“ FLAT ROPE REELS
20. To overcome the objections to conical and cylindrical drums, several other systems of hoisting have been tried, among them being one that uses a reel, Fig. 12, and a flat rope. The hub a is increased in diameter, above what is necessary for strength, to such a size as is suitable to wind the rope on. It is then cored out from the inside, so as not to contain too great a mass of metal.
Fig. 12
The arms b of the reel extend radially from the hub to confine the rope laterally when it is all wound on the drum. ”

“ A certain amount of motion is required to free the brake band from the drum, when the brake is off; this, then, limits the leverage that a man can use. Suppose, for instance, that with a strap brake the band moves from the drum 1⁄2 inch, thus increasing the diameter 1 inch, or the circumference about 3 inches. Then, supposing that a man can exert his force to advantage through 3 feet, or 36 inches, the available leverage is 36/3 = 12. That is, if a man can pull 50 pounds [Pg 40] on his hand lever, he can exert 50 × 12 = 600 pounds circumferentially on the brake band, with simple levers. ”

“ Some method must be provided for communicating between the bottom or any level of a shaft and the top landing or the engine room, also between the top landing and the engine room, so that the hoisting engineer may be notified when both the head-man and foot-man are ready for him to hoist. A common method of signaling is by means of a gong, bell, or triangle placed in the engine room and connected by a wire or small wire-rope with the point from which it is desired to signal. ”

“ Slope, or Inclined-Shaft, Hoisting.—In a slope, or inclined shaft, the mine cars are attached directly to the hoisting rope and hoisted singly or in trains for inclinations less than 35°, at which inclination the material will begin to fall from the top of the car. For steeper slopes, it is customary to use a slope cage or carriage on which the mine car is hoisted, or else to dump one or more cars of the material into a gunboat, or skip, at the bottom of the slope or at some landing along the slope, and to then hoist the gunboat, or skip. ”

“ Skips are self-dumping cars used for hoisting material from shafts or slopes. In a vertical shaft, they run in guide tracks; but in a slope they have wheels and run on a track like a car. In the anthracite region of Pennsylvania, skips are called gunboats.
As the skip is not detached from the hoisting rope, time is saved at the top over that needed to unhook and hook the cars to the rope or to remove and place the cars on the cage. ”

“ The objections to them are that they are liable to get out of order, and that in general the use of any automatic device that tends to relieve the hoisting engineer of responsibility and constant attention to his engine is not to be commended. A hoisting engineer, however, depends for his stopping point mainly on a mark made on the rope, or on the drum, or on both, and uses an indicator mostly as a guide for the position of the cage during the hoist. ”

“ On an iron drum without grooves, the rope will chafe sidewise; and furthermore if the rope winds on a hard flat surface it bears here and there on a single wire and tends to flatten, causing internal wear between the wires; while, in the case of a rope winding in a groove, it is supported on about one-quarter of its circumference, bringing many more wires to bear on the drum and dividing the pressure between them. A wooden-lagged drum causes less [Pg 8] wear on a rope than an ungrooved iron-shell drum, as grooves are gradually worn in the lagging, but is not so good as a grooved iron drum. ”

“ The net moment that the engine must overcome is the sum of the weight of the material to be hoisted, weight of the cage and car at a, and the weight of the rope attached to a, multiplied by the small radius r of the drum, minus the weight of the car and cage at b, multiplied by the large radius R of the drum. ”

“ With such loose-running drums, the engine generally runs only in the direction required to hoist the load, while the cage is lowered entirely by means of the brake. In this way, one engine provided with several drums may be used for hoisting from several shafts or from several levels in the same shaft at the same time. Such a loose-running drum is connected to the engine shaft when a load is to be hoisted by means of a clutch, of which there are two forms commonly used for hoisting machinery: jaw or piston clutches and friction clutches.
Fig. 17
32. ”

“ Such large reels are easier on the rope but require large engines, as hoisting in balance is used to only a slight extent. The large reel is easy on the rope, both from the fact that it bends the rope but little and also gives less pressure on the bottom wraps, as each wrap adds to the pressure. These reels are driven by means of plain jaw or friction clutches.
The wear of a flat rope is excessive and the rope itself costs more than a round rope of the same strength, does not last as long, and requires more care and attention. ”

“ Fortunately for the utility of safety catches, ropes are usually broken while a loaded cage is being raised, and the cage has an upward momentum; if a rope breaks when the cage is descending at a speed of 30 or 40 feet a second, its momentum is so great that either the catches or guides break. The catches generally hold and either the guides or cage suffer more or less injury under such circumstances. Instead of being placed near the top of the cage the dogs are frequently placed near the center, or near the bottom ”

“ Skip Cage.—Where a self-dumping skip is to be used in a vertical or highly inclined shaft and it is desired to use safety catches, the skip a is mounted in a cage or frame b, Fig. 21, similar to the self-dumping cage, Fig. 11. The skip being pivoted at c one side of the center, and resting on the frame of the cage, tends to remain upright until it reaches the dump; but for safety it is sometimes locked in place by the latch d, which hooks over the pin e. When near the top, the roller f on the end of the latch d comes in contact with a bar that depresses the roller and thus unhooks the latch. ”

“ Again, it is held that the surest prevention of overwinding is obtained by the employment of a sober, reliable, and competent engineer, who is held personally [Pg 48] responsible for overwinding accidents; by having a good brake and an engine thoroughly under the control of the engineer; by a reliable method of indicating the position of the cage; by sufficient height to head-sheaves to allow of considerable hoisting over and above that necessary for landing. ”

