III. DRILLS DRIVEN BY HYDRAULIC PRESSURE.—The Brandt Drill operates through a hydraulic pressure of front 100 to 120 atmospheres, and pierces the hardest rocks after the manner of diamond rock-drills, but with the use of steel tools.
The drilling - tool, which is annular in form, is given a ro tary motion while be ing held firmly against the rock. The pressure of the tool against the latter re sults from the action of water compressed in a cylinder forming a continuation of the tool-carrier. In the interior of this cylin der there is a plunger which abuts against the column that serves as a support to the apparatus. A rotary motion is given the tool by a cog wheel keyed to the cylinder and actuated by a transverse endless screw set in motion by two small hydrometers placed on either side. The number of revolutions of the drill varies i from 5 to 12 per mm ute, according to the nature of the rock. In the hardest rocks the drilling is effected at the rate of 5 revolutions per minute, and allows of an advance of 4 millimetres per revolution be ing made. The drilling-machine proper consists of a cylinder and a piston (Fig. 17); the cylinder carrying the drill-rod. liy introducing water, under pressure, into the cylinder, the same, and with it the drill-bit, is pressed against the rock. The rotary motion of the drill is imparted by two small hydraulic engines, coupled together under 90°, with differential pistons, and fastened to either side of the cylinder. The valve-motion of these engines is so arranged that I he right-hand one steers the left-hand one. and vice versa. These engines turn a worm, and by it a worm-wheel. which is connected with the rear end of the cylindrical shell surrounding the pressure-cylinder. This shell carries at its farther end the drill-rod, rotates with the worm, and therefore causes the drill-bit to rotate also. The continuous advance of the drill is effected by the direct hydraulic pressure on the cylinder. The cleaning of the drill-hole is done by the water escaping from the hydraulic engine, and led through the hol low drill-rod to the bottom of the hole.
As further illustrating the principles of the Brandt drill, the following description is given, reference being had to the accompanying engravings :—Fig. 17 is a longitudinal section of the cylinder. with the piston and a cross-section of column. The back part of the cylinder is uninterruptedly connected with the pressure-water through the port a. Now, if pressure-water is admitted through b into the other part of the cylinder and the exit at c is closed, the cylin der and with it the drill-rod and hit is pressed forward by it pressure corresponding to differ ence of the :mets of the piston. With b shut and c open, the cylinder moves backward with a
pressure corresponding to the annular area of the piston. With b and e both closed, the cylin der remains stationary. Fig. 18 explains the principle of the small hydraulic engines, turning the drill. The working-piston is a differential piston. Tke fore part of the cylinder is con tinuously connected with the pressure-water through e. The distribution of the pressure water takes place only in the back part of the cylinder by means of a piston-valve. The water used runs off through a. Fig. 19 shows the accumulator. The pressure-water is admitted uninterruptedly into the cylinder through the port a. If the pumps deliver more water than used, the piston of the accumulator rises above the upper section of the cylinder, allow ing the water to escape through b. The weight is regulated by the addition of iron plates. The whole machine is supported by a column (Fig. 20). This is constructed after the principle of the hydraulic press, with dif ferential plunger-piston.
Diamond Prospecting Drills.— The late improvements in these drills relate chiefly to the feeding mechanism, of which two kinds are now in use, the differential and the hy draulic feed: 1, The differential feed. For this feed the machines have a shaft, 5 to 7 ft. in length, of heavy hydraulic tubing, with a deep screw cut on the outside. The shaft is feathered to the lower sleeve-gear. This is a double gear, connecting by its upper teeth with a beveled driving-gear, and by its lower teeth with the release-gear—a frictional gear at the bottom of the short feed-shaft. At the upper end of the feed-shaft another gear is feathered, con necting with an upper gent on the screw-shaft. This last gear is attached to the in the thread of which runs the screw of the screw-shaft, and as the gear of the feed-shaft has one or more teeth than that of the feed lint, the nut makes fewer revolittions in a given time than the screw-shaft. thus produc ing the differential feed, The frictional gear on the bottom of the feed-shaft combines with this a frictional feed, making the drill sensi tive to the eharacter of the rock through which it is passing, by maintaining, a uniform pressure. The severe and sudden strain upon the cutting points incidental to drilling through soft into hard rock with a positive feed is thus avoided.