Some Results of a Study of an Electropneumatic Impact Unit with an Increased Number of Impacts
Abstract Generated abstract
This paper reports experimental studies of an electropneumatic percussion unit intended for column drilling hammers or rotary percussion drilling machines, where the higher weight of such units is less limiting than in hand tools. Using a test stand with varied crank radii, striker weights, blow frequencies, air cushion lengths, and compensation port positions, the study evaluates blow energy, drilling advance, power consumption, efficiency, and operating stability. The results indicate that stable operation at up to about 3000 blows per minute is possible when air leakage is compensated through a port near the piston’s extreme forward position and when the air cushion is chosen in relation to crank radius. Blow energy and efficiency generally increase with blow frequency only up to a stability limit, which is higher for larger crank radii and lighter strikers.
Full Text
Some Results of a Study of an Electropneumatic Percussion Unit with an Increased Number of Blows
A. S. Simonov
Studies of electropneumatic chipping and drilling hammers with a number of blows of 1000–1400 per minute show that, in terms of blow energy and impact power, they are not inferior to pneumatic ones [1–4]. At the same time, electropneumatic hammers are 6–8 times more economical than pneumatic hammers [5, 6]; in addition, their operation does not require large capital expenditures (there are no compressor installations, pipelines, etc.), and the transmission of energy is simplified. However, despite the considerable advantages of electropneumatic hammers, not a single industrial design of such a machine has yet been created. This is explained mainly by the fact that, for the same blow energy, electropneumatic hammers have 2–3 times greater weight than pneumatic ones. Designers in most cases failed because of their effort to create hand-held electropneumatic hammers close in weight to pneumatic ones. But such hammers turned out to be insufficiently strong and had low blow energy (1.5–2.5 kgm).
In our opinion, electropneumatic percussion units can be successfully used in the manufacture of column-type drilling hammers or rotary-percussion drilling machines, where weight is not of essential importance. In order to determine the possibility of creating and using an electropneumatic percussion unit with an increased number of blows for column-type drilling hammers or rotary-percussion drilling machines, we carried out additional studies of the percussion unit under its various parameters and operating conditions.
The experimental setup (Fig. 1) consisted of a percussion unit with an electric motor, a feed and support device, a drill steel with a support stand, and control-and-measuring equipment. The percussion unit consists of cylinder 1 (inside diameter \(d_{\mathrm{in}} = 68\) mm), piston 2, striker 3, intermediate striker 4, and crank-and-connecting-rod mechanism 5. During operation of the machine, an air cushion 6 is formed between the piston and the striker, the length of which is varied by means of washers 7. During operation of the percussive
of the unit, the striker and piston execute reciprocating motions by means of the crank-and-connecting-rod mechanism 5 from the electric motor 8 through the V-belt transmission 9. When the piston moves to the right (Fig. 1), a vacuum is created between it and the striker, and the striker is likewise displaced to the right by the excess pressure of atmospheric air. As the piston moves to the left, compression of the air between the piston and the striker begins. The striker changes its direction of motion and, at the end of the stroke, having acquired a certain velocity, delivers a blow to the impact piece 4.
To compensate for air leakage, a row of holes 10 is arranged along the cylinder barrel; when necessary, these are closed with screw plugs. The distance between the holes
Fig. 1. General view of the experimental setup.
—10 mm; the diameter of the holes—4.2 mm. The percussion unit is fastened to carriage 11, which can move along the guide grooves of the screw feed 12. The screw feed, by means of clip 13, is mounted on the horizontal crossmember 14, fastened by clamps 15 to the posts 16 of the welded frame 17.
Feed of the percussion unit is effected by weight 18 (feed force 25 kg), thrown over pulley 19 on cable 20. The percussion unit, striking rock drill rod 21, forces it to advance in clamps 22, by which it is fastened to bracket 23. In turn, the bracket is fastened by clamps 24 to support post 25. The bracket can rotate about its axis in clamps 24 (with the bolts loosened), which makes it possible to set the drill rod in the required position. The drill rod is clamped with a constant force, which was periodically checked on a press (the drill rod advanced in the clamps under a force of 1800 kg).
To determine the dependence of the magnitude of drill-rod advance on the energy of a single blow, the drill rod was calibrated on a calibration drop hammer 16 m high. For calibration, the drill rod with the bracket was removed from the support post, fastened to the crossmember of the stand (the percussion unit with the falling device was removed), and placed under the drop hammer.
A striker corresponding in weight to the intermediate striker was mounted on the jumper rod. Calibrated rammers were dropped onto the striker; their weight corresponded to the weight of the rammers of the percussion unit. The drop height of the rammer was varied from 1 to 14 m in increments of 0.5–1 m. From each height the rammers were dropped 10–15 times.
