AERIAL TRAMWAY.

The aerial tramway is another type of cable transportation, which is more satisfactory than the overhead cableway. The following information concerning an aerial tramway in operation in Alabama. may be of interest:

A-inch endless steel cable travels on supports which keep it 15 to 30 feet above the ground. The rock is carried about 8,000 feet, the cable being about 16,000 feet long. It is driven by a 35-horsepower electric motor. The drivewheel, which is about 8 feet in diameter, is provided with automatic clamps which prevent slipping. The buckets have a capacity of about 1,000 pounds each. There are 70 buckets on the cable at one time, 35 full, traveling toward the cement. plant, and 35 empty, returning to the quarry. When an empty bucket reaches the quarry it is automatically unclamped from the cable and is suspended by the carrying device from a single-rail circular track, along which it is easily pulled by hand to a position beneath any one of six rock slides from the storage bin, where it is quickly filled. The loaded bucket is then pulled by hand around the track and is automatically clamped to the traveling cable. The cable makes one complete circuit in 36 minutes and delivers approximately 1 ton of rock per minute at the cement plant. The equipment has given satisfactory service for the past six years.

One important advantage of the aerial tramway system, well illustrated in the installation described, is the ease of conveying rock over hilly ground, thus avoiding excessive cost for grading. Where the cable passes over a hill the strain on it may be somewhat increased, but the power consumption is little, if any, larger than where no hill intervenes, for the buckets descending on one side of the hill balance those ascending on the opposite side.

At one Illinois plant, having a capacity of 4,500 barrels of cement a day, all the rock is transported across a river by aerial tramway. The method is satisfactory if the equipment is closely watched and all defects or weaknesses repaired without delay.

The rock for a New York plant is transported by aerial tramway a distance of 1 mile from the top of a high hill. There are 40 buckets on the line, each having a capacity of 1,300 pounds. The maximum capacity of the tramway is about 1,500 tons per day of 24 hours. Coal required at the quarry is carried in the tramway buckets that would otherwise return empty.

At another New York plant the rock is conveyed about 1,500 feet down a steep hill by aerial tramway. The buckets are of 900-pound capacity. The tramway carries, on an average, about 400 tons per day, although its maximum capacity is much greater.

MINE HOIST.

Where rock is obtained from shaft mines an ordinary mine hoist is employed. The loaded cars are usually hauled by horses or mules to the main shaft, placed in a cage, and hoisted to the surface.

QUARRY TRACKAGE,

LEVEL OR MODERATELY INCLINED TRACKS.

Quarry trackage is an important factor in rock transportation. Efficient rock handling depends largely on arrangement of track, elimination of heavy grades, firm roadbed, and uniform gage. As a rule, tracks are standard-gage width, although narrow gage is used in many places. In any event, the gage should be wide enough to insure reasonable stability of the cars in rough places.

An uneven quarry floor may require much grading, and makes tracklaying difficult. The problem of moving and laying track is greatly simplified if the quarry floor is smooth and uniform. In quarrying limestone beds that lie approximately flat, an open bedding plane at the quarry floor is a great advantage, for it provides the smooth floor desired.

The trackage system must be modified to suit conditions. Where steam-shovel loading is employed, the system is usually simple, as loading is conducted at only a limited number of places at one time. The larger the quarry the more complicated will be the track layout, and in quarries where eight or more shovels are used, a block system and tower-signal station may be employed.

Where rock is loaded by hand in large quarries many working places must be provided. A convenient system designed for hand loading in quarries having reasonably high faces with an ample supply of rock is that shown in figure 28 (p. 122). From a main line parallel with the face a series of branch lines extend to the face. One car is placed at the end of each branch, and usually two loaders are employed at each car. Loaded cars are collected by a locomotive from various branches in succession until enough cars to form a train are obtained. Empty cars are distributed to the various branches in a similar way.

For low-faced quarries with a limited supply of rock at each working place, the face is usually very long, and a branch to every working place would require an excessive amount of trackage. Therefore in such quarries the branch tracks usually are parallel with the face, as shown in figure 29. Several cars are placed on each branch and are loaded simultaneously.

In comparing the two methods it may be pointed out that where the branches parallel the face and a number of cars are loaded on each branch, some inconvenience may result from partly loaded cars being nearer to the main line than fully loaded cars. Then all the

cars on the branch may be taken to the main line, where the partly loaded cars are cut out and returned to the branch. Where the branches meet the face perpendicularly, conflict of loaded and empty or partly filled cars is avoided. On the other hand, as only one car is placed on each branch, more switching is required to collect a train of loaded cars or to distribute a train of empties. Where the branch lines parallel the face and three, four, or more cars are on each branch, the collection or distribution of cars is a relatively simple

matter.

