61-Beam Expanded Metal Reinforced Concrete H-Bearn Bunton Pipe Separator Yellow Pine Bunton FIG. 2 I I-Beam Bunton Channel Center E Channel End originally separating the compartments. It would seem that instead of channels, H sections should have been used as better adapted to resist compression than the channels, as well as being lighter and, hence, cheaper. Steel Buntons.-Steel, in place of wood, is very commonly employed for buntons even in shafts that are not lined with concrete. Some of the various forms are shown in Fig. 2, and of these the H section appears the best and is the most generally used. Steel buntons are fireproof, but cost much more than wood; four times as much if a section as light as 35 lb. per ft. is used. On the other hand, with proper care, they will last indefinitely. Concrete and Steel Shaft Linings. Practically all concrete-lined shafts are elliptic in section, the arch form being adopted as better able to withstand pressure than the rectangular. A full description of the concrete-lined shaft at the Filbert mine, of the H. C. Frick Coke Co., Fayette County, Pa., is given on page 230. The rectangular, concrete-lined shaft of the Bunsen Coal Co., near Clinton, Ind., is shown in Fig. 3. The buntons are 6"X8" concrete beams reinforced with a 6-in. 8-lb. channel. pass through soft The ground, the ends are also In the elliptical shaft of the Tennessee Coal, Iron, and Railroad Co., at Pratt mine No. 13, near Ensley, Ala., amassive, unreinforced concrete lining is used with a minimum thickness of 15 in. through firm and 18 in. through soft material. The buntons are 6-in. steel H sections, weighing 23.8 lb. per ft., spaced 6 ft. apart. The guides are of the same material as the buntons and carry. bolted to them, cast-steel safety racks. Where the shafts HOISTING Hoisting, or winding, engines may be driven by hand, horse, or mechanical power. The mechanical power may be derived from engines, or motors, driven by steam, electricity, gasoline, compressed air, water, etc. There are two general classes of hoists: single and double. In the former, there is but one cageway in the shaft and up this the cage and loaded car are hoisted by an engine. After the load is dumped at the surface, the cage and empty car descend through the same compartment, impelled by gravity, their speed being controlled by the brakes on the engine drum. In double hoists, there are two cages which travel in separate compartments, one ascending with the loaded car as the other descends with the empty car. Double hoists are the prevailing type, the use of single hoists being confined to prospecting shafts and to unimportant operations in the metal-mining districts. There is no essential difference between stationary engines used for hoisting and for haulage. The chief distinction lies in the direction of application of the power generated by the engine. In hoisting engines, the power is applied vertically to raise a weight through a shaft; in haulage engines, the power is applied in a horizontal or approximately horizontal direction to move a weight along a track. Frequently, the same mechanism after having served its purpose as a hoisting engine is used for haulage, and vice versa. The subject of hoisting ropes is discussed under the head of Wire Ropes. HAND- AND HORSE-POWER HOISTS Hand- and horse-power hoists are of relatively small capacity and are almost entirely used for prospecting, shaft sinking, or the like. The windlass, operated by one or two men, is frequently used for sinking small shafts to depths of about 75 ft., where the loaded bucket weighs but a few hundred pounds. In form, it is similar to the hoisting device used in connection with water wells and consists of a wooden barrel, about 8 in. in diameter and 4 or 5 ft. long, provided with a 1 to 11-in. iron axle. This axle is supported at either end in A-shaped wooden standards nailed or mortised to a heavy timber base placed over the shaft. The necessary crank and handle is attached to each end for applying the power. For hoisting heavier weights, single- or double-geared iron crab winches are used. In these, the power is transmitted to the drum or barrel by rack and pinion, so that one man can raise 1 T. or more, but at the expense of speed. These hoists are single and unbalanced, the bucket being hoisted by one or two men and descends by gravity; its speed is controlled by loosening or tightening the rope upon the drum. For greater depths and heavier loads, horse whims, or gins, are used. These consist essentially of a drum mounted on a shaft to which are attached one or more cross-sweeps to each of which a horse or mule is hitched. Usually the whim is placed a little distance from the shaft and is so arranged that the movement of the car is regulated by two hand levers, which are connected to the driving gear in such a way that the movement of the drum may be stopped or reversed independently of the movement of the horse. One lever is moved to hoist and the other to lower the load, and through their use overwinding is prevented in case the animal does not stop on the instant. In the better classes of whims, the drum is placed horizontally underground or below a platform to be out of the way of the horses, motion being imparted to it from a vertical shaft through beveled gearing. The vertical shaft is provided with, two, four, or six sweeps to each of which one or two horses may be hitched, so that as many as twelve animals may be used. With four horses, 90 T. have been hoisted 600 ft. in 10 hr.; and with eight mules 60 T. have been hoisted 900 ft. in the same time. Some whims are provided with gears for hoisting heavy loads at slow speed and lighter loads at high speed. Such machines, at slow speed will hoist 2,400 lb. 22 ft. per min.; and at fast speed, 950 lb. 55 ft. per min. STEAM-POWER HOISTING ENGINES Hoisting engines are almost invariably of the duplex, or two-cylinder, type with cranks set at right angles to one