Coal - Factors Influencing the Choice of a Loading Machine

INE operators have a choice of several classi- fications of mechanical loaders. Within each classification there are many types and makes available. Table I lists loaders on which manufacturing data as to operating characteristics are available. This paper discusses the conditions met in a mine as they affect these characteristics. It is assumed that management will provide satisfactory engineering, supervision, power, maintenance, loader service within a concentration of workings, and a balanced working cycle served by balanced production equipment. These are factors which affect the optimum operational efficiency of a loader. The conditions which determine loader choice are: Height of Vein—The main limitation to the use of a loading machine is the height to which the vein is mined; i.e. a loader cannot be higher than the place in which it is to work unless rock is taken. Since there are several low vein loaders being developed and successfully applied, this does not appear to be a requisite of an efficient mining operation. The maximum useable height of a loader should be equal to the working seam thickness less a working clearance for travel and operation. A—Working seam thickness = B—Artificial roof support thickness = C—Safe headroom below support = (generally about 6 in.) D—Height of roadway = E—Total of B + C f D =_______________________ A—E = maximum loader height F—Distance from top of roadway to bottom of roof support = G—-Height of loader's coal or ore line (see Table I) = H—Difference between F and G = Size of largest broken particle + a safety factor of 2 to 3 in. H is a loadability factor and is important because the clearance over the top of the conveyor chain to the roof or roof support must be greater than the largest broken particle or else the particle and/or the conveyor chain may be broken. From this standpoint it might be desirable to use a lower height machine even though it may have a smaller capacity, though this is warranted only when increased lump realization offsets lower man-day and machine pro- duction rates. Ivan Given has stated, "Loading should not be handicapped by securing lump only to grind it in the breaker." Width of Working Place—The width of a working place is the greatest width a place may be safely driven. The working place includes not only the face but the roads the loader must tram when mucking out more than one face. The width is limited by the system of placing props with sufficient room between them for the machine runner (about 2 ft). Maximum width of place in which the loader will operate at maximum efficiency is determined by the type of mounting. With track-mounted loaders, maximum width of place is determined by maximum angular swing of the loading head and proximity of track to the face. The use of double track leads to added expense and operational complexities. Several mines that have used double-track systems have found that a substantial saving is made by the use of machines that load out wider places. Trackless loaders may work in rooms of any maximum width. Minimum width of place in which a loader will operate is determined by width of the loader plus a safe movement area for the operator. Often a barodynamic study of the mine will show that either an increase in room width and/or a change in the system of propping may be made by using roof bolting, full or part-width room timbers, removable aluminum I-beams at the face, etc. Increasing the width of a working place will, in general, increase loader operating efficiency by providing more material per fall and by decreasing the preparation and moving time per ton. A change in the system of propping that would increase the minimum width might permit the use of a higher capacity loader with safer working conditions. Proper face tirnbering is necessary to insure safety from roof falls and because the speed of preparation and loading generally increases since the men work with greater assurance and there is less chance of kicking out posts. Maximum Room Length—With the exception of the scraper and the duckbill, the limit to room