=8.= A =cage= is a carriage used for hoisting mine cars and their
contents, men, timber, etc., in both vertical and inclined shafts.
Cages are built of wood strengthened with iron or steel, or entirely of
iron or steel.
[Illustration: FIG. 6]
=9.= The cage shown in Fig. 6 is much used in the anthracite region of
Pennsylvania. It is made largely of oak strengthened with iron and the
size varies to suit the shaft, being sometimes as large as 6 feet wide
by 12 feet long. The general construction of the cage is evident from
the figure, but several appliances that should be common to all cages
in some form or other require detailed explanation.
A covering _a_, called a =bonnet=, protects persons on the cage from
objects falling down the shaft, and is required by law in some States.
This bonnet is made of steel plate with flanges or angle irons to
stiffen it, and is usually inclined. To prevent objects of moderate
size from wedging between the edge of the bonnet and the shaft lining,
the former is sometimes made shorter than the cage, so that a space of
about a foot is left between its lower edge and the shaft lining. A
short bonnet of this character does not, however, fully protect persons
on the cage. The upper part of the bonnet is fastened to the upper
cross-bar of the cage by two hinges and is held up by rods _b_ that are
attached to the bonnet and have sockets at their lower ends, which fit
over pins bolted to the uprights of the cage. By raising the rods from
the pins the bonnet can be lowered so that pipes or long timbers may be
lowered on the cage.
=10. Safety catches= are intended to prevent a cage falling in case
the hoisting rope breaks. A common form, shown at _c_, Fig. 6, and
in detail in Fig. 7, consists of a pair of toothed cams _j_, Fig. 7,
fastened on each side of the cage near the shaft guides. The drawbar
_b_ to which the rope is attached extends through the top cross-piece
of the cage and through the cylinder _d_, at the bottom of which is
a plate _c_ supplied with lugs for the rods _f_ that connect it with
the levers _g_. Inside the cylinder are three powerful rubber springs,
which are in compression so long as the cage hangs from the rope, but
are extended if the rope breaks, drawing the rods _f_ down and with
them the ends of the levers _g_ to which they are attached; and, since
the levers are pivoted, their other ends are moved upwards and with
them the rods _k_. The cams _j_ are each attached to one end of the
rods _k_ in such a manner that as the rods move upwards they rotate the
cams inwards until they come in contact with the shaft guides. The
teeth of the cams grasp the wooden shaft guides and stop the descent
of the cage. The cams are provided with projections _a_ and _l_ that
strike the guide and thus prevent the cams turning entirely around.
Fig. 7 (_a_) shows the springs extended and the dogs _j_ just about
to grasp the shaft guides, while Fig. 7 (_c_) shows the position of
the dogs when the springs are compressed as they are when hoisting.
At _e_ in cylinder _d_, Fig. 7 (_b_), there are slots for the lugs of
plate _c_ to move up and down as the spring is compressed or extended.
Instead of rubber springs, helical steel springs are sometimes used,
and with a somewhat different design flat steel springs are used.
[Illustration: (_a_) (_b_) (_c_)