Page:Popular Science Monthly Volume 90.djvu/94

 A Mechanical Rock- Worm

This apparatus gnaws its way through soHd rock, using neither drill nor dynamite

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���FOR the past fifteen years inventors have been developing a rock-tunneling machine that could bore its way through hard rock more quickly, cheaply and safely than the rock drill and dynamite. At the present time one of these machines, developed by Oliver O. App, is demon- strating its possibilities in the subway excavation under the Grand Central Terminal, in New York city.

It is designed to cut away the rock by the action of a number of pneumatic hammers, fitted '^iR n

with chisels, which turn on a longitudinal axis. It represents a dis- tinct improve- ment over for- mer apparatus of its kind in the character of the cutting and the action of the hammers. When a chisel is not bearing

against the rock, the hammer does not act. But as soon as the tool contacts firmly with the rock face the hammer operates.

The harder the rock the more air is sup- plied automatically. If the rock is soft, less air is applied; if sufficiently soft, the hammer is inactive, and the rock or dirt is cleaved off by the rotation of the tool. In short, the blow delivered is proportional to the hardness of the rock to be cut.

Until this cooperation between chisel and hammer was obtained, the tunneling ma- chine was not a success. Even in its present stage of development it is doubtful if it represents an improvement over the rock drill and blast method. In tunneling through soft rock and dirt it is, obviously, a great improvement over all existing ap- paratus. But when it is working in hard New York gneiss, for instance, the spokes- men for the rock drill and blast method say their way is safer and cheaper. In three eight-hour shifts in which the total operat- ing time was thirteen hours, the machine made an advance of nearly nine feet. The pneumatic rock drill has better records than that to its credit. It remains for the

��future to determme whether or not the machine will supersede the rock drill.

The carriage of the machine consists of a two-wheel main truck at the rear and a two-wheel guide truck at the front. The wheels, rest on a light track of standard gage. The front and rear halves are sepa- rate. The front, carrying the revolving head, is moved forward one inch per revolu- tion, by means of two lead-screws. After the front has advanced two or three feet

the rear is moved

ROD FOR CONTROLLING AIR SUPPLY TO PISTON

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��Detail showing the component parts of the hammer and chisel element

��Up by means of gearing.

The head, which supports the tool carrier, consists of a hub and four arms placed ninety degrees apart. Two arms carry four hammers each ; on each of the other two arms are three fourteen hammers are the chisels cut in

��hammers. These so arranged that concentric circles.

The power to operate the machine is furnished by a compressed-air engine located on the forward part of the carriage. A spray of air and water falls over the face of the rock to lay the dust. The broken rock is delivered on a belt conveyer that "discharges into muck cars at the rear.

The hammer and chisel element, which is illustrated herewith, is a new design. In one of the old rock-cutting machines a three-inch cylinder, with piston, valves, and springs at each end of the cylinder, was tried. In the present machine a four- inch valveless cylinder carrying a thirty- two-pound hammer twelve inches long is used. The hammer is reciprocated by the action of compressed air, the distribution of which is effected entirely by the passing of the hammer over ports in the cylinder wall, there being no distributing valves whatever. The hammer strikes a steel chisel-holder, into which the chisel is firmly inserted. Oil for lubrication enters the cylinders with the air.

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