another and therefore have no dead center; for which reason they can be quickly started from any position and run more smoothly than single-cylinder engines. Hoisting engines may be simple or compound, and tandem or cross-compound. The first is by far the most extensively used in the shallow shafts prevailing in the coal regions, where the shortness of the hoisting period and the frequent reversals of the engines are not conducive to the economical use of highpressure steam expansively. In the metal-mining regions, where vertical lifts of 1,000 ft. are usual, of 2,500 ft. fairly common, and where several of from 4,000 to over 5,000 ft. exist, refinements in compounding, etc. are successfully used. Further, in metal-mining regions, the price of coal is such (from $4 to $10 and more per ton) that it is imperative to secure all the energy possible from each pound of fuel; while at coal mines and particularly at those where slack is used under the boilers the cost of power has not, until comparatively recent years, been thought worthy of consideration. A hoisting engine may be of the slide-valve, piston-valve, or Corliss-valve type and may be condensing or non-condensing. For a large hoisting engine, a piston-valve gives a much better distribution of steam in the steam chest than a slide-valve, but not so good as a Corliss valve. A hoisting engine, to run condensing, should have an independent air pump and condenser; for if the air pump is operated by the engine it will stop when the engine stops and the vacuum will be lost, rendering the low-pressure piston, in some cases, inadequate to pick up the load at the beginning of the next hoist. In a hoisting engine, the drum on which the hoisting rope coils takes the place of a flywheel, to a certain extent. The operation of hoisting is intermittent in character, and in some cases the engine is so connected that it will run only when operating the drum; in other cases it will run continuously, either empty or under some other load than the hoisting load, the work of hoisting being put on it, when needed, by means of a friction clutch connecting the engine with the drums. Where an engine runs continuously, its surplus power may be utilized for driving air compressors, fans, electric generators, and other machinery; and, by thus concentrating the power, a higher grade engine can be made available for hoisting purposes. Second-Motion, or Geared, Hoisting Engines. In a second-motion engine, power is transmitted from the engine shaft to the drum shaft through gearing. This engine is particularly adapted for portable hoists, such as are used in shaft sinking and similar temporary work, and for shallow mines, or mines where a small tonnage is raised. It is cheaper in first cost and in installation than a first-motion hoisting engine, as a smaller engine does the same work, but it cannot hoist as rapidly; there is also less liability of overwinding. Geared engines are used ordinarily where a hoisting speed of 750 ft. per min. or less is satisfactory, while first-motion engines are used for greater speeds. To hoist the same load, a first-motion engine must be three to four times as large as a second-motion engine, while the hoisting speed and cost will also be three to four times as much. The relative number of teeth in the gears may be varied so that the piston speed may be made faster or slower or equal to that of the rope. The commonly used ratios vary from 1 to 3 to 1 to 5; that is, if the small gear-wheel on the engine shaft has, say, 20 teeth, the large gear-wheel on the drum shaft will have 60 to 100 teeth, depending on the ratio, and it will require from three to five revolutions of the engine to equal one of the drum. If the ratio is exact, the teeth on the small gear come in contact with the same teeth on the large gear during every revolution and cause excessive wear. To equalize the wear, the number of teeth in the large wheel is commonly one less or more than that demanded by the exact ratio. Thus, if the engine is geared 1 to 5, while 20 teeth on the small wheel require 100 on the large wheel, either 99 or 101 would be used. Hoists are occasionally built with metal teeth in the pinion and wooden teeth in the larger wheels. The larger wheels in such cases are cast with mortises, into which are driven maple cogs that are made secure by wedges. These wooden cogs, or teeth, wear well and are easily replaced when broken without seriously interrupting hoisting operations; they are almost noiseless. It a metal tooth breaks, the gear must be replaced, and hoisting must cease until this can be done, In cut gears, the teeth are finished by machine; this adds slightly to the cost of these gears, but they are more serviceable than rough, cast gears and make less noise. Geared engines may have single or double drums, the former being in general use at coal mines where the shafts are relatively shallow and the material is hoisted from one level. Single-drum engines are commonly used in balance, the drum being keyed directly to the shaft, one rope unwinding from the top of the drum as the other rope winds up beneath it. Double-drum engines may be used in balance, by leading the ropes as just indicated but on the separate drums; or they may be used independently, each drum hoisting as desired and both ropes leading on the drums alike, that is, both on top or both underneath. The wearing surfaces in hoisting engines, especially the main bearings, should be made large and the engines proportioned to stand severe work. In the case of two wide-faced drums on the shaft, it is sometimes necessary to have a center bearing, which should be adjustable in every direction and kept as nearly in line with the other bearings as possible. Owing to the difficulty of keeping three bearings in line, and the danger of the shaft breaking in case the bearings are not in line, it is well, where practicable, to omit the center bearing and make the shaft as-short as possible and ample in diameter. First-Motion, or Direct-Acting, Hoisting Engines.