It has been shown [1, 2] that the energy expended on fragmentation by a bit of constant mass and impact energy depends on the shape of the bit. However, these tests were made with simple impacts on a vertical laboratory impact tester. The fragmented volume was measured at an open surface, not one fragmented by previous blows as occurs at the face of a borehole.To assess the information obtained in the laboratory and to follow the laws which develop in mine conditions, we carried out experimental work. We used a BIS-1 test drill rig based on an SShDS rotary drill on which were mounted pneumatic percussion assemblies.The BIS-1 rig comprises rotary and percussive assemblies. The rotator is driven by a reduction gear and 10 kW motor with interchangeable pulleys. The available speeds of shaft rotation are 60, 90, 100, and 135 rpm. The percussion assemblies, consisting of cylinders and bits, and the tailpieces are interchangeable. Using two cylinders we achieved ax/al thrusts of the instrument on the face from 200 to 2000 kg. The number and energy of the impacts of the bit were determined from the bit travel diagram which was recorded during drilling at the face with the aid of an induction transducer of the transformer type with its core rigidly attached to the bit. The transducer was fed from a GZ-33 audio generator. The signals were recorded by an N-102 oscillograph.We tested 10 impact units with bits of various configuration and characteristics (Table 1). For all the percussion assemblies we used cylinders of 150 mm diameter of three types differing in the constructional travel of the bit: for travel of 33 mm, bits 1, 2, and 10; for travel of 44 mm, bits 6 and 7; and for travel of 55 mm, bits 3, 4, 5, 8, and 9.We used bits of lengths 160, 195, 230, and 300 mm and weights between 4.2 and 9.4 kg. They had various lengthwise mass distributions. We used bits of three constructional types: type a, a short bit with conical main mass in the head end (Fig. la); type b, a bit 1.2-1.4 times longer than the first, and with its mass concentrated in the tail part (Fig. lb); and type c, a bit equal in cross section to the rod, with its mass uniformly distributed lengthwise (Fig. lc).We tested the drilling of boreholes in rocks with hardnesses of 14-16 under the following conditions: axial pressure of instrument on face, 6a0 kg; rate of rotation of rotator, 60 or 100 rpm; mains pressure of compressed air, 5 atm (gauge); water pressure, 4 atm (gauge). The power delivered to the rotator was 10 kW. For comparability, all the holes were spaced 20-30 cm apart.Our work comprised two stages. First we drilled holes to 10 m depth successively with all ten percussion assemblies. Then from the test results we chose the four most promising percussion assemblies, namely numbers 3, 4, 8, and 9, and used them to drill the holes to 20 m. In all we drilled 49 holes of 10 m depth and seven holes of 20 m depth. The total length drilled in this series of experiments was 630 rn.During the tests we measured the average mechanical drilling speed every...

From the remits of an investigation of the principal laws of rotary percussive drilling of blast-holes, we have determined [1] the optimum characteristics for rotary percussive machines for blast hole drilling, and have also given the results of our first experiments on the drilling of blast holes of small diameter in an experimental test rig with remote pneumatic hammers and independent rotation of the drill rod by a separate motor.In 1960-1965, using the test rig and also with sample rotary percussive drills of types P-29 (BU-70), AB-2, and VP-80 which were undergoing industrial tests at Krivoi Rog mines, we continued our experimental drilling of small diameter blast-holes in rocks with hardnesses from f = 6-8 to 2 c --20. In the table below we give our chief results, from which we can determine the optimum axial feed thrust, the energy per impact, the number of impacts per rotation of the drill rod, and the torque, in relation to the hardness of the rock.The test rig for rotary percussive borehole drilling permitted us to set up pneumatic strikers with various energies of single impacts and impact power (in the experiments these ranged from 5 to 20 kg. In), and also, by means of hydraulic cylinders, to vary the axial feed thrust from 100 to 3000 kg and the rate of turn of the drill rod from 60 to 720 rpm.All the main experiments were carried out under main conditions in rocks of varying hardness, to that the results were reliable for determifiing the optirntum force parameters of drilling (the axial thrust, impact energy, numbet of impacts per revolution of the drill rod, and torque).For experimental drilling of boreholes in the faces of blind workings, drilling chambers were fitted up with compressed air, water, and electricity supplies for the test rig. The operation of the machines was measured by control and measurement devices: the air flow rate was measured by an air meter tube with interchangeable disks of 18, 24, and 32 mm diameter and a DS-50 differential manometer; the number of impacts was measured by a VA-1 vibrograph and a resonance vibrotachometer; and the rate of rotation was measured by a hand operated centrifugal tachometer, type IO-10. The feed rate was measured by a scale gauge and timer. The axial thrust, transmitted to the drill rod,was measured by a DC-5 or a DC-1 compression dynamometer, which was compressed by the forward end of the drill rod with the drilling bit removed. The compressed air pressure was monitored by a gas manometer with 10 atrn scale divisions. The electrical energy expended on rotating and feeding the drill rod was measured by a three phase meter; wear of the drilling instrument was determined from the width of the end surface due to blunting, which was measured under mine conditions by means of a magnifying glass with tenfold magnification. Under laboratory conditions, the blunting of the bit was determined with a large instrumental microscope of type EMI to within 0.005 ntm.We aimed to establish experimentaUy the main laws of rotary percussive drilling of small diam...