The carriage, [Fig. 13], is for use on slopes of a uniform inclination. It is made almost entirely of heavy timber, is stiff and simple of construction, and is easy to repair. Its details will be readily understood from the illustrations, except perhaps, the device for locking the car to prevent its running off during the hoist. The middle portion of the platform a having a piece of the car track on it, may move vertically up or down. As shown in the side elevation, it is resting on the horizontal timbers b of the carriage in a position ready for hoisting. At the end of the hoist, when the cage settles on the keeps c, shown in the end elevation, this platform reaches them first and is supported by them while the rest of the carriage descends still farther until the timbers d rest on the keeps also. The track on the platform a is then at the same level as that on d, and the car can be run off and replaced by another. When the empty car is on, the carriage is lifted from the keeps, but the platform a remains until the timbers b pick it up, when the keeps are swung back out of the way and the carriage is lowered.
Slope carriages usually have the tracks running crosswise so that the car is pushed on from the side instead of from the end.
SKIPS, OR GUNBOATS
17. 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. But since dumping the material into the skip and again on the surface produces considerable fine material, skips, or gunboats, are seldom used for any material, such as coal, that is often lessened in value by being broken. The skip, or gunboat, shown in [Fig. 14] is closed along the top a and open at the end b, which is cut at about the angle of the slope in which it is to be used, so as to remain practically level during the hoist. It is made of sheet iron, the bottom, sides, and top being stiffened by angle or T irons, and the back stiffened and protected by 3-inch planks, backed by 3" × 6" timbers. The wheels of a skip are fixed on the axles, which run in journal boxes, thus insuring smoother running than is obtained with loose wheels. The details of the journal bearings, as shown in [Fig. 15], consist of three castings, the bracket a, which is bolted or riveted to the gunboat, a pivot casting b, and the bearing proper c. The bearing c rests on the axle and carries, by means of trunnions d, the pivot casting b, on the top of which is placed a rubber cushion e to lessen the shocks between the casting and the bracket.
Fig. 14
Fig. 15
18. Method of Loading Skips.—In [Fig. 16], a skip a is shown in a slope standing immediately below a level where a car b is ready to have its load dumped into the skip. Instead of dumping the mine car directly into the skip, a bin is frequently provided at the level station, or landing, into which the mine cars are dumped and from which the material is loaded into the skip through suitable chutes. The use of such bins makes the hoisting of material largely independent of the working conditions on the levels and the hoisting can be more systematically and satisfactorily carried on.