The plan devised by Col. D. P. Brown, of Lost Creek, for No. 3. colliery (Lehigh Valley Coal Co.) is roughly shown by Fig. 46. An old drum with two grooves is used in place of two driving sheaves. The sheaves nearest the drum are placed higher than as shown by this sketch, and the diameter of the tension sheave is larger. The parts are distorted in order to clearly show the course of the rope around the sheaves. It will be observed that the rope runs over the drum twice (one three-quarter turn on each side) and around the tension and contact (two) sheaves at each winding. As these three sheaves are only about one half the diameter of the driving sheaves (drum), the wear on each sheave is twice as great as that produced by the driving sheaves. Taking the wear of the rope on a drum of this diameter, caused by one winding on one side, as a unit, we have as the comparative wear: Rope unbending from contact sheave, . Total for single rope plan,. 2222 16 Or eight times the wear caused by a drum. This ratio should be reduced by a certain allowance for the absence of the wear caused by the coils crowding together on the drum. As the wear on the drums and sheaves* is 39 per cent. of the total wear on slopes, which we may divide into 13 per cent. for the drum and 26 per cent. for the sheaves, on slopes averaging 933 feet in length, we may assume for this length of 1400 feet that the slope wear (bearing pulleys, etc.) will be double that, reducing the relative per cent. of wear on drums to 6 per cent.-the wear on such a slope due to drums will therefore be as 6 is to 61 (the wear on the slope); but if the single rope be adopted this 64 is increased nearly eight times-say six times-making this wear equal to 39. Adding to this the wear due to knuckle sheaves (26) and the wear on slope (61) we have 126: 100, or about 25 per cent. increased wear of the rope due to the substitution of this method of winding. This is the minimum-the maximum increase in wear might reach 50 per cent. Wire Ropes. Iron wire ropes were first successfully used in the Hartz mountain mining region about 1836. The principal advantages of iron or steel wire over hemp rope, are: 1. Greater durability. 2. Less weight for equal strength. 3. Reduced cost per ton of material raised. The same essential advantages can also be claimed over chains or flat bands of iron or steel. A series of figures given by Taylor (Statistics of Coal) show that the cost per ton of raising material with hemp See "Wire ropes" below, three or four pages further on. rope is about three times as much as when wire rope is used the data furnished show an average cost of 10 cents per ton in the former and only cents per ton in the latter case. These observations apply to shaft collieries only; at slope collieries the difference would be much greater on account of the great frictional wear on the bearing pulleys. In the anthracite regions the cost of rope per ton of material raised is subject to great variations, which depend principally upon the conditions enumerated below. 1. The depth. 2. Working load. 3. Diameter of sheaves, drums, and pulleys. The cost at slope collieries is much greater than at shaft collieries. The following table shows the tonnage raised by twentythree wire ropes used at eleven different slopes on dips ranging from fifteen to sixty degrees; and the tonnage raised by six ropes at three shaft collieries in the anthracite region. The cost per ton is estimated from Roebling's price list for October, 1880. The cost per ton per hundred feet of lift is seen to vary between .029 and .161 cents, but the latter figure is evidently exceptional, the rope was probably of inferior quality or it was removed some time before it was worn out. For general estimates the averages and totals may be considered to closely represent a fair average statement of the cost and tonnage. In the second table the cost at shafts per lift of one hundred feet is shown to average .053 cents per ton. This is equivalent to 0.38 cents per ton of material raised, closely approximating the figures (0.36) given by Taylor, above cited. Comparing the cost in shafts and slopes we find apparently .069 and .053 cents per ton for each one hundred feet of lift ;-but it must be remembered that the slope lifts are slope measurements of length, not of vertical depth, therefore the actual cost for each one hundred feet of vertical lift in a slope will be much greater than 0.069 cents, as given in the table. If the slope dips 30° a slope length of 200 feet will represent a vertical lift of 100 feet and the cost will therefore be 0.069×2=0.138 for a lift that in a shaft will cost but 0.053 cents. These tables have been calculated from the actual tonnage raised by each rope. As the coal raised does not exceed two-thirds this amount, the cost per ton of coal should apparently be correspondingly increased, but the value of the discarded rope, which is probably worth one-third its first cost, is a nearly equal off-set to this, and the figures above given may therefore be considered to represent the cost per ton of merchantable coal. Assuming the above average figures of cost per ton at slope and shaft collieries to represent the ratio of wear--i. e. 138 53-we have a means of approximately determining the relative amount of wear due to sheaves and drums and to knuckle and bearing pulleys (plus friction caused by dragging on the ground). Assuming an equal wear per ton per vertical lift of one hundred feet at both shaft and slope collieries from the friction due to drums and sheaves (.053), we have 138-53 85 representing the wear from friction on the knuckle and bearing pulleys; or a ratio of 85:53 as the ratio of the wear on the slope to that caused by drums and sheaves, being 61 and 39 per cent. respectively. The wear on bearing pulleys in a slope is from a rolling friction, and can be lessened only by proper attention to the condition of the pulleys and a free use of lubricants; but the wear occasioned by knuckle and deflective pulleys partakes of the character of the wear on sheaves. The policy of winding wire rope on drums of comparatively large diameter has been so frequently and urgently advocated by wire-rope makers, that mine superintendents now very generally use drums larger than the minimum diameters advised by the manufacturers. This general increase in size is doubtless due in part to the growing necessity of increased rapidity in winding. The John A. Roebling's Sons company publishes a circular, in which the minimum drum diameters are as shown in the first column of the following table; the second column |