Laboratory Studies of the BU-1 Drilling Machine
Abstract Generated abstract
This paper reports laboratory testing of the BU-1 rotary percussion drilling machine to determine actual operating parameters, compare them with specifications, and identify improvements. Separate stand tests of the feed mechanism, rotary unit, and percussion assembly measured feed force and speed, motor power, air consumption, efficiency, torque, blow frequency, impact energy, and hammer stroke under varying air pressures and settings. The feed and rotary systems generally met or exceeded required forces, speeds, and torque, although stable low-speed feeding required a higher reducer ratio and rational mode control would benefit from an axial-force regulator. The percussion unit performed below design values, with an optimum hammer design stroke of 35 to 37 mm, and the study recommends reducing the front air cushion and modifying exhaust or air-channel geometry to improve impact power.
Full Text
V. F. GORBUNOV, V. Z. DOZMAROV, V. I. BABUROV, A. P. NOVIKOV,
Yu. A. OPARIN
LABORATORY STUDIES OF THE BU-1 DRILLING MACHINE
(Presented by the Department of Mining Machines and Mine Transport)
The study of the BU-1 rotary-percussive drilling installation was carried out in order to determine its actual parameters, compare them with the design values, analyze drilling regimes, and also develop recommendations for improving its technical characteristics. The units of the machine were studied independently and according to methods described in the literature. Thus, for example, the machine rotator was tested on a stand for studying rotary-drilling machines [2], and the percussion unit on a stand for studying drilling hammers [1].
The study of the feed mechanism of the BU-1 machine was carried out in three stages:
a) the characteristics of the feed mechanism were determined with the percussion unit and rotator switched off;
b) the influence of the percussion unit, operating at idle, on the traction characteristics of the feed mechanism was determined;
c) the operation of the pneumatic motor of the feed mechanism was studied separately from the feed mechanism.
Figure 1 gives the relationship between the force and speed of feeding the drill head to the face with the percussion unit switched off. An increase in the resistance to movement of the drill head at constant air pressure in the network leads to a decrease in feed speed. At a certain maximum value of the feed force, movement of the drill head ceases.
The limits of variation in the speed and feed force of the feed mechanism of the BU-1 drilling machine as a function of the air pressure in the network are given in Table 1.
Table 1
| Indicators | Air pressure in the network, atm | Air pressure in the network, atm | Air pressure in the network, atm | Air pressure in the network, atm | Air pressure in the network, atm |
|---|---|---|---|---|---|
| 2 | 3 | 4 | 5 | 6 | |
| Maximum feed force developed by the feed mechanism, kg | 650 | 1100 | 1600 | 1900 | 2200 |
| Feed speed corresponding to the maximum feed force, m/min | 0.7–0.8 | 0.7–0.8 | 0.7–0.8 | 0.7–0.8 | 0.7–0.8 |
| Maximum feed speed (without load), m/min | 3.4 | 4.5 | 5.5 | 7.0 | 8.6 |
The feed mechanism parameters obtained in the laboratory (Table 1) differ from those given in its technical specifications [3]. According to the technical specifications, the maximum feed force is 1100 kg at an air pressure in the line of 5 atm. At an air pressure of 6 atm, the actual feed force exceeds the rated value by a factor of 2.
Fig. 1. Mechanical characteristics of the feed mechanism of the BU-1 machine.
At any air pressure, smooth feeding of the drill head to the face ceases at a feed rate of 0.7–0.8 m/min (screw rotational speed 60–70 rpm). Increasing the feed force beyond the limits indicated in Table 1 first leads to intermittent rotation of the screw feed mechanism and then to its complete stoppage. Evidently, to provide low feed rates it is advisable to increase the gear ratio of the reducer. The smooth variation in the speed of motion of the drill head when the feed force and the air pressure in the line are varied (Fig. 1) makes it possible to use the BU-1 machine over a wide range of rock hardnesses. This eliminates the need to adjust to individual drilling modes with the aid of additional devices (friction clutches, interchangeable gears, etc.), which requires additional
expenditure of time and resources. However, regulating drilling modes by changing the air pressure supplied to the feeder motor has the disadvantage that the worker sets the air pressure by referring to the speed of movement of the drilling head and to the noise level of the drill rotator. Cases are possible in which the drill-rotation motor is either underloaded (the feed force is small) or overloaded. In both cases there is a reduction in the machine drilling speed.
