RESULTS OF TECHNICAL AND HYGIENIC TESTS OF THE BSZ-135V CHIPPING HAMMER

V. F. Gorbunov, Z. M. Butkovskaya, S. S. Kaplyushin, A. I. Pashnin,
E. I. Volodina

At the laboratory of the Pneumatika plant (Leningrad), tests were carried out on the vibration characteristics of the BSZ-135V pneumatic hammer [1], with the participation of employees of the plant, the State Research Institute of Occupational Hygiene and Occupational Diseases, the Bezhitsk Steel Foundry, and the Tomsk Polytechnic Institute.

The research program included two main stages:

a) determination of the vibration characteristics of production-model hammers (BSZ-135) and of an experimental model—with vibration-isolating devices (BSZ-135V);

b) establishment of the nature of shifts in the physiological functions of the organism of the operators studied while working with the hammers.

The testing methodology and measuring instruments are described in [2].

In addition to measuring the displacement amplitudes of the hammer handles, the spectral composition of the vibrations was studied by vibration accelerations. For this purpose, a piezoelectric sensor manufactured by Brüel & Kjær was used, mounted on the hammer handles. Calibration of the acceleration signal was performed on an electrodynamic stand at the Pneumatika plant. To assess the damping of high-frequency vibrations of the chisel, the acceleration spectrum was recorded on a rubber coupling and without it.

The experimental chipping consisted in removing chips from a steel billet weighing 50 kg. The work was carried out in canvas mittens at an air pressure at the hammers of 5 atm. To protect against noise, the subjects worked in TsNIIOT-2 helmet-phones. In all, two variants of the studies were performed, including 70 experiments and about 3000 determinations of various functional indicators.

The displacement magnitude of the handles of the chipping hammers is presented in Table 1. From the data in the table it is evident that, according to the sanitary standards for vibration with the 1955 coefficients, the BSZ-135V hammer satisfies the requirements at pressing forces of more than 20 kg. At lower forces the displacement amplitude of the handle increases. Consequently, the vibration-isolation device of the BSZ-135V hammer handle requires improvement. The vibration displacement of the handle of the BSZ-135 hammer (production model) is significantly higher than that permissible under the sanitary standards.

The best vibration damping occurs in the low-frequency range (up to 200 Hz). In the mid-frequency range (200–5000 Hz), vibration acceleration is reduced to a lesser degree, while vibration components above 5 kHz practically do not change in magnitude. That is, the high harmonics of vibration acceleration are not filtered out by the spring handle. Later studies of the BSZ-135V hammer, carried out at Tomsk Polytechnic Institute, showed that the high-frequency components are well retained by a combined vibration-isolating device in the form of a conical spring and a rubber gasket [3].

Table 1

Results of vibration measurements of the BSZ-135 and BSZ-135V hammers

As a result of physiological examinations of the test subjects, it was found that, when working with the BSZ-135V hammer instead of the BSZ-135 hammer, the following positive factors are achieved.

1. After work with the BSZ-135V hammer, no change in pulse rate occurred, and after 20 min even a slowing of the pulse was observed. Work with the production hammer caused an increase in pulse rate by 6 beats per minute, and after 20 min these shifts returned to normal.

2. Work with the production hammer caused, in the left hand, a lengthening (by 22%) of the time of developed reactive hyperemia, and after 20 min the time of initial hyperemia in the right hand was prolonged. The time of appearance of reactive hyperemia during work with the experimental hammer, on the contrary, decreased somewhat.

3. After work with the hammers studied, a decrease in vibration sensitivity in both hands was observed over the entire range of frequencies investigated. However, after work with the BSZ-135 hammer, the shifts were much more pronounced than after work with the BSZ-135V hammer. The character of recovery also differed for these two hammers: after work with the BSZ-135 hammer, restoration of the initial level of sensitivity did not occur over the entire range of frequencies investigated, whereas after work with the BSZ-135V hammer a more pronounced tendency was observed toward restoration of sensitivity to oscillations with frequencies of 100 and 200 Hz, and the initial sensitivity at a frequency of 50 Hz was restored.