“ Steel frames are generally built by the structural steel companies from detailed plans and designs furnished by the mining company, or from a skeleton diagram furnished by the mining company, giving the loads on the rope and the general conditions about the shaft to which the frame must conform, the frame being then designed and erected in detail by the steel company. ”

“ To maintain a certain average speed of hoisting, the speed toward the end of the hoist is of necessity higher than the average and comes at a time when a slowing up should be taking place, so that more care must be exercised when making the landing. To prevent the rope from being drawn out of the grooves, the latter must be made deep and with a large pitch, thereby increasing the width of the face or length of the drum. ”

“ In hoisting in balance from deep shafts with cylindrical drums, if no tail-rope is used, or in hoisting from a single shaft with an unbalanced cage, the hoisting engine is not loaded equally at different points of the hoist owing to the gradually changing weight of the unbalanced rope. ”

“ Guides are used in all vertical shafts of any considerable depth and in many highly inclined shafts to keep the cage from swinging about and striking the sides of the shaft. They are made of wooden rails, iron rails, or wire ropes. In American mines, timber guides predominate, although some iron ones are used, and for small shafts at ore mines wire-rope guides are common. ”

“ This serves to equalize the load due to the rope in the same manner as the conical drum. Two reels are generally put on the same shaft, and while one is hoisting from one compartment of the shaft the other is lowering into another compartment. The periphery of the hub where the rope winds should not be round but of gradually increasing radius, for if a flat rope be wrapped about a round hub the rope will have to abruptly mount itself at the end of the first revolution and so on for every revolution. ”

“ The clutch shown is built to run in the direction indicated by the arrow, but such clutches may be built to run in either direction; they should always be run in the direction for which they are designed, so that the load may always come on the fixed arm. If the band be tightened slowly, there will be no sudden start or jerk on the rope, as the slip of the band will prevent the entire force of the grip taking effect at once; and after the drum reaches full speed, there is little or no slipping of the driving-band. ”

“ A slope carriage is a frame so constructed that when rails are placed on the top and a mine car run on them the car will be practically horizontal. The carriage is mounted on wheels and axles in order to follow the slope tracks, and is supplied with a drawbar, or with hooks, as shown in Fig. 13, for attachment to the hoisting rope. ”

“ The form of the lever arm is immaterial so long as the differential principle is retained, that is, that the shorter arm yields when the longer pulls, when the brake is thrown into action. This principle is illustrated in Fig. 26. In this brake, no provision is made for anchoring either end of the brake strap, but the entire load is thrown on the lever arms a and b. These lever [Pg 39] arms are connected with the arm c, which revolves on the same shaft d and is operated by the reach rod e. The revolution of the drum is thus resisted by the shaft d. ”

“ In such a case, when the rope starts or stops quickly, as it usually does in modern hoisting plants, the heavier the sheave the more will it lag behind the rope and the greater will be the wear on the rope due to slipping. ”

“ At the end of the hoist, if the upper cage is allowed to rest on the keep, its weight and the weight of the tail-rope are taken from the hoisting rope, and there is then not enough pull on the hoisting rope to produce sufficient friction with the drum sheave to start the next hoist. ”

“ The Strap Brake.—A strap brake consists of a wrought-iron band or strap that partly encircles the drum and is connected at its free ends to levers with which the band may be tightened on the brake wheel and the drum thus firmly held. The iron or steel band either lies directly against the wooden lagging of the drum or on wooden blocks bolted to the drum ”

“ With steam or air power, the brake would be applied with its full force almost instantaneously, thus subjecting the various parts of the mechanism to very severe and objectionable strains, unless the valves were modified so as to regulate the admission of the steam or air. ”

“ Fig. 12 shows a cage for use in a slope or steeply inclined shaft. It is made of steel with timber platform and differs from a vertical shaft cage mainly in having its upper frame inclined and in running on four [Pg 15] wheels a, b. These wheels usually run on timber guides, so that the safety dogs c will take hold of the guide in case the rope breaks. For slopes of variable inclination, the platform d may be made adjustable by means of a hand lever so as to be always level.
Fig. 12
16. ”

“ The greater the arc of contact, the more securely is the drum held by the brake. A single strap is sometimes used, but this is only satisfactory with small drums, say 8 feet or less in diameter; on large drums two straps are generally used, each extending half way around the drum. The levers for transmitting the power from the hand lever or treadle to the brake strap are variously arranged. In some cases, the force is multiplied by several short levers; in others, by one long [Pg 35] lever. The treadle or foot-lever, however, has been replaced almost entirely by the hand lever.
Fig. 23 ”

“ The Heavy Steel Cage.—The cage that is shown in Fig. 8 is made of iron and steel except the wood flooring, which is laid in two courses, one lengthwise and one diagonal. The joints should not be driven too tightly, as the wood is likely to swell. The track is bolted to the floor, or deck, of the cage. The cast-steel safety dogs are operated by steel springs a, coiled about the bars b, [Pg 11] which are connected to the drawbar c by chains, as shown. The drawbar drops if the rope breaks and thus assists the action of the springs a. ”

“ Also, in cases of overwinding, the cage goes over the top of the frame without injury to the frame, and should men be overwound they would fall only the height of the frame instead of being crushed against the top. ”