-In first-motion hoists, a pair of engines (right- and left-handed) are used with their cranks on the ends of the same shaft as the drum, the cranks being set at angles of 90° with each other to prevent the engines stopping on a dead center. A direct-acting hoisting engine is used wherever the depth of the shaft or a large output demands a high speed of hoisting. In coal-mining practice, their use was formerly limited to the deepest shafts, but the large outputs required from modern mines have caused them to be introduced at comparatively shallow shafts. HOISTING ENGINES USING OTHER POWER THAN STEAM Compressed-Air Hoisting Engines.-Where available, compressed air may be used in place of steam for power as there is no essential difference in the engines. Compressed air may be used exclusively or interchangeably with steam, and should be reheated before entering the engine cylinders. In the case of a compound engine, the reheater may be placed in the pipes leading to the high-pressure cylinder; or, still better, it may be placed before each cylinder; otherwise, the expansion will cause the moisture to freeze in the low-pressure cylinder and stop the engine. Where a hoisting engine is located on the surface and a boiler plant is necessary, steam is generally preferable to compressed air, as the loss in efficiency due to compressing the air is avoided. If, however, water-power is available, it is frequently cheaper to use compressed air instead of steam, particularly if compressed air is also used at the mine for coal cutters or rock drills; or if for any reason it is necessary to place the hoisting engine at a distance from the boiler plant, as there is much less loss of efficiency in carrying compressed air than in carrying steam. For underground hoists, compressed air has many advantages, particularly in gaseous coal mines. Further data on compressed air will be found under that heading and under the heading Haulage. Gasoline Hoisting Engines.-Gasoline hoists are adapted for sinking prospecting shafts in mountainous districts where fuel is scarce and where an easily portable engine is desirable. They are not generally used for permanent hoists in mines of any great capacity. Their operation is essentially on the lines of gasoline haulage motors, which are described under the heading Haulage. The gasoline is injected into the engine cylinder in the form of a spray and is there mixed with air and ignited by means of an electric spark, producing an explosion that moves the piston. When starting the engine, the clutch is released and the engine is rotated by pulling over the flywheel until it has received the first impulse, which usually requires from one to two complete turns. After receiving the first explosion, the engine continues to operate, drawing in a supply of gasoline and air and igniting it with an electric spark. When operating the hoisting drum, the engineer first speeds up the engine and then throws the clutch that controls the hoisting drum. Drums must be well equipped with a powerful brake in the use of either gasoline or electric hoists, to avoid accident due to the possible failure of the power. Hydraulic Hoisting Engines.-Hoisting engines using the direct energy of falling water as a source of power, while not infrequently employed in metalmining districts, are not known in the coal fields. Electric Hoisting Engines.-Electric hoists differ but slightly in mechanical construction from those operated by steam. Owing to the high speed of the ordinary motor, electric hoists are commonly double geared. The reduction between the armature shaft and the intermediate shaft is ordinarily about 1 to 4; between the intermediate shaft and the drum gear it varies according to the size of the drum and the hoisting speed desired. Motors for heavy hoisting may be either of the alternating-current induction type or of the direct-current type. Alternating-current induction motors are discussed under the subject of Electricity with further notes under Haulage. When large direct-current motors are used at a distance from the power station, the power is transmitted by alternating current to the point of its application and is there transformed to direct current, usually by means of motor-generators. The getting up of full speed (acceleration) and maximum load (coal and weight of entire rope) produce what is known as a peak, or high point, in the curve diagramming the power required from a hoisting engine; and the peak load is often double the average load upon the engines. In electric hoisting as the heating of the machines varies approximately as the square of the load it is important in order to reduce the size (and consequently the cost of the equipment) to make the load during the hoisting period as uniform as possible. The partial equalization of the load is accomplished through the use of some system of balanced hoisting, such as the Koepe described later. These systems, however, do not perfectly balance the load during all portions of the run, and various methods have been employed to produce what may be called an electric balance so that the input of electric energy may at all times be equal to the output of mechanical energy. In the Ilgner system, shown in diagram in Fig. 1, a motor-generator set is used for supplying power to the hoist motor, which is of the shunt-wound direct-current type. The operation of the hoist is controlled by varying the voltage of the generator, to which it is directly connected electrically. By reversing the excitation of the generator, the direction of rotation of the motor is also reversed. A flywheel is connected with the motor-generator set and arrangements are made to automatically vary the speed of the set so that during peak-load periods the speed of the set is decreased, and part of the energy in the flywheel is used to assist the motor in driving the generator. |