Hoisting Appliances

by International Correspondence Schools

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.

Fig. 16

Fig. 17

If the material comes to the slope as shown in [Fig. 17], it is necessary to let down a bridge a, on which the car runs, in order to reach the skip. After the car is dumped, the bridge is lifted out of the way into the dotted position, so as to leave the slope unobstructed.

19. Method of Dumping Skips. To dump a skip at the surface, the tracks are extended above the slope mouth, as shown in Figs. [18] and [19], and are arranged so that the material may be dumped directly into a bin or into cars as desired.

In the arrangement shown in [Fig. 18], the front wheel of the skip strikes a stop a and, since the bail of the skip is pivoted far down toward the lower end, as the rope continues to pull, the rear of the skip is raised and the material is dumped. The objection to this method is that if the rope is slightly overwound the skip is pulled off the track and does not then right itself on the track when the rope is released.

Fig. 18

In the Lake Superior iron and copper region, many of the dumps are built as shown in [Fig. 19]. In this dump, the rails of the main track a are curved as shown at b; a short distance back of the beginning of this curve, another track c begins outside the track a and runs in a straight line parallel to the inclination of the hoist. The track c is of a wider gauge than a, and the rear wheels of the skip have a wider tread than the front, so that they will run on c while the front wheels take the curved track until they strike the stop d. The rear of the skip will thus be raised and the material dumped. There are but two tracks in the main part of the slope.

Fig. 19

Fig. 20

Fig. 21

In the method illustrated in [Fig. 20], the rear and front wheels have the same tread, but the rear axle is longer than the front and has rollers a on each side. These strike the track b, and while the front wheels follow the curved track c these rollers run on the track b and thus raise the rear end of the skip.

20. 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. The roller g enters and travels along the guide rails h, tipping the skip. There are two rollers g, one on either side of the skip. The nose i is temporarily caught on the roller j, thus stopping the movement of the skip sidewise and away from the upright guide.