=14.= A =dumping cage= is a cage so constructed that at the proper
place it can be automatically tipped sufficiently to dump the contents
of a car that is on it and will then right itself for the down trip,
thus avoiding the necessity of removing the car from the cage, and
saving time at the head. The construction of the cage is such that
the car is held firmly in place while dumping. The principle of the
self-dumping cage is illustrated in Fig. 11, the cage being shown in
its highest and lowest positions. The cage is made in two parts _a_ and
_b_. The fixed frames _b_ slide on the guides _k_ and have attached
to them the safety catches and hoisting gear. The movable part _a_ is
united to the frame _b_ by the hinge _c_. The platform _d_, on which
the car rests, is fastened to the movable part _a_ by the support _e_
and further secured by the braces _f_. At the top of _a_ is attached
the wheel _g_ that runs along the rail _h_, keeping _a_ in an upright
position until it reaches the dumping place _i_. Here the rail _h_
is bent as shown and the wheel _g_ is made to follow it by means of
the guide _j_. This throws the top of _a_ over so as to incline the
platform and dump the car that is on it. On lowering, the cage rights
itself when _g_ passes below the point _i_. The part _b_ is kept in a
vertical position by means of shoes that slide on the main guides _k_.
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.
[Illustration: 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.
[Illustration: FIG. 13]
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.