|
MINING IN CALIFORNIA AND NEVADA.
|
25
|
||
|
|
|||
|
spindle
6 feet to outer rim, or periphery. All the appurtenances are
constructed with a view of doing a very large amount of work in a
short time; and as the companies generally enter into contracts with
the crushing mills for the supply of regular quantities of ore per
diem, some such precautions are essentially necessary. The " cables "
or flat steel ropes used there are of various sizes ; for instance,
that at the pump-shaft, for special use by the sinkers in the
combination shaft of the Virginia and California companies, Comstock,
measures but 4 inches by ^ inch, whilst the two winding ropes in their
respective shafts are 5 inches by f inch. The average amount of work of
these three winding drums amounts to 800 tons lifted in 24 hours from a
depth of 1,500 feet, but as many as 445 "cars," or trucks, weighing
1,900 lbs. each, have been landed in eight hours at the pit's mouth.
These steel cables are not only flat, but they also " taper" from their
centre to the ends, on account of the ever-varying weight of that cable
end which is deepest in the shaft. For instance, in a shaft 2,000
feet deep, a steel cable of the kind described weighs about 53 cnt.,
which, if 10 cwt. is deducted for the distance between the engine,
sheaves, and mouth of shaft, leaves 43 cwt. in the shaft; this
weight changes continually, so that when the bottom cage reaches the
surface the weight of rope will be reversed. During the first part of
the winding the power much exceeds that required half-way up, and at
the latter end the engines have actually to be "braked" in order to
meet the increasing and more than counterbalancing weight of the
descending cage and longer rope together. What strikes one as most
unusual, was the extreme care which the mine superintendents generally
bestowed on these wire ropes, and the observation of these officials,
that " they (the ropes) formed the only link by means of which many valuable lives could hope to see daylight again," appears very appropriate under the circumstances. All these ropes are stored in a drying shed, after each rope had run "four months" over
the sheaves; they are then, taken off, cleaned, and carefully repaired
wherever necessary, and finally they are given a good coat of coal tar
mixed with asphaltum warmed to liquidity. After that, they are rolled
upon wooden spiders, and allowed to dry for the next eight months,
during which frequent examinations are made to see whether they show
signs of rust, whereupon they are again cleaned and coated as before;
thus each rope is used but four months out of twelve.
Each
drum is geared with an indicator to show the position of the cages in
the shaft; this is effected by keying a small bevel wheel on the end of
the winding shaft, or next to the clutch and close to the spiders,
which works another wheel at right angles, also keyed on the bottom end
of a vertical shaft 20 feet in height, 3 inches thick, with three
square threads cut into it to the inch vertical; this screw grips into
two kinds of hands at each side of the main screw, and as this screw
exhibits 15 feet for every inch, the total depth, and over, of the
shaft is covered, and these hands show very correctly what the position
the cages are in, by their being either raised or depressed, so that
the index provided and divided into feet, as painted in large figures,
forms a correct guide for the driver.
SAFETY CATCHES AND SAFETY HOOKS.
All
the cages in California and Nevada are provided with some kind of
safety gear; in the underlay shafts this appears, however, unnecessary,
because the miners are lowered and raised by means of a separate
carriage (giraffe) of considerable capacity, holding as many as sixteen
D
|
|||
|
|
|||