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物料在圆筒旋振筛内的筛分受力情况

  在研制粮食双层圆筒旋转筛的过程中,发现现场使用的圆筒旋转筛,其转速大多偏低,影响了产量及筛分率的综合效果。为此我们对圆筒旋转筛的筛分机理、粮粒在筛筒内的受力、运动状态进行了比较深入的分析,对旋转筛转速公式的推导及应用原则进行了探讨,结合现场实际考察,设计的圆筒筛都分别提高了转速,取得了较好的筛分效果。1 粮粒在筛筒内的受力分析及滚筒转速公式的推导111 粮粒在筛筒内的受力分析首先略去种种复杂因素的影响,将问题简化,取连续进入筛筒内粮食流中的一粒米作为独立质点进行研究。粮粒在滚筒内壁受力情况如下:垂直向下的重力P、滚筒内壁的法向作用力N、切向摩擦力F。滚筒转动时,在摩擦力F作用下,粮粒开始随滚筒运转,旋转到某一转角A后,米粒将下滑与滚筒产生相对运动。粮粒被带起的高度与滚筒的转速有关。在粮粒随同滚筒一起以一定角速度X旋转上升的过程中,重力P的下滑分力与摩擦力(二力为平衡力)在不断增大,然而其下滑分力却始终小于最大静摩擦力Fmax,所以粮粒不会下滑。当粮粒被旋转到一定高度其转角为A时,摩擦力与下滑力的大小都等于最大静摩擦力,此时粮粒在切向方向处于滑动平衡状态,即此点为滑动平衡点。当滚筒转过此平衡点时,下滑力大于最大静摩擦力Fmax,平衡被破坏,粮粒将下滑。在滑动平衡点粮粒的受力状态,如图1所示。由于此时滑动摩擦阻力很小,粮粒将一直滑到滚筒底部,然后又一次被筛筒带起升高,升到一定高度后再次下滑,而在下滑的同时,粮粒还将向前运动(筛筒为锥形或内螺旋的推动)。就这样周而复始,进行筛分清理过程。实际上筛分清理过程主要是在粮粒下滑过程中进行的,因此增加粮粒下滑区段的长度,即加大转角A将提高滚筛的筛分效果。这里需要指出的是在各滑动平衡点,其最大静摩擦力Fmax是个变量不是定值,它与转角A及角速度X有关。图1
112 转速公式推导
根据达朗伯原理,作用于粮粒上的重力P、法向压力N及最大静摩擦力Fmax与其离心力G组成一汇交平衡力系,取径向坐标轴x和切向坐标轴y如图2,其平衡式为:
rX=0 N-G-PcosA=0(1)
rY=0 Fmax-PsinA=0(2)
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Screen rotation in the development process of grain double cylinder, cylinder rotating sievefound field use, its speed is usually low, affecting the comprehensive effect of yield andscreening rate. Screening mechanism, the cylindrical rotating sieve sieve grain in force, the state of motion in the cylinder of the more in-depth analysis, the derivation and application principle of rotary screen speed formula is discussed, combined with the practical field investigation, design of the cylinder screen are respectively improved speed, achieved goodsieving effect the. 1 the grain in the screen cylinder by cylinder speed formula derivation ofstress analysis and the 111 grains in the screen cylinder force analysis of the influence offirst omitted the various complicated factors, to simplify the problem, taking continuous into the sieve tube inside a grain of rice grain in the stream of particles as independent study. The grain in the inner wall of the roller stress conditions are as follows: the vertical downwardgravity P, the inner wall of the drum of the normal force, tangential frictional force of F N. The cylinder rotates under the action of friction, in F, the grain with the drum rotation to startrunning, a corner after A, rice will decline relative motion and the drum. The grain is brought up the relevant height and the rotation speed of the roller. In the grain with the cylindertogether with the angular velocity X rotation in the process of rising, falling force and friction force of gravity (two P force balance force) is increasing, but the decline is always less thanthe maximum static friction force is Fmax, so the grain will not fall. When the grain is rotated to a certain height of the angle is A, the friction force and sliding force size is equal to themaximum static friction force, at this time the grain in the tangential direction in a sliding balance state, that is the point of the sliding balance. When the drum around the equilibrium point, the sliding force is greater than the maximum static friction force of Fmax, the balance is destroyed, the grain will decline. The stress state of sliding equilibrium grain, as shown in figure 1. Because the sliding friction resistance is very small, the grain will always slip into thebottom of the drum, and then once again by the sieve tube with increased, reaching a certain height to decline again, and in the fall at the same time, the grain will also move forward(sieve tube to promote the conical or inner screw). So the cycle, for the process of cleaning up screening. In fact, screening cleaning process is mainly the process of decline in the grain,thus increasing the grain down section length, i.e. increasing angle of A will improve the screening effect of the rolling sieve. It should be noted that in the sliding balance point, themaximum static friction Fmax is a variable that is not a fixed value, it is related to the angle Aand angle velocity X. Figure 1

112 speed formula derivation

According to the D'Alembert principle, method of gravity P, acting on the grain to the pressure of N and the maximum static friction force and the centrifugal force to form a Fmax Gconcurrent force system in equilibrium, taking the radial coordinate axis X and tangential axis y as shown in Figure 2, the balance type for:

RX=0 N-G-PcosA=0 (1)

RY=0 Fmax-PsinA=0 (2)
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本文关键词:圆筒旋转筛 转速 最大静摩擦力 滑动平衡 临界转速

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