TRACTION IN MINING
In recent years electric traction engines for use in mines have been rapidly replacing horse-and mule-power, and have become important economic factors in mining operations. The pioneer of this type of locomotive seems to have been one built by Mr. W. M. Schlessinger for one of the collieries of the Pennsylvania Railroad about 1882, and which has remained in active use ever since. The total weight of this locomotive was five tons and it was equipped with thirty-two horse-power electric motors. The current was supplied through a trolley pole which took the current from a T-shaped rail placed above and at one side of the track. The train hauled by this locomotive consisted of fifteen cars, carrying from two to three tons of coal each.
Following this first mining-locomotive a great number were quickly produced. In Pennsylvania alone something like four hundred are now in use, and in Illinois two million tons of coal were hauled in this manner in twelve mines in 1901. It was estimated at the beginning of the present century that some 3,000 electric locomotives specially built for mining were in use in the United States alone.
The earlier types of mining-locomotives were much higher and bulkier than those of more recent construction, the motors being mounted above the trucks and geared downward. Very soon, however, the "turtle-back" or "terrapin-back" type was developed, with the motors brought close to the ground, so that even quite a heavy locomotive might not be much higher than the diameter of its driving-wheels. When these queer-looking machines were boxed in so that even the wheels were covered, they lost all resemblance to locomotives or vehicles of any kind, appearing like low, rectangular metal boxes placed upon the car tracks, that glided along the rails in some mysterious manner. The presence of the trolley pole helped to dispel this illusion, but in some instances this is wanting, the power being taken from a third rail.
With these locomotives, some of them not more than two and a half feet high, it was possible to haul trains even in very low and narrow passages—much lower, in fact, than could be entered by the little mules used in former years. This in itself was revolutionary in its effects, as many thin veins were thus made workable.
This type of low locomotive is the one that has come into general use throughout the world. Such locomotives range in size from two to twenty tons, with wheel gauges from a foot and a half wide to the standard railway gauge of four feet, eight and a half inches. Locomotives weighing more than twenty tons are not in general use on account of the small size of the mine entrances.
In the ordinary types the motorman sits in front, controlling the locomotive with levers and mechanical brakes placed within easy reach, but sunk as low as possible. As a rule, the motors are geared to the truck axles, either inside or outside the locomotive frame. An overhead copper wire supplies the current by contact with a grooved trolley wheel mounted on the end of the regulation trolley pole. An electric headlight is used, and the ordinary speed attained by the compact motors is from six to ten miles an hour.
The amount of work that can be performed by one of these little, flat, box-like locomotives is entirely out of proportion to its size. A 10-ton locomotive in a Pennsylvania mine hauled about 150,000 tons of coal in a year at a cost of less than one-tenth of a cent per ton for repairs. The usual train was made up of thirty-five cars, each loaded with about 3,700 pounds of coal, which was hauled up a three-per-cent grade. The cost of such haulage was only about 2.76 cents per ton, as against 7.15 cents when hauled by mule-power. These figures may be considered representative, as other mines show similar results.
THE LOCOMOTIVE "PUFFING BILLY" AND A MODERN COLLIERY TROLLEY.
This locomotive was constructed in 1813 at Wylam Colliery, England, by William Hedley. It was entirely successful, and was in operation for almost half a century, up to the time of its removal in 1862 to the South Kensington Museum. The vertical cylinders and arrangement of walking beams for transmitting power are particularly interesting. The power was transmitted through cogged wheels to the rear axle, as is done with modern automobiles.
A particular advantage has been gained by the use of electric locomotives over older methods in the process of "gathering" the cars. In many coal mines, even when the main hauling is done by electricity, the gathering or collecting of cars from the working faces of the rooms was formerly done either by mule-power or by hand. In some low-veined mines, hand power alone was used, on account of the low roof.
In such places, low, compressed-air locomotives were sometimes used; but these were very expensive. These have now been very generally replaced by "turtle-back" electric locomotives, operated at a distance from the main trolley wire by means of long, flexible cables, so geared that they can be paid out or coiled as desired.
On the main line these locomotives take the current from the trolley wire by means of the trolley pole, but when the place for gathering is reached, the connection is made by means of the flexible cable, and the trolley pole fastened down so as not to be in the way. This allows the locomotive to push the little cars into the rooms far removed from the main line, with passages too low and narrow to allow the use of the trolley pole. By the time the last cars have been delivered the first cars of the train have been filled, and the process of gathering may be begun at once, and the loaded train made up for the return trip. With such a locomotive two men can distribute and gather up from one hundred to one hundred and twenty cars in an ordinary eight-hour working-day, hauling from three hundred to three hundred and fifty tons of coal.
