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|INTRODUCTION This chapter on underground rotary drills briefly describes the equipment features, selection or applica¬tion criteria, safety features, and relative costs of both face and roof drills. After a brief description of the basic components, the application, safety, and cost con¬siderations will be explored. ROTARY DRILL COMPONENTS As illustrated in Fig. 1, an underground rotary drill consists of five basic components. These components are the energy system, chassis, boom, feed assembly, and operator's station. Energy System The energy system of a typical underground drill con¬sists of an electric motor, driving a hydraulic pump or pumps. Usually, the drill is equipped with a cable reel to store the trailing power cable from the portable power center in the mine. A simple control box is supplied to house electrical switchgear and protective devices. In addition to the pump, the hydraulic portion of the energy system includes the hydraulic cylinders, hydraulic tram motors, relief valves, control valves, etc., necessary to actuate the various machine functions. Chassis The chassis provides the frame or support structure for the other four basic components of the drill. Fre¬quently, it incorporates an oil reservoir for the hydraulic system. The chasis provides the support for the trans¬mission, which drives rubber tires or, in the case of some foreign machines, the crawler tracks. The steering link¬age and steering tires also may be considered as parts of the chassis. Boom The boom is the structure that supports the feed assembly; it is either hinged or pivoted on the front of the chassis. Hydraulic cylinders on the boom are used to lift or swing the boom relative to the chassis and to swivel or "roll" the feed assembly. Feed Assembly The feed assembly is made up of the support struc¬ture with an integral thrust mechanism, a rotation unit, centralizers to stabilize the auger, and a hose handling arrangement. In addition, most drills have an extension frame with a tilt device to aid in positioning the feed. Operator's Station The operator's station is the area from which the miner operates the drill. UNDERGROUND ROTARY DRILL APPLICATIONS Underground Face Drills Underground face drills are used in mining opera¬tions that utilize the conventional mining system. The face drill is used to drill holes in the exposed face of the material, and the face is then "shot" by means of explo¬sives or high pressure air. The loose material then is ready for loading and transporting from the face to the preparation plant. Typical specifications for under¬ground face drills are listed in Table 1. Certain parameters should be established as to where the drill is to be used and what is expected of it. To create an awareness of some of the considerations that too often are overlooked, some questions are listed that should be asked in conjunction with the selection or application of the proposed drills. Energy System: Can the drill be supplied with the proper voltage to match the available or proposed elec¬trical power system of the mine? Is the system 250, 460, 500, 550, or 950 v; dc or ac; 3-phase; 60 or 50 Hz? Is the drill equipped with an adequate electric motor to handle the proposed duty cycle? Typical motor power on a single-boom drill would range from 25 to 40 kW (35 to 50 hp); the nominal power for a dual-boom|