A trackage system employed in an Alabama quarry consists of branch lines meeting the face perpendicularly and connected with a circular main line provided with a crossover dump. The cars are hauled by mules. Formerly the quarry cars were hauled up the incline to the crusher. By means of the crossover dump they are now dumped into cable cars of much larger capacity. This arrangement has increased greatly the haulage capacity of the cable incline and has materially reduced quarry costs and increased the output of rock.

FIGURE 29.-Track arrangement suitable for quarries with low face: a, Main line; b, branch lines; c. quarry face.

Where the hand-loading method is employed in quarries worked on several levels, the trackage is more complicated. An actual example of the complexity in track arrangement that may occur in a quarry worked on four levels is shown in figure 30. The obvious difficulty of transportation under such conditions should encourage the adoption of steam-shovel loading and the working of fewer benches, if circumstances would permit such readjustment.

In many quarries the cars are taken from the quarry by locomotive. Where the quarry has a fixed floor level, this system may be permanent, but where the quarry is gradually deepened the grades may become too steep for locomotives. In some quarries the desire to avoid the expense of introducing a cable incline system has led the operators to retain locomotive haulage on very steep grades. This may make it necessary to purchase additional locomotives, for the trains travel more slowly on heavy grades and are made up of fewer and fewer cars. The installation of a cable system would probably be better than to adhere to locomotive haulage on excessively heavy grades.

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Where there is sufficient room for the additional trackage required, a system of back switching may be employed to overcome heavy grades. The system occupies considerable space and involves the first cost and maintenance of relatively long stretches of track, but it permits the handling of a number of cars at a time. In the opinion of some quarrymen, back switching is preferable to cable inclines.

INCLINED TRACKS FOR CABLE CARS.

Where the gradient of the track exceeds that on which locomotives may be operated to advantage, a cable-and-drum system of haulage

FIGURE 30.-Complex trackage system in a quarry where rock is loaded by hand on four levels: a, Upper level; b, second level; c, third level; d, lower level.

is usually employed. Single tracks are used in many quarries. In some quarries cars are operated independently on two or more tracks. In others, a car is attached to each end of the cable, one descending as the other ascends, a double track, being provided, or a three-rail track above the center switch and a single track below.

On a single track where the load is carried down grade some source of power is required to return the empty car. By the three-rail or double-track system, where two cars are operated by the cable, the descending loaded car pulls up the empty car, and no power is required. Similarly, when transportation is up the incline, the descending empty car helps to draw up the loaded car. The only power re

quired is that needed to raise the actual weight of stone moved, plus the amount consumed by friction, whereas with the single-track system the additional power necessary to move the empty car is required. A considerable saving is, consequently, effected by utilizing the force of gravity, but up to the present time few quarry operators have taken advantage of it.

The "ground hog" or "barney" type of cable haulage is employed in several quarries. A heavy buffer, mounted on four wheels and attached to the cable, operates on a narrow-gage track situated between the rails of the car track. At some distance from the foot of the incline the narrow-gage track runs into a depression below the cartrack level. When the cable is out the buffer rests in this depression. The loaded cars pass along the track over this excavation. As the cable winds on the drum the buffer comes up behind the car and pushes it up the incline. Usually one car only is taken up at a time. One advantage of this method is that the inconvenience and danger of attaching the cable to loaded cars and unhooking it from empties is eliminated.

An endless chain system is used as a substitute for a cable in some places. Cars are pulled up the incline by projections arranged at regular intervals on the chain.

TRANSPORTATION FROM POINTS OUTSIDE MAIN QUARRY.

For most cement plants a minor proportion of the raw materials is obtained outside the main quarry. Thus, where limestone and shale are used the plant is usually situated near the limestone quarry, and the shale may be obtained elsewhere. Where cement rock is used, a small amount of high calcium limestone is commonly shipped from outside points.

In some places the shale quarry has its own car tracks and incline, its transportation system being independent of that maintained at the limestone quarry.

Where raw materials are thus obtained from two sources, the tracks and storage bins should be so arranged as to avoid excessive rehandling. A convenient means of handling rock brought from a distance was noted at an Oklahoma plant. The rock is conveyed in hopper-bottom cars and dumped into a trough that opens on a belt conveyor which carries it to storage.

An example of very inefficient handling of material was noted at one Pennsylvania plant. The cement rock, which was quarried close to the plant, required the addition of a small amount of high calcium limestone brought from a distance. The limestone was carried in hopper-bottom cars to a trestle above the quarry pit, which at this point was 40 or 50 feet deep. It was dumped into the pit, loaded into quarry cars by hand, and hauled by mule to the incline up which the