| Show DRY classification by NV william Illiam E bryan the mechanical classification of dry granular material is the result of the action of several natural laws these mut must operate in conjunction with a mechanical device so arranged as to permit the balancing of the action of the various principles involved and at the same time placing the relative action of the dry granular material completely under control of the mechanical device laws involved the first active law in mechanical sizing is termed the law of selectiveness i 1 a 0 that the mixed particles of various sizes of granular material when under agitation upon a level plane the finer particles sink to the bottom and engage the surface while the coarser particles rise to the top without regard to the specific gravity of such particles the second active law is called the law of displacement or the displacement of the centers of gravity of particles upon an inclined plane the relative difference in the tendency of coarse and fine material of granular shape to move down in inclined plane is due to the difference in the displacement of their centers of gravity upon the same angle of plane the third bird active law is the law of friction of mass or the coefficient of friction mechanical apparatus close observation of the action of these laws as well as the influence of other forces has led to the design of a mechanical device simply arranged to best meet the requirements of these laws in order to assist the law of selective action on an inclined plane a series of several hundred tapered riffles fiffles or grooves are placed on the inclined surface of what is termed the deck of the device this permits the fines to sink to the bottom of these grooves and forces the discharge of larger particles over the top of the riffle in accordance with the action of tho the law of displacement of centers of gravity this is accomplished by the feeding of dry material to the inclined deck while the same is being agitated forward and backward by a specially designed head motion which pushes the deck forward at one speed and causes it to return at a higher speed this sets up what is termed a progressive action of material on the deck or causes the general manager the minerals recovery co denver colorado in the colorado school of mines magazine golden granular particles to travel in a forward direction under the government however of the law of selective action and the law of displacement aided by the law of friction of mass under operation the device is fed with dry ore sand grain or the like the feed engaging a feed board where a preliminary rough separation is accomplished by a modified application of tapered riffles fiffles rif fles the feed then engages the table deck at the head of its proper zone and here because of the length and the great number of riffles fiffles rif fles almost any desired number of carefully sized products may be taken off by replacing receptacles at the bottom and far edges of the deck from which falls when in action a constant sheet of granular material graded carefully from coarse particles to fine dust range of application mechanical sizing is applicable to every form of dry granular material such as crushed ore salt coal sand emery cereals unbroken or crushed or in fact there is no field in dry sizing now filled by metallic screen devices that cannot be filled by a mechanical sizer and often with greater economy and efficiency this is proved by the fact that metallic screens blind and lose their efficiency while the mechanical device cannot clog or blind and automatically cleans itself specific gravity has practically no effect upon mechanical sizing for the reason that granular particles of the same contour and volume when placed upon an inclined plane have the same displacement of their centers of gravity with the result hat a particle of lead and a particle of sawdust of the same size and shape will discharge from the table at the same point although the specific gravity of the one is many times that of the other |
