Test Results of the BSZ-135 Chipping Hammer

V. I. Baburov, A. I. Pashnin, A. N. Shchipunov

(Presented by the scientific seminar of the Department of Mining Machines, Mine Transport, and Mining Mechanics)

With the aim of creating a hand-held pneumatic hammer with vibration damping on the basis of the BSZ-135 hammer [8], detailed studies of it were carried out in the pneumatic-machines laboratory of TPI. In order to obtain objective and reliable data, the hammer tests were conducted under conditions close to production conditions. For this purpose, the S. I. Dobroborskii ERD-3 stand [3] was reequipped. In particular, taking into account the recommendations set forth in works [1, 6], a spring-type pressing device was used, and the energy absorber for the hammer blows was also replaced.

The pressing device is a cylindrical helical spring with a stiffness coefficient of 0.51 kg/mm. The pressing force on the hammer handle was varied within the range from 0 to 30 kg.

From the standpoint of the best transmission of energy and durability of the working tool, a chisel with a spherical tip was used.

On the whole, the research program provided for determining the energy parameters of the hammer, recording vibration diagrams, carrying out spectral analysis, and also determining the volumetric rate of steel chipping with the BSZ-135 hammer and comparing the characteristics of hammers of different designs. Frequency, impact energy, and other energy parameters were calculated from diagrams of pressure in the front and rear cavities of the cylinder as a function of time according to the known method [4, 9]. The measurement results corresponding to a pressing force of 20 kg are given in the table.

As can be seen from the table, the impact energy of the BSZ-135 hammer, according to our measurements, is 1.35 kg·m, while according to the data of the designer, G. I. Sidorenkov [8], it is 1.14 kg·m, i.e., lower by 15%.

For comparison of this hammer with those produced in series, the table includes data for the MP-6 and MP-5 chipping hammers (from the Tomsk Electromechanical Plant), which are closest in parameters to the hammer under study. In design, the BSZ-135 hammer (from the Bezhitsa Steel Foundry) is more advanced. Its weight per unit of power is less than that of the production hammers by 6–18%, and its volumetric chipping rate is higher by 14–18%. The higher values of the energy characteristics of the BSZ-135 hammer in comparison with the production hammers are explained by the fact that, at the moment of collision of the striker with the chisel, the resultant force acting on it is close to zero, whereas in the mo—

in the MP-6 and MP-5 hammers, a back-pressure impulse is observed in the front cavity at the end of the striker’s working stroke.

To study the nature of the vibration of the hammer body and to measure vibration displacements, various transducers were used.

The measurement procedure and a description of the transducer designs are given in [2]. The vibration displacement as a function of the pressing force is shown in Fig. 1. The vibration of the BSZ-135 pneumatic hammer is considerably

Table

Characteristics of pneumatic hammers

above the level permissible under the 1955 sanitary standards, and still more above these standards when allowance is made for the correction factor introduced in 1965.

The inertial forces acting on the hands of the worker using the hammer were evaluated from the maximum vibration acceleration, which was measured with a PIU-1M pointer instrument with a PDU-1 piezoelectric transducer. It was established that the hammer handle acts on the worker’s right hand with an inertial force corresponding to an acceleration of $(90—100)g$, with the acceleration increasing as the pressing force rises. An even greater force acts on the worker’s left hand through the chisel, with an acceleration of $139g$.

For a more complete evaluation of the vibration of the BSZ-135 pneumatic hammer, its harmonic analysis is necessary. For this purpose, a magnetoelectric transducer with a coil resistance of 500 ohms was used. The magnet was made of the alloy YuNDK35T5. Since the signal in the transducer is proportional to velocity, this signal was integrated in order to obtain displacement vibrograms. The signal was integrated by an integrating circuit (Fig. 2). The signal was recorded on magnetic tape and then fed to an ASChKh spectrum analyzer; monitoring of the oscillation recording process and signal reproduction was carried out using an EO-7 oscillograph. To interpret the spectrograms, a calibration signal was also recorded on the magnetic tape by means of a measuring transducer mounted on an electromagnetic stand. The oscillation frequency of the stand was 50 Hz.

Correction of the spectrograms was carried out on the basis of the frequency characteristic of the tape recorder.