For each case the following were determined:
a) the energy of a single rammer blow
\[ A_{\text{bl}} = Q_{\text{r}} h \ \text{kgm}, \]
where \(Q_{\text{r}}\) is the weight of the rammer, kg;
\(h\) is the rammer drop height, m;
b) the penetration of the jumper rod per blow
\[ l = \frac{S}{z} \ \text{mm}, \]
where \(S\) is the penetration of the jumper rod in \(z\) blows, mm.
Fig. 2. Dependence of jumper-rod penetration on the energy of a single blow:
\(\circ — Q_{\text{r}} = 0.55\) kg; \(\square — Q_{\text{r}} = 0.70\) kg; \(\triangle — Q_{\text{r}} = 1.0\) kg; \(\times — Q_{\text{r}} = 1.35\) kg.
On the basis of the obtained values, a graph was constructed of the dependence of the jumper-rod penetration on the energy of a single blow (Fig. 2) for four rammers \(Q_{\text{r}}\) (0.55; 0.70; 1; 1.35 kg).
From Fig. 2 it is evident that there is a linear relationship between the blow energy and the jumper-rod penetration. At the same time, the magnitude of the jumper-rod penetration depends not only on the blow energy but also on the weight of the rammer. The graph presented makes it possible to determine the blow energy for any operating mode of the percussion unit when the weight of the rammer is known and the magnitude of the jumper-rod penetration per blow is known.
The percussion unit was studied with three different crank radii \(R\) (20; 25 and 30 mm), at different
the weight of the strikers \(Q_b\) (0.55; 0.70; 1.0; 1.35 kg) and different numbers of blows \(z\) (1500, 2000, 2500, 3000 blows/min).
In the course of the experiment, the length of the air cushion, the position of the compensation port, the power consumed, the drilling advance, and the duration of the test were determined.
On the basis of the experimental data, the following were determined:
b) the drilling advance per blow
\[ l=\frac{60S}{zt}\ \text{mm}, \]
where \(S\) is the drilling advance during the test, mm;
\(z\) is the number of blows per minute;
\(t\) is the duration of the test, sec;
c) the energy of a single blow (Fig. 2);
d) the efficiency of the percussion unit
\[ \eta=\frac{A_{\text{bl}}z}{60\cdot102\cdot N}. \]
where \(A_{\text{bl}}\) is the blow energy, kgm;
\(N\) is the power consumed, kW.
The studies carried out show that the stable operating regime of the percussion unit depends on the correct choice of the position of the compensation port and the length of the air cushion. To clarify the dependence of the operating regime of the percussion unit on the position of the compensation port, for various crank radii the extreme forward point of the piston was taken as the origin of the coordinate axes (Fig. 3). In this case the abscissa axis runs along the cylinder axis.
From Fig. 3 it is evident that the blow energy reaches its greatest value when air leakage is compensated through a port located at a distance of 5 mm from the extreme forward point of the piston, regardless of the number of blows and the weight of the striker. When air leakage is compensated through other ports, jolts and strong heating of the cylinder are observed. This is especially noticeable at a large number of blows and when operating compensation ports close to the extreme rear position of the piston (Fig. 3, left half of the graph).
The power consumed by the percussion unit depends little on the position of the compensation port; therefore the curves of change in efficiency almost completely correspond to the curves of change in blow energy.
Fig. 4 shows the dependence of blow energy on the length of the air cushion. The percussion unit operates with compensation of leakage through the optimum compensation port—the port located at a distance of 5 mm from the extreme forward point of the piston. As the length of the air cushion changes, the operating regime of the percussion unit and its blow energy change. With an increase in the length of the air cushion, the blow energy increases to
Fig. 3. Dependence of impact energy on the position of the compensating hole:
○ — \(Q_b = 0.55\) kg; □ — \(Q_b = 0.70\) kg; △ — \(Q_b = 1.0\) kg;
× — \(Q_b = 1.35\) kg; \(1\)—\(R = 30\) mm; \(2\)—\(R = 25\) mm; \(3\)—\(R = 20\) mm.
Fig. 4. Dependence of impact energy on the length of the air cushion:
○ — \(Q_b = 0.55\) kg; □ — \(Q_b = 0.70\) kg; △ — \(Q_b = 1.0\) kg;
× — \(Q_b = 1.35\) kg; \(1\)—\(R = 30\) mm; \(2\)—\(R = 25\) mm;
\(3\)—\(R = 20\) mm.
of a certain maximum, the value of which depends on the radius of the crank. Thus, when the percussion unit operates with a crank radius \(R = 30\) mm, an increase in impact energy occurs when the length of the air cushion is increased to \(l_0 = 40 \div 50\) mm, while when operating with a crank radius \(R = 20\) mm the maximum impact energy occurs at an air-cushion length \(l_0 = 30 \div 40\) mm, i.e., the optimum length of the air cushion is approximately equal to or slightly greater than \(1.5R\). With a further increase in the length of the air cushion, the impact energy does not increase, and the steady operating regime is gradually disturbed. At a certain maximum value of the air-cushion length \(l_{\max}\), the striker is not picked up and the impact energy decreases to zero. Experiments show that the percussion unit operates steadily at \(l_0 \geq 1.5R\) only when \(l_{\max} > 2R\).
