Patent GB-853376-A (GB)
Title: Improvements in devices for boring holes of large diameter in hard ground or rock
IPC: E21D1/06
Filed: 1959-02-17
Abstract: 853,376. Boring rock. NELD€S, N. T. Feb. 17, 1959 [Feb. 26, 1958], No. 5523/59. Class 85. Apparatus for boring large diameter holes in hard ground, e.g. rock, comprises a number of percussion drills 18 arranged to work on a substantially conical rock surface and mounted in a head 1 which is rotatable in a carrier 2 longitudinally displaceable relatively to a guide member- 3. The member 3 is locked to the wall of the borehole by clamps 6 which are thrust outwardly by hydraulic cylinders 5 supplied from a pump 4 or a pressure supply line. The head 1 is carried by a tubular shaft 51 rotated through gearing by a motor 24, and a concentric hollow shaft 8, driven by a motor 7, carries cams which drive the drills 18 through linkages 10. The drills are arranged with axes at an angle to the axis of the head, or some may be parallel thereto, and the lowest drill is skewed to produce a pilot hole 16 to receive a guide collar 23. If a pilot hole is drilled in advance in the rock to receive the collar 23, the bottom drill 18 may be omitted. The drills have chisel edges 54 which, in each cutting level, are arranged alternately at opposite angles to radial lines, so that the cutting lines cross one another. The shanks 55 are each secured to a rod 12 carrying a spring- case 12a which is kept floating in the casing 14 by springs 15. The impacts imparted to the rod 11 by the linkage 10 are transmitted to the chisel through springs 13, the springs 15 being such that the natural frequency of oscillation of the system 12, 13 is equal to or somewhat lower than the frequency imparted to the rod 11. The casings 14 are rigidly secured to the head 1, except that the upper casings are retractable by springs 20 to permit the apparatus to be withdrawn from the hole, and are thrust forward automatically when boring restarts by hydraulic cylinders 22 supplied from a pressure line or from a pump 21. The carrier 2 and head 1 are supported from the guide 3 by hydraulic cylinders 25 which bleed, past a valve 28 to a tank 27, to allow the drill head to feed into the rock. When the end of the feed motor is reached, the clamps 6 are released allowing the guide 3 to fall, the fluid being returned to the cylinders 25 past valve 30, the guide is again clamped to the rock walls and drilling proceeds. A hoist rope 26 is provided, and water is supplied to a ring-spray at the top of the casing 3, the rock chips and water being extracted by a pump 33 through a suction pipe 34, pipe 36 passing through the shaft 8, pipe 35 and discharge pipe 37. Rollers 38, 39 on the members 2, 3 facilitate movement in the borehole, and, if the apparatus is used for horizontal or slightly inclined holes, the rollers may be driven and the cylinders 25 may be double-acting. Deviations of the borer from the intended line may be indicated by a pendulum in the carrier 2, which sweeps over electric contacts, and the deviation is corrected by a modified arrangement of clamps 6, viz, three vertically spaced pairs the supply of pressure fluid to which is varied according to the indicated deviation. In starting the drilling a pilot hole 16 is first produced, either independently, or by centering the present apparatus by a removable guide plate attached to the rock and the body of the apparatus may be temporarily steadied by a framework having guides for the rollers 38, 39.