress distribution and the displacement, observe if there is concentration of a too large stress in the screen body during working. Finally, since the vibrating screen is working under the exciting force whose frequency is fixed, it is necessary to do harmonic response analysis for it and consider the harmonic response situation to avoid harmonic resonance response 56. Modal analysis is used to determine the vibrating screens vibration characteristics which are the natural frequencies and shape modes, so it is an important step in the dynamic design. The typical basic equation of non-damped modal analysis is the classical feature value problem:Where K is Stiffness matrix, i is the vibration-based vector in the first I order modes, i is the natural frequency in the first I order modal M is Mass matrix. Modal analysis consists of four steps: modeling, applied load and solve, modal expansion, results-view and post-processing. The model can be the finite element model established in this section 7; the only one effective “payload“ is the zero-displacement constraints in the vibrating screen modal analysis, while the other loads are ignored in the mode extraction. In addition, the orders to solve is also need to be set up, that is to solve how many orders natural frequency and the mode expansion is to write the vibration mode into the outcome document. After doing that the mode shape can be observed in the post-processor. Finally,look at the natural frequency and the vibration mode of the vibrating screen model, while the vibration mode can be observed in the form of animation 8 In the ANSYS software, the natural frequency values of sieve box in the top 30-order are solved and showed in table 2. Seen from table 4.5, the frequency close to the screen box: Operating frequency f (0) =800/60=13.33HZ It is the natural frequency in the 25th, the 26th, the 27thorder. In the ANSYS, vibration mode diagram with the ordernatural frequency can be obtained by extending the vibrationmode. Figure4 are the vibration pattern map of the screen box in the 26th order.From the table 2 which lists the modal frequency and these modal shape maps, it can be seen that the mode formation in the 26th-order is mostly consistent with the actual motion state and its natural frequency is also in line with the actual. All of these illustrate the accuracy of the model. Furthermore, the modal frequencies adjacent to the natural frequency in the 26thorder are over 10% above the work frequency. For the vibrating screen works beyond the resonant, therefore its operating frequency is far away from the