沥青搅拌设备振动筛设计【机械类毕业-含CAD图纸】
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译文题目： Dynamics and screening characteristics ofa vibrating screen with variable elliptical trace 变椭圆轨迹振动筛的动力学和筛选特性Dynamics and screening characteristics ofa vibrating screen with variable elliptical traceAbstract: the ideal motion characteristics for the vibrating screen was presented ,vibrating screen with variable elliptical trace was proposed. An accurate mechanical model was constructed according to the required structural motion features.Applying multi-degree-of-freedom vibration theory,characteristics of the vibrating screen was analyzed.Kinematics parameters of the vibrating screen which motion traces were linear,circular or elliptical were obtained.The stable solutions of the dynamic equations gave the motions of the vibrating screen by means of computer simulations.Technological parameters,including amplitude,movement velocity and throwing index,of five specificpoints along the screen surface were gained by theoretical calculation .The results show that the traces of the new designed vibrating screen follow the ideal screening motion .The screening efficiency and processing capacity may thus be effectively improved.Keywords:variable elliptical trace;screening process with constant bed thickness; dynamic model;motion characteristic;screening characteristics1 Introduction Screening operations are an important part of coal processing. The vibrating screen is one of the most extensively used screening tools. Vibrating screens, such as linear vibrating screen, circular vibrating screen or elliptical vibrating screen, have a simple translational motion. The motion follows the same path everywhere on the screen and so the screen has constant transport velocity and throwing index, which leads to low screening efficiency. Augmenting the throwing index to improve breaks the exciting motors processing capacity lowers the working.In this paper , we report on the design of a new vibrating screen with variable motion traces that is based on the principle of screening process with constant bed thickness34.Different parts of the vibrating screen traverse different elliptical traces and the resulting motion agrees well with the ideal motion .Thus the screen processing capacity and efficiency can both be improved.2 Ideal motion for a screen surface and the proposal of a vibrating screen with variable elliptical trace2.1 Screening characteristics of common vibrating screensVibrating screens commonly work at a fixed vibration intensity .Material on the screen surface moves by throwing, rolling or sliding motions .For common screeners ,material granularity is widely distributed at the feed end .The energy imparted to the material particles from the vibrating screen is severely dissipated .Consequently ,a large number of particles become laminated only a short distance from the feed end .The material penetrates the screen within the first 1/4 to 1/2 of the screen ,which affects screening and lowers processing capacity 5.The decrease of fine-grained material causes the ratio of particles close in size to ,or larger than ,the mesh to increase .Thus ,the screening efficiency declines dramatically .The material granularity simultaneously becomes uniform and the energy imparted from the vibrations to the material suffers little loss .Hence ,the amplitude and velocity of the material particles increase .This causes the material bed depth at the feed end to be thick while at the discharge end it is thin .This kind of motion leads to an asymmetrical penetration along the screen surface,which influences the screening efficiency and processing capability 6.Common screening