To set the machine to the most rational drilling mode, an air-pressure regulator for the feeder motor (an axial-force regulator) is needed, operating as a function of the drill speed (the torque on the drill).
Investigation of the feeder of the BU-1 unit with the percussion unit idling showed that operation of the percussion unit has practically no effect on the feeder characteristic.
Depending on the rotational speed of the feed screw, the effective power of the feeder gear motor changes (Fig. 1). With an air pressure in the line of 4–6 ati, the maximum effective motor power of 2.0–3.8 hp corresponds to the feed-screw speed interval of 400–500 rpm.
The feeder of the BU-1 drilling machine must provide a drilling speed of 0.6–2.0 m/min. The feed-motor power corresponding to this speed interval is presented in Table 2.
Table 2
| Air pressure in the line, ati | Feed-motor power, hp | Feed force, kg |
|---|---|---|
| 3 | 0.4–1.0 | 1100–700 |
| 4 | 0.55–1.45 | 1600–1080 |
| 5 | 0.75–2.0 | 1900–1420 |
| 6 | 0.9–2.5 | 2200–1720 |
From a comparison of Table 2 and Fig. 1 it is evident that, in the drilling process, the feeder motor develops a power 1.5–2 times lower than the possible value.
The power required to move the drilling head during drilling is less than the power required for the reverse movement of the drilling head. At an air pressure in the line of 5 ati, drilling at speeds of 0.6–1.2 m/min requires a feeder-motor power of 0.3–0.45 hp, while withdrawing the rotator at a speed of 6 m/min requires 0.66 hp, i.e., 1.5–2 times more. Consequently, the operating mode and characteristics of the drilling-machine feeder must be selected so that the maximum motor power corresponds to the idle travel of the drilling head. The feeder of the BU-1 machine satisfies this condition.
The minimum specific air consumption of the feeder motor corresponds to an air pressure in the line of 4–6 ati and output-shaft speeds of 300–500 rpm. As the air pressure increases, its specific consumption decreases. At feeder-motor shaft speeds of 50–170 rpm, corresponding to drilling speeds of 0.6–2.0 m/min, the specific air consumption is 2–4 m³/min·hp, which is approximately 2 times higher than the specific air consumption at maximum motor power. The total air consumption by the feeder motor increases with increasing air pressure in the line.
In order to evaluate the entire feeder mechanism and its individual links, values of the efficiency of the pneumatic motor, of the mechanical-
of the efficiency of the feeding device and the overall efficiency of the feeder. The investigations showed that the feeder of the BU-1 machine has an overall efficiency of 3–8% (Fig. 2), with the maximum efficiency values obtained in the feed-rate range of 2–5 m/min. When the feed rate is increased from 0.6 to 2.0 m/min, corresponding to drilling speeds, the overall efficiency of the feeder is practically independent of the air pressure in the network and increases from 3 to 7%.
Fig. 2. Dependence of the efficiency of the screw feeder on the rotational speed of the screw: 1 — motor efficiency; 2 — mechanical efficiency; 3 — overall efficiency of the feeder.
The maximum values of the feeder-motor efficiency correspond almost exactly to the no-load speeds of the percussion head and vary depending on the air pressure (Table 3).
