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Is a knuckle desirable just ahead of the loading

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Unformatted text preview: ectly into the transportation units, which could be tracked or trackless. While handling the ore in underground, one of the problems is that with the ore passes and car loading, should the transfer be vertical or inclined? Is a knuckle desirable just ahead of the loading chute in order to break the momentum of fall? What are the optimum dimensions of the transfer? The decision involves a knowledge of bulk solids flow, particularly for the specific ore to be handled? Designs are made on the basis of past experience and model flow studies. The important factors5 that must be considered while designing an ore pass are: ● ● The size distribution and size segregation of the particles (ore fragments) in the ore mass. The shear strength (s) of the ore mass, with s c p tan , where c is the cohesive strength, p – compressive loading on the material, tan – coefficient of internal friction. © 2005 by Taylor & Francis Group, LLC EXCAVATIONS IN UPWARD DIRECTION – RAISING 353 ● ● ● ● The height of fall in the ore passes, as related to the tendency of ore to crush and to pack. The characteristics of the wall rock of the ore pass – its resistance to slabbing and abrasive wear, with a resultant friction factor ( ) between sliding ore mass and wall. The flow rate and storage capacity desired. The climatic conditions (heat, humidity, presence of water etc.) The mechanics of the ore flow in the vertical and inclined passes have been compared in figures5,12 13.12(a) and (b). Some of the important aspects in this regard, as described by David, J.S. and Pfleider, E.P.5 are discussed below: ● ● ● ● Arching phenomenon is of great importance. The forces and strengths developed in an arch are due to various reasons and amongst them are the tendencies of an ore to pack or segregate, which can have profound effect in this respect. Experience has shown that ore passes generally will not “hang up” if the least cross sectional dimension is four to six times in dia. of the largest ore pieces. However, of the broken ore have a large percentage of fines, which develop considerable shear strength when moist, the mass tends to form arch. This can happen in cold climates during a prolonged shutdown, generally calcium chloride is employed in such situations. It is felt that for the ore passes of equal dimensions, the ore flow is better in the inclined ore pass than the vertical one, for the reason that arch forming is more pronounced in vertical ore passes than in the inclined once where the weight of flowing media keeps breaking the arch on the upper side of the ore pass. However, the ore has got a greater tendency to pack and hold on the footwall side of an inclined ore pass. In order to minimize the damage of the orepass’s walls (wear and slabbing) it should be put normal to dip of the formations. The orepass collar’s elevation should be such that maximum tonnage above this elevation are available. If there is choice between a vertical or inclined ore pass, the merits and limitations of each should be noted....
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