In the accompanying illustration, we present to our readers a mammoth
excavator, built by the Osgood Dredge Company of Albany, N.Y., for the
Pacific Guano Company of California, for uncovering their phosphate
deposits on Chisholm Island, South Colombia.
[Illustration: THE OSGOOD MAMMOTH EXCAVATOR.]
In order to bring out more clearly the principal problem involved in the
construction of this machine, we shall state first the proposed method of
its operation. This is as follows, viz.: The excavator is to dig a trench
thirty feet wide, down to the phosphate rock, and the entire length of the
bed--about one quarter of a mile--dumping the earth of the first cut to
one side. The phosphate is taken out behind the excavator. On reaching the
end of the bed, the excavator is reversed and starts back, making a second
cut thirty feet wide, and dumping now into the cut from which the
phosphate has just been removed. In this way the entire bed is traversed,
the excavator turning over the earth in great furrows thirty feet wide,
and giving an opportunity to simultaneously get out all the phosphate.
As will be seen, the main problem presented was to turn the car around at
each end of the cut in a very limited space. To accomplish this, the car
is mounted on a fixed axle at each end and on a truck under its center of
gravity; this is somewhat forward of the geometrical center of the car.
The frame of the truck is circular, thirteen feet in diameter, made of I
beams curved to shape. The circle carries a track, on which a ring of
coned rollers revolves, which in turn supports the car. By pulling out the
track from under both ends of the car, the whole weight is balanced on
this central turntable truck, thus admitting of the car being turned, end
for end, within its own length. This method of turning the car, and the
size of the machine, are the principal features.
The car is 40' × 13', with arched truss sides. The track is seven feet
gauge, the spread between tracks 20 feet, the height of the A frame 38
feet, length of boom 40 feet, swinging in a circle of 30 feet radius, and
through two-thirds of the entire circle. It has a steel dipper of 46 cubic
feet capacity, 1 inch steel chains, 10" × 12" double cylinder hoisting
engine, and 6¼" × 8" double cylinder reversible crowding engine. The
drums are fitted with friction clutches. Owing to the great distance at
which the dipper is handled, its size is reduced, and because it swings on
the arc of so large a circle the capacity of this machine is only one-half
of that of the No. 1 excavator built by the Osgood Dredge Company.
Nevertheless it will do the work of from 75 to 100 men, since its capacity
is from 800 to 1,000 cubic yards per day, the amount of rock _uncovered_
depending, of course, upon the depth of earth overlying it. The excavator
will dump 30 feet from the center line of the car, and 26 feet above the
track, which is laid on the rock. Total weight about fifty tons. The crew
required for its operation consists of 1 engineer, 1 fireman, 1 craneman,
and 4 to 5 pit men to tend jacks, move track, etc.
In the illustration the boiler connections are omitted, also the housing
for the protection of the crew. The design is characterized by the evident
care which has been bestowed upon securing simplicity and
durability.--_American Engineer._
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