From consideration of the character of the physiological shifts, it is evident that after work with the production pneumatic chipping hammer BSZ-135, more pronounced shifts arise than after work with the experimental pneumatic chipping hammer with the vibration-damping device BSZ-135V. Thus, the increase in pulse rate and the reduction in endurance after work with the BSZ-135 hammer indicate a more pronounced work load; the lengthening of the time of reactive hyperemia indicates a tendency toward spasm of the peripheral vessels; and changes in vibration sensitivity confirm the specific effect of the tool’s vibration.

Work with the BSZ-135V hammer does not cause a tendency toward peripheral vasospasm; circulation in the working hand is not disturbed. This point is confirmed by a shortening of the time of reactive hyperemia and by an exacerbation of pain sensitivity. However, there are some changes in functions after work with this hammer that cannot be ignored. These include a change in vibration sensitivity (although considerably smaller than when working with the BSZ-135 hammer), a reduction in endurance in the left hand, and a change in muscle tone. Obviously, these shifts are connected, first, with the fact that the vibration of the BSZ-135V hammer does not fully meet hygienic standards, and, second, with the increased weight of the hammer.

Physiological-hygienic tests of the BSZ-135 and BSZ-135V hammers showed that the BSZ-135V hammer with vibration damping has an unquestionable advantage over the serial BSZ-135 hammer without vibration damping.

As can be seen from the materials measuring the vibration levels of the BSZ-135V hammer, the design of this hammer (the handle is separated from the body by a conical spring) makes it possible to reduce handle vibration significantly. At a pressure of 20 kg and higher, the displacement amplitude of the handle almost satisfies Sanitary Standards No. 191-55 of 11/VIII-55, with correction factor No. 527-65 of 8/V-65. The nature of vibration damping is especially clearly manifested when considering the vibration spectrum of the BSZ-135V hammer in comparison with the spectrum of the BSZ-135 hammer.

The vibration-damping rubber sleeve fitted onto the chisel to protect the worker’s left hand may also be assessed positively. The vibration characteristics of the tool also account for the results obtained in the study of physiological functions. The shifts in the organism that occurred after short-term work with the BSZ-135V hammer were small and recovered quickly. However, the noncompliance of the BSZ-135V hammer with sanitary standards under certain conditions must be taken into account in further work on its design. After technical refinement of the design, the recoil values of the hammer must be brought into compliance with sanitary standards. The following technical refinement of the design must be carried out.

1. Reduce the weight of the hammer by replacing the steel handle with a lighter one made of impact-resistant plastics, capron, or other materials.

2. Increase the strength and durability of the damping spring.

3. For ease of assembly, replace the fine thread (for screwing the handle onto the false barrel) with a normal metric thread.

4. As an additional shock absorber, in addition to the conical spring, provide for a rubber gasket.

Most of the recommendations of the commission for testing the prototype of the BSZ-135V pneumatic chipping hammer have been implemented. The Bezhitsa Steel Foundry has manufactured a batch of hammers for trial operation and further physiological-hygienic tests under production conditions.

REFERENCES

1. V. I. Baburov, A. I. Pashnin. Pneumatic Hammer with Vibration-Damping Devices BSZ-135V. Proceedings of TPI, vol. 158. TSU Publishing House, Tomsk, 1967.

2. V. F. Gorbunov, Z. M. Butkovskaya, V. I. Baburov, Yu. A. Oparin, E. I. Volodina, A. N. Shchipunov, S. S. Karpushin, Yu. S. Shevchenko. Re-

sults of the development and hygienic study of pneumatic hammers with vibration isolation. Izv. TPI, vol. 146, published by TSU, Tomsk, 1966.

1. A. I. Pashnin, V. F. Gorbunov, V. I. Baburov. Effectiveness of vibration isolation of hand-held pneumatic hammers by combined shock absorbers. (This collection.)