When the percussion unit operates with an air-cushion length less than \(1.5R\), shocks and strong heating of the cylinder are observed.
The power consumed by the percussion unit is almost independent of the length of the air cushion; therefore the efficiency, like the impact energy, has its greatest value at \(l_0 \geq 1.5\).
Experiments show that the maximum air-cushion length depends on the number of blows. As the number of blows is increased from 1500 to 3000 per minute, \(l_{\max}\) decreases by a factor of 1.5–2.0, which leads to disturbance of the operating regime of the percussion unit. In Fig. 5 the dependence of the ratio
\[ \frac{l_{\max}}{R} \]
on the number of blows is given (the percussion unit operates at the optimum compensation opening). When operating in zone \(A\), where
\[ \frac{l_{\max}}{R} > 2, \]
the most stable operating regime of the percussion unit is observed. \(B\) is the zone of unstable operating regimes of the percussion unit. A percussion unit with \(z = 1500\) blows/min operates in a stable regime for all three crank radii and all four strikers. As the number of blows is increased to \(z = 3000\) per minute, the percussion unit operating with strikers of weight \(Q_b = 1.0\) and \(1.35\) kg passes into an unstable operating regime and operates at the stability limit with strikers of weight \(Q_b = 0.55\) and \(0.70\) kg. Obviously, with a further increase in the number of blows, the percussion unit operating with strikers of weight \(Q_b = 0.55;\ 0.70\) kg will also prove to be in an unstable regime.
Figures 6 and 7 show the dependence of the impact energy and the consumed power on the number of blows. The percussion unit operates at the optimum compensation opening and with an air cushion of length \(l_0 = 40\) mm, since with this cushion stable and comparatively optimum operating regimes of the percussion unit were obtained for all three crank radii (Fig. 4).
It is evident from Fig. 6 that the impact energy increases with an increase in the number of blows up to a certain maximum value, and then, when the stable operating regime is disturbed, rapidly decreases to
Fig. 5. Dependence of the ratio \(\dfrac{l_{\max}}{R}\) on the number of blows:
○ — \(Q_b = 0.55\ \text{kg}\); □ — \(Q_b = 0.70\ \text{kg}\); △ — \(Q_b = 1.0\ \text{kg}\); × — \(Q_b = 1.35\ \text{kg}\);
1 — \(R = 30\ \text{mm}\); 2 — \(R = 25\ \text{mm}\); 3 — \(R = 20\ \text{mm}\).
Fig. 6. Dependence of impact energy on the number of blows:
○ — \(Q_b = 0.55\ \text{kg}\); □ — \(Q_b = 0.70\ \text{kg}\); △ — \(Q_b = 1.0\ \text{kg}\); × — \(Q_b = 1.35\ \text{kg}\);
1 — \(R = 30\ \text{mm}\); 2 — \(R = 25\ \text{mm}\); 3 — \(R = 20\ \text{mm}\).
zero. The maximum value of the impact energy and the stable operating regime of the percussion unit depend both on the radius of the crank and on the weight of the striker. The smaller the radius of the crank and the greater the weight of the striker, the smaller the maximum value of the impact energy, and at a lower number of blows the stable operating regime is disturbed. Thus, a percussion unit with crank radius \(R = 30\) mm and with a striker weighing \(Q_b = 0.55\) kg operates stably up to 3000 blows/min and develops a maximum impact energy of 14 kgm. With the same crank radius, but with a striker weighing \(Q_b = 1.35\) kg, the percussion unit
Fig. 7. Dependence of consumed power on the number of blows:
\(\circ\)—\(Q_b = 0.55\) kg; \(\square\)—\(Q_b = 0.70\) kg; \(\triangle\)—\(Q_b = 1.0\) kg; \(\times\)—\(Q_b = 1.35\) kg;
\(1\)—\(R = 30\) mm; \(2\)—\(R = 25\) mm; \(3\)—\(R = 20\) mm.
operates stably only up to 2200–2300 blows/min, and the maximum impact energy in this case reaches only 8 kgm. A further increase in the number of blows when operating with striker \(Q_b = 1.35\) kg leads to a reduction of the impact energy to zero.
The stable operating regime of the percussion unit with crank radius \(R = 20\) mm is disturbed at a lower number of blows than with \(R = 30\) mm, and the maximum impact energy when operating with the same strikers has a significantly smaller value.