natural frequency. These show the Vibrating screen design is reasonable. Seen from vibration mode in the 27th order, the shaker reverse horizontally, so in the practical work, install 4 damping springs in the lower part of the sieve box to buffer the stress and displacement.V. CONCLUSIONSAccording to finite element analysis of static mechanics,we get the stress distribution of sieve boxes, find the weaknesses in the structure of the sieve box and improve them. Using flange to connect the bottom screen frame with the side panels, the field use prove that it causes no crack, and effectively extends the life of screening machines.through the modal analysis, we obtain the natural frequency and vibration mode of the screen box in the top 30 orders, the operating frequencies are far away from the natural frequency(over 10% beyond),and the motor parameters chosen are reasonable.The vibrating screen structure has a relatively dense distribution of low-mode, and its vibration is a rigid-body vibration. When in the vicinity of the excitation frequency, the whole structure is mainly doing horizontal swing,pitching vibration and to torsion vibration. Because both the bottom of the material discharge port and the top of the feed inlet have large deformation, we can locally install strengthen tendons.REFERENCES1 Wen Bangchun, Liu Shuying. Mechanical vibration theory and dynamic design methodM.beijing: Machinery Industry Press,2001. 2 Cui xiangyang,Chinese version of ANSYS elementM.hunan: Hunan University Press,2006. 3 Gao Xueqing,Han Xiaoming. Screen box dynamic response finite element analysis of the Circular Vibrating Screen J. Coal Mine Machinery, 2008,29(11):6365. 4 Li Wenying. Dynamic analysis and Dynamic Design of large vibrating screenC.shanxi; Taiyuan Institute of Technology, 2004. 中文译文超重型振动筛筛箱有限元及模态特性分析郭年琴 罗乐平江西理工大学机电工程学院 江西赣州 341000摘要 采用通用有限元分析软件 ANSYS 建立超重型振动筛有限元模型 对筛箱整体进行有限元分析 揭示了静载荷作用下结构内部应力分布情况 同时分析了超重型振动筛筛箱结构的动态特性 获得了筛箱的低阶固有频率与模态振型 找出了筛箱在额定载荷下各部位应力和变形的分布规律 为筛箱的设计改进及动态强度的试验研究提供了必要的依据关键词 ANSYS 有限元 圆振动筛 强度 动态特性 1 圆振动筛的工作原理圆振动筛由偏心块式激振器、筛箱、电动机、底座及支承装置组成,具有结构简单、运转平稳、工作可靠等特点。筛箱采用了焊接结构,坚固可靠,其结构如图 1 所示。在振动器的主轴上除中间部分制出偏心外,在主轴的两端装有可调节偏心重的偏心轮。电动机经三角带使激振器偏心块产生高速旋转,运转的偏心块产生很大的离心力,激发筛箱产生一定振幅的圆运。弹簧是支承筛箱用的,同时也减轻了筛子在运转时传给基础地基的动力1。2 振动筛筛箱模型的建立超重型振动筛以 2YAC2460 型为研究对象,建立筛箱的有限元模型,可以有两种方法.一种是从 CAD 软件中建立实体模型导入到 ANSYS 中,这种方法不但耗费的建模时间较长,也需要较长计算时间,甚至有可能计算不出任何结果;第二种方法是利用 ANSYS 中的单元建立筛箱的有限元模型,此方法可以快速地建立模型,而且计算快,结果准确23。A.筛箱有限元模型的建立为了准确合理地对筛箱进行模拟,文中通过采用shell63、beam188、combin14、mass21 四种单元分别对侧板、上筛架、下筛架、弹簧和激振器进行模拟2,单元选择如表 1所示。需要注意一点,即模型在划分完单元网格后,不同厚度的侧板的交界处,以及侧板与横梁和加强梁的连接处,其单元必须要有公共的节点,以传递载荷,否则在计算过程中板单元之间以及板单元与梁单元会发生脱离,导致结果不准确,模型建立失败。