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FIRE IN THE EARTH
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correctly-shaped spray of oil is delivered, it seems, and the
efficiency of the nozzle is not impaired by action of grit or acid in the oil, or by the high heat. Boring the hole in a diamond for a die or a nozzle, by the way, is an interesting process; a needle, impregnated with diamond dust, hammers away on the stone for about a week before the hole is bored. And this drilling operation costs seven times as much as the diamond itself!
To
get back to diamond core drills used by geologists and mining
engineers: The drill-bit is a hollow steel cylinder, the bottom of
which is studded with diamonds, to act as a "cutting edge." The bit is
screwed to the end of a long column of pipe and bores into the depths
of the earth when the pipe is revolved. As the bit goes downward, a
round core of rock rises inside the pipe and is held by a clip, so that
a sample of rock is obtainable every time the pipe is pulled out of the
hole. Geologists, testing the rocks for oil, coal, or other minerals,
thus have a complete record of the formations through which the drill
hole penetrates. These drills also are most valuable to civil
engineers, as we have seen. In sawing a stone a diamond-impregnated
blade has an average life of 2500 sawing hours (3-1/2 months, night and
day) working in granite or marble, before the diamonds must be reset.
In these machines, as in core-drills, the wearing action has little
effect on the diamond, but care must be taken that the steel setting
does not wear from around the stones, causing them to fall out and be
lost. Thus the diamonds are set as deeply and solidly in the steel as
possible.
Imports
of industrial diamonds to speed America's defense machinery reached a
new all-time high in 1940, according to figures of the Bureau of
Customs Statistics. More than 1676 pounds (3,801,834 carats) valued at
(244)
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