礦物加工外文翻譯(存儲(chǔ)版)
【正文】 ctions。 dynamic model。 Technology,Xuzhou,Jiangsu 221116,China 2 capacity and efficiency can both be improved. 2 Ideal motion for a screen surface and the proposal of a vibrating screen with variable elliptical trace Screening characteristics of mon vibrating screens Vibrating screens monly work at a fixed vibration intensity .Material on the screen surface moves by throwing, rolling or sliding motions .For mon 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 bee laminated only a short distance from the feed end .The material perates the screen within the first 1/4 to 1/2 of the screen ,which affects screening and lowers processing capacity [5].The decrease of finegrained 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 bees 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 peration along the screen surface,which influences the screening efficiency and processing capability [6].Common screening characteristics are shown in . 3 Ideal motion for screen surface and implementing scheme The 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 perate and causes rapid delaminating. Earlier lamination of material increases the probability of finegrained 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 finegrained materials and for perating 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 plete peration of the mesh. Two methods are currently used to improve screening efficiency [7– 8].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 plicated 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 m m,the feed granularity is 0 to 50 mm and the classification granularity
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