Fig. 1. Effect of the pressing force on the vibration displacement \((S)\) and vibration acceleration \((g)\) of the BSZ-135 hammer

Fig. 2. Integrating circuit of the vibration-displacement sensor

\[ \frac{U_{\text{in}}}{U_{\text{out}}}=f(\omega), \]

where \(U_{\text{in}}\) is the input voltage;
\(U_{\text{out}}\) is the voltage at the output of the tape recorder;
\(\omega\) is the signal oscillation frequency, Hz.

The frequency characteristic of the MAG-59 tape recorder is shown in Fig. 3. Analyzing the spectrogram obtained at a pressing force of 20 kg and a pressure of 5 atm, it may be noted that the higher harmonics of the oscillations have smaller amplitude values, while the components of oscillations at high audio and ultrasonic frequencies are insignificant or absent altogether (Fig. 4).

The low-frequency oscillations of the pneumatic hammer are a consequence of the periodic change in air pressure in its cavities, the nature of which is determined by the operating conditions and the design of the hammer. The nature of the high-frequency harmonics lies in the impact character of the interaction between parts and in the excitation of the frequencies of their natural oscillations.

Since the magnitude of the high-frequency components of the oscillations is small, their vibration suppression can be accomplished by pneumatic shock absorbers, springs, dynamic absorbers, by changing the internal working process \([7, 9]\), etc.

To evaluate the BSZ-135 chipping hammer with respect to noise, noise spectrograms were recorded using a set of MIU instruments. The noise spectrogram at a pressing force of 20 kg is shown in Fig. 5. The overall noise level is 112.5 dB. As can be seen from the spectrogram, the noise is most intense at frequencies of 400 Hz and 3–4 kHz.

The studies carried out on the vibration characteristics of the BSZ-135 hammer show that reducing them is extremely necessary, and this can—

Fig. 3. Frequency response of the MAG-59 tape recorder

—be accomplished by means of damping elements operating in the post-resonance region.

Fig. 4. Spectrogram of the vibrational displacement of the BSZ-135 hammer

Conclusions

1. The results of studies of the BSZ-135 hammer showed that its design is more advanced in comparison with production chipping hammers close to it in terms of their energy parameters.

The BSZ-135 hammer has a lower weight per unit of power, and its volumetric chipping rate is 14–18% higher than that of the MR-5 and MR-6 hammers.

Fig. 5. Noise spectrograms of the BSZ-135 hammer

1. In order to improve working conditions and increase workers’ productivity, it is necessary to substantially reduce the vibration of the BSZ-135 hammer. As the investigations have shown, this can be done by introducing damping elements operating in the post-resonance zone, or by changing the working cycle.

REFERENCES

1. G. S. Vilner. Stand and apparatus for vibration testing of pneumatic chipping hammers. Collection: Scientific Works of the Institutes of Labor Protection of the All-Union Central Council of Trade Unions, issue 1 (27), Profizdat, 1964.

2. V. F. Gorbunov, G. S. Zhartovskii, Yu. A. Oparin. On the question of developing vibration-measuring apparatus. Article in the present collection.

3. S. I. Dobroborskii. Investigation of methods for measuring the impact work of pneumatic hammers. Candidate dissertation. Leningrad, 1955.

4. N. N. Esin. Methodology for investigating and refining pneumatic hammers. Novosibirsk, 1965.

5. V. Z. Kleimenov. Influence of the processed medium on the working process of pneumatic breaker hammers. TsNIITEI Uglya. Mining Machines and Automation, No. 58, 1965.

6. A. I. Pashnin, V. F. Gorbunov, V. I. Baburov, A. F. Kozlov. Investigation of the characteristics of pressing devices of pneumatic hammers. Article in the present collection.

7. A. M. Petreev. On some methods for increasing the vibration safety of hand-held pneumatic percussion machines. Candidate dissertation. Novosibirsk, 1965.

8. G. I. Sidorenkov. Pneumatic chipping hammers. Bulletin of Machine Building, No. 11, 1956.

9. B. V. Sudnishnikov, N. N. Esin. Elements of the dynamics of percussion machines. Novosibirsk, 1965.