The power consumed by the percussion unit increases with an increase in the number of blows, but to a lesser extent than the impact energy. Therefore, the efficiency of the percussion unit increases as the number of blows rises. Thus, when the number of blows is increased from 1500 to 3000 per minute while operating with strikers weighing \(Q_b = 0.55\) kg and 0.70 kg, the efficiency of the machine increases from 40–50 to 60–65%.
CONCLUSIONS
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The study of the electropneumatic percussion unit shows that it can operate steadily when the number of blows is increased to 3000 per minute and more. The stable operating mode of the percussion unit depends on the correct choice of its parameters and on the position of the compensating orifice.
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The most stable and optimal operating mode of the percussion unit occurs in the case of:
a) compensation of air leakage through an orifice located at a distance of 5 mm from the extreme forward point of the piston;
b) an air-cushion length \(l_0 \geq 1.15R\).
In this case, the length of the maximum air cushion should be \(l_{\max} > 2R\). As the number of blows increases, the length of the maximum air cushion decreases.
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The impact energy increases with an increase in the number of blows, but only up to a certain limit, which depends on the crank radius and the weight of the striker. The larger the crank radius and the smaller the weight of the striker, the higher this limit and the farther it is shifted toward a higher number of blows.
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The use of a percussion unit with an increased number of blows will make it possible to increase significantly the productivity and efficiency of electropneumatic drilling machines.
LITERATURE
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P. M. Alabuzhev. Study of the working process of electropneumatic percussion-action machines. Doctoral dissertation. TPI Library, Tomsk, 1954.
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A. S. Simonov, Ya. A. Serov, V. F. Gorbunov, N. N. Rodyukov. Study of the percussion unit of an electropneumatic drilling hammer. Izvestiya TPI, vol. 88, Tomsk, 1956.
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S. V. Veselitskii, L. Ya. Grigor’ev, N. I. Liberman, O. M. Todes. Fundamentals of the theory and calculation of electropneumatic hammers. Calculations, design, and testing of mining machines, Collection 2. Ugletekhizdat, 1955.
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N. M. Batuev. Energy characteristics of electric hammers and ways of increasing their productivity. Study of vibrators and electric hammers, VI, VNII Stroydormash. Mashgiz, 1951.
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A. I. Moskvitin. Electric machines of reciprocating motion. Academy of Sciences of the USSR, 1950.
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O. D. Alimov. Technical characteristics of pneumatic drilling hammers. Izvestiya TPI, vol. 78, Tomsk, 1955.
NOTED MISPRINTS
| Page | Line | Printed | Should be | Due to |
|---|---|---|---|---|
| 13 | 1 from bottom | 7-10 | T-10 | Corr. |
| 14 | 13 from bottom | R-754 | RH-754 | » |
| 28 | 1 from bottom | \(A_y=\dfrac{mV_{\sigma}^{2}}{2}\) | \(A_y=\dfrac{mV_y^{2}}{2}\) | Author |
| 34 | 18–20 from bottom | 2 — diagram of oscillations of the hammer body; 3—diagram of the angular displacement of the drill; 4—diagram of the air pressure in the rear cavity of the hammer cylinder; 5 — diagram of the pressure in the front cavity; | Author | |
| 35 | 1 from bottom | Scerving Stiense | Serving Science | Ed. |
| 46 | 14 from bottom | changes | changes | Typ. |
| 90–91 | Figs. 7 and 8 | interchange places, while retaining in place the undersigned captions | interchange places, while retaining in place the undersigned captions | Author |
| 97 | 10 from bottom | drilling hammer | automatic feeder | » |
| 107 | 2–3 from bottom | stops | stop | » |
| 156 | 2 from top | surfaces | surface | Corr. |
| 166 | 14 from bottom | drilled out | drilled | Author |
| 179 | 9 from top | kinetic | kinematic | Corr. |
| 189 | 5 from top | (59–200 mm) | (50–200 mm) | » |
| 192 | 10 from bottom | will expand | expander | Typ. |
| 197 | 1 from top | kinetics | kinematics | Corr. |
| 198 | 3–6 from top | Read the fifth line after the second line | Read the fifth line after the second line | Typ. |
| 199 | 14 from bottom | kinetics | kinematics | Author |
| 212 | 12 from top | L. B. Levenmon | L. B. Levenson | Author |
| 219 | 3 from bottom | \(A=a+h\ldots+h.\) | \(A=a+h\ldots+h.\ (16)\) | Corr. |
| 223 | 3 from top | \(-\left(30\dfrac{\omega}{\omega_0}\right)^2+5\) | \(-30\left(\dfrac{\omega}{\omega_0}\right)^2+5\) | Typ. |
| 224 | 19–20 from top | increased | was increasing | Corr. |
| 229 | 10 from top | AOF4-2 | AOF42-2 | Author |
| 243 | 11 from top | 1,15 | 1,5 | Corr. |
Order 39.