characteristics are shown in Fig.1.2.2 Ideal motion for screen surface and implementing schemeThe ideal motion for screen surface is described below, according to the principle of screening process with constant bed thickness .The feed end of the screen has a bigger throwing index and a higher material delivery velocity ,which makes bulk material quickly penetrate and causes rapid delaminating. Earlier lamination of material increases the probability of fine-grained material passing through the mesh .The screen has an appropriate throwing index and a little higher material delivery velocity in its middle part .This is of benefit for stabilizing fine-grained materials and for penetrating uniformly along the screen length .A lower throwing index and material delivery velocity near the discharge end causes the material to stay longer on the screen and encourages more complete penetration of the mesh. Two methods are currently used to improve screening efficiency 78.The first is to add material to the screen from multiple feed ports. This is troublesome in practical use especially in terms of controlling the distribution of differently granulated materials .Hence it is rarely used in practical production. The second way is to adopt new screening equipment like, for example, a constant thickness screen. The motion of the new screen surface causes material to maintain the same, or an increased, thickness .It achieves a rather more ideal motion.The main problem with the constant thickness screen is that it covers a bigger area and that the structure is complicated and hard to maintain .A simple structure with good screening efficiency is still a necessity. We have designed a new vibration screen with a variable elliptical trace that is based upon an ideal screen motion for use in raw coal classification. The size of the vibrating screen is 3.6 m7.5 m,the feed granularity is 0 to 50 mm and the classification granularity is 6mm.Elliptically vibrating screens combine the basic advantages of both circular and linear vibrating screens 910.The long axis of the ellipse determines material delivery and the short axis influences material loosening, to be exact.3 Dynamics model analysis of vibrating screen with variable elliptical traceWe made the exciting force deviate from the center of gravity,to change the motion pattern of the new vibrating screen.The stiffness matrix of the vibration isolation spring was not zero under these circumstances and the vibrating system had multiple degrees of freedom.Minor transverse wagging was neglected to simplify the research.The motion was considered to be a linear vibration of a rigid beam in the longitudinally symmetrical plane.At each point the vibration is a combination of the translation of the center of gravity and the screen pitching about the center of gravity.Previous studies neglected the influence of elastic forces in the horizontal and vertical direction on the swing of the vibrating screen 3,11.An accurate dynamic model consisting of three differential equations that include coupling of degrees of freedom in the vertical,horizontal and swing directions is proposed.The mathematical model of the vibrating screen is shown in Fig.2.The center of gravity, is taken as the origin of a rectangular coordinate system at staticequilibrium, in accordance with rigid motion on the plane 12.Simultaneous differential equations in generalized coordinates using center of gravity coordinates,(x,y),and the swing declination angle, ,may be written aswhere M is the mass of the vibrating screens the moment of inertia of M relative to the center of gravity,O;x and y the displacements in the x and y0directionas;x and y the velocities