In certain regions, a system of third-rail current-supply is used, this rail being also a tooth rail with which a cog on the locomotive works frictionally. For climbing steep grades this system of cogged rails has many advantages over other systems.
Another type of electric locomotive used in some mines is a self-propelling or automobile one equipped with storage batteries. Such locomotives do away with the inconvenience and dangers of contact rails or trolley wires, but are heavy and expensive. A compromise locomotive, particularly useful for gathering, is one equipped with both trolley pole and storage batteries. This locomotive is so made that the storage batteries are charged while it is running with the trolley connection, so that no time is lost in the charging process. Such locomotives have been found very satisfactory for many purposes, and but for the imperfections common to all storage batteries would be ideal in many ways. They can be worked over any improvised track, regardless of distance, which is an advantage over the flexible-cable system where distances are limited by the length of cable; and the first cost of the battery is no more than the outlay on trolley wires and supports. It is also claimed that the cost of maintenance is relatively low, but it is doubtful if it equals the trolley or third-rail systems in this respect.
Closely allied to the systems of traction by electric locomotives, is the modern electric telpherage system. Until quite recently the haulage of ores and other raw materials used in mining, when done aerially, has been by means of travelling rope or cable. When distances to be travelled in this manner are short, such as across streams or valleys, where no supports are used, the term "cableway" is generally applied; but where the distance is so long that supports are necessary, the term "tramway cable" is used. It is to these longer systems that electric telpherage is particularly applicable.
The advantage of such an electric system over the older method is the same as the advantages of the trolley road over the cable, all ropes and cables being stationary, the electric motor, or "telpher," travelling along on one cable and taking its current by means of a trolley pole from a wire above. For heavier work metal rails supported between posts are employed in place of a flexible cable, and over such systems loads of several tons can be hauled.
Such an electric telpher system is used in one of the Cuban limestone quarries, the telpher and cars travelling a long distance upon cables, except at some of the curves, where solid rails are substituted, hauling a load of a thousand pounds at a speed of from twelve to fifteen miles an hour. The current comes from a distant source, and the telpher is so arranged that it travels automatically when the current is turned on, stopping when the current is cut off. This is quite a common arrangement for smaller telphers, but in the larger ones a man travels with the telpher and load, controlling the train just as in the case of the ordinary trolley system.
The various processes of hoisting in mines by electricity is closely akin to that of traction, since, after all, "an elevator is virtually a railway with a 100-per-cent grade." As such work is done spasmodically, long periods of rest intervening between actual periods of work, a great deal of energy is wasted by steam hoisting engines, where a certain pressure of steam in the boiler must be maintained at all times. For this reason electrical energy for hoisting has come rapidly into popularity in recent years. "The throttling of steam to control speed," said Mr. F. O. Blackwell in addressing the American Institute of Mining Engineers, "the necessity for reversing the engine, the variation in steam pressure, the absence of condensing apparatus, the cooling and large clearance of cylinders, and the condensation and leakage of steam pipes when doing no work, are all against the steam hoisting engine. One of the largest hoisting engines in the world was recently tested and found to take sixty pounds of steam per indicated horse-power per hour. The electric motor, on the other hand, is ideal for intermittent work. It wastes absolutely no energy when at rest, there being no leakage or condensation. Its efficiency is high, from one-quarter load to twice full load."
There seems to be practically no difference as far as the element of danger is concerned between steam and electric hoists. The difference is largely one of economy. The importance of this is shown by the recent comparisons in a gold mine which has replaced its steam apparatus by electricity. In this mine the hoist moves through the shaft at a rate of over twelve hundred feet per minute, elevating five hundred tons of ore daily on double-decked cages. It is estimated that this system shows an efficiency of 75 per cent, taking into account losses of all kinds, with a resulting reduction of cost of from seven to twenty dollars per horse-power per month.
Results comparing very favorably with these have been obtained also in some of the mines in Germany and Bohemia, where electricity has been introduced extensively in mining. In one of these mines the daily hoisting capacity is twenty-seven hundred tons from a depth of over sixteen hundred feet, at a speed of over fifty-two feet per second. In the Comstock mine, at Virginia City, Nev., electric hoists are used which obtain their power from a plant situated on the Truchee River thirty-two miles away.