Electric Rock Drills

Electric Rock Drills.

A successful rock drill is a piece of machinery that the mining and quarrying world has been looking for in vain for some time. Quarrymen and miners will therefore be interested to learn that an electric drill has finally been perfected, and is ready to take its place in the electrical equipment of mines and quarries. The advantages of the electrical system of transmitting energy are becoming better appreciated every day, and many of the most progressive mine managers are equipping their plants with electrical machinery. Electrical applications in this direction, however, have been seriously retarded by the impossibility of securing an electric percussion drill. Photo of Type B Marvin Electric Drill The importance of this machine and its value in mining and quarrying has induced much effort in this direction, but the extremely difficult conditions encountered in the construction of such a machine for a long time baffled the efforts of those who worked upon the subject. A modern rock drill must be so simple in its design that it can be taken care of by the most ordinary mechanic. It must be so rugged in its construction that it will endure the utmost abuse and an almost total absence of care and judgment on the part of the drill runner. It must be powerful enough to drill with a rapidity commensurate with the rapid progress made in modern rock excavation. It must be of such weight that it can be readily handled by the ordinary force of men employed in the different operations. The electrical pressure employed must be so low as not to endanger or inconvenience persons accidentally encountering unprotected wires. All of these conditions seem now to be met by the Marvin Electric Drill, which has recently been placed upon the market by the Marvin Electric Drill Company, of Canastota, N. Y. This machine is operated upon the somewhat well known Marvin system. The drill, itself, consists essentially of two coils of wire, placed end for end and surrounding a solid steel plunger, which very closely resembles the piston of the steam drill. Electrical impulses are transmitted alternately through these two coils of wire, with the result that the plunger moves to and fro precisely like the piston of a steam engine. The current is led to the drill from a dynamo of special construction, over three wires, which constitute two independent circuits. There is no commutator upon the drill and nothing resembling a valve, the current being shifted at the dynamo. The coils of the drill are insulated entirely with mica, and hermetically sealed in a boiler tube jacket. The drill is mounted and operated on a column or tripod, in the usual manner. Drills operated on this system were put in operation in various parts of the country some years ago, but while they afforded striking evidence of the superiority of the electric system, the drills, themselves, were not of sufficient capacity, and were not built strong enough to fulfill all that was required of them. The Marvin company has been steadily working upon the problem, however, and has finally produced a machine which appears to afford a satisfactory solution of the problem. About two years ago a plant of their improved drills was installed at the quarry of the Solvay Process Company, at Syracuse, N. Y. The rock drilled is a hard quality of blue and gray limestone, quite seamy, and on that account somewhat difficult to drill. Two sizes of machines are used, the larger size drilling holes six to eight feet in depth and two and one-half inches in diameter, the smaller machine drilling holes about twenty inches in depth and one and one-quarter inches in diameter. The average performance of the large machines is about sixty feet of hole in ten hours, although the machine has drilled over 100 feet in ten hours. The average performance of the small drill, which is readily handled by one man, is over one hundred feet of one and one-fourth inches hole in ten hours. The operation of the plant has been uninterrupted since the start, no time having been lost by reason of the failure of any part of the electrical apparatus. No expert help is required in the maintenance of the plant, and it is a significant fact that the drill runners are paid no higher wages than the ordinary quarrymen. Photo of Marvin Electric Drill Type E The extreme simplicity and strength of construction of the electric drill makes it preëminently adapted to mining work. The conditions under which these machines are operated are entirely hostile to all tight fittings and close adjustments. In the electric drill no such constructions are required. There is, as before stated, nothing resembling a valve motion about the machine. The plunger runs so freely in its bearings that they are not readily cut out by grit, and in fact, it does no harm if they are very badly worn and loose, as the machine does not lose any of its efficiency or power under such conditions. The machinery may be pounded and banged about, buried in mud and water, exposed to the flying debris of a blast, and in other ways misused, without injury. In operation the machine is equally durable. It is impossible to injure it by unskillful handling. If the drill runner is careless and does not feed the machine up to the rock, no possible injury can result to the drill, as the plunger is automatically cushioned by the electric action in case the stroke becomes too long. This result is accomplished by the shifting of the current at the dynamo, as the plunger of the drill moves in synchronism with the dynamo armature. This is a point which will be appreciated by all who have had experience with broken front heads and side rods. Another peculiarity of the machine is that its stroke can be shortened indefinitely.

The machine may be fed up to the rock until the stroke of the plunger is a quarter of an inch or less, but the motion of the plunger continues with the same regularity in speed as when running with a full six or eight-inch stroke. This feature is of great assistance in starting a hole and in working through seams. As all the parts of the drill work very freely, very little oil is used to lubricate the machine. In the operation of an electric drill the wires are led to within a short distance of the place where it is desired to operate and the drill is connected to the wires by means of a flexible cable, containing three conductors. The cables are very durable, as the wear upon them is much less than the wear on hose where steam is used.

The dynamo which furnished the current for the operation of the drills, is characterized by the same simplicity of design and strength of construction employed in the drills. As the dynamo runs in synchronism with the drills its speed is very low, being from 350 to 400 revolutions per minute, according as it is desired to run the drills with greater or less rapidity.

The winding of the armature consists of a single coil composed of a few turns of stranded wire. Should any accident happen to the machine, the armature winding can be renewed by an ordinary mechanic in a few hours' time without removing the armature from the dynamo room. Having large self-oiling bearings, and requiring no adjustment of the brushes, the dynamo does not require much more attention or expense for maintenance than a Pelton water wheel. Both armature and field of this machine are made up of sheet iron punching. The field coils are wound upon frames and slid into place in the machine, together with the armature which they surround. As the winding of the armature is but a few hours' work, the construction of the machine is such that it can be very readily subdivided for transportation on mule back in inaccessible regions without materially increasing the cost of the machine. The voltage used in this system is 130 volts, alternating, but the pulsations are so slow, about 350 a minute, that little or no shock is received from the wires, and there is no possible danger from contact with any part of the system.

Photo of Quarry Work with Marvin Type E Drill

The overheating of the machine, which was a troublesome feature of the former drills, has been entirely overcome, yet the drills are so constructed, being insulated entirely with mica, that an excess of current cannot in anyway injure them, as they could be heated red hot without the slightest injury.

There is a wide field for the electric drill. In mining work, the ease with which the power can be conveyed over broken and mountainous country and into mines, on wires, is well understood, and the simple and rugged character of the electric drill perfectly adapts it to mining usage. In quarry work, the advantages of the central station system are becoming recognized, and attempts are being made to distribute power about quarries as it is done in mine, by compressed air. For this purpose, however, no method can equal the electric system, which is so perfectly flexible in its conductors, so simple in apparatus, and so economical in power distribution. For contracting and tunnel work where the nature of the plant is temporary, the electric system, by reason of its easy installation and efficient operation, offers many advantages. All sizes of drills can be built on this system, and it is the intention of the Marvin company to bring out a line of channelling machines and coal cutters at an early date.

"The times are very hard, and $2.00 now is considerable more than two hundred cents used to be but STONE is essential to any live man in the trade. I can't economize on that point. Send it along for another year with the usual amount of trade news and information, and it will be $2.00 well invested."-A. F. Weaver, Philadelphia, Pa..

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