in the x and y directions and y the accelerations in the x and y directions; is the swing angular displacement; the installation angle;fx,f yond father damping coefficients in the x,y and directions;x k and k the stiffness coefficients of the supporting spring along the x and y directions; A0 the amplitude of the exciting force, given by2 0 A =mr, where r is the radius of eccentricity the mass of the eccentric block and the exciting angular frequency; L1 and L2 the distances between each supporting spring and the center of gravitys the distance between the rotating center of the eccentric block and the center of gravity; and,the included angle between the l and x directions. The damping force is rather small and can be neglected. Then Eq. (1) can be simplified to Eq.(2).4 Motion and screening effect analysis of a vibrating screen with variable elliptical trace 4.1 Analysis of the motion parameters Multiple degree-of-freedom vibration theory was used to find a stable solution for the forced vibration 13,as follows:When E 2 S 2 +C 2 H 2 +2 ESCH=0, the trace of point D is a line. When E =Sand C =H, the trace of point D is a circle. In general. (6) expresses the equation of an ellipse.The xoy coordinate was rotated degrees anticlockwise to give a new set of x oycoordinates. A standard elliptical equation was then obtained after eliminating D D x y in Eq.(7).From this we know that some points on the screen move in a line or a circle while others move in an ellipse .As long as the relative position of the rotating center of the eccentric block and the center of gravity are properly adjusted, variable elliptical motion of the screen will be obtained .This provides a reasonable throwing index and material delivery velocity and improves screening efficiency.4.2 Analysis of motion trace and screening efficiency The stable solution of a vibrating system, in terms of the vibrating screen, can be given by the equations of motion for any point on the vibrating screen areEq.(8)shows that the center of gravity traces an approximate circle and that the amplitude in the horizontal and vertical directions is between 3.5 mm and 5 mm.Fig.3 shows how the center of gravity moves in three degrees of freedom.Fig.3 gives theangular phase difference between the horizontal and vertical directions as well as the amplitude of the swing angle.5 Conclusions1)A new vibrating screen with variable elliptical motion trace was proposed according to the principle of screening process with constant bed thickness.Different points on the vibrating screen trace different elliptical paths.The motion pattern agrees well with the ideal motion characteristic for a screening surface. Thus,screening capacity and process efficiency can be increased.2)A theoretical kinematic analysis of the vibrating screen was done to study how varying different parameters affects the motion of the screen.Kinematics parameters of the vibrating screen that motion traces are linear,circular or elliptical are obtained.3) Motion traces of total vibrating screen were gained through computer simulations.Screening technological parameters,including amplitude, velocity and throwing index,of five specific points along the screen surface were calculated. Theseparameters are related to screening efficiency. The results show that the motion pattern of the designed vibrating screen conforms to an ideal screening motion and that the design is able to effectively improve screening efficiency.4)The position of the exciter axle center,relative to the center of gravity of the vibrating screen,is extremely important for screening efficient.Thus,we can design a vibrating screen with higher processing capacity without