Table 3
| Air pressure in the network, atm | Maximum value of the feeder-motor efficiency | Rotational speed of the feed screw corresponding to the maximum efficiency |
|---|---|---|
| 3 | 0.15–0.16 | 150–300 |
| 4 | 0.20–0.21 | 250–400 |
| 5 | 0.24–0.25 | 300–400 |
| 6 | 0.25–0.26 | 300–450 |
At drilling speeds of 0.6–2.0 m/min, the efficiency of the feed motor is 0.07–0.12, which is two times lower than the maximum efficiency values.
The mechanical efficiency of the screw feed mechanism decreases as the rotational speed of the feed screw increases. In the range of operating feed speeds of 0.6–2.0 m/min it has maximum values of 0.39 and 0.47, respectively, for air pressures of 6 and 3 ati (Fig. 2).
The rotary unit of the BU-1 drilling machine was investigated on a universal test stand [2] for testing rotary-action machines. The load on the drill was produced by a friction clutch.
From Fig. 3, which presents the mechanical characteristic of the rotary unit, it is evident that the rotary unit develops a maximum torque of 47 kgm at an air pressure of 6 ati. Its overload capacity,
Fig. 3. Mechanical characteristics of the rotary unit of the BU-1 machine.
\[ \frac{M_{\max}}{M_{\mathrm{nom}}}=1.6\text{–}2.0. \]
The design value \(M_{\mathrm{cr}}=25\text{–}30\ \text{kgm}\) is reached at an air pressure of 6 ati and a drill rotational speed of 150 rpm.
When the air pressure is reduced to 4 ati, the required torque can be provided by lowering the rotational speed to 80–90 rpm.
The maximum power of the gear motor for drill rotation corresponds to the design drill speed of 150 rpm (Fig. 3); therefore, during drilling, the energy capabilities of the motor are used fully.
The air consumption by the rotary unit increases with increasing pressure and drill rotational speed. At the design drill rotational speed of 150 rpm, the air consumption by the rotary unit is 4, 5, 6, and 7 m³/min, respectively, for air pressures in the network of 3, 4, 5, and 6 ati. The minimum air consumption per unit of power corresponds to the spindle-speed interval of 100–175 rpm and is 1.2–1.6 m³/min·hp at air pressures in the network of 4–6 ati, respectively. As the air pressure in the network increases, the specific air consumption by the gear motor for drill rotation decreases.
The maximum efficiency of the drive of the BU-1 unit corresponds to drill rotation speeds of 100–150 rpm and is equal to 0.21–0.26.
The unit for studying the impact assembly of the BU-1 machine was equipped with apparatus for oscillographic recording of diagrams of the working process of the impact assembly (variation of air pressure in the cylinder cavities over time, the moment of impact of the striker on the drill, etc.) [1, 3].
During the tests, the length of the design stroke of the striker was varied in increments of 1.5–2 mm within the range 31–38 mm, and the air pressure in the line was varied from 2 to 6 ati.
Processing of the pressure oscillograms was carried out according to the method proposed by B. V. Sudnishnikov [5].
As a result of processing the oscillograms, dependences were obtained for the blow frequency, the length of the working stroke of the striker, the impact energy, and the power on the air pressure in the line and the specified design stroke of the striker; the efficiency of the impact assembly was determined.
As a result of the tests it was established that, with a design stroke length of the striker of 31 and 33.4 mm, the impact assembly operates very unstably, with an actual stroke length of only 16–18 mm. With a design stroke of the striker of 36.8 mm, the impact energy and the efficiency of the assembly have their greatest value. Further lengthening of the striker stroke leads to a reduction in the impact energy and in the efficiency of the impact assembly. The optimum value of the design stroke of the striker lies within 35–37 mm. Deviation from these values leads to a reduction in the impact energy (Fig. 4) and in the power of the assembly. The length of the working stroke of the striker in the zone of optimum design-stroke values is 24–26 mm at an air pressure in the line of 4–5 ati.
Fig. 4. Influence of the piston-striker stroke length on the impact energy of the drilling head of the BU-1 machine.
The blow frequency, as the design stroke of the striker is increased, gradually decreases.