侧板由若干面组成,面与面的边界线是加强梁,面的边界线的交点是横梁与侧板的连接点,这样在模型划分完单元网格之后,不论是通过焊接连接,还是法兰连接,在模型中都由公共的节点来表示在筛箱侧板的模型中,由于铆钉和法兰盘处,无论其质量还是刚度对筛箱系统的影响都很小,如果在模型中建立,又会给单元网格的划分带来很大麻烦,无形中会增加许多单元,因此将其忽略。通过对模型的处理得到筛箱的有限元模型,如图 2 所示。B. 计算工况及筛箱的受力情况分析筛箱在工作过程中受到重力、激振力、弹簧回复力和阻尼力。由于该振动筛为惯性筛 在振动过程中主要是激振器偏心质量旋转时所产生的惯性力,即惯性力起主导作用,弹簧回复力和阻尼力可以忽略不计。因此在对筛箱进行强度分析时,筛箱所受载荷为重力和激振力,偏心块旋转运动所产生的激振力,是等效地作用于侧板两边的集中力,然后再向 方向分解,2()ijFmryx、得到激振力: 。cos,inxyFtt对于激振器的模拟,利用 ANSYS中设定刚性区域,将激振器看作点质量单元的方法,分别在四组偏心轮的旋转中心建立点质量单元,这四个点质量单元为每组偏心质量,作为主节点;筛箱侧板上安装激振器的位置处设定 16 个节点,模拟激振器与侧板的法兰盘,作为从节点。通过建立 ANSYS中刚性区域的命令,将主节点与从节点连接。圆振动筛两激振偏心轴等速同步旋转,并且合力大小呈正弦规律变化,将激振力沿水平方向和竖直方向分解并计算偏心轴的质量,平均施加在侧板与激振器连接孔周围的节点上。振动的角速度由电机与大小皮带轮的传动比确定: r286=140r/min;523.7/;6r.;m09nadskg小电 机 大偏 心 距偏 心 重C.边界条件在进行筛箱结构有限元分析时,为了使数值解确定唯一,必须进行边界条件约束处理, 将支撑螺旋弹簧简化为拉压弹簧边界元,从而确定了计算模型的边界条件。利用 ANSYS 中的弹簧阻尼单元模拟橡胶弹簧,该单元一端与筛箱短横梁节点连接,另一端全约束。3 筛箱静力学分析在 ANSYS 软件中将 typeofanalysis 设为 Static,解算程序将自动对模型进行求解,得出结果后在 Post1 后处理器中即可查看求解结果。振动筛静载荷作用下的应力云图如图 3 所示。由图 3 可知振动筛下梁横梁钢管受的弯曲应力值为整个筛箱的应力极值,侧板受力最大处分别为激振器孔四周、筋板连接处以及下梁钢管与侧板的连接处,应力最大值为 317Mpa,从实际振动筛的运行情况看,在激振器的下方,有时是侧板和横梁的连接处产生裂纹,有限元分析计算结果与实际情况相符。4 筛箱模态分析由于振动筛是靠筛体的快速振动来进行工作的,所以存在工作频率,如果工作频率正好处于或者过于接近固有频率,则会发生共振现象。发生共振时,理论上振幅无限大,振动筛结构会很快破坏,而且产生很大噪声。此外,筛体在周期性变化的激振力作用下,产生变化的位移和应力响应,某些位置可能会在工作频率下,有过大的响应,或者应力过大 极易发生疲劳破坏。比如,通过使用大型振动筛的现场经验发现,振动筛的主要故障为横梁的断裂。因此,对于振动筛的静力分析是远远不够的。对于大型振动筛的动力学分析,应当进行三个方面的分析:首先进行模态分析,根据其固有频率和振型,对该振动筛进行评价并修改,避免固有频率等于或接近工作频率;然后进行动应力分析,通过应力分布云图以及位移云图观察筛体在工作过程中是否存在过大的应力集中;最后由于振动筛是在频率固定的激振力的作用下工作的,所以还应进行谐响应分析,考虑其谐响应情况,避免谐响应共振56。模态分析是用于确定直线振动筛的振动特性,即固有频率和振型,是动态设计中的重要一步.典型的无阻尼模态分析求解的基本方程是经典的特征值问题: 2iiiiKMi式 中 : -刚 度 矩 阵 ;第 阶 模 态 的 振 型 向 量 ;第 阶 模 态 的 固 有 频 率 ;质 量 矩 阵 。进行模态分析包含四个步骤,即建立模型、施加载荷并求解、扩展模态、察看结果和后处理。模型使用本节已建立的有限元模型7;对振动筛的模态分析中唯一有效的“载荷”是零位移约束,位移约束以外的其他载荷,在模态提取时都被忽略,此外还要设定求解的阶数,即求解多少阶固有频率;扩展模态就是将振型写入到结果文件中才能够在后处理器中观察到振型;最后是察看振动筛模型的固有频率和振型,并可以动画的形式观察振型8。在 ANSYS软件中求解了振动筛筛箱前 30阶固有频率,结果如表 2所示。从表 2可以看出与该振动筛工作频率 ,比较接近的是80()13.6fHz25、26、27 阶固有频率。在 AN-SYS中,可以通过扩展振型获得各阶固有频率下的振型图,图 4图 5和图 6分别为振动筛第 25阶 、26 阶和第 27阶的振型图。从表 2列出的模态频率和部分模态振型图可以看出:第 26阶模态阵型与实际运动状态最具一致性,其固有频率也与实际相符,在此说明了模型的准确性,再者,与第 26阶固有频率相邻的模态频率均在工作频率的上下 10%以上,因为振动筛是过共振区工作,所以其工作频率远离固有频率,即振动筛设计比较合理。从第 27阶振型看,振动筛横向扭转,所以实际工作中在筛箱下部装设四个阻尼弹簧,以起到对应力和位移的缓冲作用。5 结论振动筛在工作过程中,侧板上存在多出应力集中区,但各部位应力值较小,小于许用应力,筛箱结构满足强度要求。振动筛结构低阶模态分布较为密集,属刚体振动,主要为结构整体横向摆动、俯仰振动和扭转振动。出料端下方与进料口上方的变形较大,可设局部加强筋。振动筛的工作频率必须远离其固有频率(上下 10以上),电机参数选择合理。参考文献1 闻邦椿,刘树英 振动机械的理论与动态设计方法 M 北京: 机械工业出版社 20012 崔向阳ANSYS 单元中文版 M 长沙: 湖南大学出版社 20063 高雪琴,韩晓明 圆振动筛筛箱的动态响应有限元分析J 煤矿机械 2008 29 (11) 63654 李文英 大型振动筛动力学分析及动态设计D 太原:太原理工大学 2004
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