increasing power consumption by adjusting the relative position of the axle center.This is a point that requires further study.References1Wen B C,Liu F Q.Theory and Application of Vibration Machines.Beijing:China Machine Press,1982.2Gu Q B,Zhang E G.Study on complex-locus vibration screen.Mining&Processing Equipment,1998(1):4246.3Hao F Y.Coal Preparation Manual:Technology and Equipment.Beijing:China Coal Industry Publishing House,1993.4Yan F.Screening Machines.Beijing:China Coal Indus-try Publishing House,1995.5Liu C S,Zhao Y M.Study on nonlinear characteristics of single particle on screening surface.Mining&Processing Equipment,1999(1):45486Tao Y J,Luo Z F,Zhao Y M.Experimental research on desulfurization of fine coal using an enhanced centri- fugal gravity separator.Journal of China University ofMining&Technology,2006,16(4):399403.7Zhang E G.Screening,Crushing and Dewatering Equipments. Beijing: China Coal Industry Publishing House,1991.8 Khoury D L.Coal Cleaning Technology .USA:Noyes Data Corporation,1981.9Shang N X,Na J F.2TYA1842 elliptical vibration screen. Mining&Processing Equipment,1990(2):2024. 10YeHD.Elliptical isopachous screening technology andits application.Sintering and Palletizing,1999,5(3):3033.11Wen B C,Liu S Y,He Q.Theory and Dynamic Design Method of Vibration Machines.Beijing:China Machine Press,2001. 12Wang F,Wang H.Screening Machines.Beijing:China Machine Press,2001.13Ni Z H.Vibration Mechanics.Xian:Xian Jiaotong University Press,1989.14Zhu W B.Working principle and computer simulation of vibrating screen with complicated motion trace.Mining &Processing Equipment,2004(10):3436.15Peder M.The mogensen E-seriesa new screening oncept.Mineral Processing,1996,7(37):311315.16Wen B C.Synchronization theory of self-synchronous vibrating machines with ellipse motion locus. Boston:American Society of Mechanical Engineers,1987:495500.变椭圆轨迹振动筛的动力学和筛选特性摘要：根据振动筛的理想运动特性，提出了变椭圆轨迹的振动筛。根据所需的结构运动特性建立了一个精确的力学模型。应用多自由度振动理论，对振动筛的特性进行了分析。获得了线性的、圆形或椭圆形的运动轨迹振动筛的运动学参数。通过计算机模拟振动筛的运动动态方程得以有效的求解。通过理论计算求得振动筛上五个具体点的工艺参数,包括振幅、运动速度和抛掷指数。结果显示，新设计的振动筛的轨迹遵循理想的筛选运动。筛分效率及处理能力可能因此而得到有效改进。关键字：变椭圆轨迹；等厚筛分；动态模型；运动特性；筛分特性1前言筛分操作是一个重要的煤矿处理组成部分。振动筛是最广泛使用的筛选工具之一。振动筛，如直线振动筛、圆振动筛或椭圆振动筛，都有一个简单的平移运动。运动在振动筛上到处都遵循相同的路径,所以振动筛有恒定的运输速度和抛掷指数，从而导致低的筛分效率。增强抛掷指数来改善激振电机在工作中的较低的处理能力。在本文中，我们就一个基于等厚筛分理论的新的可变的运动轨迹振动筛的设计做报告34。振动筛的不同部分有着不同的椭圆运动轨迹，由此产生的运动与理想的运动轨迹相吻合。因此振动筛的处理能力和效率都可以得到改善。2振动筛表面的理想运动轨迹和变椭圆轨迹振动筛的建议2.1振动筛常见的筛选特性 振动筛通常工作在一个固定的振动强度。材料在筛面上抛掷、滚动或滑动运动。对于常见的筛网，物料颗粒在入料端广泛的分布。振动筛给予物料颗粒的能量被大量的浪费。因此，大量的颗粒只在入料端附近很短的一段距离里分层。材料进入振动筛在第一个1/4到1/2的筛体，它影响筛选并降低加工能力5。细质级材料的减少，导致粒子的比例接近或大于网格增加的大小。因此,筛选效率急剧下降。物料粒度同时统一的，从振动源给予物料的能量损失很小。因而物料粒子的振幅和速度增加。这导致了物料的垂直深度在入料端厚，而在出料端薄，进而影响了筛分效率和处理能力。常见的筛分特性如图1.2.2振动筛表面的理想运动和实施方案振动筛表面的理想运动描述如下，根据筛选过程的等厚筛分原则。振动筛的入料端有一个较大的抛掷指数和较高的材料传递速度，这使得大部分材料迅速渗透,导致快速分层。材料的快速分层增加细粒度的材料通过筛网的概率。振动筛有一个适当的抛掷指数和高一点材料传递速度的中间部分。这有利于稳定处理细粒度材料并沿着振动筛的长度方向穿过。靠近出料端较低的抛掷指数和材料递送速度导致材料在振动筛上停留更长的时间并完成更细致的筛分。有两种方法目前用于提高筛选效率78。第一种方法是材料从多个入料口添加到振动筛上。这在实际应用是麻烦的尤其是在控制粒状材料不同的分布这方面。因此，这很少用于实际生产。第二种方法是采用新的筛选设备，例如一个等厚振动筛。新的振动筛的表面运动使材料保持相同，或者增加厚度。它达到一个更理想的运动。等厚振动筛的主要问题是,它涵盖了一个更大的区域,结构复杂,难以维护。一个结构简单切具有良好的筛选效率的振动筛仍然是必需的。我们设计了一个基于理想振动筛运动轨迹的新的变椭圆轨迹振动筛用于原煤分类。振动筛的大小为3.6 m7.5 m，进料粒度是0到50毫米和分类粒度是6毫米。椭圆轨迹振动筛结合了圆轨迹振动筛和直线振动筛两者的基本优势910。确切地说，椭圆轨迹的长轴决定材料的运送速度，短轴影响材料的松散程度。3 变椭圆轨迹振动筛的动力学模型分析我们使激振力偏离中心，来改变新的振动筛的运动模式。隔振弹簧的刚度矩阵并不是零，在这种情况下,振动系统有多个自由度。小的横向摇摆被忽略来简化研究。运动被认为是一个刚性梁的纵向对称平面上的线性振动。在每个点的振动是平移重心和振动筛重心的结合。先前的研究忽略了振动筛水平方向上的弹性力与竖直方向上的摆动3,11。由三个耦合垂直、水平和摆动方向自由度的微分方程组成一个精确的动态模型。图2 振动筛的数学模型振动筛的数学模型如图2所示。重心被作为一个静力平衡直角坐标系的原点，与平面上的刚体运动相一致12。使用重心坐标(x,y)和摆动倾斜角在义坐标联立微分方程可以写成：式中M是振动筛的质量相对于重心的惯性矩，x和y表示在x方向和y方向上的位移，和表示x方向和y方向的速度，和表示在x方向和y方向的加速度，为振动角位移，是安装倾角，和表示在x方向和y方
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