It is possible to dispense with the guide rail h by attaching a flange to the top of a at the back, to slide on the main guide k. This flange should be shorter than the shoe on b. The main guide is cut away at the point where this flange comes when the wheel g enters the curved guide j, leaving an opening just large enough to allow the flange on a to pass through. The shoe on b, being longer, completely spans the space and cannot pass through, but makes b move straight up on the main guides.
The bottom of the cage in [Fig. 11] has an interrupted track, and at the bottom of the shaft the track is also interrupted, as shown in the plan at the bottom of the figure, but in such a way that when the cage is resting at the bottom this portion of the track n projects up through the bottom of the cage and makes a continuous track. When the cage is raised the wheels of the car drop into the spaces n in the cage bottom, thus preventing the car from running off the cage during hoisting or dumping.
15. 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.
[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 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. 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.
These carriages are sometimes built to run on a slope track of the same gauge as the mine cars, but to insure stability they have generally a broader gauge. The headroom necessary is governed not so much by the form of the carriage as by the length of the car and the inclination of the seam. This height is less when the cars are placed on the carriage with their length across the slope than when they are run on lengthwise; but this arrangement increases the width of the slope. When the inclination is very steep, the wheels are sometimes placed on the sides of the carriage and above its center of gravity and run between two tracks or guides, on each side of the slope.
Fig. 13