The parameters of the impact assembly of the BU-1 unit obtained as a result of the investigations are given in Table 4 in comparison with the data of the technical specification.
When installing the percussion unit in the housing of the rotator of the drilling machine, the articulation of the units must be selected so that the position of the point of impact of the hammer against the drill shank corresponds to the rational stroke of the hammer or, in other words, so that the front air cushion in the cylinder of the percussion unit has a definite value.
Table 4
| Indicators | Value of indicators according to factory data | Value of indicators according to test data |
|---|---|---|
| Air pressure, atm | 4–5 | 4–5 |
| Frequency of blows per minute | 3800–4000 | 3200–3500 |
| Impact energy, kg·m | 4–5 | 3–3.75 |
| Impact power, hp | 3.38–4.45 | 2.1–2.9 |
| Working stroke of the hammer, mm | 30 | 24–26 |
| Length of the front cushion, mm | 8 | 5–5.5 |
| Length of the rear cushion, mm | 3 | 10.5–11.5 |
| Air consumption, m³/min | — | 2.9–3.5 |
| Efficiency, % | — | 25–26 |
We have established that the length of the front air cushion given in the technical specification is too great. Reducing it to 5–5.5 mm increases the impact power of the unit by 6–16% and at the same time reduces the magnitude of the rear air cushion by 5–5.5 mm.
When the percussion unit operates with an air pressure in the line of 4–6 atm, insufficient exhaust from the rear cavity is observed. Because of this, the length of the working stroke of the hammer decreases, the length of the front air cushion increases, and the energy indicators of the percussion unit deteriorate. As the investigations carried out have shown, shifting the exhaust ports of the percussion unit toward the valve chest by 5–6 mm or increasing their cross section will improve the operation of the percussion unit, since the working stroke of the hammer will increase owing to a reduction in the rear air cushion.
Conclusions
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The feed mechanism of the BU-1 drilling machine provides the maximum feed forces and speeds specified by the technical specification. The feed speed of the rotator can be smoothly regulated, depending on changes in the hardness of the rocks being drilled, by changing the pressure of the air supplied. However, the feed mechanism does not provide a stable feed speed below 0.6–0.7 m/min. This shortcoming can be eliminated by somewhat increasing the gear ratio of the feed-motor reducer.
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The feed mechanism of the drilling machine has a high reverse speed (6–7 m/min), which makes it possible to substantially reduce the time of auxiliary operations during drilling.
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The maximum power of the drill rotator of the BU-1 installation corresponds to the design drill-rotation speed of 150 rpm, and the required torque can be provided at an air pressure of 4–6 atm.
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The optimum design stroke of the hammer for the percussion unit tested is 35–37 mm. In this case the percussion unit has the best energy indicators for this design, although they are below the design values.
- In order to improve the operation of the percussion unit and increase its power, it is advisable to reconsider the arrangement of the air-supply channels of the percussion unit in accordance with the recommendations given in the text. In this case, the parameters specified by the plant in the technical specifications can be achieved.
REFERENCES
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O. D. Alimov, I. G. Basov, V. F. Gorbunov, D. N. Malikov. Drilling Machines. Gostekhizdat, 1960.
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O. D. Alimov, L. T. Dvornikov, N. S. Kolodyazhnyi. A method for laboratory testing of rotary drilling machines. Mechanisms and machines of percussion, rotary, and rotary-percussion action. Interuniversity collection of papers, issue 1, Novosibirsk, 1963.
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V. I. Baburov, V. F. Gorbunov, Yu. A. Oparin. Experimental installation for the study of cutting-and-riveting hammers. Article in the present collection.
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New developments in the drilling of blast-holes and boreholes. Collected volume Explosive Work, 46/3, Gostekhizdat, 1961.
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B. V. Sudnishnikov. The influence of forward-stroke parameters on the power and efficiency of a pneumatic hammer. Collected volume Percussion-Rotary Drilling. Percussion Machines, Novosibirsk, 1956.